23.10: Cerego- The Immune System - Biology

23.10: Cerego- The Immune System - Biology

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It is tempting to view different topics as completely separate, but in fact the ideas we cover in this course are often connected to one another. Using this practice set can help you do well both in this module and as you move through the course.

Click here to view the practice set for The Immune System. You’ll need to create a free log-in to practice these items, if you haven’t already.

Do Human Brains Carry Microbiota? Scientists Can't Agree

Is the healthy human brain home of a microbiome? originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.

Answer by Tirumalai Kamala, Immunologist, Ph.D. Mycobacteriology, on Quora:

Does the healthy human brain have its own stable microbiota? Thus far, at least one peer-reviewed study ( 1 ) appears to suggest that 'healthy' human brains could have their own share of microbiota.

A simple enough study ( 1 ), the authors performed deep sequencing of white matter-derived RNA from 4 HIV patients, 4 other disease controls and 2 cerebral surgical resections from epilepsy patients, and found alpha-proteobacteria in all of them as well as some herpes viruses and bacteriophages. Given that none of the brains were technically from 'healthy' individuals, results from such a small study are inconclusive and will remain so until replicated or until other studies report finding other micro-organisms in healthy human brains. However, such a task is very much uphill and definitely not for the faint-hearted.

Human gut microbiota is unremarkable because it's entirely expected. On the other hand, brain microbiota is far more controversial simply because microbes are unexpected in such supposedly sterile organs as the healthy brain. Any and every critique applied to human brain microbiota is just as applicable to human gut microbiota since similar methods are used to analyze microbiota anywhere.

After all, microbiota analysis methods have considerable problems in the form of study design flaws, poor data quality and reproducibility, and ambiguous and questionable statistical approaches used for data analysis ( 2 , 3 , 4 , 5 , 6 , 7 , 8 ), except such critiques are usually glossed over in human gut microbiota studies even as they would likely be the centerpiece of focus about microbiota found in unexpected places such as the human brain.

Finding microbes in the healthy human brain would thus get parsed using much more stringent critiques that just don't get applied to human gut microbiota analysis. Unsurprising then that the result of this sole study was easily considered suspect and discredited with the argument that microbiota such as alpha-proteobacteria are often found as contaminants ( 9 ). Casting doubt on the method casts doubt on the results.

Rightly or wrongly, the brain is typically privileged as the seat of the super-self. Microbes in the healthy brain necessitates some means of surveillance by the immune system but for a mindset that privileges the brain, both microbes and the immune system are potentially threatening invaders, given their unpredictable capacity for invasion, damage and just plain downright mischief. No surprise then that for a long time the consensus has been that the brain has systems in place to keep both the immune system and microbes at bay.

One of the clearest examples of such a system is the notion of Immune privilege , an idea initially articulated by Peter Medawar , which holds that being exquisitely vulnerable to irreversible inflammatory damage, certain parts of the body such as the brain limit their interaction with the environment beyond, and with the immune system in particular. The Blood–brain barrier (BBB) embodies immune privilege in the form of a physical barrier, preventing the immune system from fully accessing the brain. If the circulating immune system itself is supposed to have limited access to the brain, it's not surprising that it then follows that microbes in the brain would be considered not a feature of health but of disease.

However, the notion of immune privilege lacks evolutionary coherence. Any part of the body inaccessible, or poorly, or less accessible to the immune system renders it unprotected. Akin to open sesame to pathogens, such an idea makes no evolutionary sense whatsoever. All the more flabbergasting then that this idea remained an entirely acceptable construct for decades and lingers on even in current thinking, as evidenced by an entire Wikipedia article devoted to it that discusses it wholly at face value, without ever referring to the hugely problematic implication of its evolutionary unworkability.

A steady drumbeat of data in recent years has however provided a couple of countervailing pieces of evidence that suggest the ground may be fast getting cut out from under the bastions holding the old ideas of immune privilege and BBB in place,

  • Numerous studies (see reviews 10 , 11 , 12, 13 , 14 ), especially in preclinical animal models, have now shown gut microbiota influence many if not most aspects of brain development and function.
  • The 2015 report that contrary to long-held dogma, the (rodent) brain isn't devoid of lymphatics ( 15 , 16 , 17 ). The so-called BBB may not be an unimpregnable barricade after all.

There remains then only the small (ahem!) matter of reconciling current immune system theory to healthy human brain microbiota as in how could the immune system tolerate them without constant, protracted inflammation? It's doable if one accepts that any commensal microbiota that applied evolutionary selection pressure would be tolerated through the process of thymic Central tolerance wedded to antigen-specific Regulatory T cell development and function.

However, current immunological dogma would consider such an argument heretical since it assumes the immune system ontogenetically learns within each individual's lifetime to distinguish what is self from what is not. On the other hand, microbiota in the healthy human brain is not a problem for those like me who believe immune, especially T cell, development to be a phylogenetically powered process that is being perfected over the evolutionary history of a species. Only time and weight of scientific evidence favoring one or the other view will settle that debate.

1. Branton, William G., et al. "Brain microbial populations in HIV/AIDS: α-proteobacteria predominate independent of host immune status." PloS one 8.1 (2013): e54673.

2. Lozupone, Catherine A., et al. "Meta-analyses of studies of the human microbiota." Genome research 23.10 (2013): 1704-1714. Meta-analyses of studies of the human microbiota

3. Goodrich, Julia K., et al. "Conducting a microbiome study." Cell 158.2 (2014): 250-262.

4. McMurdie, Paul J., and Susan Holmes. "Waste not, want not: why rarefying microbiome data is inadmissible." PLoS computational biology 10.4 (2014): e1003531.

5. Sinha, Rashmi, et al. "The microbiome quality control project: baseline study design and future directions." Genome biology 16.1 (2015): 276. https://genomebiology.biomedcent.

6. Weiss, Sophie, et al. "Correlation detection strategies in microbial data sets vary widely in sensitivity and precision." ISME J 10.7 (2016): 1669-1691.

7. Boers, Stefan A., Ruud Jansen, and John P. Hays. "Suddenly everyone is a microbiota specialist." Clinical Microbiology and Infection 22.7 (2016): 581-582. http://www.clinicalmicrobiologya.

8. Bik, Elisabeth M. "Focus: microbiome: the hoops, hopes, and hypes of human microbiome research." The Yale journal of biology and medicine 89.3 (2016): 363.

9. Salter, Susannah J., et al. "Reagent and laboratory contamination can critically impact sequence-based microbiome analyses." BMC biology 12.1 (2014): 87.

10. Diamond, Betty, et al. "It takes guts to grow a brain." Bioessays 33.8 (2011): 588-591.

11. Al-Asmakh, Maha, et al. "Gut microbial communities modulating brain development and function." Gut microbes 3.4 (2012): 366-373.

12. Collins, Stephen M., Michael Surette, and Premysl Bercik. "The interplay between the intestinal microbiota and the brain." Nature reviews. Microbiology 10.11 (2012): 735.

13. Tillisch, Kirsten. "The effects of gut microbiota on CNS function in humans." Gut microbes 5.3 (2014): 404-410.

14. Sampson, Timothy R., and Sarkis K. Mazmanian. "Control of brain development, function, and behavior by the microbiome." Cell host & microbe 17.5 (2015): 565-576.

15. Louveau, Antoine, et al. "Structural and functional features of central nervous system lymphatics." Nature 523.7560 (2015): 337.

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The human immune system helps us avoid infections and many diseases and protects us from cancer (1, 2). With the ability to recognize its own and non-self substances, the body’s immune system can produce natural immune tolerance to its own components and eliminate non-self foreign bodies to maintain the internal environment’s stability (3). Cancer occurs when normal cells change and begin to lose control. Since cancer cells are derived from normal cells and are indistinguishable from normal cells, the immune system’s ability to recognize cancer cells is minimal (4, 5). Cancer cells can avoid being attacked by the immune system when the immune system mistakenly thinks tumor cells are self-components. The surveillance of the immune system is also progressively weakened by mutations in the tumor. Tumor cells that activate the immune system are gradually screened out until they produce tumor molecules that are not recognized by the immune system. This process is also known as immunoediting of tumor. In this way, tumor cells successfully escape the damage of the immune system and have a chance to develop. What’s more, because cancer cells themselves can also release many substances that block the immune system, tumor immune response is often selectively suppressed around the tumor tissue (6, 7), which explains the ineffectiveness of immunotherapy in many patients: it is the failure to activate the immune response around the tumor tissue rather than the inability to activate the immune response systematically (6𠄹). In addition, inflammation can promote the development of tumors. Inflammation can release a large number of immunosuppressive cytokines locally in tumor tissue and suppress the immune system through a variety of ways. So cancer still could be caused even with a normal immune system. To overcome this problem, researchers have been looking for ways to help the immune system enhance its antitumor immune responses and improve its capacity to suppress tumor. In recent years, immunotherapy has developed rapidly and become a mature cancer treatment strategy in addition to surgery, chemotherapy and radiotherapy. Immunotherapy has shown a significant therapeutic effect in many human malignant tumors by using the immune system to eliminate cancer cells (10).

With the wide application of high-throughput omics and the development of neoantigen prediction technology, immunotherapy based on neoantigen has become a new research hotspot. Neoantigens are mainly tumor-specific antigens generated by mutations in tumor cells, which are only expressed in tumor cells (11). Neoantigens can also be produced by viral infection, alternative splicing and gene rearrangement (12�). They are ideal targets for T cells to recognize cancer cells and can stimulate strong anti-tumor immune response. Studies in the past five years have shown that neoantigens play a key role in tumor immunotherapy. The identification, screening and identification of neoantigens accelerate the development of personalized immunotherapy for tumor patients, which will benefit more patients (15). As more scientific and clinical data reveal the remarkable effects of neoantigen-based vaccine therapies in a variety of cancer types, there is ample reason to believe that neoantigen-based therapies will be a promising area of cancer immunotherapy.

23.10: Cerego- The Immune System - Biology

Cell death is a critically important biological process. Disruption of homeostasis, either by excessive or deficient cell death, is a hallmark of many pathological conditions. Recent research advances have greatly increased our molecular understanding of cell death and its role in a range of diseases and therapeutic treatments. Central to these ongoing research and clinical efforts is the need for imaging technologies that can locate and identify cell death in a wide array of in vitro and in vivo biomedical samples with varied spatiotemporal requirements. This review article summarizes community efforts over the past five years to identify useful biomarkers for dead and dying cells, and to develop molecular probes that target these biomarkers for optical, radionuclear, or magnetic resonance imaging. Apoptosis biomarkers are classified as either intracellular (caspase enzymes, mitochondrial membrane potential, cytosolic proteins) or extracellular (plasma membrane phospholipids, membrane potential, surface exposed histones). Necrosis, autophagy, and senescence biomarkers are described, as well as unexplored cell death biomarkers. The article discusses possible chemotherapeutic and theranostic strategies, and concludes with a summary of current challenges and expected eventual rewards of clinical cell death imaging.

Application of Strain-Promoted Azide–Alkyne Cycloaddition and Tetrazine Ligation to Targeted Fc-Drug Conjugates
  • Joshua D. Thomas ,
  • Huiting Cui ,
  • Patrick, J. North ,
  • Thomas Hofer ,
  • Christoph Rader , and
  • Terrence R. Burke Jr., *

We have previously described an approach whereby antibody Fc fragments harboring a single C-terminal selenocysteine residue (Fc-Sec) are directed against a variety of targets by changing the peptide or small molecule to which they are conjugated. In the present work, we describe methodology for improving the efficacy of these Fc-Sec conjugates by incorporating cytotoxic drugs. The Fc-Sec protein is first programmed to target specific tumor cell types by attachment of a bifunctional linker that contains a “clickable” handle (e.g., cyclobutane or cyclooctyne) in addition to a tumor cell-binding peptide or small molecule. Following Fc-Sec conjugation, a cytotoxic warhead is then attached by cycloaddition reactions of tetrazine or azide-containing linker. To validate this approach, we used a model system in which folic acid (FA) is the targeting moiety and a disulfide-linked biotin moiety serves as a cytotoxic drug surrogate. We demonstrated successful targeting of Fc-Sec proteins to folate-receptor expressing tumor cells. Tetrazine ligation was found to be an efficient method for biotin “arming” of the folate-targeted Fc-Sec proteins. We also report novel bioconjugation methodologies that use [4 + 2] cycloaddition reactions between tetrazines and cyclooctynes.

Phototriggered DNA Phosphoramidate Ligation in a Tandem 5′-Amine Deprotection/3′-Imidazole Activated Phosphate Coupling Reaction
  • Jonathan L. Cape ,
  • Joseph B. Edson ,
  • Liam P. Spencer ,
  • Michael S. DeClue ,
  • Hans-Joachim Ziock ,
  • Sarah Maurer ,
  • Steen Rasmussen ,
  • Pierre-Alain Monnard , and
  • James M. Boncella*

We report the preparation and use of an N-methyl picolinium carbamate protecting group for applications in a phototriggered nonenzymatic DNA phosphoramidate ligation reaction. Selective 5′-amino protection of a modified 13-mer oligonucleotide is achieved in aqueous solution by reaction with an N-methyl-4-picolinium carbonyl imidazole triflate protecting group precursor. Deprotection is carried out by photoinduced electron transfer from Ru(bpy)32+ using visible light photolysis and ascorbic acid as a sacrificial electron donor. Phototriggered 5′- amino oligonucleotide deprotection is used to initiate a nonenzymatic ligation of the 13-mer to an imidazole activated 3′-phospho-hairpin template to generate a ligated product with a phosphoramidate linkage. We demonstrate that this methodology offers a simple way to exert control over reaction initiation and rates in nonenzymatic DNA ligation for potential applications in the study of model protocellular systems and prebiotic nucleic acid synthesis.

Reversible Metal-Dependent Destabilization and Stabilization of a Stem-Chelate-Loop Probe Binding to an Unmodified DNA Target
  • Joel R. Morgan* ,
  • David V. X. Nguyen ,
  • Angela R. Frohman ,
  • Sara R. Rybka , and
  • John A. Zebala

Herein, we report the discovery of a novel DNA probe with a stem-chelate-loop structure, wherein the stability of the probe–target duplex can be modulated lower or higher using a narrow concentration range of dilute transition metal ions (0.1–10 μM). Oligonucleotide probes containing two terpyridine (TPY) ligands separated by 15 bases of single-stranded DNA, with or without a flanking 5 base self-complementary DNA stem, were tested in thermal transition studies with linear target DNA and varying amounts of ZnCl2. Without the stem, addition of Zn2+ resulted only in reversible destabilization of the probe–target duplex, consistent with assembly (up to 1 equiv Zn2+) and disassembly (excess Zn2+) of the intramolecular Zn2+-(TPY)2 chelate. Surprisingly, probes including both the intramolecular chelate and the stem gave a probe–target duplex that was reversibly destabilized and stabilized upon addition of Zn2+ by ±5–7 °C, a phenomenon consistent with assembly and then disassembly of the entire stem-Zn2+-(TPY)2 motif, including the DNA stem. Stem-chelate-loop probes containing dipicolylamine (DPA) ligands exhibited no metal-dependent stabilization or destabilization. The stem-Zn2+-(TPY)2 motif is readily introduced with automated synthesis, and may have broad utility in applications where it is desirable to have both upward and downward, reversible metal-dependent control over probe-target stability involving an unmodified DNA target.

Uniformly Cationized Protein Efficiently Reaches the Cytosol of Mammalian Cells
  • Midori Futami ,
  • Yasuyoshi Watanabe ,
  • Takashi Asama ,
  • Hitoshi Murata ,
  • Hiroko Tada ,
  • Megumi Kosaka ,
  • Hidenori Yamada , and
  • Junichiro Futami*

Protein cationization techniques are powerful protein transduction methods for mammalian cells. As we demonstrated previously, cationized proteins with limited conjugation to polyethylenimine have excellent ability to enter into cells by adsorption-mediated endocytosis [Futami, J., et al. (2005) J. Biosci. Bioeng. 99, 95–103]. In this study, we show that proteins with extensive and uniform cationization covering the protein surface reach the cytoplasm and nucleus more effectively than proteins with limited cationic polymers or proteins that are fused to cationic peptides. Although extensive modification of carboxylates results in loss of protein function, chicken avidin retains biotin-binding ability even after extensive amidation of carboxylates. Using this cationized avidin carrier system, the protein transduction ability of variously cationized avidins was investigated using biotinylated protein as a probe. The results revealed that cationized avidins bind rapidly to the cell surface followed by endocytotic uptake. Small amounts of uniformly cationized avidin showed direct penetration into the cytoplasm within a 15 min incubation. This penetration route seemed to be energy dependent and functioned under cellular physiological conditions. A biotinylated exogenous transcription factor protein that penetrated cells was demonstrated to induce target gene expression in living cells.

Dimerization of an Immunoactivating Peptide Derived from Mycobacterial hsp65 Using N-Hydroxysuccinimide Based Bifunctional Reagents Is Critical for Its Antitumor Properties
  • Karel Bezouška* ,
  • Zuzana Kubínková ,
  • Jiří Stříbný ,
  • Barbora Volfová ,
  • Petr Pompach ,
  • Marek Kuzma ,
  • Milada Šírová , and
  • Blanka Říhová

We have shown previously that a short pentapeptide derived from the mycobacterial heat shock protein hsp65 can be highly activating for the immune system based on its strong reactivity with the early activation antigen of lymphocytes CD69. Here, we investigated an optimal form of presentation of this antigen to the cells of the immune system. Four different forms of the dimerized heptapeptide LELTEGY, and of the control inactive dimerized heptapeptide LELLEGY that both contained an extra UV active glycine-tyrosine sequence, were prepared using dihydroxysuccinimidyl oxalate (DSO), dihydroxysuccinimidyl tartarate (DST), dihydroxysuccinimidyl glutarate (DSG), and dihydroxysuccinimidyl suberate (DSS), respectively. Heptapeptides dimerized through DST and DSG linkers had optimal activity in CD69 precipitation assay. Moreover, dimerization of active heptapeptide resulted in a remarkable increase in its proliferation activity and production of cytokines in vitro. Furthermore, while DST and DSG dimerized heptapeptides both significantly enhanced the cytotoxicity of natural killer cells in vitro, only the DSG dimerized compound was active in suppressing growth of melanoma tumors in mice and in enhancing the cytotoxic activity of tumor infiltrating lymphocytes ex vivo. Thus, while the dimerization of the immunoactive peptide caused a dramatic increase in its immunoactivating properties, its in vivo anticancer properties were influenced by the chemical nature of linker used for its dimerization.

In Situ SVVYGLR Peptide Conjugation into Injectable Gelatin-Poly(ethylene glycol)-Tyramine Hydrogel via Enzyme-Mediated Reaction for Enhancement of Endothelial Cell Activity and Neo-Vascularization
  • Kyung Min Park ,
  • Yunki Lee ,
  • Joo Young Son ,
  • Jin Woo Bae , and
  • Ki Dong Park*

Tissue engineering therapies require biocompatible and bioactive biomaterials that are capable of encouraging an angiogenic response for effective tissue regeneration. In this study, a SVVYGLR peptide, which functions as a potent angiogenic factor, was conjugated into injectable gelatin–poly(ethylene glycol)–tyramine (GPT) hydrogels in situ to enhance endothelial cell activities and neo-vascularization. SVVYGLRGGY (SV–Y) conjugated GPT (SV–GPT) hydrogels were formed in situ via enzyme-mediated reaction using horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). The physico–chemical properties were characterized and could be controlled depending on the feed peptide and H2O2 concentration. The concentration of conjugated peptide ranged from 0.37 to 0.81 μmol/mL, and the elastic moduli (G′) of the hydrogels were 600–4900 Pa. In vitro cell studies using human umbilical vein endothelial cells (HUVECs) and in vivo subcutaneous injection studies were performed to confirm the effect of the SVVYGLR peptide on HUVEC activity and neo-vascularization. Obtained results demonstrated that the in situ conjugation of SVVYGLR sequences into phenol residues of GPT hydrogels enhanced the activity of HUVECs in vitro and stimulated the formation of new blood vessels in the hydrogel matrices in vivo. From the results, we suggest that in situ conjugation of SV–Y to GPT hydrogels via the enzymatic reaction may be an efficient tool to prepare injectable bioactive hydrogels that can enhance endothelial cell activities and promoting angiogenesis for tissue regeneration.

PNA FIT-Probes for the Dual Color Imaging of Two Viral mRNA Targets in Influenza H1N1 Infected Live Cells
  • Susann Kummer ,
  • Andrea Knoll ,
  • Elke Socher ,
  • Lucas Bethge ,
  • Andreas Herrmann* , and
  • Oliver Seitz*

Fluorogenic hybridization probes that allow RNA imaging provide information as to how the synthesis and transport of particular RNA molecules is orchestrated in living cells. In this study, we explored the peptide nucleic acid (PNA)-based FIT-probes in the simultaneous imaging of two different viral mRNA molecules expressed during the replication cycle of the H1N1 influenza A virus. PNA FIT-probes are non-nucleotidic, nonstructured probes and contain a single asymmetric cyanine dye which serves as a fluorescent base surrogate. The fluorochrome acts as a local intercalator probe and reports hybridization of target DNA/RNA by enhancement of fluorescence. Though multiplexed hybridization probes are expected to facilitate the analysis of RNA expression, there are no previous reports on the dual color imaging of two different viral mRNA targets. In this work, we developed a set of two differently colored PNA FIT-probes that allow the spectrally resolved imaging of mRNA coding for neuraminidase (NA) and matrix protein 1 (M1) proteins which execute distinct functions during the replication of the influenza A virus. The probes are characterized by a wide range of applicable hybridization temperatures. The same probe sequence enabled live-cell RNA imaging (at 37 °C) as well as real-time PCR measurements (at 60 °C annealing temperature). This facilitated a comprehensive analysis of RNA expression by quantitative (qPCR) and qualitative (imaging) means. Confocal laser scanning microscopy showed that the viral-RNA specific PNA FIT-probes neither stained noninfected cells nor cells infected by a control virus. The joint use of differently colored PNA FIT-probes in this feasibility study revealed significant differences in the expression pattern of influenza H1N1 mRNAs coding for NA or M1. These experiments provide evidence for the usefulness of PNA FIT-probes in investigations on the temporal and spatial progression of mRNA synthesis in living cells for two mRNA species.

Investigation of the Drug Binding Properties and Cytotoxicity of DNA-Capped Nanoparticles Designed as Delivery Vehicles for the Anticancer Agents Doxorubicin and Actinomycin D
  • Colleen M. Alexander ,
  • James C. Dabrowiak* , and
  • Mathew M. Maye*

Oligonucleotide-functionalized gold nanoparticles (AuNP) were designed and synthesized to be delivery vehicles for the clinically used anticancer drugs doxorubicin (DOX) and actinomycin D (ActD). Each vehicle contains a tailorable number of DNA duplexes, each possessing three high-affinity sequences for the intercalation of either DOX or ActD, thus allowing for control of drug loading. Drug binding was evaluated by measuring changes to DNA melting temperature, Tm, hydrodynamic diameter, Dh, and surface plasmon resonance wavelength, λspr, with drug loading. These studies indicate that DOX intercalates at its high-affinity sequence bound at the AuNP, and that ActD exhibits relatively weaker binding to its preferred sequence. Agarose gel electrophoresis further confirmed drug binding and revealed that particle mobilities inversely correlate with Dh. The equilibrium binding constant, K, and dissociation rate constant, β, were determined by dialysis. Results indicate that the high negative electrostatic potential within the DNA shell of the particle significantly decreases β and enhances K for DOX but has little effect on K and β for ActD. The cytotoxicity of the vehicles was studied, with IC50 = 5.6 ± 1.1 μM and 46.4 ± 9.3 nM for DOX-DNA-AuNP and IC50 = 0.12 ± 0.07 μM and 0.76 ± 0.46 nM for ActD-DNA-AuNP, in terms of drug and particle concentrations, respectively.

Acid-Triggered Release via dePEGylation of Fusogenic Liposomes Mediated by Heterobifunctional Phenyl-Substituted Vinyl Ethers with Tunable pH-Sensitivity
  • Hee-Kwon Kim ,
  • Jeroen Van den Bossche ,
  • Seok-Hee Hyun , and
  • David H. Thompson*

A new family of heterobifunctional phenyl-substituted vinyl ether (PIVE) coupling agents with tunable acid-sensitivity has been developed. The PIVE compounds are designed to hydrolyze under acidic conditions with hydrolysis rates that can be varied by rational selection of the phenyl ring substituent. These reagents were incorporated within 2-methoxypoly(ethylene glycol) PEG-conjugated 1,3-dioctadecyl-rac-glycerol lipids to produce the acid-cleavable lipopolymers mPEG-[H-PIVE]-DOG, mPEG-[F-PIVE]-DOG, mPEG-[Me-PIVE]-DOG, and mPEG-[MeO-PIVE]-DOG. These lipopolymers were hydrolyzed under acidic conditions (pH 3.5 or 4.5) at rates that were dependent on the electron donating or withdrawing character of the α-phenyl vinyl ether substituent, while remaining stable at pH 7.4. Blending of these compounds with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) in a 10:90 mPEG-PIVE-Lipid:DOPE ratio produced stable liposomes at neutral pH however, acidification of the solution led to dePEGylation and release of the liposomal cargo in a manner that correlated with the PIVE proton affinity. Specifically, we observed 70% calcein release within 12 h from mPEG-[MeO-PIVE]-DOG-containing liposomes at pH 4.5, whereas only 22% calcein release was observed from mPEG-[F-PIVE]-DOG:DOPE liposomes over this same time scale and pH. These results indicate that dePEGylation following acidification is a triggering mechanism that can be rationally designed and controlled through the appropriate selection of PIVE moieties.

Covalent Attachment of Biomacromolecules to Plasma-Patterned and Functionalized Carbon Nanotube-Based Devices for Electrochemical Biosensing
  • Joon Hyub Kim ,
  • Joon-Hyung Jin ,
  • Jun-Yong Lee ,
  • Eun Jin Park , and
  • Nam Ki Min*

The interface between biomacromolecules and carbon nanotubes (CNTs) is of critical importance in developing effective techniques that provide CNTs with both biomolecular recognition and signal transduction through immobilization. However, the chemical inertness of CNT surfaces poses an obstacle to wider implementation of CNTs in bioanalytical applications. In this paper, we present a review of our recent research activities related to the covalent attachment of biomacromolecules to plasma-patterned and functionalized carbon nanotube films and their application to the fabrication of electrochemical biosensing devices. The SWCNT films were spray-deposited onto a miniaturized three-electrode system on a glass substrate and activated using highly purified atomic oxygen generated in radiofrequency plasma this introduced oxygen-containing functional groups into the SWCNT surface without fatal loss of the original physicochemical properties of the CNTs. The carboxylated SWCNT electrodes were then selectively modified via amidation or esterification for covalent immobilization of the biomacromolecules. The plasma-treated SWCNT-based sensing electrode had an approximately six times larger effective area than the untreated SWCNT-based electrode, which significantly amplified the amperometric electrochemical signal. Finally, the efficacy of plasma-functionalized SWCNT (pf-SWCNT) as a biointerface was examined by immobilizing glucose oxidase, Legionella pneumophila (L. pneumophila)-specific antibodies, L. pneumophila-originated DNAs, and thrombin-specific aptamers on the pf-SWCNT-based three-electrode devices. The pf-SWCNT films were found to support direct covalent immobilization of the above-listed biomacromolecules on the films and to thereby overcome the many drawbacks typically associated with simple physisorption. Thus, pf-SWCNT sensing electrodes on which biomacromolecules were covalently immobilized were found to be chemically stable and have a long lifetime.

Development of Copper-Catalyzed Azide–Alkyne Cycloaddition for Increased in Vivo Efficacy of Interferon β-1b by Site-Specific PEGylation
  • Natalie W. Nairn* ,
  • Kurt D. Shanebeck ,
  • Aijun Wang ,
  • Thomas J. Graddis ,
  • Michael Pete VanBrunt ,
  • Kenneth C. Thornton , and
  • Kenneth Grabstein

The development of protein conjugate therapeutics requires control over the site of modification to allow for reproducible generation of a product with the desired potency, pharmacokinetic, and safety profile. Placement of a single nonnatural amino acid at the desired modification site of a recombinant protein, followed by a bioorthogonal reaction, can provide complete control. To this end, we describe the development of copper-catalyzed azide–alkyne cycloaddition (CuAAC, a click chemistry reaction) for site-specific PEGylation of interferon β-1b (IFNb) containing azidohomoalanine (Aha) at the N-terminus. Reaction conditions were optimized using various propargyl-activated PEGs, tris(benzyltriazolylmethyl)amine (TBTA), copper sulfate, and dithiothreitol (DTT) in the presence of SDS. The requirement for air in order to advance the redox potential of the reaction was investigated. The addition of unreactive PEG diol reduced the required molar ratio to 2:1 PEG–alkyne to IFNb. The resultant method produced high conversion of Aha-containing IFNb to the single desired product. PEG–IFNbs with 10, 20, 30, and 40 kDa linear or 40 kDa branched PEGs were produced with these methods and compared. Increasing PEG size yielded decreasing in vitro antiviral activities along with concomitant increases in elimination half-life, AUC, and bioavailability when administered in rats or monkeys. A Daudi tumor xenograft model provided comparative evaluation of these combined effects, wherein a 40 kDa branched PEG–IFNb was much more effective than conjugates with smaller PEGs or unPEGylated IFNb at preventing tumor growth in spite of dosing with fewer units and lesser frequency. The results demonstrate the capability of site-specific nonnatural amino acid incorporation to generate novel biomolecule conjugates with increased in vivo efficacy.


Schistosomes have evolved an indirect life cycle featuring both an intermediate gastropod host in which they undergo asexual replication and a mammalian definitive host, including humans, in which adult worms inhabiting the bloodstream undergo sexual reproduction. This complex life cycle has led schistosomes to develop a bevy of mechanisms to avoid being killed by the immune system of either the snail or human hosts. In snails, a mixture of molecular mimicry and E/S products from the developing larvae are utilized to target host hemocytes and prevent their movement, engagement, and killing of the parasite. In humans, various proteases are used to enter the host, after which each life cycle stage produces numerous factors meant for the specific targeting of particular cell types relevant to survival at each stage of development within the host. Given recent advancements in praziquantel administration efforts correlating with a decrease in estimated schistosome infections worldwide, hope exists for the eventual elimination of this deadly and debilitating disease (186). That having been said, an estimated 200 million people are still infected with schistosomiasis, highlighting the need for alternative therapeutics, as well as the possible development of a vaccine. Research into understanding the mechanisms employed by the parasite to survive in both hosts remains crucial in better understanding infection outcomes. The progression in this field from basic observational research all the way to targeted gene deletions suggests a bright future for research into schistosome immune evasion strategies.

A newly developed enzyme-immunoassay for measuring the tissue contents of PACAP in fish

We have developed a novel and easy enzyme-immunoassay (EIA) for pituitary adenylate cyclase-activating polypeptide (PACAP). We used it to determine immunoreactive PACAP levels in the central nervous system (CNS) and peripheral tissues of two fishes, a teleost (the stargazer) and an elasmobranch (a stingray). An antiserum was raised in a white rabbit immunized with a conjugate of synthetic stargazer PACAP27 plus keyhole limpet hemocyanin. The EIA system used an antiserum/biotin-labeled PACAP/avidin/biotin-conjugated enzyme complex, and a double antibody method was used to precipitate the immune complexes. We call the system the avidin-biotin complex detectable EIA (ABCDEIA) for PACAP. ABCDEIA with biotin-labeled PACAP27 detected only PACAP27, recognizing neither the longer forms of PACAP nor any other peptides. PACAPs with 27, 38, and 44 residues cross-reacted in another ABCDEIA with biotin-labeled PACAP38 or PACAP44. Whole brains of both fishes contained much higher levels of PACAP, 6-30 times as high as the levels in the mammalian brain, but unexpectedly, no immunoreactive PACAP27 was found in any CNS or peripheral tissue in either fish. The gastrointestinal tracts of fish also contained lower, but significant amounts of PACAP.

23.2 Stems

In this section, you will explore the following questions:

  • What is the main function and basic structure of a plant stem?
  • What are the roles of dermal tissues, vascular tissues, and ground tissues?
  • What is the difference between primary growth and secondary growth in stems?
  • What is the origin of annual rings in stems? How are annual rings used to approximate the age of a tree?
  • What are examples of modified stems?

Connection for AP ® Courses

Much content described in this section is not within the scope of AP ® . You are not required to memorize the different types of tissues that comprise the plant stem. However, in the Transport of Water and Solutes in Plants module we will explore in detail the roles vascular tissues (xylem and phloem), epidermal guard cells, stomata, and trichomes play in transpiration, the uptake of carbon dioxide and the release of oxygen and water vapor. Trichomes—hair-like structures on the epidermal surface—also defend leaves against predation (see the Plant Sensory Systems and Reponses module).

Except for the concepts described in the AP ® Connection, information presented in this module, and the examples highlighted, does not align to the content and AP ® Learning Objectives outlined in the AP ® Curriculum Framework.

Stems are a part of the shoot system of a plant. They may range in length from a few millimeters to hundreds of meters, and also vary in diameter, depending on the plant type. Stems are usually above ground, although the stems of some plants, such as the potato, also grow underground. Stems may be herbaceous (soft) or woody in nature. Their main function is to provide support to the plant, holding leaves, flowers and buds in some cases, stems also store food for the plant. A stem may be unbranched, like that of a palm tree, or it may be highly branched, like that of a magnolia tree. The stem of the plant connects the roots to the leaves, helping to transport absorbed water and minerals to different parts of the plant. It also helps to transport the products of photosynthesis, namely sugars, from the leaves to the rest of the plant.

Plant stems, whether above or below ground, are characterized by the presence of nodes and internodes (Figure 23.4). Nodes are points of attachment for leaves, aerial roots, and flowers. The stem region between two nodes is called an internode. The stalk that extends from the stem to the base of the leaf is the petiole. An axillary bud is usually found in the axil—the area between the base of a leaf and the stem—where it can give rise to a branch or a flower. The apex (tip) of the shoot contains the apical meristem within the apical bud.

Stem Anatomy

The stem and other plant organs arise from the ground tissue, and are primarily made up of simple tissues formed from three types of cells: parenchyma, collenchyma, and sclerenchyma cells.

Parenchyma cells are the most common plant cells (Figure 23.5). They are found in the stem, the root, the inside of the leaf, and the pulp of the fruit. Parenchyma cells are responsible for metabolic functions, such as photosynthesis, and they help repair and heal wounds. Some parenchyma cells also store starch.

Collenchyma cells are elongated cells with unevenly thickened walls (Figure 23.6). They provide structural support, mainly to the stem and leaves. These cells are alive at maturity and are usually found below the epidermis. The “strings” of a celery stalk are an example of collenchyma cells.

Sclerenchyma cells also provide support to the plant, but unlike collenchyma cells, many of them are dead at maturity. There are two types of sclerenchyma cells: fibers and sclereids. Both types have secondary cell walls that are thickened with deposits of lignin, an organic compound that is a key component of wood. Fibers are long, slender cells sclereids are smaller-sized. Sclereids give pears their gritty texture. Humans use sclerenchyma fibers to make linen and rope (Figure 23.7).

Visual Connection

  1. The cortex and pith are made of parenchyma cells.
  2. The companion cells of the phloem are parenchyma cells.
  3. Fiber cells of the sclerenchyma
  4. Sieve elements and tracheids of the xylem

Like the rest of the plant, the stem has three tissue systems: dermal, vascular, and ground tissue. Each is distinguished by characteristic cell types that perform specific tasks necessary for the plant’s growth and survival.

Dermal Tissue

The dermal tissue of the stem consists primarily of epidermis, a single layer of cells covering and protecting the underlying tissue. Woody plants have a tough, waterproof outer layer of cork cells commonly known as bark, which further protects the plant from damage. Epidermal cells are the most numerous and least differentiated of the cells in the epidermis. The epidermis of a leaf also contains openings known as stomata, through which the exchange of gases takes place (Figure 23.8). Two cells, known as guard cells, surround each leaf stoma, controlling its opening and closing and thus regulating the uptake of carbon dioxide and the release of oxygen and water vapor. Trichomes are hair-like structures on the epidermal surface. They help to reduce transpiration (the loss of water by aboveground plant parts), increase solar reflectance, and store compounds that defend the leaves against predation by herbivores.

Vascular Tissue

The xylem and phloem that make up the vascular tissue of the stem are arranged in distinct strands called vascular bundles, which run up and down the length of the stem. When the stem is viewed in cross section, the vascular bundles of dicot stems are arranged in a ring. In plants with stems that live for more than one year, the individual bundles grow together and produce the characteristic growth rings. In monocot stems, the vascular bundles are randomly scattered throughout the ground tissue (Figure 23.9).

Xylem tissue has three types of cells: xylem parenchyma, tracheids, and vessel elements. The latter two types conduct water and are dead at maturity. Tracheids are xylem cells with thick secondary cell walls that are lignified. Water moves from one tracheid to another through regions on the side walls known as pits, where secondary walls are absent. Vessel elements are xylem cells with thinner walls they are shorter than tracheids. Each vessel element is connected to the next by means of a perforation plate at the end walls of the element. Water moves through the perforation plates to travel up the plant.

Phloem tissue is composed of sieve-tube cells, companion cells, phloem parenchyma, and phloem fibers. A series of sieve-tube cells (also called sieve-tube elements) are arranged end to end to make up a long sieve tube, which transports organic substances such as sugars and amino acids. The sugars flow from one sieve-tube cell to the next through perforated sieve plates, which are found at the end junctions between two cells. Although still alive at maturity, the nucleus and other cell components of the sieve-tube cells have disintegrated. Companion cells are found alongside the sieve-tube cells, providing them with metabolic support. The companion cells contain more ribosomes and mitochondria than the sieve-tube cells, which lack some cellular organelles.

Ground Tissue

Ground tissue is mostly made up of parenchyma cells, but may also contain collenchyma and sclerenchyma cells that help support the stem. The ground tissue towards the interior of the vascular tissue in a stem or root is known as pith, while the layer of tissue between the vascular tissue and the epidermis is known as the cortex.

Growth in Stems

Growth in plants occurs as the stems and roots lengthen. Some plants, especially those that are woody, also increase in thickness during their life span. The increase in length of the shoot and the root is referred to as primary growth, and is the result of cell division in the shoot apical meristem. Secondary growth is characterized by an increase in thickness or girth of the plant, and is caused by cell division in the lateral meristem. Figure 23.10 shows the areas of primary and secondary growth in a plant. Herbaceous plants mostly undergo primary growth, with hardly any secondary growth or increase in thickness. Secondary growth or “wood” is noticeable in woody plants it occurs in some dicots, but occurs very rarely in monocots.

Some plant parts, such as stems and roots, continue to grow throughout a plant’s life: a phenomenon called indeterminate growth. Other plant parts, such as leaves and flowers, exhibit determinate growth, which ceases when a plant part reaches a particular size.

Primary Growth

Most primary growth occurs at the apices, or tips, of stems and roots. Primary growth is a result of rapidly dividing cells in the apical meristems at the shoot tip and root tip. Subsequent cell elongation also contributes to primary growth. The growth of shoots and roots during primary growth enables plants to continuously seek water (roots) or sunlight (shoots).

The influence of the apical bud on overall plant growth is known as apical dominance, which diminishes the growth of axillary buds that form along the sides of branches and stems. Most coniferous trees exhibit strong apical dominance, thus producing the typical conical Christmas tree shape. If the apical bud is removed, then the axillary buds will start forming lateral branches. Gardeners make use of this fact when they prune plants by cutting off the tops of branches, thus encouraging the axillary buds to grow out, giving the plant a bushy shape.

Link to Learning

Watch this BBC Nature video showing how time-lapse photography captures plant growth at high speed.

Watch this BBC Nature video showing how time-lapse photography captures plant growth at high speed.
  1. opening of a flower
  2. tendrils looping around a support
  3. growth of an apical bud
  4. closing of leaflets on a lightly touched mimosa leaf

Secondary Growth

The increase in stem thickness that results from secondary growth is due to the activity of the lateral meristems, which are lacking in herbaceous plants. Lateral meristems include the vascular cambium and, in woody plants, the cork cambium (see Figure 23.10). The vascular cambium is located just outside the primary xylem and to the interior of the primary phloem. The cells of the vascular cambium divide and form secondary xylem (tracheids and vessel elements) to the inside, and secondary phloem (sieve elements and companion cells) to the outside. The thickening of the stem that occurs in secondary growth is due to the formation of secondary phloem and secondary xylem by the vascular cambium, plus the action of cork cambium, which forms the tough outermost layer of the stem. The cells of the secondary xylem contain lignin, which provides hardiness and strength.

In woody plants, cork cambium is the outermost lateral meristem. It produces cork cells (bark) containing a waxy substance known as suberin that can repel water. The bark protects the plant against physical damage and helps reduce water loss. The cork cambium also produces a layer of cells known as phelloderm, which grows inward from the cambium. The cork cambium, cork cells, and phelloderm are collectively termed the periderm. The periderm substitutes for the epidermis in mature plants. In some plants, the periderm has many openings, known as lenticels, which allow the interior cells to exchange gases with the outside atmosphere (Figure 23.11). This supplies oxygen to the living and metabolically active cells of the cortex, xylem and phloem.

Annual Rings

The activity of the vascular cambium gives rise to annual growth rings. During the spring growing season, cells of the secondary xylem have a large internal diameter and their primary cell walls are not extensively thickened. This is known as early wood, or spring wood. During the fall season, the secondary xylem develops thickened cell walls, forming late wood, or autumn wood, which is denser than early wood. This alternation of early and late wood is due largely to a seasonal decrease in the number of vessel elements and a seasonal increase in the number of tracheids. It results in the formation of an annual ring, which can be seen as a circular ring in the cross section of the stem (Figure 23.12). An examination of the number of annual rings and their nature (such as their size and cell wall thickness) can reveal the age of the tree and the prevailing climatic conditions during each season.

Stem Modifications

Some plant species have modified stems that are especially suited to a particular habitat and environment (Figure 23.13). A rhizome is a modified stem that grows horizontally underground and has nodes and internodes. Vertical shoots may arise from the buds on the rhizome of some plants, such as ginger and ferns. Corms are similar to rhizomes, except they are more rounded and fleshy (such as in gladiolus). Corms contain stored food that enables some plants to survive the winter. Stolons are stems that run almost parallel to the ground, or just below the surface, and can give rise to new plants at the nodes. Runners are a type of stolon that runs above the ground and produces new clone plants at nodes at varying intervals: strawberries are an example. Tubers are modified stems that may store starch, as seen in the potato (Solanum sp.). Tubers arise as swollen ends of stolons, and contain many adventitious or unusual buds (familiar to us as the “eyes” on potatoes). A bulb, which functions as an underground storage unit, is a modification of a stem that has the appearance of enlarged fleshy leaves emerging from the stem or surrounding the base of the stem, as seen in the iris.

Link to Learning

Watch botanist Wendy Hodgson, of Desert Botanical Garden in Phoenix, Arizona, explain how agave plants were cultivated for food hundreds of years ago in the Arizona desert in this video: Finding the Roots of an Ancient Crop.

  1. sweetener for drinks and cooking
  2. proteins to supplement the daily diet
  3. lipids for cooking and baking
  4. starch for thickening desserts and stews

Some aerial modifications of stems are tendrils and thorns (Figure 23.14). Tendrils are slender, twining strands that enable a plant (like a vine or pumpkin) to seek support by climbing on other surfaces. Thorns are modified branches appearing as sharp outgrowths that protect the plant common examples include roses, Osage orange and devil’s walking stick.

Stem regions at which leaves are attached are called ________.

Which of the following cell types forms most of the inside of a plant?

Tracheids, vessel elements, sieve-tube cells, and companion cells are components of ________.

The primary growth of a plant is due to the action of the ________.

Which of the following is an example of secondary growth?

Secondary growth in stems is usually seen in ________.

Describe the roles played by stomata and guard cells. What would happen to a plant if these cells did not function correctly?

Stomata allow gases to enter and exit the plant. Guard cells regulate the opening and closing of stomata. If these cells did not function correctly, a plant could not get the carbon dioxide needed for photosynthesis, nor could it release the oxygen produced by photosynthesis.

Compare the structure and function of xylem to that of phloem.

Xylem is made up tracheids and vessel elements, which are cells that transport water and dissolved minerals and that are dead at maturity. Phloem is made up of sieve-tube cells and companion cells, which transport carbohydrates and are alive at maturity.

Explain the role of the cork cambium in woody plants.

In woody plants, the cork cambium is the outermost lateral meristem it produces new cells towards the interior, which enables the plant to increase in girth. The cork cambium also produces cork cells towards the exterior, which protect the plant from physical damage while reducing water loss.

What is the function of lenticels?

In woody stems, lenticels allow internal cells to exchange gases with the outside atmosphere.

Besides the age of a tree, what additional information can annual rings reveal?

Annual rings can also indicate the climate conditions that prevailed during each growing season.

Give two examples of modified stems and explain how each example benefits the plant.

Answers will vary. Rhizomes, stolons, and runners can give rise to new plants. Corms, tubers, and bulbs can also produce new plants and can store food. Tendrils help a plant to climb, while thorns discourage herbivores.

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    Introduction to Inflammation

    Concepts: Homeostasis, inflammation, sensors, effector cells, mediators, and resolution

    00:00:1500 Hello.
    00:00:1600 My name is Ruslan Medzhitov.
    00:00:1700 I'm a professor at Yale University School of Medicine, and an Investigator from
    00:00:2117 Howard Hughes Medical Institute.
    00:00:2310 In this lecture, I will discuss inflammation, and I'll give a brief overview of the
    00:00:2821 field of inflammation and its role in both host defense and homeostasis, as well as in pathologies.
    00:00:3719 So, inflammation is an enormously huge field with a lot of details known about some aspects
    00:00:4400 of inflammation.
    00:00:4500 And to be able to summarize it in this short overview, I will use a couple of perspectives
    00:00:5128 that summarize some key features of inflammation, and specifically I will start by putting inflammation
    00:01:0009 in the context of the better-understood and better-defined phenomenon of homeostasis,
    00:01:0615 and I'll show the similarities, parallels, and how the two types of processes
    00:01:1313 interact with each other, causing both beneficial and detrimental outcomes.
    00:01:1807 So, just to remind you, homeostasis maintains stability of biological systems
    00:01:2513 in the face of perturbations.
    00:01:2700 And perturbations could be either external or internal to the system.
    00:01:3115 And inflammation is induced when these perturbations exceed homeostatic capacity of the system.
    00:01:3709 So schematically, this could be summarized as follows.
    00:01:4015 If we imagine the position of this ball as the state of the system, here, in the center
    00:01:4626 -- you can see, in the normal state -- the homeostasis is maintained by keeping
    00:01:5413 the state of the system in the desired position.
    00:01:5722 And when it deviates from that position, homeostatic mechanisms will bring it back.
    00:02:0220 But if perturbation is large enough and the system goes outside of its normal control zone,
    00:02:1006 outside of its normal homeostatic range, then homeostatic capacity is no longer sufficient
    00:02:1708 to keep the system in a desired state, and that's when inflammation is induced,
    00:02:2214 to force the system back into the homeostatic state.
    00:02:2517 That's one way to think about connections between homeostasis and inflammation.
    00:02:3021 So, inflammation is something that forces the system to go back into the homeostatic state,
    00:02:3600 when perturbations are large enough and when they overwhelm homeostatic capacity.
    00:02:4304 In modern terms, we can describe homeostasis using the idea of a control circuit.
    00:02:4922 And this is a very simple but very fundamental concept.
    00:02:5404 So here, what is summarized on this slide is key components of a homeostatic circuit.
    00:03:0026 And whenever we speak about homeostasis, that means that we talk about maintenance of
    00:03:0802 some variable of the system.
    00:03:0909 It could be blood sugar it could be temperature it could be sodium it could be any of the
    00:03:1503 variables of the system that the system cares about and wants to maintain.
    00:03:1911 So, that's what's denoted here as X.
    00:03:2124 And when we refer to homeostasis of this variable, that means we want to keep it close to
    00:03:2726 some desired value.
    00:03:2914 And that's what's called the setpoint value, X' here.
    00:03:3302 So, that is. it is the value of that variable, or the difference of that variable value from
    00:03:3920 the setpoint value, that is monitored by the sensor.
    00:03:4300 The sensor is the component of a homeostatic circuit that monitors the value of the variable
    00:03:4728 the system cares about.
    00:03:5101 And the second essential part of the system is the effector part, and that's the part
    00:03:5624 that can change that value.
    00:03:5826 So, the sensor monitors the value the effector can change the value.
    00:04:0206 And they need to communicate with each other through a signal that's denoted as C, here.
    00:04:0716 So for example, in the case of systemic homeostasis of blood glucose, X would be the actual concentration
    00:04:1523 of glucose in the blood, X' would be the setpoint value, which is in humans about 5 millimolar,
    00:04:2223 and the sensors would be pancreatic alpha and beta cells that monitor how much glucose
    00:04:2704 we have in the blood.
    00:04:2808 Are you eat, glucose level goes up.
    00:04:3026 Beta cells in the pancreas will detect that and will start producing insulin, which is
    00:04:3506 the example of the signal, shown here, which will go on to act on its effectors,
    00:04:4106 which include skeletal muscle, fat, and liver.
    00:04:4404 And the effect of insulin on these target tissues will be to lower blood glucose level,
    00:04:4904 for example by inducing uptake into those tissues or conversion into glycogen or lipids.
    00:04:5424 If the glucose level is lower than the setpoint value, then alpha cells of the pancreas
    00:05:0108 will detect that, a low lev. a low level, and start producing a different hormone,
    00:05:0605 which is glucagon, which will act exactly, again, on effector cells. effector tissues and organs,
    00:05:1125 for example liver, and cause them to start producing glucose to raise it.
    00:05:1707 to raise the level to the desired value.
    00:05:2006 So, that's how a homeostatic circuit works at. at an organismal level, a tissue level,
    00:05:2710 and a cellular level.
    00:05:3012 Now, the origin of the concept of inflammation goes back to. it can be credited to many people,
    00:05:3814 but the two that I want to highlight here are Rudolf Virchow Elle Metchnikoff,
    00:05:4401 who were contemporaries and colleagues.
    00:05:4901 And so, Virchow, of course, is credited with the development of the modern science of pathology,
    00:05:5325 of cellular pathology.
    00:05:5615 And he was an extremely influential scientist in Europe at the time.
    00:06:0101 And Elle Metchnikoff, of course, is known for his discovery of phagocytes and its.
    00:06:0710 their role in innate immunity.
    00:06:0912 But in the context of inflammation, these two individuals provided very important
    00:06:1515 conceptual contributions.
    00:06:1615 But there was one important difference between them, in that Virchow primarily viewed inflammation
    00:06:2115 as a pathological process, whereas Metchnikoff recognized early on that, in addition to these
    00:06:2717 pathological outcomes of inflammation, that the. the primary reason for an
    00:06:3403 inflammatory response is to provide protection from infections.
    00:06:3824 And he visualized and conceptualized the inflammatory response as being part of a spectrum,
    00:06:4728 where at the base of the spectrum would be what he called "harmony/disharmony balance",
    00:06:5328 and this is what we currently would call homeostasis, but the term homeostasis wasn't coined yet,
    00:06:5922 until 1929.
    00:07:0027 Then, the next level would be physiological inflammation, when inflammation plays
    00:07:0711 beneficial roles in host defense.
    00:07:0920 And then pathological inflammation, and finally immunity.
    00:07:1308 And that. that concept of physiological inflammation and the spectrum of
    00:07:1828 inflammatory response from homeostasis to immunity is actually a very profound insight which was
    00:07:2510 largely forgotten until very recently.
    00:07:2711 And only now we are starting to rediscover and realize these fundamental connections
    00:07:3227 between physiological processes and inflammation.
    00:07:3818 So, taking that, Metchnikoff's idea, and putting it in. looking from different dimensions,
    00:07:4613 we can summarize it as follows, as the spectrum of degrees of deviation from homeostatic states.
    00:07:5306 So here, on the. on the left side, you see the range of conditions of a system that
    00:08:0002 would be within a homeostatic state.
    00:08:0223 If it deviates far enough from that, that's what. what we would call a stress response,
    00:08:0711 or we could also call it a physiological inflammatory response.
    00:08:1107 And if it deviates much further than that, that's what we would call inflammation proper.
    00:08:1623 And so this. any deviation from a normal state, therefore, can be. can lead to
    00:08:2207 the induction of the inflammatory response.
    00:08:2418 So, the causes of inflammation from that perspective can be summarized as follows.
    00:08:3209 In the center here, in the middle, you can see that loss of homeostasis per se is sufficient
    00:08:3627 to lead to inflammation as. as I just mentioned.
    00:08:4102 But in addition, there could be exogenous perturbations that can lead to loss of homeostasis.
    00:08:4811 And the two major types of such perturbations will be pathogens (during infection)
    00:08:5325 as well as toxins and allergens and virulence factors produced by pathogens.
    00:08:5902 So, both pathogens and. and toxins can cause loss of inflammation. loss of homeostasis
    00:09:0614 that. and that can lead to inflammation.
    00:09:0910 But in addition, the immune system developed two pre-emptive mechanisms to trigger a protective
    00:09:1504 inflammatory response, even before pathogens or allergens can cause damage to the system.
    00:09:2207 And there are two fundamental ways that the immune system detects these inducers of inflammation.
    00:09:2710 At the top here, what I call structural feature recognition is the property of the
    00:09:3217 innate immune system to detect invariant structures associated with microbial cells.
    00:09:4003 This is sometimes called the pattern recognition system, where receptors of the immune system
    00:09:4610 detect conserved structures that have found in most microbes, for example we lipopolysaccharides
    00:09:5310 of the cell wall or peptidoglycans, lipoteichoic acids, and so on.
    00:09:5807 And detection of these structures is sufficient to trigger inflammation.
    00:10:0223 On the other hand, allergens and toxins and virulence factors, they're extremely diverse.
    00:10:0700 There. there are many different types and there is no way to detect them all based on
    00:10:1108 structural features, because they don't share any structural features.
    00:10:1509 And the strategy of recognition here is what I would call a functional feature recognition,
    00:10:2016 because what is detected is not specific structures but rather specific biochemical activities,
    00:10:2702 such as protease activities, lipase activities, lipid binding, membrane perturbations,
    00:10:3325 pore formation, and so on.
    00:10:3516 Those functional features are detected by that system, and that also can lead to inflammation.
    00:10:4013 And that type of strategy is particularly important in allergic inflammation.
    00:10:4607 So, based on these ideas, we now can summarize how the immune system operates based on
    00:10:5320 the simple logic of the control circuits.
    00:10:5705 So, we know that the immune system. one of the major functions of the immune system
    00:11:0118 is to detect pathogens and to provide a protective response against them by, for example,
    00:11:0901 destroying them or expelling them from the organism.
    00:11:1400 To do so, the immune system has to have two essential components.
    00:11:1704 It has to have a pathogen-sensing component, or pathogen-sensing cells, and it has to have
    00:11:2510 antimicrobial effector cells, and sensor and effector cells have to communicate with
    00:11:3106 each other through a signal, and once the effector receives the signal from the sensor, it elicits
    00:11:3622 a response that leads to defense from the pathogen.
    00:11:4002 So, that's a very simplified view of the immune system.
    00:11:4513 And the signals that are involved in communication between sensors and effectors are what contributes
    00:11:5102 to this enormous complexity of inflammation and understanding of the immunity.
    00:11:5710 There are many different types of signals in the context of inflammation.
    00:12:0128 The signals are usually called inflammatory mediators.
    00:12:0613 And two major types of inflammatory mediators are signals called chemokines and cytokines.
    00:12:1414 Chemokines are short polypeptides that are produced upon infection by sensor cells
    00:12:2405 that detect pathogens or tissue damage.
    00:12:2708 And what chemokines do is they recruit effector cells to the site of infection.
    00:12:3315 For example, macrophages that function as sensor cells, when they detect bacterial pathogens,
    00:12:4004 will produce chemokines that will recruit neutrophils to the site of infection,
    00:12:4324 and then neutrophils will take care of the pathogens.
    00:12:4711 The second type of inflammatory mediators are cytokines.
    00:12:5026 And this is a. again, a very diverse group of signals that belong to different structural families,
    00:12:5614 but basically what cytokines do. they. they, again, are produced by sensor cells
    00:13:0114 when they detect infection, and they activate effector cells to elicit various
    00:13:0916 antimicrobial functions.
    00:13:1125 So, with this in mind, we now can summarize much of the inflammation and diversity of inflammation
    00:13:2202 into these simple and universal components of the inflammatory pathway.
    00:13:2800 Any type of inflammation includes these four universal components.
    00:13:3112 There is always some type of an inducer of inflammation, for example, pathogen, toxin,
    00:13:3622 tissue damage, or loss of homeostasis.
    00:13:3913 There are sensors that detect the inducers.
    00:13:4219 These include various types of cells of the innate immune system, such as macrophages
    00:13:4804 and mast cells, but also various types of sensory neurons.
    00:13:5427 And the sensor cells produce inflammatory mediators, which include cytokines, chemokines,
    00:14:0115 as well as bioactive amines like histamine, peptides, like bradykinin, as well as
    00:14:0728 lipid mediators called eicosanoids, which include, for example, prostaglandins.
    00:14:1307 And these mediators then act on various target tissues.
    00:14:1625 And almost any tissue in the body can be a target for different types of inflammatory mediators.
    00:14:2301 So here, I'm showing liver, vasculature, epithelial cells, and neutrophils.
    00:14:3021 When mediators act on these effector cells, they cause appropriate changes in their
    00:14:3616 state and their function, or in their positioning.
    00:14:3902 Again, chemokines can recruit neutrophils to the site of infection.
    00:14:4411 Cytokines acting on hepatocytes sites or vascular endothelium will cause their activation,
    00:14:5221 changing protein secretion or permeability of the epithelium.
    00:14:5602 And in the case of mucosal epithelium, they can change the production of antimicrobial
    00:15:0221 peptides or mucus.
    00:15:0421 So, this is this inflammatory pathway.
    00:15:0800 And as you. as you may notice, there is. this is very much related to. it's the
    00:15:1721 same kind of a control circuit we just discussed for homeostasis, where we have a sensor,
    00:15:2326 a signal that connects sensor to the effector, and the effector.
    00:15:2806 The only difference is that in this case what is monitored is not a homeostatic variable,
    00:15:3315 but rather some inducer of inflammation, such as a pathogen or toxin.
    00:15:3822 So, there are these clear parallels between homeostatic and inflammatory control circuits.
    00:15:4504 The reason for that has to do with the fundamental importance of these type of control circuits.
    00:15:5002 They're everywhere, from engineering systems to biological systems.
    00:15:5504 And again, the differences between them are related to the types of inducers that are.
    00:16:0318 that are detected by sensors, or homeostatic variables detected by homeostatic sensors.
    00:16:1007 But we should also keep in mind that sometimes the differences between homeostatic and inflammatory
    00:16:1610 control circuits can be arbitrary, because inflammatory mediators used by homeostatic.
    00:16:2116 by inflammatory circuits can also have some homeostatic functions, and homeostatic signals
    00:16:2911 used by homeostatic circuits can participate in regulation of the inflammatory response.
    00:16:3710 There are actually two different designs. versions of the control circuits.
    00:16:4524 Here on the top is the control circuit I just mentioned.
    00:16:4819 That's the simplest one, where you just have sensor and an effector, and the signal
    00:16:5224 that connects them.
    00:16:5421 There is another type of a circuit which has an additional component in between.
    00:17:0012 And that's what's called a controller or integrating unit.
    00:17:0404 So, here we have a sensor that monitors an inflammatory inducer or homeostatic variable.
    00:17:1121 It produces a signal that then acts on the controller, and then the controller does
    00:17:1523 some type of a computation, and then sends a second signal to the effector.
    00:17:1928 This type of a design is particularly prevalent in both immune and nervous systems.
    00:17:2802 In the case of the immune system, the control. the role of a controller is typically played
    00:17:3117 by a lymphocyte.
    00:17:3303 And in the case of the nervous system, it's played by various types of interneurons.
    00:17:3904 So, sensor cells, again, after detecting the inducer, produce one signal, and then
    00:17:4624 the controller produces a second signal.
    00:17:4820 And these two types of signals are distinct in the immune system, as we will discuss.
    00:17:5510 So from that perspective, we can summarize the entire operation of the immune system
    00:18:0200 as. as connections between pathogen sensors and effectors.
    00:18:0911 And there are three types of disconnections.
    00:18:1117 The simplest one is shown at the top, where the sensor and the effector is the same entity,
    00:18:1710 the same cell.
    00:18:1916 The sensor would be, for example, a receptor, and the effector would be, for example,
    00:18:2405 an antimicrobial enzyme.
    00:18:2711 The second type is when the sensor produces a signal that acts on the effector,
    00:18:3207 as we just discussed.
    00:18:3316 And the third type when there is a lymphocyte in between.
    00:18:3622 And the first two types belong entirely to the domain of the innate immune system,
    00:18:4122 and the second. the. the third one, it can be either innate or adaptive immune system,
    00:18:4807 depending on the type of lymphocyte involved.
    00:18:5026 So, we will go through the different versions of these circuits to illustrate how they operate
    00:18:5809 in the context of infection.
    00:18:5925 So, the simplest one is when a cell like a macrophage encounters a pathogen, like a bacterium, phagocytoses then kills it.
    00:19:0813 So in this case, the sensor would be receptors that detect the microbe, and the effectors
    00:19:1317 would be phagocytic machinery and lysosomal enzymes that will kill the microbe.
    00:19:1724 So, that's the simplest one.
    00:19:1916 And more. more commonly, when macrophages detect pathogens, they will produce a signal
    00:19:2527 that will connect them to the effector, such as a neutrophil, and it will either recruit.
    00:19:3122 recruit or activate neutrophils.
    00:19:3305 And neutrophils are specialized in killing bacteria fungi, and they will proceed to do so.
    00:19:3916 And then the system operates in this manner to provide protection from infection.
    00:19:4714 And finally, the third system. the third design would be when cells. sensor cells
    00:19:5225 like macrophages again detect pathogens, then they produce cytokines that act on, now.
    00:19:5812 on lymphocytes first.
    00:20:0023 And then lymphocytes -- that could involve T cells or different types of innate versions
    00:20:0802 of T cells that I'll describe in a second -- which then produce the second-order cytokines.
    00:20:1321 In this case, a first-order cytokine would be IL-12 produced by macrophages, which acts
    00:20:1811 on lymphocytes, and causes lymphocytes to produce second-order cytokine
    00:20:2208 such as interferon-gamma,
    00:20:2408 which will then act on effector cells -- that will be macrophages -- and cause them to
    00:20:2823 become activated to kill bacteria.
    00:20:3023 So, this design is actually. it captures most of the operation of the immune system.
    00:20:3728 And most of the complexity comes from the generation of lymphocytes and their
    00:20:4224 functional heterogeneities.
    00:20:4412 So, we will now. we'll go quickly through different components of these systems,
    00:20:4915 starting with sensors.
    00:20:5104 There are several cell types that can function as sensors in the inflammatory and immune
    00:20:5615 pathways.
    00:20:5715 These include macrophages, mast cells, epithelial cells, dendritic cells, and plasmacytoid dendritic cells.
    00:21:0510 So, these are different sensor cells that have different types of specializations.
    00:21:1106 Macrophages, mast cells, and epithelial cells are kind of general-purpose sensors.
    00:21:1613 They detect a large variety of pathogens and other types of inflammatory inducers.
    00:21:2423 Dendritic cells are specialized on activating T cells.
    00:21:2807 And plasmacytoid dendritic cells are specialized on antiviral responses.
    00:21:3321 The lymphocyte part is. that's where a lot of complexity comes in.
    00:21:4011 They can be. there are two versions of circuits, depending on what kind of lymphocyte is used.
    00:21:4620 And broadly speaking, there are innate lymphocytes that participate in the innate immune system,
    00:21:5215 and lymphocytes involved in the adaptive immune system, which are T and B cells.
    00:21:5722 The innate lymphocytes, again, come in two versions.
    00:22:0004 There are so-called innate lymphoid cells, which are. have been relatively
    00:22:0416 recently discovered.
    00:22:0516 They don't have T cell receptor.
    00:22:0726 They reside in tissues and they respond to cytokines produced by sensor cells,
    00:22:1315 and in turn produce cytokines that affect effectors.
    00:22:1607 Then there are inmate-like lymphocytes that have T cell receptor, but it's not a random receptor
    00:22:2305 it's invariant, so it's designed to detect very specific subsets of antigens.
    00:22:2910 And finally, the adaptive immune system of course has antigen receptors, T cell receptor
    00:22:3500 and immunoglobulin receptor for B cells, and these are the most complicated cells of the
    00:22:4121 immune system because of the way that they develop and because of the way that
    00:22:4602 their receptors are assembled, and all the additional steps that are involved to make the cells functional,
    00:22:5118 because their receptors are generated at random.
    00:22:5515 Again, when lymphocytes detect cytokines, they respond by producing cytokines.
    00:23:0203 And what's summarized here are some of the types of cytokines that. on the left side,
    00:23:0721 that act on lymphocytes and the different types of lymphocytes
    00:23:1224 and the second-order cytokines produced by lymphocytes.
    00:23:1602 And then these things. cytokines produced by lymphocytes and, again, act on the effector cells,
    00:23:2107 which are. examples are shown here: macrophages, neutrophils, basophils, eosinophils,
    00:23:2706 mast cells, and epithelial cells.
    00:23:3006 Depending on the type of cytokine produced, there would be different type of change
    00:23:3318 in these cells, effector cell types.
    00:23:3706 And in addition to these specialized effectors of the innate immune system, practically
    00:23:4306 any cell in the body can be an effector, because most cells express receptors for at least
    00:23:4815 some of the cytokines produced by lymphocytes.
    00:23:5210 So, now we will quickly go over. with these concepts in mind, we will go over some of
    00:24:0100 the key features of the inflammatory response.
    00:24:0408 And we have to start with one of the oldest notions in the field of inflammation,
    00:24:1105 which is the cardinal signs of inflammation.
    00:24:1310 These were first defined by a Roman physician, Cornelius Celsus, in the first century AD.
    00:24:2212 He defined them as redness and swelling with heat and pain.
    00:24:2725 That was his description of how to diagnose inflammation.
    00:24:3310 And much later, Rudolph Virchow added a fifth cardinal sign of inflammation, which is disturbance
    00:24:3914 of function or loss of function of tissues.
    00:24:4222 The four cardinal signs described by Celsus are a consequence of the changes that
    00:24:4909 occur during acute inflammation.
    00:24:5207 And these are local changes due to alterations in the local vasculature, as we will discuss next.
    00:25:0115 So, this is what typically happens during the most common types of inflammatory responses,
    00:25:0627 when you have a mild infection or papercut or some other splinter or some other injury
    00:25:1503 to the epithelial surfaces.
    00:25:1804 So, microbes or damage to the tissue are detected by sensor cells such as macrophages, dendritic cell,
    00:25:2827 and mast cells, as I just mentioned.
    00:25:3124 And once they detect microbes or tissue damage, these cells start producing inflammatory mediators
    00:25:3700 such as cytokines and chemokines.
    00:25:4000 And one of the effects of these inflammatory mediators, locally, within the tissue,
    00:25:4407 is to act on the local microvasculature.
    00:25:4726 And specifically, they. by acting on postcapillary venules, they cause several characteristic
    00:25:5426 changes of the endothelium of the venules.
    00:25:5904 They cause vasodilation, so there is increased blood flow.
    00:26:0313 And increased blood flow causes heat and redness.
    00:26:0720 And it causes increased vascular permeability, so that plasma starts going from the
    00:26:1502 inside of blood vessels into extravascular spaces within tissues.
    00:26:1912 And that causes swelling, or edema.
    00:26:2312 And together the edema, and effects of inflammatory mediators, also can cause pain.
    00:26:2913 So, redness, swelling, heat, and pain are all [results] of these vascular changes
    00:26:3509 that occur locally.
    00:26:3704 Another important change that happens is that endothelium within postcapillary venules becomes
    00:26:4219 activated, in the sense that it now becomes. acquires adhesive properties such that neutrophils
    00:26:5109 and monocytes and other cell types that go through blood vessels. normally, they would
    00:26:5613 pass through.
    00:26:5716 But when. if there is a local inflammation, the local endothelium becomes sticky, so that
    00:27:0302 these cells now adhere or attach to endothelium, and ultimately they crawl through the endothelial wall
    00:27:1106 into the tissue.
    00:27:1300 And that's the process called extravasation.
    00:27:1601 And the point of that process is to deliver the circulating effector cells to
    00:27:2105 the site of infection.
    00:27:2205 And actually, Elle Metchnikoff was the first to recognize that that's the point of vascular
    00:27:2708 changes during inflammation.
    00:27:3000 So, once neutrophils and other effector cells get to the site of the inflammation,
    00:27:3500 where inflammation is induced, they will then seek out pathogens and will destroy them or
    00:27:4121 repair the damaged tissue.
    00:27:4427 Another important point that was realized probably in the last decade or so is that
    00:27:5511 once inflammation accomplished its goal, which is elimination of pathogens, for example,
    00:28:0223 that is not enough to get back to the normal state.
    00:28:0625 If you just eliminated the cause of inflammation, it doesn't mean that the system automatically
    00:28:1108 goes back by default into homeostatic state.
    00:28:1422 There is another phase between inflammation and homeostatic state -- that's called resolution --
    00:28:1920 that needs to be actively engaged.
    00:28:2224 This is analogous to a situation if you have, for example, a broken pipe and there's flooding
    00:28:2715 in the system.
    00:28:2815 The cause of the mess would be the broken pipe, so let's say you fix the pipe.
    00:28:3213 That doesn't mean that the system is now back into its original state.
    00:28:3611 Now you have all the water on the floor and you need to get rid of it to return actively
    00:28:4020 back to homeostatic state.
    00:28:4204 So, that's what resolution does.
    00:28:4409 After inflammation accomplishes its goal, there's a lot of mess within the tissue --
    00:28:5011 there are many dead cells, there is destroyed extracellular matrix, and all of that has to be cleaned up
    00:28:5726 and changed back to the original state.
    00:29:0104 And of course this is something that requires a highly orchestrated and regulated process.
    00:29:0806 And that's what resolution does.
    00:29:1006 And resolution of inflammation is a very important but still not fully understood process,
    00:29:1621 but it's. it's well recognized now that it's an active process -- it's not just
    00:29:2200 passive cessation of inflammation -- and that it's needed to restore the homeostatic state.
    00:29:2723 An additional important point to understand about inflammation is that there are
    00:29:3513 not just different types of inflammation based on the causes, but there are also different modalities
    00:29:4004 of inflammation.
    00:29:4104 And they are historically defined as acute and chronic modalities of the inflammatory response.
    00:29:4912 So they, as the names imply, acute and chronic inflammation obviously differ in duration.
    00:29:5416 Acute inflammation can last from hours to days, and chronic inflammation typically
    00:30:0102 can last from weeks to months to years.
    00:30:0622 But more importantly, it's not just the kinetics of the response, but more importantly
    00:30:1121 acute and chronic inflammation are qualitatively distinct.
    00:30:1720 And the common causes of chronic inflammation include failure to eliminate the inflammatory inducer,
    00:30:2305 for example, if there is a persistent infection.
    00:30:2704 It's a failure of resolution of inflammation.
    00:30:3117 And in some cases it could be a positive feedback, such that the consequence of the inflammatory response,
    00:30:3722 for example, collateral tissue damage, may also be a cause for a secondary inflammatory response.
    00:30:4403 And potentially that can sustain the inflammatory state.
    00:30:4907 The qualitative differences between acute and chronic inflammation have to do with
    00:30:5316 the types of cells involved.
    00:30:5427 It's mostly neutrophils and eosinophils in acute inflammation, but mostly lymphocytes
    00:31:0119 in chronic inflammation, as well as macrophages.
    00:31:0513 And there are many other differences related to the type of the mechanism used to.
    00:31:1219 to deal with a persistent inflammatory inducer that's used during chronic inflammation.
    00:31:1801 Like other defenses, inflammation always operates at a cost.
    00:31:2301 And these costs can be divided into distinct categories.
    00:31:2706 The first class of causes of. the first type of costs of inflammation has to do with
    00:31:3514 intentional suppression of physiological functions that are lower priority than the inflammatory response
    00:31:4300 and that are somehow incompatible with the inflammatory response.
    00:31:4724 For example, if you're sitting on the couch and watching TV and there is a fire,
    00:31:5224 then watching TV, as a function, would be incompatible with dealing with the fire.
    00:31:5728 And it also would be obviously lower priority than dealing with the fire.
    00:32:0208 So, you will intentionally stop watching TV, so that would be a cost, but it's a low cost
    00:32:0717 compared to the benefit of putting away the fire.
    00:32:1205 And then the second type of course is unintentional cost.
    00:32:1610 That is, it's not something you want, but it's something you can't avoid.
    00:32:2103 It's unintentional and unavoidable costs, such as collateral tissue damage.
    00:32:2420 So, when you're putting out the fire and putting water on it, you will cause perhaps some
    00:32:3026 collateral damage to the rest of the room.
    00:32:3321 So, these are two different types of costs.
    00:32:3617 And the sum of these two costs has to be lower than the benefit provided by inflammation
    00:32:4015 for. for. for the system to be evolutionarily stable.
    00:32:4520 So, inflammation can be pathological, therefore, for several reasons.
    00:32:5117 And what's important to understand is that even an appropriately controlled inflammatory response
    00:32:5706 operates at the expense of other functions.
    00:33:0004 So, it's often said that inflammation is beneficial but when dysregulated can be pathological.
    00:33:0501 We should appreciate that even perfectly controlled inflammatory responses operate at a cost,
    00:33:0921 and sometimes these costs can manifest as symptoms that we may refer to as a disease.
    00:33:1708 The second reason for pathology of inflammation is when the response is excessive and.
    00:33:2426 either in magnitude or in duration.
    00:33:2701 And the third cost would be when the response is induced when it shouldn't be induced,
    00:33:3026 for example when it's mistargeted against something that is not harmful.
    00:33:3722 And this is summarized in this schematic.
    00:33:4124 When inflammation causes swelling, pain, fever, mucus overproduction, coughing, sneezing, diarrhea,
    00:33:4711 these are all defenses.
    00:33:4926 These are all manifestations of defenses.
    00:33:5125 They are protective from different types of noxious challenges, but obviously all of them
    00:33:5717 are processes that come at a cost.
    00:34:0115 We do feel ill when we experience those reactions, even though they are protective.
    00:34:0706 And what makes it worse is when they're protective but excessive.
    00:34:1108 Then they would be clearly just pathological.
    00:34:1513 And so these are two different outcomes that need to be distinguished: when pathology is
    00:34:1923 due to excessive response versus when pathology is simply the cost we have to pay for a normal response.
    00:34:2703 And then the third type of pathological outcome is more obvious.
    00:34:3106 It's when there is a. just collateral tissue damage or a mistargeted response.
    00:34:3609 So, when we put it this way, it's clear that the three types of pathological outcomes
    00:34:4201 are very different.
    00:34:4305 And. for example, you don't want to interfere with the first one, you want to dial down
    00:34:4716 the second one, and you want to stop the third one.
    00:34:5024 And the challenge is to be able to distinguish which one they belong to so that we know
    00:34:5519 what to do with them.
    00:34:5708 So, the take-home messages in this brief overview is that inflammation is normally
    00:35:0320 a protective response to infection and injury and other. and loss of tissue homeostasis,
    00:35:1006 that it's induced when homeostatic capacity is overwhelmed, and that all of the diversity and complexity
    00:35:1808 of inflam. of inflammation can be summarized in terms of the inflammatory pathway that
    00:35:2222 consists of inducers, sensors that detect them, mediators they produce, and the effectors
    00:35:2810 that eliminate the inducers.
    00:35:3202 And inflammation is normally followed by a resolution phase, which returns the system
    00:35:3612 to homeostasis.
    00:35:3916 And an inflammatory response always operates at a cost to incompatible lower-priority functions.
    00:35:4816 And inflammation can cause pathology when it's excessive, inappropriately induced,
    00:35:5305 or due to collateral damage.
    00:35:5522 And that completes this overview.
    00:35:5902 I will discuss in the next talk some specific examples of inflammation in the context of
    00:36:0808 inflammatory diseases.
    00:36:0927 And thank you for your attention.

    Covid-19 blood plasma therapy has limited effect, study finds

    Early analysis from a different trial suggested a reduction in deaths among those who received plasma with high levels of antibodies early in the course of their disease. Photograph: Lindsey Wasson/Reuters

    Early analysis from a different trial suggested a reduction in deaths among those who received plasma with high levels of antibodies early in the course of their disease. Photograph: Lindsey Wasson/Reuters

    It has been touted as a breakthrough treatment by Donald Trump, and there are hopes that blood plasma containing coronavirus antibodies may help British patients during the second wave of Covid-19 as well.

    But a study, which is published in the British Medical Journal (BMJ) on Friday, suggests “convalescent plasma” has only limited effectiveness and fails to reduce deaths or stop the progression to severe disease.

    Plasma is the clear, yellowish liquid part of the blood which carries red and white blood cells and platelets around the body. After an infection, plasma is often packed with antibodies generated by the immune system. As such, it is sometimes harvested from people who have recovered from a disease and transfused into patients who are fighting it. This convalescent plasma therapy was used during the 1918 flu pandemic, as well as during more recent global health emergencies, treating patients with Sars or Ebola.

    Various trials around the world are exploring whether convalescent plasma could help reduce deaths and serious complications from Covid-19, with the largest randomised controlled trial taking place in the UK.

    Despite the findings of the latest published study, convalescent plasma may yet prove to be effective against Covid-19.

    The research involved 464 adults with moderate Covid-19 who were admitted to hospitals in India between April and July. Approximately half received two transfusions of convalescent plasma, 24 hours apart, alongside standard care, while the control group received standard care only.

    One month later, 19% of those who received the plasma had progressed to severe disease or had died of any cause, compared with 18% in the control group. Plasma therapy did, however, seem to reduce symptoms, such as shortness of breath and fatigue, after seven days.

    A spokesperson for NHS Blood and Transplant, which is collecting plasma from people who have recovered from Covid-19, emphasised that UK-based studies are only infusing plasma that contains high levels of coronavirus antibodies. He said the Indian study used plasma with antibody levels around six to 10 times lower than that.

    The Indian researchers agreed that further studies using high antibody levels may find it to be more effective. An interim analysis of 136 Covid-19 patients in a trial at Houston Methodist hospital in Texas suggested a significant reduction in deaths among patients who received plasma with high levels of antibodies early in the course of their disease.

    Followup data from all 351 patients in the Texas study has been published as a preprint and supports this conclusion, although plasma transfusion later in the course of the disease had no significant effect on death rates regardless of antibody levels. “With respect to altering mortality, our analysis identified an optimal window of 44 hours post-hospitalisation for transfusing Covid-19 patients with high titre convalescent plasma,” they wrote.

    Prof Paul Morgan, the director of the Systems Immunity Research Institute at Cardiff University and a member of the British Society for Immunology’s expert taskforce on immunology and Covid-19, said there were other reasons for optimism. For one thing, he said, the study suggested plasma therapy was associated with a reduction in viral load, “so, there does seem to be an antiviral effect of the therapy, even if it isn’t reflected in the final outcomes”.

    The study also hinted that infusing patients with large amounts of donated plasma could lead to a small but significant increase in deaths. “It might be worth considering, rather than giving just convalescent plasma, taking the antibodies out of the plasma and using those,” Morgan said. Such purified antibodies are already used to treat patients with antibody deficiencies.


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    Keywords: aryl hydrocarbon receptor, tumor immunity, tumor development, immune surveillance, cancer immunotherapy

    Citation: Xue P, Fu J and Zhou Y (2018) The Aryl Hydrocarbon Receptor and Tumor Immunity. Front. Immunol. 9:286. doi: 10.3389/fimmu.2018.00286

    Received: 31 July 2017 Accepted: 31 January 2018
    Published: 13 February 2018

    Yongsheng Li, Third Military Medical University, China

    William K. Decker, Baylor College of Medicine, United States
    Zong Sheng Guo, Harvard University, United States

    Copyright: © 2018 Xue, Fu and Zhou. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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