Immunology and Vaccinology (PHM221) Lecture 3 Summer 2024 PDF

Department of Microbiology and Immunology Immunology and Vaccinology (PHM221) Lecture 3 ▪ Innate Immunity...

Department of Microbiology and Immunology Immunology and Vaccinology (PHM221) Lecture 3 ▪ Innate Immunity ▪ Second-line of defense – Part II Summer 2024 Immunology and Vaccinology PHM221 2 References References Abbas, A. K., Lichtman, A. H., & Pillai, S. (2021). Cellular and Molecular Immunology (10th ed., South Asia Edition-E-Book). Elsevier Health Sciences. Bawa, R., Davis, P. J., Doshi, J. K., & Others. (2022). Advances in clinical immunology, medical microbiology, COVID-19, and big data. Publisher. Carlberg, C., & Velleuer, E. (2022). Molecular immunology: How science works. Springer Nature. Detrick, B., Hamilton, R. G., & Schmitz, J. L. (Eds.). (2020). Manual of molecular and clinical laboratory immunology. John Wiley & Sons. Flaherty, D. (2011). Immunology for Pharmacy-E-Book. Elsevier Health Sciences. Levinson, W. (2014). Review of medical microbiology and immunology. McGraw-Hill Education. Miller, L. E., & Stevens, C. D. (2021). Clinical immunology and serology: A laboratory perspective (5th ed.). Publisher. Murphy, K., & Weaver, C. (2016). Janeway's immunobiology. Garland Science. Owen, J. A., Punt, J., Stranford, S. A., & Jones, P. P. (2013). Kuby immunology (Vol. 27). New York: WH Freeman. Runte, F., Renner IV, P., & Hoppe, M. (2019). Kuby immunology. Sompayrac, L. M. (2022). How the immune system works. John Wiley & Sons. Tortora, G. J., Funke, B. R., & Case, C. L. (2015). Microbiology: An Introduction, Books a la Carte Edition. Benjamin-Cummings. 3  In-class activities (individual assignment) (5 marks) → The in-class activities will be conducted during the lectures 1 to 6 (Weeks 1-3). → For each lecture, there will be a questions-sheet you'll answer directly during the lecture. → Procedures: Question sheets will be distributed at each lecture. Complete the question sheet. A model answer sheet will be provided every Thursday. Use a red pen to correct your answers based on the model. Submission: Take clear digital photos of your corrected question sheets. Upload the photos to the designated area on the e-learning platform by the following Saturday. → Grading Each completed and self-corrected question sheet will earn you 1 point. Two colors should be used, and red is recommended for corrections. The maximum total points for these in-class activities is 5 points 4  References Teaching Interactive ▪ MCQs and other questions are included after each topic in the lecture to engage the students. ▪ Case studies ▪ Videos and animations with links and QR codes are embedded in the slides. 5 Lecture Lecture1 Learning 3 OutlineOutcomes ❑ Innate immunity → Second-line of defense o Opsonization o Neutrophil Extracellular Traps (NETs) o Antiviral Interferons o NK Cell Antiviral Response o Acute Phase Proteins Complement system C-reactive protein (CRP) Cytokine storm o Tissue repair 6 Lecture Learning1 Learning OutcomesOutcomes Describe the mechanisms by which opsonization enhances phagocytosis. Define neutrophil extracellular traps (NETs) and their formation. Analyze the significance of interferons in antiviral immunity and immune regulation. Discuss the mechanism by which NK cells recognize and target infected cells. NK N 7 Innate Immunity: Pathogens (viruses, bacteria, fungi) First-Line Defenses 1 Anatomical and Physiological Barriers Innate Immunity First-Line Defenses (External) (Skin, mucous membranes, antimicrobial substances) Second-Line Defenses - Keep pathogens on the outside or Immunity Innate neutralize then before infection begins. 2 Inflammation, Fever, and Phagocytosis Second-Line Defenses (Phagocytes, Granulocytes, Complement, Cytokines) - Slow down infections after falling the 3 first-line defenses. Humoral and Cellular Immunity T-cells, B-cells, Cytokines Third-Line Defenses Adaptive - Target specific pathogens for destruction, when Immunity the second-line defense can’t contain the infection. - This defense mechanism incudes a memory component that allows the immune system to be effectively respond to the same pathogen in the future. Adaptive Immunity 8 Defense Systems 1. Can pathogens escape phagocytosis? o Yes Yes o No 9 Innate Immunity: Second Line of Defense A. Acute Inflammation Phagocytosis Examples of virulence factors protect the bacterial cell from phagocytosis. ‫مدرعة‬ Ooops!..‫البسوا المموه‬ Ooops! I can’t phagocytose it ‫بيخافوا منه‬ Macrophage Opsonization Macrophage Coagulase Neutrophil Neutrophil Some bacteria have capsules surrounding the cell wall. Coagulases are bacterial enzymes that coagulate Capsules can cover/hide the PAMPs in microbial cell (clot) the fibrinogen in blood into fibrin, the threads walls and, consequently, prevent their binding to that form a blood clot. The fibrin clot may protect the endocytic PRR on the surface of the phagocytic cells. bacterium from phagocytosis and isolate it from other host defenses. E.g. Streptococcus pneumniae, Neisseria meningitidis. 10 E.g. Staphylococcus aureus. Innate Immunity: Second Line of Defense A. Acute Inflammation Opsonization What is the difference between…? Phagocytosis by opsonization Phagocytosis 11 Innate Immunity: Second Line of Defense A. Acute Inflammation Opsonization Phagocytosis by Phagocytosis opsonization C3b (opsonin) Antibody (opsonin) 12  Innate Immunity: Second-Line of Defense Opsonization C3b (opsonin) Antibody (opsonin) 13 Innate Immunity: Second Line of Defense A. Acute Inflammation Opsonization Phagocytosis by opsonization Capsule Pathogen- associated molecular patterns (PAMPs) Endocytic pattern- recognition receptors (PRRs) Phagocytic Cell 14 https://youtu.be/oIZwbfvMY5Q  A. Acute Inflammation Innate Immunity: Second Line of Defense Opsonization Activation of phagocytosis can occur indirectly by phagocyte r: receptor recognition of soluble proteins that have bound to microbial surfaces, thus enhancing phagocytosis, a process called Antibody Fcr opsonization (from the Greek word for “to make tasty”). (IgG, IgA) The phagocytosis-enhancing proteins are called opsonins and C3b bind to specific antigens or PAMPs. C3br Encapsulated Once bound to microbe surfaces, opsonins are recognized by Opsonins bacteria membrane opsonin receptors on phagocytes, activating phagocytosis. Macrophage Examples: Opsonin receptor Immune Microbe-binding Opsonin on phagocyte Defense C3b (complement protein) C3b receptor Innate MBL (Mannose-binding lectin) C1q receptor Innate CRP (C-reactive protein) Fc receptor Innate Antibodies (IgG and IgA) Fc receptor Adaptive N.B. Fc receptors are essential for the opsonizing activity of IgA and IgG antibodies. After binding specifically to antigens on microbe surfaces, the Fc regions of these antibodies can be recognized by specific FcRs, triggering phagocytosis. (will be discussed later). 15 Innate Immunity: Second Line of Defense A. Acute Inflammation Opsonization Why is Bacabeco (bacteria) in danger? When bacteria, such as the hypothetical “Bacabeco”, get opsonized by an antibody, they are marked for destruction by the immune system since opsonins enhances the ability of phagocytes to recognize and attach to the bacteria. The Fc portion of the antibody binds to an Fc receptor on the phagocyte. This binding facilitates phagocytosis, a process where the bacteria are engulfed and destroyed by the phagocytes. Bacabeko 16  Innate Immunity: Second-Line of Defense Neutrophil Extracellular Traps (NETs) 17  A. Acute Inflammation Innate Immunity: Second Line of Defense Neutrophil Extracellular Traps Neutrophils are the most abundant innate immune effector cells of the human immune system. Neutrophils are armed with broadly effective antimicrobials that are stored predominately in specialized granules. Given that this neutrophil arsenal can also damage host tissues, its deployment is tightly regulated through three major strategies: Phagocytosis → Degranulation → the release of Neutrophil Extracellular Traps (NETs). Phagocytosis Degranulation Neutrophil Extracellular Traps Bacteria Bacteria (NETs) Phagosome Phagolysosome Histone DNA Myeloperoxidase Bacteria Elastase Neutrophils also degranulate Neutrophils can also produce extracellular Phagocytosis involves the ingestion of and release extracellularly the traps (NETs) formed by DNA fibers and the microorganism into a phagocytic contents of their granules. proteins from the granules. vacuole that upon maturation becomes a phagolysosomes. Rosales, C., 2018. Neutrophil: a cell with many roles in inflammation or 18 several cell types?. Frontiers in physiology, 9, p.113. Innate Innate Immunity: Immunity: Second Second Line Line of of Defense Defense A. Acute Inflammation Neutrophil Extracellular Traps (NETs) Is it possible for certain pathogens to escape the Neutrophil Extracellular Traps (NETs) formed by neutrophils? A. Yes B. No NETs NETs DNA Proteins Bacteria Secreted DNase Neutrophil Yes, it is indeed possible for certain pathogens to evade the Neutrophil Extracellular Traps (NETs). Some extracellular pathogens, such as Staphylococcus aureus and Streptococcus pyogenes, have evolved to secrete nucleases (DNase) that allow them to cut through and escape Cell-bound DNase from these NETs. This is similar to chopping off a spider web to escape. This Bacteria are trapped in DNA Bacterial DNases degrade the NETs released from neutrophils and (DNA traps), freeing the bacterial cells adaptation allows these pathogens to killed by associated factors. and protecting them from being killed. survive and continue their invasion. 19 Innate Immunity: Second Line of Defense The second-line of innate immunity defense handles pathogens in TWO general ways: Remember 20 Innate Immunity: Second Line of Defense B. Antiviral response How does innate immunity deal with viruses? When a virus infects a human cell, it takes over the Virus: let’s escape cell’s machinery and uses it to produce many more from phagocytes inside the host cell. copies of the virus. Eventually, the infected cell bursts and the newly made viruses go out to infect other cells. The innate system can use different mechanisms to defend against viruses while they are outside of cells; for example: Virus: opsonins tag viruses for phagocytosis by Macrooo!!, macrophages and neutrophils. you can’t complement proteins can destroy some viruses. catch me now Once a virus has entered a cell (intracellular) to begin its reproductive cycle, the above Virus: Oh mechanisms are ineffective; however, there are Oh! I forgot other unique mechanism to eliminate the about NK intracellular pathogen, which mainly are: cells Natural Killer (NK) cells Interferons (IFNs): IFN-α and IFN-β 21  Innate Immunity: Second-Line of Defense Interferons Dendritic cell 22  B. Antiviral response Innate Immunity: Second Line of Defense Interferons The term interferon derives from the ability of these cytokines to Viral infected cell interfere with viral replication. Indeed, the innate system weapon that viruses fear most is the interferon system. Interferon Virus When a virus attack is detected by pattern-recognition receptors (PRRs), signals are generated to stimulate “many different cells” to express genes encoding for type I interferons (IFN-α and IFN-β). The most potent stimuli for type I interferons (IFN) synthesis are viral nucleic acids. These type I IFNs are secreted from the cells and act on other cells to prevent the spread of viral infection. Alerts Activates neighboring The most important type I IFNs in viral defense are: immune Signals uninfected (1) IFN-α (13 proteins) are produced mainly by DCs and mononuclear neighboring cells cells phagocytes (monocytes and macrophages). infected to undergo cells antiviral (2) IFN-β (a single protein) is produced by many cell types in response to state to viral infection. undergo apoptosis 23 Innate Immunity: Second Line of Defense The second-line of innate immunity defense handles pathogens in TWO general ways: Remember 24  Innate Immunity: Second-Line of Defense Natural Killer (NK) Cell Granzymes Hi there! NK Perforin 25 Innate Immunity: Second Line of Defense B. Antiviral response Natural Killer (NK) Cell NK cells are members of the innate immune response. NK cells share a common early progenitor with T-cells, but they do not develop in the thymus but in bone marrow. NK activity does not generate immunologic memory. They exhibit the capacity to kill virally infected cells and tumor cells in addition to bacteria, parasites, and fungi. Most NK cells are found in the blood or the spleen and liver (two organs that store blood), and relatively few NK cells reside in tissues not under attack. So, like neutrophils, NK cells are mostly on call. Innate Immunity: Second Line of Defense B. Antiviral response Natural Killer (NK) Cell Natural killer cells can play two roles in defending us against infections: (1) NK releases cytokines such as IFN-γ (type II IFN), which activate macrophages to destroy phagocytosed microbes. (2) During infection, NKs are activated by several signals according to the pathogen type; for example: - In viral infection, NK cells can be activated by type I IFN (IFN-α or IFN-β) and IL-12. - In bacterial infection, NK cells can be activated when their surface receptors detect the bacterial component (LPS). 1 3 2 27 Innate Immunity: Second Line of Defense B. Antiviral response Natural Killer (NK) Cell What does happen when NK cells are ACTIVATED? Activated NK cells Like CTLs, NK cells kill via the mechanisms of inducing apoptosis (by forcing infected cells to commit suicide). Granule exocytosis Unlike CTLs: releases granule proteins o NK cells do not express antigen-specific receptors. to the target cell o NK recognition for antigens or viral peptides is not MHC-restricted. Perforin facilitates the entry of other granule proteins (granzymes) in the cytosol of target cells Target cell Granzymes (proteolytic enzymes) cause death of the target cells by apoptosis. Apoptosis https://youtu.be/BvZV3uVpGkY 28 CTL = Cytotoxic T-Lymphocyte = CD8+ T-cell Innate Immunity: Second Line of Defense B. Antiviral response Natural Killer (NK) Cell How could NK cells differentiate between Host-Infected/Tumor Cell and Host Healthy Cell? NK cells employ 2 categories of receptors: o Killer Activating Receptor (KAR) → killing signal → NK becomes Cytotoxic (KAR ligands are stress proteins that are expressed only when cells are infected or undergoing transformation → i.e., change in phenotype, e.g., carcinogenesis). o Killer Inhibitory Receptor (KIR) → stop killing signal (KIR ligand is MHC-1; MHC class I molecules are found on the surface of all nucleated cells in the body. These molecules present peptides from within the cell to the immune system). What if …? KIR If only KARs If both the KIRs Don’t kill! and the KARs are engaged NK Cell Target are ligated Cell the target cells Kill! KAR Stress will be the target cell protein killed lives29 Therefore, the inhibitory signals stop the activation signals. (no killing) Innate Immunity: Second Line of Defense B. Antiviral response Natural Killer (NK) Cell Tumor or virus-infected cells may cause MHC down- regulation, allowing NK cell triggering via activating receptors and consequent target cell killing. Humans with genetic defects which make them deficient in NK cell function have great difficulty Why it would be a good idea to have NK cells destroy controlling herpes virus (HSV) and human cells that do not express class I MHC molecules? papillomavirus (HPV) infections. HSV and HPV are particularly Later in adaptive immunity, by examining peptides skillful at avoiding detection displayed by class I MHC proteins, CD8+ CTLs can by CD8+ CTLs. These viruses recognize “look inside” cells to see if anything is can block the MHC class I Target Cell wrong e.g., intracellular infection or cancer. I can’t presentation pathway by which (Before recognize antigenic peptides are Infection) But what if some clever virus can turn off (down the cell, No presented on infected cells to regulate) expression of MHC molecules in the cells MHC-1 CD8+ CTLs. it infects?! Those virus-infected cells will be unrecognizable “invisible” to CD8+ CTLs. No Thus, in those cases, it would be great to have worries, another killer (cytotoxic) cell that could kill the virus- I can Target Cell (After Infection) infected cells that don’t display MHC molecules on their CTL surface (i.e., a cytotoxic cell that has a recognition HPV HSV mechanism that is not MHC-restricted). NK 30 Innate Innate Immunity: Immunity: Second Line of Defense B. Antiviral response Natural Killer (NK) Cell The responses of cells resemble those of humans, displaying variations and distinct reactions based on the ligands of their Column A Column B receptors. A notable example is NK cells’ Activated (Cytotoxic) Scenario 1 responses to host cells. Accordingly, correlate the provided scenarios of NK cell attachment to the host cell in column A with the MHC-1 NK Cell corresponding activation status in column B. Host cell Killing Scenario 2 Not Activated NK Cell NK Cell Host cell 31 No Killing Innate Immunity: Second Line of Defense The principal components of innate immunity are: (Second-Line of Defense) (First-Line of Defense) (Second-Line of Defense) Molecules Physical and Chemical Cellular blood proteins, including components of (Physiological) Barriers The receptors (PRRs) on the cells of the innate the complement system, interferons, Skin and Mucous membranes immunity recognize structures (PAMPs) that are common to groups of related microbes and do not Acute phase proteins (APP) and other distinguish fine differences among microbes. mediators of inflammation. Next Lecture 32 Lecture 1 Learning Outcomes ❑ Innate immunity → Second-line of defense o Other innate immune cells (antiparasitic) o Acute Phase Proteins C-reactive protein (CRP) Cytokine storm and Sepsis Complement system o Tissue repair ❑ The Link between Innate Immunity and Adaptive Immunity ❑ Adaptive immunity → Third-line of defense o Antigenicity vs Immunogenicity 33 Lecture Learning1 Learning OutcomesOutcomes Define and describe the functions of acute phase proteins in the context of the innate immune response. Discuss the significance of C-reactive protein (CRP) as a marker of inflammation and its role in identifying potential infections or tissue damage. Explore the concept of a cytokine storm and its implications in the immune response to various infections and diseases. Examine the mechanisms and functions of the complement system as a critical component of innate immunity. Investigate the process of tissue repair and its importance in restoring damaged tissues following an immune response. Identify the link between innate immunity and adaptive immunity, emphasizing how innate immunity sets the stage for the third line of defense. Differentiate between antigenicity and immunogenicity, highlighting the key characteristics that make a substance either antigenic or immunogenic. 34 Innate Immunity: Pathogens (viruses, bacteria, fungi) First-Line Defenses 1 Anatomical and Physiological Barriers Innate Immunity First-Line Defenses (External) (Skin, mucous membranes, antimicrobial substances) Second-Line Defenses - Keep pathogens on the outside or Immunity Innate neutralize then before infection begins. 2 Inflammation, Fever, and Phagocytosis Second-Line Defenses (Phagocytes, Granulocytes, Complement, Cytokines) - Slow down infections after falling the 3 first-line defenses. Humoral and Cellular Immunity T-cells, B-cells, Cytokines Third-Line Defenses Adaptive - Target specific pathogens for destruction, when Immunity the second-line defense can’t contain the infection. - This defense mechanism incudes a memory component that allows the immune system to be effectively respond to the same pathogen in the future. Adaptive Immunity 35  Innate Immunity: Second-Line of Defense “Extracellular Killing” Immune Cells against Helminthes (Worms) 36 Fighters: Immune Cells Eosinophil They circulate in the blood. Some eosinophils are normally present in peripheral tissues, especially in mucosal linings of the respiratory, gastrointestinal, an genitourinary tracts. Cytotoxic to helminth (worms). They express cytoplasmic granules containing enzymes that are harmful to the cell walls of parasites. https://www.youtube.com/shorts/w DvxLSA6kN4?feature=share 37 Fighters: Immune Cells Basophil and Mast cell Basophils circulate in the blood. Mast cells are most abundant in the skin and mucosal epithelia (tissue). They release many potent inflammatory mediators that defend against infections by helminthic parasites (worms). They cause symptoms of allergic diseases, e.g., Hay fever. Type I Hypersensitivity (will be discussed later). 38 Defense Systems What is the main function of eosinophils? a. Fighting bacterial infections b. Fighting viral infections c. Fighting fungal infections d. Fighting parasites 39 Defense Systems As we've learned in previous lectures, molecules are crucial in the immune system. They assist in guiding phagocytes through chemotaxis and make pathogens easier to capture by labeling them through opsonization. Which of the following are molecules of the innate immune system? Acute Phase Reactants Cytokines N.B. Cytokines can be produced by innate and adaptive immune Complement System cells. Antibodies 40 Fighters: Molecules Remember Acute Phase Reactants Cytokines Complement System Antibodies They are inflammation They are a large group of proteins, peptides The complement system is Antibodies, aka markers that exhibit significant or glycoproteins that are secreted by specific an enzyme cascade that Immunoglobulins (Ig), changes in serum concentration cells of immune system. Cytokines are a helps defend against are glycoproteins during inflammation. They are category of signaling molecules that infection. Many produced by plasma produced in the liver during mediate and regulate immunity, complement proteins cells. They are secreted acute and chronic inflammatory inflammation and hematopoiesis. occur in serum as inactive by plasma cells, which states. Cytokine is a general name; other names enzyme precursors are protein-making cells are defined based on their presumed (zymogens); others reside C-reactive protein (CRP) that participate in function, cell of secretion, or target of action. Fibrinogen on cell surfaces. It causes humoral immune For example: Ferritin o Lymphokines: cytokines made by the opsonization and responses against Serum amyloid A lymphocytes. Many of the lymphokines are killing of bacteria. foreign antigens. Mannose-binding lectin (MBL) also known as interleukins (ILs). Serum amyloid P component o Monokines: cytokines secreted by IgM Alpha-1 acid glycoprotein monocytes or macrophages. IgG Haptoglobin o Chemokines: cytokines with chemotactic IgA Ceruloplasmin activities. IgE IgD Interleukins (IL) Chemokines Colony-stimulating factors (CSF) Interferons (INF) Tumor necrosis factor (TNF) Transforming growth factors (TGF) 41  Innate Immunity: Second-Line of Defense Complement System Let’s kill some bacteria 42 Innate Immunity: Second Line of Defense C. Molecules Complement System 1 2 3 The complement system consists of over 30 proteins CLASSICAL ALTERNATIVE LECTIN produced by the liver that circulate in blood serum and pathway pathway pathway within tissues throughout the body. MBL The system is so named because it “completes,” or enhances, cells of the immune system in destroying microbes. The complement system proteins are inactive (zymogens) until split into fragments (products), which activates them. Therefore, they form a proteolytic cascade, where serine proteases activate each other by limited proteolysis in a strictly ordered manner. MAC There are THREE pathways to activate the complement “membrane system: attack complex” 1. Classical pathway 2. Alternative pathway 3. Lectin pathway Innate Immunity: Second Line of Defense C. Molecules Complement System Pathways of Complement Activation Mannose -binding lectin (MBL) Inflammation (Chemotaxis and Anaphylatoxin) “membrane attack complex” Opsonization MAC Inflammation (Chemotaxis and Anaphylatoxin) MAC Cytolysis [Membrane Attack Complex] Inflammation Opsonization 44 Cytolysis Inflammation Opsonization Cytolysis Innate Immunity: Second Line of Defense C. Molecules Complement System The classical pathway: The alternative pathway: The lectin pathway: It is initiated and activated when Unlike the classical pathway, it does Unlike the classical pathway, it does not antibodies bind to antigens. not involve antibodies. involve antibodies. 1. Antibodies attach to antigens (for The alternative pathway is activated by When macrophages ingest bacteria, example, proteins or large contact between C3b and a pathogen. viruses, and other foreign matter by polysaccharides on the surface of a phagocytosis, they release cytokines that 1. C3, constantly present in the blood, bacterium or other cell), forming stimulate the liver to produce lectins, combines with complement proteins antigen–antibody complexes. proteins that bind to carbohydrates. called factor B, factor D, and factor P 2. The antigen–antibody complexes bind to (properdin) on the microbe’s surface. 1. Mannose-binding lectin (MBL) binds to and activate C1. the carbohydrate mannose. 2. The complement proteins are attracted to 3. Next, activated C1 activates C2 and C4 microbial cell surface material (mostly 2. As a result of binding, MBL functions as by splitting each of them. lipid–carbohydrate complexes of an opsonin to enhance phagocytosis and certain bacteria and fungi, e.g., LPS activates C2 and C4. 4. Then C2 splits into fragments C2a and (endotoxin)). 3. C2b and C4b activate C3. C2b, and C4 is split into C4a and C4b. 3. Once the complement factors (B,D,P) 4. Splitting of C3 into two fragments: 5. C2b and C4b activate C3. combine and interact to activate C3. C3a → inflammation. 6. Splitting of C3 into two fragments: C3b → cytolysis and opsonization 4. Splitting of C3 into two fragments: C3a → (anaphylatoxin) inflammation. C3a → inflammation. C3b → cytolysis and opsonization. N.B. MBL binds to many pathogens because MBL C3b → cytolysis and opsonization. molecules recognize a distinctive pattern of carbohydrates that includes mannose, which is found in bacterial cell walls and on some viruses. 45 Innate Immunity: Second Line of Defense C. Molecules Complement System https://www.youtube.com/watch?v=YdVhrf1V0F4&t=3s 46 Innate Immunity: Second Line of Defense C. Molecules Complement System The classical pathway The alternative pathway The lectin pathway Splitting of C3 into two fragments: C3a → inflammation (anaphylatoxin and chemotactic factor) C3b → cytolysis and opsonization Imp. Notes: Anaphylatoxins (C3a and C5a) induce Mast cells to Cytolysis of microbial cells involves the membrane degranulate histamines. attack complex (MAC= C5b,C6,C7,C8,C9): Gram-negative bacteria are more susceptible to 1. C3b splits C5 into C5a and C5b. cytolysis because they have a few layers of C5a is a anaphylatoxin and chemotactic factor. peptidoglycan to protect the plasma membrane from the effects of complement. 2. Fragments C5b, C6, C7, and C8 bind together sequentially Gram-positive bacteria have many layers of and insert into the plasma membrane of the invading cell. peptidoglycan, which limit complement’s access to the 3. C5b through C8 act as a receptor that attracts a C9 plasma membrane and thus interfere with cytolysis. fragment. Bacteria that are not killed by the MAC are said to be 4. Additional C9 fragments polymerize and form a MAC resistant. transmembrane channel (a hole) allowing for flow of MAC is effective against enveloped viruses. extracellular fluid into the pathogen. The fluid inflow 47 bursts the microbial cell. Innate Immunity: Second Line of Defense C. Molecules Complement System Outcomes of Complement Activation A) Cytolysis B) Opsonization C) Inflammation Mast Cell Microbes burst as extracellular fluid flows in Coating microbes with C3b Increase the permeability of blood through transmembrane channel formed by enhances phagocytosis. vessels, and chemotactic agents 48 membrane attack complex (MAC). attract phagocytes to area. Innate Immunity: Second Line of Defense C. Molecules Complement System Which of the following is/are anaphylatoxin(s)? A. C5b B. C3a C. C3b B&E You are very You are so D. C3 and C5 brave strong E. C5a Thanks for the compliments Which of the following is more susceptible of cytolysis of the complement system? A. Gram positive bacteria B. Gram negative bacteria B C. Non-enveloped viruses 49  Innate Immunity: Second-Line of Defense Acute Phase Proteins 50 Innate Immunity: Second Line of Defense C. Molecules Acute Phase Proteins Proinflammatory mediators (released due to injury and activation of tissue resident macrophages and mast cells) Acute Phase Protein Histamine - Leukotrienes – These are enzymes and factors whose production is induced by tissue injury: Cytokines (IL-1b and IL-18) C-reactive protein (CRP) Plasma fibronectin (1) Activate the classical pathway of (1) Opsonize ECM debris. complement system. (2) Activates macrophages so that LOCAL Inflammation major events (2) Act as an opsonin. they can phagocytize the debris. proinflammatory mediators (ECM = Extracellular matrix) (TNF-α, IL-1, IL-6) Mannose-binding lectin (MBL) (1) Activate the lectin pathway of Lipopolysaccharide–binding complement system. protein (LBP) (2) Act as an opsonin. (1) Bind to bacterial LPS (endotoxin) SYSTEM to inhibit LPS-induced cellular Inflammatory Responses Fibrinogen stimulation. (1) Induces clot formation. (2) Transfer LPS to immune cell Fibrinogen –(reflects in)→ ESR. receptors –(resulting in)→ activation Complement system proteins of immune cells and production of (1) Opsonize pathogens (e.g. C3b). inflammatory factors. (2) Induce a series of inflammatory Ferritin (protein that stores iron) responses that help to fight infection (1) Sequesters iron to inhibit microbial (e.g. C5a). iron scavenging. Remember (3) Microbial lysis (MAC complex). 51 Innate Immunity: Defense SystemsSecond Line of Defense C. Molecules C-Reactive Protein (CRP) Which of the following best describes the role of C-reactive protein (CRP) in the body? A. CRP is primarily involved in blood clotting. B. CRP is a type of white blood cell that fights infections. C C. CRP is an opsonin produced by the liver in response to infection. D. CRP is responsible for transporting oxygen in the blood. 52  Innate Immunity: Second-Line of Defense Cytokines 53 Innate Immunity: Second Line of Defense C. Molecules Cytokines Remember Classification of Cytokines Remember 1 2 3 4 5 Interleukins (IL) Interferons Chemokines Tumor Necrosis Hematopoietic colony- They are a group of (IFNs) Factors (TNFs) stimulating factors cytokines, which are They are signaling (HCSF) They are a group of proteins secreted by They are a group of secreted proteins and cytokines, which are signaling proteins cells of the immune They are a family of glycoproteins that signal molecules, that are signaling proteins made and released by system that play a major role in the proliferation, expressed and secreted secreted by cells of the host cells in response stimulate the differentiation, and survival of by white blood cells immune system. They are to the presence of movement of other primitive hematopoietic stem (leukocytes) and some mainly produced by several viruses. cells. Their name is other body cells. The macrophages, but can be and progenitor cells. human genome encodes derived from IMP e.g. chemotaxis. produced by other cells as more than 50 interleukins well. 6 and related proteins. Type I IFN: IFN-α TNFs play a major role in Transforming growth IMP e.g. IMP e.g. promoting the IFN-β factors (TGFs) IL-1β IL-8 inflammatory process IL-18 Type III They are a group of proteins that IL-2 regulate numerous cellular functions IFN: IFN-λ IMP e.g. IL-6 such as cell growth, cell IL-12 Type II IFN: TNF- α proliferation, cell differentiation, IL-10 IFN-γ and apoptosis. 54 Innate Immunity: Second Line of Defense C. Molecules Cytokines Main Function Cytokine Main Producer IL-1β Tissue resident macrophages Proinflammatory IL-18 (inflammasome) Important Examples Proinflammatory: Activation of endothelium of Increase vascular permeability IL-1 Cytokines Leukocytosis IL-6 Tissue resident macrophages Activation of lymphocytes TNF-α Increase antibody production APP and Fever Activated CD4+ and CD8+ T-cells Proinflammatory IL-2 (Lecture 5) Chemokine IL-8 Tissue resident macrophages Activation of NK cells IL-12 Tissue resident macrophages Activation of macrophages Type II IFN: IFN-γ NK cells Type I IFN: IFN-α DCs, monocytes, and macrophages Antiviral response IFN-β many cell types Type III IFN: IFN-λ epithelial cells and DCs 55 Anti-inflammatory IL-10 Monocytes and some T-lymphocytes  C. Molecules Innate Immunity: Second Line of Defense Sepsis and Cytokine storm The early phase of sepsis is caused by cytokines Cell damage Early produced by macrophages (early cytokine burst) cytokine Microbes that are activated by PAMPs or DAMPs. These burst DAMPs inflammatory cytokines are mainly IL-1, IL-6, TNF-α, IFN-γ, and IL-12. Immune Microbes cells PAMPs Therefore, cytokine release syndrome (aka Endothelial cytokine storm) is a life-threatening systemic Immune cells cells inflammatory condition characterized by secretion Cytokines PRR of massive amounts of inflammatory DAMPs cytokines by immune cells. Cytokines Cytokine +ve receptor These cytokines give feedback to the immune feedback cells to elicit yet more cytokines. PAMP loops Cytokines Normally, these positive feedback loops represent effective modes of immune DAMP Endothelial cells amplification, which are usually kept in check by Inflammatory DCs and self-regulating immune mechanisms, e.g., the Responses Lymphocytes Cytokine activation of regulatory T cells (T-regs). e.g. coagulation, apoptosis Chousterman BG, et al. Cytokine storm and sepsis disease pathogenesis. Semin Immunopathol. 2017 Jul;39(5):517-528. doi: Multiple organ failure 10.1007/s00281-017-0639-8. Epub 2017 May 29. PMID: 28555385. 56 Cytokine cascade during sepsis