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Innate Immunity - 2.1
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Innate Immunity - 2.1

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Questions and Answers

What is the principal function of intraepithelial lymphocytes in TLR4 signalling?

  • Activation of complement
  • Lysis of infected cells
  • Prevent microbial entry
  • Microbial killing (correct)

    • Which cytokine is primarily involved in promoting inflammation during TLR4 signalling?

  • IL-10
  • IL-15
  • Type I interferons
  • TNF (correct)

    • Which effector cells are primarily responsible for early phagocytosis and killing of microbes?

  • NK cells
  • Neutrophils (correct)
  • Macrophages
  • Intraepithelial lymphocytes

    • What is the function of complement in the innate immune response mediated by TLR4?

    <p>Opsonisation of microbes</p> Signup and view all the answers

    How does Type II interferon contribute to TLR4 signalling?

    <p>Activates macrophages</p> Signup and view all the answers

    What primary function do interferons serve in the immune response?

    <p>Inhibiting viral replication in neighboring cells</p> Signup and view all the answers

    Which interferon is primarily released from macrophages and activates NK cells?

    <p>IFNy</p> Signup and view all the answers

    Which Toll-like receptor is specifically involved in recognizing flagellin?

    <p>TLR5</p> Signup and view all the answers

    How does IFNa and IFNb protect healthy cells during a viral infection?

    <p>By making them release protein kinase R</p> Signup and view all the answers

    Which of the following outcomes is NOT a result of IFNy binding to its receptor in macrophages?

    <p>Inhibition of bacterial phagocytosis</p> Signup and view all the answers

    What type of pathogen recognition is primarily facilitated by Toll-like receptors (TLRs)?

    <p>Recognition of exogenous ligands</p> Signup and view all the answers

    Which of the following is a direct action of IFNy within the immune system?

    <p>Activation of macrophage killing mechanisms</p> Signup and view all the answers

    Which Toll-like receptor is involved in recognizing double-stranded RNA?

    <p>TLR8</p> Signup and view all the answers

    Which of the following cytokines is known to activate macrophages and enhance their functionality?

    <p>IFNy</p> Signup and view all the answers

    Which of the following receptors recognizes lipopolysaccharide (LPS)?

    <p>TLR4</p> Signup and view all the answers

    Which of the following cytokines is primarily responsible for the differentiation of T cells into Th1 cells?

    <p>IL-12</p> Signup and view all the answers

    What is the major function of chemokine CCL5?

    <p>Causes osteodegradation</p> Signup and view all the answers

    The interaction of mannose with lectin initiates which of the following immune processes?

    <p>Activation of C4</p> Signup and view all the answers

    Which pattern recognition receptor is primarily associated with recognizing double-stranded RNA from viruses?

    <p>TLR3</p> Signup and view all the answers

    How does IL-10 mainly exert its effects in the immune response?

    <p>Inhibition of pro-inflammatory cytokines</p> Signup and view all the answers

    What is the primary cellular target for IL-6 in the context of acute-phase response?

    <p>Liver</p> Signup and view all the answers

    Which receptor is associated with the chemokine CXCL8?

    <p>CXCR1</p> Signup and view all the answers

    Which cytokine is particularly critical in inducing fever through its action on the hypothalamus?

    <p>IL-1</p> Signup and view all the answers

    What type of cells predominantly produce Type I interferons?

    <p>Macrophages</p> Signup and view all the answers

    Which pattern recognition receptor recognizes lipopolysaccharides found in Gram-negative bacteria?

    <p>TLR4</p> Signup and view all the answers

    Which interleukin is known to cause proliferation of NK cells?

    <p>IL-18</p> Signup and view all the answers

    Which cytokine enhances cytolytic activity in NK cells and T cells?

    <p>IL-12</p> Signup and view all the answers

    Which receptor type primarily engages in macrophage activation through recognizing N-formylmethionyl peptides?

    <p>N-formylmethionyl peptide receptors</p> Signup and view all the answers

    What does the complement component C3b act as in the immune response?

    <p>Opsonin</p> Signup and view all the answers

    What is the primary function of the membrane attack complex (MAC)?

    <p>Create pores in bacterial membranes</p> Signup and view all the answers

    How do C3a and C5a influence white blood cells during an immune response?

    <p>Promote migration through chemotaxis</p> Signup and view all the answers

    What happens to a bacterial cell upon the accumulation of fluids and ions due to MAC activity?

    <p>The cell undergoes lysis</p> Signup and view all the answers

    Which receptor on macrophages allows them to bind to C3b during phagocytosis?

    <p>C3b receptor</p> Signup and view all the answers

    What is formed from the cleavage of C5b through C9 in the complement cascade?

    <p>Membrane pore</p> Signup and view all the answers

    In the analogy relating bacteria to food, what does Nutella represent?

    <p>Opsonization enhancing activity</p> Signup and view all the answers

    What is the significance of the fluid movement facilitated by the MAC into the bacterial cell?

    <p>Leads to osmotic lysis of the bacterial cell</p> Signup and view all the answers

    What can occur to C3b once the membrane attack complex is formed?

    <p>It can enhance inflammatory responses</p> Signup and view all the answers

    How do neutrophils respond differently compared to macrophages after recognizing pathogens?

    <p>They exocytose antigens</p> Signup and view all the answers

    What term is used to describe the process of pathogens being marked for ingestion by phagocytes?

    <p>Opsonization</p> Signup and view all the answers

    Which function do C3a and C5a serve in enhancing the immune response?

    <p>Act as pro-inflammatory mediators</p> Signup and view all the answers

    What role does the C3a component specifically play during the immune response?

    <p>Promotion of leukocyte recruitment</p> Signup and view all the answers

    What is a sign that a bacterial cell is undergoing lysis due to MAC function?

    <p>Fluids seep into the cell</p> Signup and view all the answers

    What is the specific sugar molecule that serves as an antigen on the bacteria?

    <p>Manos</p> Signup and view all the answers

    Which protein specifically binds to the sugar Manos?

    <p>Mannose binding lectin</p> Signup and view all the answers

    In the lectin pathway of the complement system, which component directly binds after mannose binding lectin?

    <p>C4</p> Signup and view all the answers

    Which components form the membrane attack complex (MAC) in the complement system?

    <p>C5b, C6, C7, C8, C9</p> Signup and view all the answers

    What is the primary role of the C3b receptor on immune cells?

    <p>Opsonization enhancement</p> Signup and view all the answers

    What cellular response does C3b initiate when it binds to its receptors?

    <p>Phagocytosis</p> Signup and view all the answers

    What is the function of C3a and C5a in the context of the immune response?

    <p>Increasing vascular permeability and chemotaxis</p> Signup and view all the answers

    Which of the following best describes the complement proteins?

    <p>Circulating proteins activated during an immune response</p> Signup and view all the answers

    What initiates the lectin pathway of the complement system?

    <p>Mannose binding by lectin</p> Signup and view all the answers

    What is the complement system classified as in terms of immunity?

    <p>Non-specific innate immune system</p> Signup and view all the answers

    Which immune pathway is stimulated by the presence of mannose on bacterial surfaces?

    <p>Lectin pathway</p> Signup and view all the answers

    What is the architecturally distinctive feature of the membrane attack complex (MAC)?

    <p>It consists of pentameric protein components</p> Signup and view all the answers

    How are C3b and C3a activated during the complement process?

    <p>Through proteolytic cleavage</p> Signup and view all the answers

    What type of immune cells are primarily targeted by C3b for activation?

    <p>Macrophages and neutrophils</p> Signup and view all the answers

    What is the primary purpose of opsonization in the immune response?

    <p>To enhance the recognition and uptake of pathogens by immune cells</p> Signup and view all the answers

    Which component initiates the classical pathway of complement activation?

    <p>C1 activating through antibody binding</p> Signup and view all the answers

    What role does C3a play in the immune response?

    <p>It enhances the inflammatory response</p> Signup and view all the answers

    Which pathway is described as having no antibody-mediated effects?

    <p>Alternative pathway</p> Signup and view all the answers

    What is the end result of the membrane attack complex (MAC) formation?

    <p>Direct lysis of pathogen cells</p> Signup and view all the answers

    What triggers the release of C3a and C5a during complement activation?

    <p>Proteolytic cleavage of complement proteins</p> Signup and view all the answers

    Which receptor type on phagocytes enhances the process of opsonization?

    <p>C3b receptors</p> Signup and view all the answers

    What is the overall effect of the alternative pathway of complement activation?

    <p>To promote inflammation while lysing pathogens</p> Signup and view all the answers

    Which component acts directly to bind to bacterial antigens in the classical pathway?

    <p>C3b</p> Signup and view all the answers

    Which complement components are sequentially activated after C3b in the complement pathway?

    <p>C5b, C6, C7, C8, C9</p> Signup and view all the answers

    What does the alternative pathway enhance to primarily aid in the immune response?

    <p>Phagocytosis via opsonization</p> Signup and view all the answers

    What additional factor is mentioned that can play a role in the alternative pathway?

    <p>Factor B</p> Signup and view all the answers

    During the complement activation process, what is the role of C5a?

    <p>Enhances the inflammatory response</p> Signup and view all the answers

    What does the term 'membrane attack complex' refer to in complement activation?

    <p>A set of proteins that kill pathogens directly</p> Signup and view all the answers

    What is a consequence of C3b being exposed during complement activation?

    <p>It can bind neutrophils enhancing phagocytosis</p> Signup and view all the answers

    What is the role of the complement protein C3b in the immune response?

    <p>It binds to bacterial antigens for opsonization.</p> Signup and view all the answers

    What is the significance of the FC portion of an antibody in the complement system?

    <p>It serves as a binding site for complement proteins.</p> Signup and view all the answers

    How are C3a and C5a activated during the inflammatory response?

    <p>Through the action of proteases released from mast cells.</p> Signup and view all the answers

    What are the two components into which C3 is split during the complement cascade?

    <p>C3a and C3b</p> Signup and view all the answers

    Which cell type is primarily responsible for releasing histamine during an inflammatory response?

    <p>Mast cells</p> Signup and view all the answers

    What is the primary function of complement proteins in inflammation?

    <p>Enhancing phagocytosis and attracting immune cells.</p> Signup and view all the answers

    Which complement protein directly interacts with the FC portion of antibodies?

    <p>C1</p> Signup and view all the answers

    In the complement cascade, what is the role of C5b?

    <p>It assists in the formation of the membrane attack complex.</p> Signup and view all the answers

    What is the consequence of the activation of C3a and C5a in the immune response?

    <p>They stimulate the release of inflammatory mediators.</p> Signup and view all the answers

    Which complement proteins are primarily involved in opsonization?

    <p>C3b and C5a</p> Signup and view all the answers

    What triggers the complement cascade to begin?

    <p>Binding of antibodies to antigens.</p> Signup and view all the answers

    What is the effect of complement activation on blood vessels during inflammation?

    <p>Vasodilation and increased permeability.</p> Signup and view all the answers

    Which pathway initiates the complement system when antibodies bind to an antigen?

    <p>Classical pathway</p> Signup and view all the answers

    Study Notes

    TLR4 Signalling

    • TLR4 signalling has two main mechanisms
    • TLR4 is a pattern recognition receptor that plays a key role in the innate immune response to bacterial infections
    • TLR4 recognizes lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria
    • TLR4 signalling leads to the production of pro-inflammatory cytokines, including TNF-α, IL-1β, and IL-6, as well as type I interferons

    Complement System

    • The complement system is a part of the innate immune system that helps to fight infection
    • It is composed of a series of serum proteins that are activated in a cascade
    • Activation of the complement system results in the formation of the membrane attack complex, which can lyse bacterial cells.
    • Three pathways can activate the complement system: the classical pathway, the alternative pathway, and the lectin pathway
    • **The classical pathway ** is activated by the binding of C1 to an antibody-antigen complex
    • The alternative pathway is activated by the spontaneous hydrolysis of C3
    • The lectin pathway is activated by the binding of mannose-binding lectin (MBL) to bacterial cell surface carbohydrates
    • The complement components C3 and C4 are essential for the activation of all three complement pathways
    • C3 cleaves into C3a and C3b
    • C3a is an anaphylatoxin - a component of the immune system - involved in mast cell degranulation and inflammation
    • C3b coats the surface of bacteria and can be cleaved by C5 convertase into C5a and C5b
    • C5a is an anaphylatoxin and opsonin
    • C5b binds with C6, C7, C8 and C9 components to form the membrane attack complex (MAC)
    • The MAC is a transmembrane pore that can lyse bacterial cells

    Cytokines

    • Cytokines are a diverse group of small proteins (20-60 amino acids) secreted by immune cells that act as intercellular messengers and are involved in regulating the intensity and duration of the immune response
    • TNF - tumor necrosis factor alpha
      • Size: 15 kD; 51 kD homotrimer
      • Source: Macrophages, T cells
      • Targets: Endothelial cells, neutrophils, hypothalamus, liver, muscle, fat, many cell types
      • Biological Effects: Activation of endothelial cells (inflammation, coagulation), Activation of neutrophils, Fever, Synthesis of acute-phase proteins, Catabolism (cachexia), Apoptosis
    • IL-1 - interleukin-1
      • Size: 17 kD mature form; 33 kD precursor
      • Source: Macrophages, endothelial cells, some epithelial cells
      • Targets: Endothelial cells, hypothalamus, liver, T cells
      • Biological Effects: Activation of endothelial cells (inflammation, coagulation), Fever, Synthesis of acute-phase proteins, Th17 differentiation
    • IL-12 - interleukin-12
      • Size: Heterodimer of 35 kD (p35) and 40 kD (p40) subunits
      • Source: Macrophages, dendritic cells
      • Targets: T cells, NK cells
      • Biological Effects: Th1 differentiation, IFN-γ synthesis, Increased cytolytic activity
    • Type I interferons
      • Size: IFN-α: 15 - 21 kD, IFN-β: 20 - 25 kD
      • Source: Macrophages, plasmacytoid DCs for IFN-α, fibroblasts for IFN-β
      • Targets: All cells, NK cells
      • Biological Effects: Antiviral state, increased class I MHC expression, activation of NK cells, Causes cells to release protein kinase R
    • IL-10 - interleukin-10
      • Size: Homodimer of 34-40 kD and 18 kD subunits
      • Source: Macrophages, T cells (mainly Tregs)
      • Targets: Macrophages, dendritic cells
      • Biological Effects: Inhibition of IL-12, co-stimulators and class II MHC molecules, anti-inflammatory
    • IL-6 - interleukin-6
      • Size: 19 - 26 kD
      • Source: Macrophages, endothelial cells, T cells
      • Targets: Liver, B cells, T cells
      • Biological Effects: Synthesis of acute-phase proteins, Proliferation of antibody producing cells, Th17 differentiation
    • IL-15 - interleukin-15
      • Size: 13 kD
      • Source: Macrophages, others
      • Targets: NK cells, T cells
      • Biological Effects: NK cell proliferation, T cell proliferation (memory CD8+ cells)
    • IL-18 - interleukin-18
      • Size: 17 kD
      • Source: Macrophages
      • Targets: NK and T cells
      • Biological Effects: IFN-γ synthesis
    • IL-23 - interleukin-23
      • Size: Heterodimer of a 19 kD (p19) and 40 kD (p40) subunits
      • Source: Macrophages and dendritic cells
      • Targets: T cells
      • Biological Effects: Development and maintenance of IL-17 producing T cells (Th17)
    • IL-27 - interleukin-27
      • Size: Heterodimer of 28 kD and 13 kD subunits
      • Source: Macrophages and DCs
      • Targets: T cells, NK cells
      • Biological Effects: Th1 differentiation, inhibition of Th17 cells, IFN-γ synthesis

    Chemokines

    • Chemokines are a family of small chemotactic cytokines that are produced by cells of the immune system and other tissues to attract specific types of leukocytes to sites of inflammation and infection
    • CCL2 - (MCP-1)
      • Chemokine receptor: CCR2
      • Major Function: Mixed leukocyte recruitment
    • CCL3 - (MIP-1α)
      • Chemokine receptor: CCR1, CCR5
      • Major Function: Mixed leukocyte recruitment
    • CCL4 -(MIP-1β)
      • Chemokine receptor: CCR5
      • Major Function: T cell, DC, monocyte and NK recruitment; HIV coreceptor
    • CCL5 - (RANTES)
      • Chemokine receptor: CCR1, CCR3, CCR5
      • Major Function: Mixed leukocyte recruitment, causes osteo degregation
    • CCL11 - (EOTAXIN)
      • Chemokine receptor: CCR3
      • Major Function: Eosinophil, basophil and Th2 recruitment
    • CCL19 - (MIP-β)
      • Chemokine receptor: CCR7
      • Major Function: T cell and DC migration into parafollicular zones of lymph nodes
    • CCL21 - (SLC)
      • Chemokine receptor: CCR7
      • Major Function: T cell and DC migration into parafollicular zones of lymph nodes
    • CCL22 - (MDC)
      • Chemokine receptor: CCR4
      • Major Function: Lymphocyte recruitment into intestine
    • CXCL1 - (GROα)
      • Chemokine receptor: CXCR2
      • Major Function: Neutrophil recruitment
    • CXCL8 - (IL-8)
      • Chemokine receptor: CXCR1, CXCR-2
      • Major Function: Neutrophil recruitment
    • XCL1 - (LYMPHOACTIN)
      • Chemokine receptor: XCR1
      • Major Function: T cell and NK cell recruitment
    • CX3CL1 - (FRACTALINE)
      • Chemokine receptor: CX3CR1
      • Major Function: T cell, NK cell and monocyte recruitment

    Innate Immune Recognition

    • The innate immune system is the first line of defense against infection
    • It is composed of cells and molecules that are able to recognize and respond to a wide range of pathogens
    • Pattern recognition receptors (PRRs) are a class of receptors expressed by cells of the innate immune system that recognize patterns of molecules associated with pathogens.
    • Recognition of these patterns triggers the release of cytokines, antimicrobial peptides, and other effector molecules that help to control infection

    PAMPS/DAMPS and PRRs

    • PAMPs - Pathogen-associated molecular patterns are molecular structures that are found on pathogens but not on host cells
      • dsRNA - double stranded RNA, source: replicating viruses. Pattern recognition receptor: TLR3. Principal innate immune response: Type I interferon production
      • LPS - lipopolysaccharide, source: Gram negative bacterial cell wall. Pattern recognition receptor: TLR2/4*/CD14. Principal innate immune response: Macrophage activation
      • Unmethylated CpG nucleotides - source: bacterial DNA. Pattern recognition receptor: TLR9. Principal innate immune response: Macrophage activation
      • N-formylmethionyl peptides - source: bacterial proteins. Pattern recognition receptor: N-formylmethionyl peptide receptors. Principal innate immune response: Neutrophil and macrophage activation
      • Mannose rich glycans - source: microbial glycoproteins or glycolipids. Pattern recognition receptor: 1. Macrophage mannose receptor, 2. Plasma mannose binding lectin. Principal innate immune response: 1. Phagocytosis by macrophages, 2. Opsonisation and complement activation
      • Phosphorylcholine and related molecules - source: microbial membranes. Pattern recognition receptor: Plasma C-reactive protein. Principal innate immune response: Opsonisation and complement activation
    • DAMPs - Damage-associated molecular patterns are molecules that are released from damaged or stressed cells
    • PRRs - Pattern recognition receptors are receptors that are expressed by cells of the innate immune system that can recognize PAMPs and DAMPS
      • TLR - Toll-like receptors
      • NLR - NOD-like receptors
      • RLR - RIG-I-like receptors
      • CLR - C-type lectin receptors
      • CDS - DNA sensors

    Interferons

    • Interferons (IFNs) are cell signaling proteins produced by the immune system in response to the presence of pathogens like viruses, bacteria, parasites, tumor cells.
    • IFN-γ
      • Released from: Macrophages, NK cells
      • Causes: Binds to gamma interferon receptors, causing macrophage activation and proliferation, killing of phagocytosed bacteria, antiviral and tumor response, activates Mos (macrophages), NK cells, cell mediated immunity
    • IFN-β
      • Released from: Platelets
    • IFN-α and IFN-β
      • Released from: Virus infected cell
      • Causes: Makes nearby healthy cell release protein kinase R to protect against virus, activate NK cells

    Toll-like Receptors

    • TLRs are type I transmembrane proteins that are expressed on the surface of cells of the innate immune system, primarily immune cells but also non-immune cells
    • They act as sentinels, recognizing specific microbial structures referred to as pathogen-associated molecular patterns (PAMPs)
    • Each TLR recognizes a distinct PAMP or a group of similar PAMPs
    • The activation of TLRs leads to the production of cytokines and other signaling molecules, triggering an immune response
    • Functions include:
      • Recognizing invading pathogens
      • Initiating the adaptive immune system
      • Stimulating inflammation
      • Promoting the clearance of pathogens
    • On cell membrane: TLR1, TLR2, TLR4, TLR5, TLR6
    • Inside cell: TLR3, TLR7, TLR8, TLR9
    • Toll like receptor | Exogenous ligand
      • TLR1* | Lipoproteins, Lipopeptides
      • TLR2* | Lipoglycans, Modified Lipopolysaccharide, Lipoteichoic Acid, Peptidoglycan, Zymosan, Phospholipomannan, Protozoan GPI anchor, Viral envelope proteins, dsRNA
      • TLR4 | Lipopolysaccharide, Lipid-A, Glycoinositolphospholipids, Mannan, Viral envelope proteins, RSV F-protein
      • TLR5 | Flagellin
      • TLR6* | Multiple diacyl lipopeptides
      • TLR7 | ssRNA
      • TLR8 | ssRNA
      • TLR9 | CpG DNA, dsDNA
      • TLR10 | ?

    Complement Proteins

    • The liver continuously produces complement proteins, which circulate in plasma.

    • Complement proteins can be activated upon inflammatory response and migrate to the site.

    • Complement proteins can kill microorganisms by three pathways - the classical pathway, the alternative pathway, and the lectin pathway.

    The Classical Pathway

    • This pathway is triggered by antibodies binding to bacterial antigens.

    • The FC region of the antibody attracts complement proteins, initiating a cascade: C1, C4, C2, C3, C5, C6, C7, C8, C9.

    • C3a and C5a enhance inflammation by attracting white blood cells (chemotactic agents).

    • C5b, C6, C7, C8, C9 form the membrane attack complex (MAC), which punctures the bacterial cell membrane, causing lysis.

    • C3b acts as an opsonin, making bacteria more attractive for phagocytosis by macrophages and neutrophils, by binding to C3b receptors on these cells.

    The Alternative Pathway

    • This pathway is triggered by direct binding of C3b to the bacterial surface, without antibody involvement.

    • C3a and C5a enhance inflammation.

    • MAC formation leads to lysis.

    • C3b acts as an opsonin, enhancing phagocytosis.

    The Lectin Pathway

    • This pathway is initiated by binding of a protein called mannose-binding lectin to mannose, a sugar on the bacterial surface.

    • The cascade begins with C4, followed by C2, C3, C5, C6, C7, C8, C9.

    • MAC formation leads to lysis. ### Complement system

    • The complement system is a part of the innate immune system.

    • It's a non-specific immune response.

    • Complement proteins are produced by the liver and circulate in the plasma in an inactive form.

    • Activation occurs during the inflammatory response.

    • Complement proteins are activated by specific changes in the microcirculation, such as increased vascular permeability.

    • The complement system acts through two pathways: antibody-mediated (classical) and non-antibody mediated (alternative).

    • The classical pathway is activated by antibodies bound to antigens on the surface of pathogens.

    • The alternative pathway is activated by the direct binding of C3b to the surface of pathogens.

    • The lectin pathway is activated by the binding of mannose-binding lectin to mannose sugars on the surface of pathogens.

    •  C3b acts as an opsonin, enhancing phagocytosis by binding to the C3b receptor on phagocytes.

    • The membrane attack complex (MAC) is a pentameric protein complex formed by C5b, C6, C7, C8, and C9.

    • The MAC forms pores in bacterial cell membranes, causing lysis.

    • C3a and C5a can be converted to their active forms by proteases secreted by mast cells.

    • Active C3a and C5a enhance the inflammatory response through chemotaxis.

    • The complement system helps to eliminate pathogens and promote tissue repair.

    ### Classical pathway

    • Begins with the binding of C1 to the Fc portion of antibodies bound to antigens on the surface of pathogens.
    • This binding activates C1, which then activates C4 and C2.
    • C4b and C2a form a complex that activates C3, leading to the formation of C3b and C3a.

    ### Alternative pathway

    • Starts with the direct binding of C3b to pathogen surfaces.
    • This binding triggers a cascade of reactions, leading to the formation of more C3b.
    • C3b then activates C5, leading to the formation of C5a and C5b.

    ### Lectin pathway

    • Initiated by the binding of mannose-binding lectin to mannose sugars on pathogen surfaces.
    • Mannose-binding lectin activates C4 and C2, similar to the classical pathway.

    ### Membrane Attack Complex (MAC)

    •  Formed by the proteins C5b, C6, C7, C8, and C9.
    • C5b initiates the formation of the MAC by binding to C6, C7, and C8.
    •  C9 then polymerizes to form a pore in the pathogen's membrane.
    •  The MAC creates a channel in the pathogen's cell membrane, causing lysis.

    ### Opsonization

    • The process by which C3b enhances phagocytosis.
    • C3b binds to the surface of pathogens, making them more attractive targets for phagocytes.
    • Phagocytes have receptors for C3b, so they can recognize and engulf the opsonized pathogens.

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    This quiz focuses on key aspects of TLR4 signaling in the immune response, including the role of intraepithelial lymphocytes, the cytokines involved in inflammation, and the function of complement. Test your knowledge about the effector cells that are crucial for phagocytosis and the contribution of Type II interferon in TLR4 signaling.

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