Lec 4 Quiz
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Questions and Answers

Which of the following is the correct assembly of the classical C3 convertase?

  • C3b2Bb
  • C4bC2a (correct)
  • MBL-MASP-1
  • C3bBb

    • What is the primary mechanism by which α-2 macroglobulin helps suppress pathogen infections?

  • Enhancing phagocytosis of infected cells.
  • Blocking viral entry into host cells.
  • Inactivating proteases secreted by pathogens. (correct)
  • Directly lysing bacterial cell walls.

    • Which of the following complement components are known as anaphylatoxins?

  • C5b and C6
  • C3a and C5a (correct)
  • C3b and C4b
  • C2a and C4a

    • What is the outcome of the terminal complement components forming membrane-attack complexes (MAC)?

    <p>Pore formation in the pathogen's lipid bilayer (B)</p> Signup and view all the answers

    Which acute-phase protein binds to phosphocholine on bacterial surfaces, acting as both an opsonin and a complement activator?

    <p>C-reactive protein (CRP) (A)</p> Signup and view all the answers

    Which complement activation pathway is initiated by the binding of mannose-binding lectin to pathogen surfaces?

    <p>Lectin Pathway (C)</p> Signup and view all the answers

    What is the primary role of C3b in complement activation?

    <p>Opsonizing pathogens to enhance phagocytosis. (A)</p> Signup and view all the answers

    Which of the following best describes the sequence of activation for the three complement pathways?

    <p>Alternative, Lectin, then Classical (A)</p> Signup and view all the answers

    What is the function of DAF (Decay-Accelerating Factor) and MCP (Membrane Cofactor Protein) in regulating complement activation?

    <p>They disrupt C3 convertase activity on human cell surfaces. (D)</p> Signup and view all the answers

    How does the complement system contribute to innate immunity?

    <p>By initiating a rapid, amplified response to foreign organisms through a cascade of enzymatic reactions. (B)</p> Signup and view all the answers

    What is the role of CD59 protein in regulating complement activation?

    <p>It binds to the C5b678 complex, preventing the recruitment of C9 and formation of the MAC. (A)</p> Signup and view all the answers

    Which of the following is the correct definition of opsonization?

    <p>The coating of pathogens with complement proteins to enhance phagocytosis. (B)</p> Signup and view all the answers

    C-reactive protein (CRP) binds to what?

    <p>Specific antigen on pathogen surface (A)</p> Signup and view all the answers

    Flashcards

    Alternative Pathway

    First pathway activated by pathogen surface, cleaving C3 to enhance opsonization and inflammation.

    Lectin Pathway

    Second pathway initiated by mannose-binding lectin on pathogen surface, leading to C3 cleavage.

    Classical Pathway

    Third pathway triggered by antibody or C-reactive protein binding to pathogen, also cleaving C3.

    Opsonization

    Process where complement proteins coat pathogens, enhancing phagocytosis by immune cells.

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    Complement System

    A group of proteins that plays a crucial role in initiating innate immunity via activation pathways.

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    DAF

    Decay-accelerating factor that disrupts C3 convertase on human cell surfaces, regulating complement.

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    CD59

    Prevents recruitment of C9, thus halting membrane attack complex formation to protect human cells.

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    C-Reactive Protein (CRP)

    Protein produced in the liver that binds to pathogens and is used as a clinical marker for inflammation.

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    C3 convertase

    An enzyme complex crucial for complement activation; two types are C4bC2a (classical) and C3bBb (alternative).

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    Anaphylatoxins

    Peptides (C3a and C5a) that promote inflammation and immune response; they increase vascular permeability and attract immune cells.

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    Acute phase proteins

    Proteins produced by the liver in response to inflammation-inducing cytokines (IL-1, IL-6, TNF-a).

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    α-2-macroglobulin

    A protein that inactivates proteases used by pathogens, preventing their infection potential.

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    Study Notes

    Complement Pathways

    • Alternative Pathway: Pathogen surfaces trigger complement activation. C3 is cleaved, creating C3a and C3b. This leads to inflammation (via C3a), opsonization (C3b), and pathogen lysis. It acts first.
    • Lectin Pathway: Mannose-binding lectin binds to pathogen surfaces, initiating complement activation. C3 is cleaved to C3a and C3b. This leads to inflammation, opsonization, and pathogen lysis. It acts second.
    • Classical Pathway: Antibodies or C-reactive protein (CRP) bind pathogen surfaces. Complement activation follows, cleaving C3 to C3a and C3b, leading to inflammation, opsonization, and pathogen lysis. It acts third.

    Complement System and Innate Immunity

    • The complement system is a crucial part of the innate immune response, rapidly reacting to foreign invaders.
    • It's a system of ~30 proteins in blood, lymph, and extracellular fluids.
    • A cascade of activation amplifies the initial response to a stimulus very quickly.

    Opsonization

    • Opsonization is the process where complement proteins coat pathogens, making them easier for phagocytes (immune cells) to engulf and destroy.

    Complement Activation Regulation

    • DAF (Decay-accelerating factor) and MCP (Membrane cofactor protein): Prevent complement activation on healthy human cells by disrupting the C3 convertase.
    • CD59: Prevents the formation of the membrane attack complex (MAC) by binding to the C5b-C9 complex, essentially stopping the formation of the cell-damaging pore.

    C-Reactive Protein (CRP)

    • Induction: Cytokines (IL-1, IL-6, TNF-α) trigger the liver to produce CRP. Bacteria also induce CRP production.
    • Production Site: Liver.
    • Binding: CRP binds to phosphocholine on bacterial surfaces, acting as an opsonin and complement activator.
    • Clinical Use: CRP levels in the blood are clinically monitored to detect infection and inflammation.

    C3 Convertases

    • Classical Pathway: C4bC2a.
    • Alternative Pathway: C3bBb.

    Anaphylatoxins

    • C3a and C5a: These complement components act as anaphylatoxins. They promote inflammation, increase vascular permeability, stimulate mast cell degranulation (histamine release), and chemotaxis (calling immune cells to the site).

    Acute Phase Proteins

    • Induction: Cytokines (IL-1, IL-6, TNF-α) induce the liver to produce acute-phase proteins like CRP.

    Mannose-Binding Lectin (MBL)

    • MBL is a protein that binds to carbohydrates on pathogens, initiating the complement pathway.

    Complement System and Infection Suppression

    • Complement enhances phagocytosis by opsonization and, via the terminal complement pathway, forms the membrane attack complex (MAC).
    • MAC creates pores in pathogen membranes, causing pathogen lysis (death).

    α2-Macroglobulin

    • α2-macroglobulin is a protein that inactivates pathogen proteases, preventing them from degrading host tissues.

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    Description

    This quiz covers the three complement pathways: the Alternative, Lectin, and Classical pathways, explaining their roles in the innate immune response. It details how these pathways are activated and the consequences for pathogen lysis, inflammation, and opsonization. Test your understanding of this essential aspect of immunology.

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