Complement System Regulation
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Questions and Answers

What is the function of Clusterin and S protein in the complement system?

  • To enhance the Alternative pathway
  • To activate the Lectin pathway
  • To inhibit the formation of MAC (correct)
  • To induce the production of cytokines

    • Which complement receptor has a decay accelerating activity towards C3 and C5 convertases?

  • CD59
  • DAF
  • CR1 (correct)
  • MCP

    • What is the role of C1-INH in the complement system?

  • To induce the production of cytokines
  • To remove activated C1qrs complexes from surfaces (correct)
  • To inhibit the formation of C3 convertase
  • To activate the Alternative pathway

    • Which complement protein binds to C3b and acts as a cofactor for factor I?

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

    What is the function of CD59 in the complement system?

    <p>To inhibit the formation of MAC</p> Signup and view all the answers

    What is the role of DAF in the complement system?

    <p>To dissociate C3 and C5 convertases</p> Signup and view all the answers

    What is the process by which bacteria are labelled to be more efficiently engulfed by phagocytes?

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

    What is the term for the engulfing and ingestion of bacteria or other foreign bodies by phagocytes?

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

    What is the main function of Complement C1 inhibitor (C1-INH)?

    <p>To prevent spontaneous activation of the proenzymes C1r and C1s</p> Signup and view all the answers

    What is the role of Factor H in the alternative pathway?

    <p>To accelerate the decay of the alternative pathway C3 convertase</p> Signup and view all the answers

    What is the function of C4 binding protein (C4bp)?

    <p>To prevent the formation of C3 convertase by inhibiting the binding of C4b with C2</p> Signup and view all the answers

    Which of the following is a membrane bound regulator of the complement system?

    <p>Complement receptor 1 (CR1)</p> Signup and view all the answers

    What is the function of Complement factor I?

    <p>To cleave C3b and C4b generating iC3b and iC4b</p> Signup and view all the answers

    What is the function of Decay accelerating factor (DAF)?

    <p>To protect host cells from complement mediated attack</p> Signup and view all the answers

    Which of the following is a fluid phase regulator of the complement system?

    <p>C4 binding protein (C4bp)</p> Signup and view all the answers

    What is the role of Clusterin in the complement system?

    <p>To regulate the fluid phase of the complement system</p> Signup and view all the answers

    What is the approximate distance between the C9 molecules in the Membrane Attack Complex?

    <p>70-100 Å</p> Signup and view all the answers

    Which of the following is NOT a recognition molecule in the Lectin Pathway?

    <p>C1-esterase inhibitor (C1-inh)</p> Signup and view all the answers

    Which enzyme is responsible for activating C4 and C2 in the Lectin Pathway?

    <p>MASP-2</p> Signup and view all the answers

    What is the function of C1-esterase inhibitor (C1-inh) in the complement system?

    <p>To inhibit C1r and C1s</p> Signup and view all the answers

    Which of the following is NOT a type of ficolin?

    <p>N-ficolin (found in neutrophils)</p> Signup and view all the answers

    What is the outcome of the Lectin Pathway activation?

    <p>Formation of the C3-convertase</p> Signup and view all the answers

    Which of the following collectins is NOT involved in the activation of the complement system?

    <p>Collectin lung 1 (CL-13)</p> Signup and view all the answers

    What is the function of the C3-convertase in the complement system?

    <p>To cleave C3</p> Signup and view all the answers

    Study Notes

    Complement System Regulation

    • C1-INH removes activated C1qrs complexes from surfaces and blocks further activation.
    • Clusterin and S protein are regulators of the terminal activation cascade of complement, binding to C5b-7 complex and preventing the insertion of C8 and C9, leading to the inhibition of MAC formation.

    Membrane Bound Regulators

    • Complement receptor 1 (CR1) is expressed by many cells, including erythrocytes and lymphocytes, and has a decay accelerating activity towards C3 and C5 convertases.
    • CR1 serves as a cofactor for factor I, which degrades C3b and C4b.
    • Membrane cofactor protein (MCP) binds to C3b and acts as a cofactor for factor I, facilitating the inactivation of C3b.
    • CD59 is a regulator of the MAC that binds to C8 and C9, and subsequently inhibits binding to C5b-7 and formation of MAC.
    • Decay accelerating factor (DAF) is attached to cell membranes and dissociates C3 and C5 convertases.

    Phagocytosis and Opsonization

    • Phagocytosis is the engulfing and ingestion of bacteria or other foreign bodies by phagocytes.
    • Opsonization is the process by which bacteria are labeled in such a manner that they become more efficiently engulfed by phagocytes.

    Role of Complement System

    • The complement system plays a crucial role in the immune response.

    Complement Regulation

    • Fluid phase regulators:
      • Complement C1 inhibitor (C1-INH)
      • C4 binding protein (C4bp)
      • Factor H
      • Clusterin and S protein
    • Membrane bound regulators:
      • Complement receptor 1 (CR1)
      • Protectin (CD59)
      • Membrane cofactor protein (MCP)
      • Decay accelerating factor (DAF)
      • Complement factor I

    Complement Factor I

    • Soluble glycosylated serine protease found in plasma
    • Protects host cells from complement-mediated attack
    • Cleaves C3b and C4b, generating iC3b and iC4b, and prevents complement convertases formation

    Factor H

    • Main fluid phase regulator of the alternative pathway
    • Accelerates the decay of the alternative pathway C3 convertase (C3bBb) by binding to C3b and removing it from the complex
    • Acts as a cofactor in the factor I-mediated conversion of C3b to iC3b, C3c, and C3dg

    C4 Binding Protein (C4bp)

    • Major regulator of the complement system
    • Binds with C4b and inhibits its binding with C2, preventing the formation of C3 convertase
    • Acts as a cofactor in the factor I-mediated conversion of C4b to iC4b, C4e, and C4d

    Complement C1 Inhibitor (C1-INH)

    • Serine protease inhibitor that binds to C1 complex and prevents spontaneous activation of the proenzymes C1r and C1s
    • Forms a complex with active enzymes to trap and inactivate them

    Lectin Pathway of Complement Activation

    • Homologous to the classical pathway, differing only in the complement initiator molecular complexes
    • Ag-Ab independent
    • Initiated by mannan-binding lectin (MBL), ficolins, or collectins complexes that encounter microbial carbohydrates or N-acetyl groups decorating the surface of a pathogen (PAMP)
    • This binding leads to the activation of the MBL-associated serine proteases (MASPs), of which MASP-2 acts on C4 and C2 in a similar manner to C1s in the classical pathway, resulting in the formation of the C3-convertase

    Lectin Pathway Recognition Molecules

    • Mannan binding lectin (MBL) binds to carbohydrates on the surface of cells
    • Ficolins:
      • L-ficolin (serum protein)
      • H-ficolin (serum protein)
      • M-ficolin (found in monocytes and neutrophils)
    • Collectins:
      • Collectin liver 1 (CL-10)
      • Collectin kidney 1 (CL-11)
      • Collectin placenta 1 (CL-12)

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    Description

    This quiz covers the regulation of the complement system, including the role of C1-INH, Clusterin, and S protein in inhibiting the activation cascade and MAC formation.

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