Classical Pathway in Immunological Disorders
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Questions and Answers

What is the function of C1q in the recognition stage of the classical pathway?

  • It releases anaphylatoxin to recruit phagocytes
  • It acts as an opsonin that helps in phagocytosis
  • It cleaves C4 into C4a and C4b
  • It binds to antigen-antibody complex on the surface of a pathogen (correct)
  • What is the function of C3a in the continue activation stage of the classical pathway?

  • It cleaves C4 into C4a and C4b
  • It binds to antigen-antibody complex on the surface of a pathogen
  • It is an anaphylatoxin that helps in the recruitment of phagocytes (correct)
  • It forms C3-convertase with C4b2a
  • What is the role of C2b in the activation stage of the classical pathway?

  • It forms C3-convertase with C4b2a
  • It is released in the fluid phase (correct)
  • It cleaves C3 into C3a and C3b
  • It acts as an opsonin that binds covalently to the surface of the pathogen
  • What happens to the smaller fragment C4a during the activation stage of the classical pathway?

    <p>It will be released in the fluid phase</p> Signup and view all the answers

    What is formed when C2a remains attached to C4b during the activation stage of the classical pathway?

    <p>C3-convertase (C4b2a)</p> Signup and view all the answers

    Study Notes

    Function of C1q in Recognition Stage

    • C1q is a crucial protein that initiates the classical complement pathway.
    • It recognizes and binds to antibodies (IgM or IgG) that are attached to pathogens or antigen surfaces.
    • This binding is essential for the subsequent activation of the complement system.

    Function of C3a in Continued Activation Stage

    • C3a is a small peptide fragment generated during the complement activation process.
    • It functions as an anaphylatoxin, promoting inflammation and recruiting immune cells to sites of infection.
    • C3a enhances vascular permeability and contributes to the inflammatory response.

    Role of C2b in Activation Stage

    • C2b is involved in the formation of the C3 convertase during the classical pathway activation.
    • It pairs with C4b to form the C4b2a complex, which is crucial for cleaving C3 into C3a and C3b.
    • This conversion is a pivotal step in amplifying the complement cascade.

    Fate of C4a During Activation Stage

    • C4a is the smaller fragment produced from the cleavage of C4.
    • Unlike C4b, which is active in forming enzyme complexes, C4a acts as a weak anaphylatoxin but is rapidly degraded.
    • As C4a is released, it plays a minimal role in the overall complement activation process compared to other fragments.

    Formation of C4b2a Complex

    • When C2a remains attached to C4b, they form the C4b2a complex, known as C3 convertase.
    • This complex has a central role in the complement cascade, leading to further cleavage of C3.
    • C4b2a effectively enhances the immune response by amplifying complement activation.

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    Description

    Test your knowledge of the classical pathway in immunological disorders with this quiz. Learn about the recognition stage, C1 complex subunits, and their interactions with antigens and antibodies.

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