Complement System Overview
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Complement System Overview

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Questions and Answers

What can cause biologic effects of complement activation?

  • Nutritional deficiencies
  • Persistent infection or autoantibodies (correct)
  • Environmental toxins
  • Genetic mutations only

    • What effect does complement activation have on disease pathology?

  • It has no significant effects
  • It may contribute to inflammation and lysis (correct)
  • It exclusively promotes healing
  • It inhibits the inflammatory response

    • What is a common result of elevated complement levels?

  • Specific diagnosis of infections
  • Improved tissue regeneration
  • Decreased immune response
  • Association with inflammatory conditions (correct)

    • Which of the following best explains decreased complement levels?

    <p>Complement is currently being consumed</p> Signup and view all the answers

    What role does the C1 inhibitor (C1INH) play in the complement system?

    <p>Blocks activities of C1</p> Signup and view all the answers

    Which component is targeted by MAC inhibitors?

    <p>C5b-7 complex</p> Signup and view all the answers

    Deficiencies in complement are linked to which of the following?

    <p>Primary immunodeficiencies</p> Signup and view all the answers

    What is the function of complement receptor type I (CRI or CD35)?

    <p>Inactivate C4b and C3b</p> Signup and view all the answers

    What is the primary function of the complement system in relation to pathogens?

    <p>Facilitates direct phagocytosis of pathogens</p> Signup and view all the answers

    Which of the following correctly describes the activation of complement components?

    <p>Activation requires cleavage by proteolytic enzymes</p> Signup and view all the answers

    Which component of the complement system is synthesized mainly by hepatocytes?

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

    What are the three main physiological activities of the complement system?

    <p>Host defense, interaction with adaptive immunity, waste disposal</p> Signup and view all the answers

    Which complement pathway is independent of mannose?

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

    What happens to complement components once they are activated?

    <p>They catalyze the next step in the pathway</p> Signup and view all the answers

    Which statement about the complement system is false?

    <p>It functions mainly through signaling pathways</p> Signup and view all the answers

    Which of the following groups of components is specifically involved in the classical pathway of complement activation?

    <p>C1q, C1r, C1s</p> Signup and view all the answers

    What is the function of C3 convertase?

    <p>It converts C3 into C3a and C3b.</p> Signup and view all the answers

    Which factor is involved in the formation of the C5 convertase?

    <p>C4b2b</p> Signup and view all the answers

    What role does properidin play in the complement system?

    <p>It stabilizes the C3b-Bb complex.</p> Signup and view all the answers

    What is the result of C3 and C5 complement activation in the immune response?

    <p>Stimulates mast cells and basophils.</p> Signup and view all the answers

    In the presence of pathogen components like LPS, what happens to Factor H?

    <p>It is inhibited, affecting C3 convertase function.</p> Signup and view all the answers

    What three main physiological activities are associated with the complement system?

    <p>Cell lysis, opsonization, and anaphylatoxin release.</p> Signup and view all the answers

    What stimulates mast cells and basophils during complement activation?

    <p>C3a, C4a, and C5a</p> Signup and view all the answers

    Which of the following is NOT a component of the classical pathway of complement activation?

    <p>C5 convertase</p> Signup and view all the answers

    What happens if complement complexes accumulate in tissues?

    <p>They might lead to tissue damage.</p> Signup and view all the answers

    Study Notes

    Complement Proteins

    • Over 20 serum glycoproteins
    • Synthesized by hepatocytes (except C1)
    • Important for killing pathogens, recruiting inflammatory cells, opsonizing pathogens, and clearing immune complexes
    • Many circulate as proenzymes (inactive enzymes) that require proteolytic cleavage for activation.
    • Once activated, components catalyze the next step of the pathway.
    • Activated components remain active for a short time.

    Functions of the Complement System

    • Three main functions
      • Host defense against infection
      • Interface between innate and adaptive immunity
      • Disposal of waste

    Complement System Activation Pathways

    • Three main pathways
      • Classical
      • Alternative
      • Mannose-binding lectin

    Classical Pathway

    • Initiated by antigen-antibody complexes or certain pathogen components
    • C1q binds antigen-antibody complexes or pathogen surface
    • C1r and C1s are activated.
    • C1s cleaves C4, generating C4a and C4b
    • C2 binds C4b and is cleaved by C1s, generating C2a and C2b
    • C4b2a complex forms the classical pathway C3 convertase.
    • C3 convertase cleaves C3 to C3a and C3b.
    • C4b2a3b complex forms the classical pathway C5 convertase.
    • C5 convertase cleaves C5 resulting in C5a and C5b.

    C1q

    • Binds to antigen-antibody complexes and pathogen surfaces.

    C1r & C1s

    • Cleave C4 and activate complement by triggering the classical cascade.

    C4

    • Cleaved by C1s.

    C2

    • Cleaved by C1s after binding to C4b

    Properidin

    • Stabilizes the alternative pathway C3 convertase (C3bBb).

    Results of Complement Activation

    • C3a, C4a, C5a activate mast cells and basophils.
    • C5a activates neutrophils and monocytes.
    • C5b-9 forms the membrane attack complex (MAC), which can lyse cells.

    Complement Activation and Disease

    • Elevated complement levels can be associated with inflammatory conditions, trauma, and acute illness.
    • Decreased complement levels can be associated with excessive complement activation, complement consumption, or genetic deficiencies in specific complement components.

    Complement Regulation

    • Control mechanisms ensure complement system activation is regulated and does not cause excessive damage:
      • C1 inhibitor (C1INH): blocks C1 activity
      • Anaphylatoxin inactivator: inactivates C4a, C3a, and C5a.
      • MAC inhibitors: inactivate C5b-7.
      • Complement receptor type I (CRI or CD35): inactivates C4b and C3b.

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    Description

    Explore the essential components and functions of the complement system in this quiz. Understand how it plays a crucial role in host defense, immune response, and waste disposal through various activation pathways. Dive into the details of classical, alternative, and mannose-binding lectin pathways.

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