Complement

• What is the primary function of the adaptive immune system?


  To provide a specific immune response against pathogens.
• What are the mechanisms of antibody clearance of pathogens?

  1. Opsonization

  2. Neutralization

  3. Antibody-dependent cellular cytotoxicity

  4. Complement activation
• What occurs during opsonization?

  The antibody coats the antigen, enhancing phagocytosis.
• How does neutralization work in the immune response?

  Antibodies block the antigen from binding to a receptor.
• What is antibody-dependent cellular cytotoxicity?

  It is when antibodies mediate the degranulation of effector molecules after binding to the antigen.
• What role does complement activation play in the immune response?

  It mediates the activation of the complement system to enhance pathogen clearance.
• What are the steps in the classical pathway of complement activation?

  1. Binding of antibody to antigen

  2. Activation of coagulation and bradykinin

  3. Formation of enzyme complex c1

  4. Stabilization and formation of C3 convertase

  5. Formation and stabilization of C5 convertase

  6. Activation of Membrane Attack Complex(MAC)
• What are the substrates for the C3 convertase?

  C3
• What is the function of the membrane attack complex (MAC)?

  It forms pores in the pathogen's membrane, leading to cell lysis.
• What triggers the alternative pathway of complement activation?

  1. C3b binding to Factor B

  2. Formation of C3 convertase

  3. Recruitment of C6, C7, C8, and C9 to form MAC
• What is the most abundant complement protein in circulation?

  C3b.
• What is the role of lectin in the lectin pathway of complement activation?

  • Lectin binds to mannose sequences on pathogens.
  • It recruits Mannose Associated Serine Protease (MASP).
  • Activates the complement system.
• What is the function of complement regulatory proteins?

  They inhibit the formation of C3 convertase and regulate complement activation.
• What happens when the complement system is activated?

  It enhances inflammation, opsonization, and membrane destruction.
• What are the biological functions of complement proteins?

  • Opsonization
  • Chemotaxis
  • Enhancement of inflammation
  • Membrane destruction
• Which cells express Complement Receptor 1 (CR1)?

  Erythrocytes, macrophages, mast cells, eosinophils, and follicular dendritic cells.
• What is the role of CR2 in the immune response?

  It acts as a receptor for C3d, C3Bg, iC3b and enhances B-cell activation.
• How do pathogens evade the complement system?

  By possessing capsules, inactivating anaphylatoxins, or preventing MAC insertion.
• What are the effects of elevated levels of anaphylatoxins?

  • Mimics an allergic reaction
  • Enhances inflammation
  • Promotes opsonization
• What is hereditary angioedema associated with?

  Absence of the C1 inhibitor esterase.
• What is the significance of Factor H in the complement system?

  It regulates complement activation and prevents damage to host cells.
• How does the presence of DAF and CD58 affect the complement system?

  They prevent intravascular hemolysis of RBCs and regulate complement activation.