The Complement Activation Pathways
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Questions and Answers

What is the key site for the activation of the complement?

  • Phagocytic cells
  • Inflammatory response
  • Surface of pathogens (correct)
  • Inert enzymes

    • How do some components of the complement system protect against pathogens?

  • By inhibiting phagocytic cells
  • By promoting microbial adhesion
  • By increasing microbial growth
  • By creating pores in microbial membranes (correct)

    • What is the role of opsonization in the immune response?

  • Promoting microbial growth
  • Inhibiting pathogen uptake by antigen presenting cells
  • Binding covalently to pathogens for phagocytosis (correct)
  • Damaging pathogens' membranes

    • How do some components of the complement system contribute to inflammation?

    <p>Acting as chemoattractants for phagocytic cells</p> Signup and view all the answers

    What happens when complement proteins bind covalently to pathogens?

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

    How does the complement system contribute to killing microbes?

    <p>Creating pores in microbial membranes</p> Signup and view all the answers

    Which complement component is cleaved to produce C4a and C4b?

    <p>C4</p> Signup and view all the answers

    Which complement component's larger cleavage fragment is designated as C2a?

    <p>C2</p> Signup and view all the answers

    Which complement component is initiated by binding to the surface of a pathogen?

    <p>C1q</p> Signup and view all the answers

    Which complement component's cleavage products are designated as Ba and Bb?

    <p>Factor B</p> Signup and view all the answers

    Which complement component is not designated with a letter C and a number?

    <p>Factor D</p> Signup and view all the answers

    Which complement component's smaller cleavage fragment is designated with a lower case 'a'?

    <p>C4</p> Signup and view all the answers

    What protein complex is responsible for making a hole in the target membrane to lyse and kill microbes?

    <p>Membrane Attack Complex (MAC)</p> Signup and view all the answers

    Which protein is responsible for stabilizing the alternative C3 convertase (C3bBb)?

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

    What is the role of Factor I in the complement system?

    <p>Accelerate decay of C3 convertase (C3bBb)</p> Signup and view all the answers

    Which of the following proteins inhibits the activities of C3 convertase (C3bBb) on cell membranes?

    <p>Complement receptor I (CD35)</p> Signup and view all the answers

    What is the function of Decay-accelerating factor (CD55) in the complement system?

    <p>Accelerate decay of C3 convertase (C3bBb)</p> Signup and view all the answers

    Which protein binds to C5b678 and prevents C9 recruitment and MAC formation?

    <p>Protectin (CD59)</p> Signup and view all the answers

    What is the function of Complement control protein, C4b-binding protein?

    <p>Binds C4b; accelerates decay of the classical and lectin C3 convertase (C4b2a)</p> Signup and view all the answers

    What is the main role of Factor D in the complement system?

    <p>Creating more C3b by cleaving plasma C3</p> Signup and view all the answers

    Which protein complex serves as the alternative C5 convertase in the complement pathway?

    <p>C5 convertase (C3bBb3b)</p> Signup and view all the answers

    What happens when Cobra Venom Factor complexes with Factor Bb and Factor P?

    <p>It forms a stable alternative C5 convertase</p> Signup and view all the answers

    Which protein regulates or stops downregulation at key points in the classical, lectin, and alternative pathways of complement activation?

    <p>Complement control proteins</p> Signup and view all the answers

    What is the role of C4b2a in the complement pathway?

    <p>C4b2a cleaves C3, leading to the deposition of C3b on the surface of microbes</p> Signup and view all the answers

    What is the significance of the spontaneous hydrolysis of C3 in the alternative pathway?

    <p>It is a mechanism to prevent unwanted complement activation on host cells</p> Signup and view all the answers

    What is the role of factor H in the complement pathway?

    <p>Factor H and factor I inactivate and degrade inappropriately bound C3b</p> Signup and view all the answers

    Which of the following statements about the alternative pathway is true?

    <p>The alternative pathway utilizes the nonspecific, low-level hydrolysis of C3</p> Signup and view all the answers

    What is the role of C3b in the complement pathway?

    <p>C3b binds to a microbial surface or is degraded</p> Signup and view all the answers

    What is the role of sialic acid residues in the complement pathway?

    <p>Sialic acid residues promote the binding of C3b to factor H</p> Signup and view all the answers

    What is the role of C3 convertase in complement activation?

    <p>It continually hydrolyses C3 (and C5), leading to complement depletion and severe local tissue damage</p> Signup and view all the answers

    What are the outcomes of complement activation on tissue inflammation?

    <p>Activation of mast-cell degranulation leading to release of vasoactive amines (histamine and serotonin)</p> Signup and view all the answers

    What is the effect of cobra envenomation on tissues?

    <p>Severe tissue necrosis requiring amputation</p> Signup and view all the answers

    What is the role of C5a in complement activation?

    <p>Upregulation of adhesion molecules, phagocytic receptors, and antimicrobial effectors by neutrophils and monocytes</p> Signup and view all the answers

    What is the role of C3b and iC3b in complement activation?

    <p>Enhancement of particle phagocytosis by macrophages and neutrophils</p> Signup and view all the answers

    What is the effect of C3dg in complement activation?

    <p>Enhancement of B-cell activation and retention of antigen complexes in B-cell follicles</p> Signup and view all the answers

    Which complement component is an exception where the larger cleavage fragment is designated as C2a?

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

    What designates the smaller cleavage fragment in complement components?

    <p>A lowercase 'b'</p> Signup and view all the answers

    Which pathway is initiated by the binding of C1q to the surface of a pathogen?

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

    How are the complement components of the alternative pathway designated?

    <p>By factors with capital letters</p> Signup and view all the answers

    What is the designation of the larger fragment resulting from the cleavage of Factor B in the alternative pathway?

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

    In what order were the native complement components numbered?

    <p>[C1, C4, C2, C3, C5, C6, C7, C8, C9]</p> Signup and view all the answers

    Which of the following is true about the complement system?

    <p>Complement components play no role in protecting against pathogens.</p> Signup and view all the answers

    What is the consequence of the activation of the complement system?

    <p>Generation of molecules important for inflammatory responses.</p> Signup and view all the answers

    What is one way in which complement components contribute to protecting against pathogens?

    <p>Acting as chemoattractants to recruit phagocytic cells to sites of infection.</p> Signup and view all the answers

    Which statement correctly describes the role of opsonization by complement components?

    <p>Opsonization promotes the uptake of microbes by antigen presenting cells.</p> Signup and view all the answers

    Which factor is responsible for creating pores in microbial membranes during the complement activation process?

    <p>Final components of the complement activation</p> Signup and view all the answers

    How does the complement system contribute to activating adaptive immunity?

    <p>Opsonization by complement components promotes uptake of microbes by antigen presenting cells.</p> Signup and view all the answers

    What is the role of Factor P in the stabilization of complement convertases?

    <p>Stabilizes the alternative C3 convertase (C3bBb)</p> Signup and view all the answers

    Which protein complex is responsible for initiating the terminal Membrane Attack Complex (MAC) formation?

    <p>C5b678</p> Signup and view all the answers

    What is the function of Decay-accelerating factor (CD55) in the complement system?

    <p>Accelerates decay of C3 convertase (C3bBb)</p> Signup and view all the answers

    Which protein functions by binding to C3b and C4a and inhibiting alternative and classical/lectin C3 Convertases?

    <p>Protectin (CD59)</p> Signup and view all the answers

    What is the main goal of the terminal Membrane Attack Pathway in the complement system?

    <p>Construct a protein complex that makes a hole in the target membrane to kill microbes</p> Signup and view all the answers

    Which protein primarily inhibits the protease activities or facilitates the degradation of activated complement complexes or convertases in the complement system?

    <p>Control proteins</p> Signup and view all the answers

    What occurs when venom from a cobra snake complexes with Factor Bb and Factor P in the complement system?

    <p>Forms a stable analogue of C3b that further activates the pathway</p> Signup and view all the answers

    What is the function of C1 inhibitor in plasma and serum in the classical and lectin pathways?

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

    What is the primary role of Complement receptor I (CD35) on cell membranes?

    <p>Inhibits alternative and classical/lectin C3 convertases</p> Signup and view all the answers

    How does Factor H contribute to complement activation in plasma and serum?

    <p>Binds to C3b and accelerates decay</p> Signup and view all the answers

    Which protein is responsible for the rapid degradation of C3b on healthy host cell membranes?

    <p>Factor H</p> Signup and view all the answers

    What is the role of sialic acid residues in complement activation on host cells?

    <p>They promote binding of C3b to Factor H</p> Signup and view all the answers

    Which protein complex acts as the C3 convertase in the alternative pathway?

    <p>C3bBb</p> Signup and view all the answers

    How does the spontaneous hydrolysis of C3 contribute to complement activation in the alternative pathway?

    <p>It leads to the formation of C3a and C3b</p> Signup and view all the answers

    What is the role of C5 convertase in the terminal membrane attack pathway?

    <p>It cleaves C5 into C5a and C5b</p> Signup and view all the answers

    Which protein acts as a negative regulator of complement activation on host cells?

    <p>Factor H</p> Signup and view all the answers

    What happens when Cobra Venom Factor complexes with Factor Bb and Factor P?

    <p>It forms a convertase that is not recognized by the regulatory proteins factor H and I, and thus it will continually hydrolyse C3, leading to complement depletion and severe local tissue damage.</p> Signup and view all the answers

    What is the effect of cobra envenomation on tissues?

    <p>It causes severe tissue necrosis due to the depletion of complement.</p> Signup and view all the answers

    Which of the following proteins inhibits the activities of C3 convertase (C3bBb) on cell membranes?

    <p>Decay-accelerating factor (CD55)</p> Signup and view all the answers

    Which protein binds to C5b678 and prevents C9 recruitment and MAC formation?

    <p>S protein</p> Signup and view all the answers

    Which protein regulates or stops downregulation at key points in the classical, lectin, and alternative pathways of complement activation?

    <p>Factor H</p> Signup and view all the answers

    What happens when complement proteins bind covalently to pathogens?

    <p>The pathogens are opsonized for phagocytosis.</p> Signup and view all the answers

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