69 Questions
What is the key site for the activation of the complement?
Surface of pathogens
How do some components of the complement system protect against pathogens?
By creating pores in microbial membranes
What is the role of opsonization in the immune response?
Binding covalently to pathogens for phagocytosis
How do some components of the complement system contribute to inflammation?
Acting as chemoattractants for phagocytic cells
What happens when complement proteins bind covalently to pathogens?
Opsonization for phagocytosis
How does the complement system contribute to killing microbes?
Creating pores in microbial membranes
Which complement component is cleaved to produce C4a and C4b?
C4
Which complement component's larger cleavage fragment is designated as C2a?
C2
Which complement component is initiated by binding to the surface of a pathogen?
C1q
Which complement component's cleavage products are designated as Ba and Bb?
Factor B
Which complement component is not designated with a letter C and a number?
Factor D
Which complement component's smaller cleavage fragment is designated with a lower case 'a'?
C4
What protein complex is responsible for making a hole in the target membrane to lyse and kill microbes?
Membrane Attack Complex (MAC)
Which protein is responsible for stabilizing the alternative C3 convertase (C3bBb)?
Properdin
What is the role of Factor I in the complement system?
Accelerate decay of C3 convertase (C3bBb)
Which of the following proteins inhibits the activities of C3 convertase (C3bBb) on cell membranes?
Complement receptor I (CD35)
What is the function of Decay-accelerating factor (CD55) in the complement system?
Accelerate decay of C3 convertase (C3bBb)
Which protein binds to C5b678 and prevents C9 recruitment and MAC formation?
Protectin (CD59)
What is the function of Complement control protein, C4b-binding protein?
Binds C4b; accelerates decay of the classical and lectin C3 convertase (C4b2a)
What is the main role of Factor D in the complement system?
Creating more C3b by cleaving plasma C3
Which protein complex serves as the alternative C5 convertase in the complement pathway?
C5 convertase (C3bBb3b)
What happens when Cobra Venom Factor complexes with Factor Bb and Factor P?
It forms a stable alternative C5 convertase
Which protein regulates or stops downregulation at key points in the classical, lectin, and alternative pathways of complement activation?
Complement control proteins
What is the role of C4b2a in the complement pathway?
C4b2a cleaves C3, leading to the deposition of C3b on the surface of microbes
What is the significance of the spontaneous hydrolysis of C3 in the alternative pathway?
It is a mechanism to prevent unwanted complement activation on host cells
What is the role of factor H in the complement pathway?
Factor H and factor I inactivate and degrade inappropriately bound C3b
Which of the following statements about the alternative pathway is true?
The alternative pathway utilizes the nonspecific, low-level hydrolysis of C3
What is the role of C3b in the complement pathway?
C3b binds to a microbial surface or is degraded
What is the role of sialic acid residues in the complement pathway?
Sialic acid residues promote the binding of C3b to factor H
What is the role of C3 convertase in complement activation?
It continually hydrolyses C3 (and C5), leading to complement depletion and severe local tissue damage
What are the outcomes of complement activation on tissue inflammation?
Activation of mast-cell degranulation leading to release of vasoactive amines (histamine and serotonin)
What is the effect of cobra envenomation on tissues?
Severe tissue necrosis requiring amputation
What is the role of C5a in complement activation?
Upregulation of adhesion molecules, phagocytic receptors, and antimicrobial effectors by neutrophils and monocytes
What is the role of C3b and iC3b in complement activation?
Enhancement of particle phagocytosis by macrophages and neutrophils
What is the effect of C3dg in complement activation?
Enhancement of B-cell activation and retention of antigen complexes in B-cell follicles
Which complement component is an exception where the larger cleavage fragment is designated as C2a?
C3
What designates the smaller cleavage fragment in complement components?
A lowercase 'b'
Which pathway is initiated by the binding of C1q to the surface of a pathogen?
Classical pathway
How are the complement components of the alternative pathway designated?
By factors with capital letters
What is the designation of the larger fragment resulting from the cleavage of Factor B in the alternative pathway?
Bd
In what order were the native complement components numbered?
[C1, C4, C2, C3, C5, C6, C7, C8, C9]
Which of the following is true about the complement system?
Complement components play no role in protecting against pathogens.
What is the consequence of the activation of the complement system?
Generation of molecules important for inflammatory responses.
What is one way in which complement components contribute to protecting against pathogens?
Acting as chemoattractants to recruit phagocytic cells to sites of infection.
Which statement correctly describes the role of opsonization by complement components?
Opsonization promotes the uptake of microbes by antigen presenting cells.
Which factor is responsible for creating pores in microbial membranes during the complement activation process?
Final components of the complement activation
How does the complement system contribute to activating adaptive immunity?
Opsonization by complement components promotes uptake of microbes by antigen presenting cells.
What is the role of Factor P in the stabilization of complement convertases?
Stabilizes the alternative C3 convertase (C3bBb)
Which protein complex is responsible for initiating the terminal Membrane Attack Complex (MAC) formation?
C5b678
What is the function of Decay-accelerating factor (CD55) in the complement system?
Accelerates decay of C3 convertase (C3bBb)
Which protein functions by binding to C3b and C4a and inhibiting alternative and classical/lectin C3 Convertases?
Protectin (CD59)
What is the main goal of the terminal Membrane Attack Pathway in the complement system?
Construct a protein complex that makes a hole in the target membrane to kill microbes
Which protein primarily inhibits the protease activities or facilitates the degradation of activated complement complexes or convertases in the complement system?
Control proteins
What occurs when venom from a cobra snake complexes with Factor Bb and Factor P in the complement system?
Forms a stable analogue of C3b that further activates the pathway
What is the function of C1 inhibitor in plasma and serum in the classical and lectin pathways?
Inactivates C1r, C1s, and MASPs
What is the primary role of Complement receptor I (CD35) on cell membranes?
Inhibits alternative and classical/lectin C3 convertases
How does Factor H contribute to complement activation in plasma and serum?
Binds to C3b and accelerates decay
Which protein is responsible for the rapid degradation of C3b on healthy host cell membranes?
Factor H
What is the role of sialic acid residues in complement activation on host cells?
They promote binding of C3b to Factor H
Which protein complex acts as the C3 convertase in the alternative pathway?
C3bBb
How does the spontaneous hydrolysis of C3 contribute to complement activation in the alternative pathway?
It leads to the formation of C3a and C3b
What is the role of C5 convertase in the terminal membrane attack pathway?
It cleaves C5 into C5a and C5b
Which protein acts as a negative regulator of complement activation on host cells?
Factor H
What happens when Cobra Venom Factor complexes with Factor Bb and Factor 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.
What is the effect of cobra envenomation on tissues?
It causes severe tissue necrosis due to the depletion of complement.
Which of the following proteins inhibits the activities of C3 convertase (C3bBb) on cell membranes?
Decay-accelerating factor (CD55)
Which protein binds to C5b678 and prevents C9 recruitment and MAC formation?
S protein
Which protein regulates or stops downregulation at key points in the classical, lectin, and alternative pathways of complement activation?
Factor H
What happens when complement proteins bind covalently to pathogens?
The pathogens are opsonized for phagocytosis.
Explore the mechanisms of complement activation, including the self-assembling enzymatic cascade and generation of biologically active molecules. Learn about the key site of complement activation on pathogens and the three distinct pathways of activation.
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