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Questions and Answers
What type of proteolytic cleavage occurs in the activation of the complement system?
What type of proteolytic cleavage occurs in the activation of the complement system?
How many major pathways of complement activation are there?
How many major pathways of complement activation are there?
What is the trigger for the alternative pathway of complement activation?
What is the trigger for the alternative pathway of complement activation?
What is the outcome of the binding of C3b to microbial surfaces?
What is the outcome of the binding of C3b to microbial surfaces?
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What is the role of Factor B in the alternative pathway?
What is the role of Factor B in the alternative pathway?
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What is the outcome of the formation of C5 convertase in the alternative pathway?
What is the outcome of the formation of C5 convertase in the alternative pathway?
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What stabilizes the C3bBb complex in the alternative pathway?
What stabilizes the C3bBb complex in the alternative pathway?
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What is the outcome of the binding of C3b molecules to the surface of the microbe?
What is the outcome of the binding of C3b molecules to the surface of the microbe?
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What is the initial step in the classical pathway of complement activation?
What is the initial step in the classical pathway of complement activation?
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What is the function of C1q in the classical pathway?
What is the function of C1q in the classical pathway?
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What is the result of the early steps of complement activation?
What is the result of the early steps of complement activation?
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What is the difference between the classical and lectin pathways of complement activation?
What is the difference between the classical and lectin pathways of complement activation?
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What is the function of C2a and C4b in the classical pathway?
What is the function of C2a and C4b in the classical pathway?
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What is the role of the alternative pathway of complement activation?
What is the role of the alternative pathway of complement activation?
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What is the result of the late steps of complement activation?
What is the result of the late steps of complement activation?
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Which of the following is NOT a result of the early steps of complement activation?
Which of the following is NOT a result of the early steps of complement activation?
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What is the primary function of the complement system?
What is the primary function of the complement system?
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What is the most important function of complement in defense against microbes?
What is the most important function of complement in defense against microbes?
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What is the result of the late stage of complement activation?
What is the result of the late stage of complement activation?
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What is the role of C3a and C5a in the complement system?
What is the role of C3a and C5a in the complement system?
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What is the role of follicular dendritic cells in the complement system?
What is the role of follicular dendritic cells in the complement system?
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What is the effect of the complement system on B cell responses?
What is the effect of the complement system on B cell responses?
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What is the result of the formation of a membrane attack complex (MAC)?
What is the result of the formation of a membrane attack complex (MAC)?
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What is the purpose of regulatory proteins in the complement system?
What is the purpose of regulatory proteins in the complement system?
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Study Notes
Complement System
- The complement system plays a crucial role in eliminating microbes during innate and adaptive immune responses.
- The system has three main functions: opsonization, cell lysis, and inflammation.
Opsonization
- Coating microbes with C3b, which is recognized by complement receptor 1 (CR1/CD35), leading to phagocytosis.
- Most important function of complement in defense against microbes.
Cell Lysis
- Effective against microbes with thin cell walls or no glycocalyx.
- Involves late-stage complement activation, allowing water and ions to enter the microbe, leading to osmotic lysis.
Inflammation
- Triggered by C3 and C5 proteolysis, releasing C3a and C5a, which stimulate the release of inflammatory mediators from leukocytes.
- Leads to the movement of leukocytes to the site of infection.
Complement System Regulation
- Inhibition of complement activation can be expressed in mammalian cells via regulatory proteins (plasma or membrane proteins).
Complement System Pathways
- Three major pathways: alternative, classical, and lectin.
- Alternative pathway is initiated by microbes in the absence of antibodies.
- Classical pathway is initiated by a certain isotype of antibodies attached to antigens.
- Lectin pathway is initiated by microbes in the absence of antibodies.
Alternative Pathway
- Triggered by spontaneous hydrolysis of C3 in plasma at a low level.
- Leads to the formation of C3b, which is deposited on the surface of the microbe.
- Forms stable covalent bonds with microbial proteins and polysaccharides.
- C3 convertase breaks down more C3, leading to the recruitment of more C3b and C3bBb molecules to the microbe.
Classical Pathway
- Triggered when IgM or IgG binds to antigen on a microbial cell surface.
- C1 complement protein binds to the Fc region of the antibody, leading to the binding and cleavage of C2 and C4 protein.
- C4b2a complex forms the classical pathway C3 convertase.
Lectin Pathway
- Initiated by the attachment of the mannose-binding lectin (MBL) to microbes.
- Serine proteases, related to C1, lead to the binding and cleavage of C2 and C4 protein.
- C4b2a complex forms the classical pathway C3 convertase.
Early Steps of Complement Activation
- The net result is that microbes acquire a coat of covalently attached C3b.
- Alternative and lectin pathways are part of innate immunity, while the classical pathway is part of humoral immunity.
Late Steps of Complement Activation
- Initiated by the binding of C5 to C5 convertase and subsequent proteolysis of C5, generating C5b.
- The remaining components (C6, C7, C8, and C9) bind sequentially to a complex nucleated by C5b.
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Description
Learn about the functions of the complement system, including opsonization, cell lysis, and inflammation, in defense against microbes during innate and adaptive immune responses.
