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How does the complement system enhance immune response? (p.14-15)
- Complement – term for group of plasma proteins that play role in immunity and inflammation
- Consists of 9 separate proteins – C1-C9
- Present in inactive forms in plasma
- Once activated, functions as complement cascade
- Amplifies immune response once activated by antigen-antibody complex
- Net effect = formation of cytotoxic complex that helps kill cells
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What activates classical pathway? (p.14)
- Activated by C1 fixation on antibody-antigen complex (IgG, IgM)
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What activates alternate pathway?
- Initiated by polysaccharides (endotoxins on bacteria IgA)
- Different set of serum components involved in first 2 steps (properidin P, factors B and D)
- Activation of C3 occurs in both
- Net results same – histamine release and chemotaxis
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What split products of complement components are referred to as anaphylatoxins? (p.14)
- C3a and C5a
- Increase vascular permeability and vasodilation by causing histamine release from mast cells
- C5a also activates lipoxygenase pathway of arachidonic acid (AA) metabolism in neutrophils and monocytes
- Also causes release of inflammatory products
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