Q.5 In complement systems which is not the example of anaphylatoxins –
- C4a
- C3a
- C7
- C5a
C7 is not an example of an anaphylatoxin in the complement system. The primary anaphylatoxins are C3a, C4a, and C5a, which are small peptides generated during complement activation to promote inflammation.
Question Solution
This multiple-choice question tests knowledge of complement system components, specifically identifying which option does not function as an anaphylatoxin.
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C4a: An anaphylatoxin derived from cleavage of C4; it induces mast cell degranulation and increases vascular permeability, though less potent than others.
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C3a: A key anaphylatoxin from C3 cleavage; it triggers histamine release, chemotaxis, and smooth muscle contraction.
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C7: Not an anaphylatoxin; it is a late complement component (MAC family) that binds to C5b-6 and initiates membrane attack complex assembly for cell lysis.
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C5a: The most potent anaphylatoxin from C5; it drives strong chemotaxis, neutrophil activation, and inflammation.
Correct Answer: C7 (Option 3). Anaphylatoxins are specifically C3a, C4a, and C5a, produced early in all complement pathways.
Complement system anaphylatoxins play a vital role in innate immunity by triggering inflammation during pathogen defense. In competitive exams like GATE Life Sciences, questions like “In complement systems which is not the example of anaphylatoxins – C4a, C3a, C7, C5a” test precise recall of these components.
What Are Anaphylatoxins?
Complement system anaphylatoxins are small, stable peptides (C3a, C4a, C5a) released by proteolytic cleavage of C3, C4, and C5 during classical, lectin, or alternative pathway activation. They bind G-protein-coupled receptors on immune cells, causing mast cell degranulation, histamine release, vasodilation, and chemotaxis.
Role of Each Option
Component Anaphylatoxin? Function in Complement System C4a Yes Mild inflammation; vascular permeability from C4 cleavage. C3a Yes Histamine release, immune cell recruitment from C3. C7 No Late component; forms MAC pores for lysis, not inflammation. C5a Yes Potent chemotaxis, neutrophil activation from C5. C7 stands out as it belongs to the terminal pathway, unrelated to anaphylatoxin activity.
Why C7 is Not an Anaphylatoxin
Unlike early fragments C3a/C4a/C5a, C7 integrates into target membranes without promoting allergic-like responses. This distinction is key for exams, as anaphylatoxins bridge innate immunity but C7 focuses on cytolysis.
Exam Relevance for GATE Life Sciences
Mastering complement system anaphylatoxins helps in PYQs on immunology. Focus on their receptors (C3aR, C5aR1) and differences from opsonins like C3b.
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