IMMUNOGLOBULINS
COMPLEMENT SYSTEM
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Directly injures bacteria.
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Is an anaphylatoxin.
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Is the inactive form of C3.
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Opsonizes bacteria.
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Detailed explanation-1: -C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis.
Detailed explanation-2: -(1) A pathogen coated in C3b binds to complement receptor 1 (CR1) expressed on the surface of phagocytes (including APCs). These cells then easily engulf and destroy the invader. The C3b is said to be acting as an opsonin in this case because it enhances the ability of an entity to be phagocytosed.
Detailed explanation-3: -C3b is an integral component of both the classical and alternative pathway C5 convertases (C4bC3b, C2a and C3bC3b, Bb, respectively), which cleave C5 to initiate membrane attack complex (C5b-9) formation.