Which molecule acts as an opsonin to enhance phagocytosis in the complement system?

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Study for the Success! In Clinical Laboratory Science – Immunology Test. Prepare with flashcards and multiple choice questions, each question offers hints and explanations. Get ready for your exam!

Multiple Choice

Which molecule acts as an opsonin to enhance phagocytosis in the complement system?

Explanation:
Opsonization marks pathogens for phagocytosis. In the complement system, C3 is split into C3a and C3b; C3b attaches covalently to microbial surfaces and serves as a tag that phagocytes recognize through C3b receptors (CR1). This binding dramatically enhances engulfment and clearance of the microbe. By contrast, C3a and C5a are inflammatory mediators that recruit and activate immune cells, not surface tags for phagocytosis. C1q helps initiate the classical pathway by recognizing antibodies or microbial surfaces, rather than acting as an opsonin for phagocytosis. So the molecule that functions as the opsonin to boost phagocytosis is C3b. (Degradation products like iC3b can also support phagocytosis via other receptors, but the primary opsonizing molecule is C3b.)

Opsonization marks pathogens for phagocytosis. In the complement system, C3 is split into C3a and C3b; C3b attaches covalently to microbial surfaces and serves as a tag that phagocytes recognize through C3b receptors (CR1). This binding dramatically enhances engulfment and clearance of the microbe. By contrast, C3a and C5a are inflammatory mediators that recruit and activate immune cells, not surface tags for phagocytosis. C1q helps initiate the classical pathway by recognizing antibodies or microbial surfaces, rather than acting as an opsonin for phagocytosis. So the molecule that functions as the opsonin to boost phagocytosis is C3b. (Degradation products like iC3b can also support phagocytosis via other receptors, but the primary opsonizing molecule is C3b.)

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