Which fragment of the complement system is primarily responsible for opsonization?

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Multiple Choice

Which fragment of the complement system is primarily responsible for opsonization?

Explanation:
Opsonization is tagging a pathogen so phagocytes can recognize and engulf it. The fragment that does this most effectively is C3b. When C3 is cleaved by C3 convertase, C3b binds covalently to the surface of microbes. This marks the invader for phagocytosis by binding to complement receptors on macrophages and neutrophils, greatly enhancing uptake. C3b can also help amplify the cascade by forming part of the C5 convertase, but its key role in opsonization is tagging surfaces for phagocytosis. The other fragments have different roles: C3a and C5a are inflammatory mediators that recruit and activate immune cells, while C4a is a less potent inflammatory peptide.

Opsonization is tagging a pathogen so phagocytes can recognize and engulf it. The fragment that does this most effectively is C3b. When C3 is cleaved by C3 convertase, C3b binds covalently to the surface of microbes. This marks the invader for phagocytosis by binding to complement receptors on macrophages and neutrophils, greatly enhancing uptake. C3b can also help amplify the cascade by forming part of the C5 convertase, but its key role in opsonization is tagging surfaces for phagocytosis.

The other fragments have different roles: C3a and C5a are inflammatory mediators that recruit and activate immune cells, while C4a is a less potent inflammatory peptide.

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