opsonin

Any blood serum protein that binds to antigens, enhancing phagocytosis ( e.g., C3b of the complement system, specific antibodies). [G. opson, boiled meat, provisions, fr. hepso, to boil, + -in]

- common o. SYN: normal o..

- immune o. SYN: specific o..

- normal o. o. normally present in the blood, i.e., without stimulation by a known, specific antigen such as certain complement components; it is relatively thermolabile and reacts with various organisms. SYN: common o., thermolabile o..

- specific o. antibodies formed in response to stimulation by a specific antigen, either as a result of an attack of a disease or as a result of injections with a suitably prepared suspension of the specific microorganism. SYN: immune o., thermostable o..

- thermolabile o. SYN: normal o..

- thermostable o. SYN: specific o..

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op·so·nin 'äp-sə-nən n any of various proteins (as complement or antibodies) that bind to foreign particles and microorganisms (as bacteria) making them more susceptible to the action of phagocytes

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n.

a serum complement component that attaches itself to invading bacteria and apparently makes them more attractive to phagocyte and thus more likely to be engulfed and destroyed.

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op·so·nin (opґsə-nin) [Gr. opsōnein to buy victuals] any substance that binds to particulate antigens and induces their phagocytosis by macrophages and neutrophils. In current usage the term is used to refer to substances of two types, opsonizing antibodies (IgM, IgG1, and IgG3, immunoglobulins specific for the antigen) and certain complement fragments (C3b, C3d, and C4b, which become bound to the antigen during complement activation), both of which trigger phagocytosis by binding to specific cell-surface receptors, Fc receptors, and complement receptors on neutrophils and macrophages. opsonic adj