AskDefine | Define opsonin

Dictionary Definition

opsonin n : an antibody in blood serum that attaches to invading microorganisms and other antigens to make them more susceptible to the action of phagocytes

User Contributed Dictionary



  1. Any antibody that causes an invading species to be more susceptible to phagocytosis


an antibody

Extensive Definition

An opsonin is any molecule that acts as a binding enhancer for the process of phagocytosis, for example, by coating the negatively-charged molecules on the membrane.


Both the membrane of a phagocytosing cell, as well as its target, have a negative charge (zeta-potential), making it difficult for the two cells to come close together. During the process of opsonization, antigens are bound by antibody and/or complement molecules. Phagocytic cells express receptors that bind opsonin molecules. These include the Fc receptors. With the antigen coated in these molecules, binding of the antigen to the phagocyte is greatly enhanced. Most phagocytic binding cannot occur without opsonization of the antigen.
Furthermore, opsonization of the antigen and subsequent binding to an activated phagocyte will cause increased expression of complement receptors on neighboring phagocytes.


Examples of opsonin molecules include:
The most important are IgG and C3b.


External links

opsonin in German: Opsonin
opsonin in French: Opsonine
opsonin in Italian: Opsonina
opsonin in Japanese: オプソニン化
opsonin in Norwegian: Opsonin
opsonin in Polish: Opsoniny
opsonin in Portuguese: Opsonina
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