Dictionary Meaning and Definition on '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
Wikipedia Meaning and Definition on 'Opsonin'
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 and its target have a negative charge (zeta-potential), making it difficult for the two cells to come close together. During the process of opsonization (also, opsonisation), antigens are bound by antibody or complement molecules. Phagocytic cells express receptors, CR1 and Fc receptors, that bind opsonin molecules, C3b and antibody, respectively. 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.[See more about Opsonin at Dictionary 3.0 Encyclopedia]