A substance capable of enhancing phagocytosis. Opsonins include antibodies and the C3b molecule of the complement system.

A serum protein that renders microorganisms and other foreign material more susceptible to phagocytosis.

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

A substance, usually an antibody, that combines with the surface of a microbe to increase phagocytosis.

A substance, usually antibody or complement component, which coats a particle such as a bacterium and enhances phagocytosis by phagocytic cells.

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 phagocytising 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.