OPSONIN

opsonin

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

Source: WordNet® 3.1

Etymology

Noun

opsonin (plural opsonins)

Any chemical produced by the body, including antibodies and complement proteins, that causes a pathogen to be more susceptible to phagocytosis.

Source: Wiktionary