(ŏp-sō'nĭn )

[Gr. opsonein, to purchase food]

A substance that coats foreign antigens, making them more susceptible to macrophages and other leukocytes, thus increasing phagocytosis of the organism. Complement and antibodies are the two main opsonins in human blood.

opsonic,

(-sŏn'ĭk )

immune o.Opsonin formed after stimulation by a specific antigen.