Definition of opsonin in US English:



  • An antibody or other substance which binds to foreign microorganisms or cells making them more susceptible to phagocytosis.

    • ‘By some unknown process, Acupuncture raises levels of triglycerides, specific hormones, prostaglandins, white blood counts, gamma globulins, opsonins, and overall anti-body levels.’
    • ‘In all infants, the spleen provides important protection against invading bacteria; it is also a source of opsonins and fixed-tissue macrophages, as well as antibody production.’
    • ‘Note that an opsonin is a blood serum protein or fragment which when deposited on the surface of a bacteria, virus, immune complex, or other particulate material acts a signal for phagocytosis to cells bearing the appropriate receptors.’
    • ‘A mixture of opsonins adhere to the bacterium and facilitate ingestion by alveolar macrophages.’
    • ‘Complement molecules can function as opsonins in the recognition of bacterial pathogens and in their elimination by phagocytosis of the bound complexes.’


Early 20th century: from Latin opsonare ‘buy provisions’ (from Greek opsōnein) + -in.