Opsonin
Opsonin
Any substance that promotes cellular phagocytosis.
Opsonization by humoral components:
- the mannose-binding protein, which binds
mannans and is recognized by the C1q receptor.
- the surfactant protein A, which binds
carbohydrates and is recognized by a transmembrane receptor, SPR210.
- complement proteins
- C3bi
fragment fixed non specifically to the carbohydrate surface of pathogens via
the alternative pathway, which is recognized by the C3bi receptors (CRs) on
macrophages (CR1, CR3, and CR4), responsible for particule internalization.
- complement
fixed to IgM that specifically recognizes epitopes on the surface of the
pathogen.
- antibodies
- antibodies
which recognize epitopes on infections agents and are recognized by the Fc
receptors (FcRs).
- IgG
antibodies are much more effective opsonins than IgM antibodies in the absence
of complement, but IgM antibodies are more effective opsonins in the presence
of complement.