Opsonization of bacteria takes place when immunoglobulin G (IgG) molecules bind to specific epitopes on bacterial surface antigens through the antigen-binding site of the IgG molecule.

What triggers opsonization?

Opsonization of a pathogen can occur by antibodies or the complement system. Classical pathway: The formation of the antigen-antibody complex triggers the classical pathway. The antigen-antibody reaction activates C1, which then cleaves inactive C4 to active C4a and C4b.

What can act as an Opsonin?

First, specific antibody alone may act as an opsonin. Specific antibody may also act as an opsonin in concert with complement, by activating C3 via the classic pathway of C1, C4, and C2. Finally, there is a nonspecific mechanism of opsonization present in nonimmune animals called the heat-labile opsonin system.