opsonizan

Opso­nizan, in English commonly called opsonization, is the process by which pathogens are marked by opsonins to promote their recognition and ingestion by phagocytes. Opsonins include antibodies, especially IgG, as well as complement components such as C3b and C4b, and certain lectins like mannose-binding lectin that participate in the lectin pathway. These molecules bind to the surface of microbes and coat them, creating a molecular handle for immune cells.

The marking works by engaging receptors on phagocytes. Antibody-coated pathogens are recognized by Fc gamma receptors, while complement-coated particles interact with complement receptors such as CR1 and CR3. This receptor engagement stimulates phagocytosis, leading to internalization of the microbe and its destruction inside the phagocyte via reactive oxygen species and lysosomal enzymes.

Opsonization enhances the efficiency of the immune response and is especially important for combating bacteria with protective capsules, which may resist direct phagocytosis. By coating such organisms, opsonins overcome capsule-imposed barriers and facilitate clearance by macrophages and neutrophils. Opsonization is also a key mechanism by which vaccines confer protection, by inducing the production of opsonizing antibodies.

Clinically, deficiencies in antibodies or components of the complement system can impair opsonization, resulting in increased susceptibility to infections, particularly with encapsulated bacteria. Understanding opsonization clarifies how humoral and complement systems cooperate to mark pathogens for destruction and maintain host defense.