opsonisering

Opsonisering, or opsonization, is an immunological process in which pathogens are marked for attack by phagocytes. Opsonins, including antibodies (primarily IgG) and complement fragments (such as C3b and C3d), bind to the surface of a microbe and form a coating that promotes recognition by phagocytes. Phagocytes express receptors for these opsonins, such as Fc receptors for IgG and complement receptors for C3b. Engagement of these receptors enhances phagocytosis, leading to internalization of the microbe into a phagosome, which fuses with a lysosome to form a phagolysosome where digestion occurs.

Opsonization increases the efficiency of pathogen clearance and can facilitate antigen presentation, linking innate and adaptive immunity. Additional opsonins include collectins and mannose-binding lectin, which tag microbes via lectin pathways. Some bacteria express capsules or other factors that impede opsonization, reducing phagocytosis; antibodies or complement can often overcome this in susceptible cases. Clinically, deficiencies in complement components (for example C3) or in antibody-mediated opsonization raise the risk of recurrent infections, particularly with encapsulated bacteria. Loss of splenic function also impairs opsonizing antibody production and deposition, contributing to increased susceptibility to infection.