Antibodyopsonized

Antibodyopsonized, often written as antibody-opsonized, refers to particles, cells, or pathogens that have been coated with antibodies, thereby marking them for attack by phagocytic immune cells. Opsonization increases the efficiency of phagocytosis and helps the immune system distinguish targets from self. The principal opsonins in antibodyopsonized particles are IgG antibodies and components of the complement system, particularly C3b, which can be deposited on the surface.

Mechanism: Antibodies bind to specific antigens on a microbe’s surface. The Fc region of bound IgG is recognized by Fc gamma receptors on macrophages, neutrophils, and dendritic cells, triggering phagocytosis. Complement-coated targets bind to complement receptors and further promote uptake. Opsonization enhances engulfment, intracellular killing within phagolysosomes, and can aid in antigen presentation in some cases.

Clinical and biological significance: Opsonization is central to humoral immunity and a key mechanism by which vaccines and therapeutic antibodies promote pathogen clearance. Some pathogens have evolved capsules or surface proteins to impede opsonization, contributing to virulence. Defects in antibody production or Fc receptor function can impair antibody-mediated phagocytosis, increasing susceptibility to bacterial infections. Laboratory assays often measure antibodyopsonized killing to assess functional antibody responses or the efficacy of monoclonal antibody therapies.