Opsonization- Definition, Mechanism, Opsonins, Examples


Opsonization is a process in which molecules, microbes, or apoptotic cells are chemically modified to have stronger interactions with cell surface receptors on phagocytes and antibodies . This process is important in host defense and makes particles or complexes readily ingestible for uptake by phagocytic cells. Opsonins, such as antibodies and complement components, coat dangerous antigens and mark them for destruction by phagocytes . Without opsonization, the recognition and destruction of invading agents such as bacteria would be inefficient. The complement system plays a major role in opsonization by coating particles such as bacteria with fixed C3 and C4.

Opsonization can be defined as the molecular mechanism whereby molecules, microbes, or apoptotic cells are marked for an immune response or marked dead cells for recycling. An opsonin is any molecule that enhances phagocytosis by marking an antigen for an immune response or marking dead cells for recycling. The purpose of opsonization is to make the antigens palatable to the antibody or the phagocytic cells.

Opsonization can occur via antibodies or the complement system. Antibody-mediated opsonization involves the coating of pathogens with antibodies so that they are recognized and phagocytosed by innate immune cells. Complement-mediated opsonization involves the cleavage of C3 into C3a and C3b, which binds to the surface of the particle and serves as an opsonin. Phagocytic cells have receptors for C3b and Fc portion of IgG antibodies, which mediate binding and ingestion of opsonized particles .

Opsonization is an essential immune process that helps to clear infection and prevent disease. Opsonins have important roles in the immune system like marking of dead and dying cells for clearance by macrophages and neutrophils. Besides, opsonins also aid in activating the complement proteins and destruction of cells by natural killer (NK) cells. Opsonization is one of the ways that the immune system identifies and targets foreign particles for elimination.