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Antibody opsonization is the process by which the pathogen is marked for ingestion and eliminated by the phagocytes.

Given normal inflammatory circumstances, microbial pathogen-associated molecular patterns (PAMPs) bind with the endocytic pattern recognition receptors (PRRs) of phagocytes, which mediates neutrophil mediation or macrophage phagocytosis. As well as endocytic PRRs, Phagocytes furthermore express opsonin receptors such as Fc receptor and complement receptor 1 (CR1). Should the microbe be coated with opsonising antibodies or C3b complement, the co-stimulation of endocytic PRR and opsonin receptor increases the efficacy of the phagocytic process, enhancing the lysosomal elimination of the infective agent. This mechanism of antibody-mediated recognition leading to increased phagocytic efficacy is termed opsonization.

Opsonization involves the binding of an opsonin, e.g., antibody, to an epitope on a pathogen. '''A key system that is needed for opsonization is the complement system. In this system, the C3 protein is cleaved into smaller proteins, C3a and C3b, via enzymes from the complement system. C3b is the protein that is able to bind with pathogen surfaces. The bound C3b produces smaller fragments which are then recognized by different receptors; including the macrophage phagocytic receptor. Phagocytes are then called in order to aid in the destruction of the pathogen. Another important contribution from the complement system can be seen by the need of CRIg, a complement receptor for the immunoglobulin family. Once the complement and opsonin complex comes in contact with the macrophage CRIg endosomes are called to help form phagosomes by providing them with membrane. This brings about enhanced binding to the macrophage surfaces leading to more efficient phagocytosis.''' The Fab portion of the antibody binds to the antigen, whereas the Fc portion of the antibody binds to an Fc receptor on the phagocyte, facilitating phagocytosis. The core receptor + opsonin complex also creates byproducts like C3b and C4b which are important components for the efficient function of the. These components are deposited on the cell surface of the pathogen and aid in its destruction.

The cell can also be destroyed by a process called antibody-dependent cell-mediated cytotoxicity, in which the pathogen does not need to be phagocytized to be destroyed. During this process, the pathogen is opsonized and bound with the antibody IgG via its Fab domain. This allows the antibody binding of an immune effector cell via its Fc domain. Antibody-dependent cell-mediated inherent mediation then triggers a release of lysis products from the bound immune effector cell (monocytes, neutrophils, eosinophils and NK cells). Lack of mediation can cause inflammation of surrounding tissues and damage to healthy cells.

References[edit]

 * 1) ^ Definition: opsonization from Online Medical Dictionary
 * 2) ^ Parham, P. (2005). The Immune System," Garland Science Publishing, New York, NY.
 * 3) ^ Kumar, V., Abbas, A. K., & Fausto, N. (2005). Pathologic basis of disease. Philadelphia: Elsevier Saunders