Fc receptor is a antibody receptor involved in antigen recognition which is located at the membrane of certain immune cells including B lymphocytes, natural killer cells, macrophages, neutrophils, and mast cells. Such receptors recognize Fc fragment of antibodies and that is the name of Fc receptor derived from. Fc receptors binding to antibodies that are attached to infected cells or invading pathogens contributes to the protective functions of the immune system.Their activity stimulates phagocytic or cytotoxic cells to destroy microbes, or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity.
Fc receptors deliver signals when they are aggregated by antibodies and multivalent antigens at the cell surface. The aggregation of Fc receptors with immunoreceptor tyrosine-based activation motifs (ITAMs) activates sequentially src family tyrosine kinases and syk family tyrosine kinases. These kinases connect the transduced signals with common activation pathways. ITAM is composed of a twice-repeated YxxL sequence flanking seven variable residues. Fc receptors with ITAM cause cell activation, endocytosis and phagocytosis.
Fc receptors are found on a number of cells in the immune system including phagocytes like macrophages and monocytes, granulocytes like neutrophils and eosinophils, and lymphocytes of the innate immune system (natural killer cells) or adaptive immune system (e.g., B cells). They allow these cells to bind to antibodies that are attached to the surface of microbes or microbe infected cells and help these cells to identify and eliminate microbial pathogens. Activation of phagocytes is the most common function attributed to Fc receptors.
There are several types of Fc receptors dpending on the kind of antibody that they recognize. Fc receptors recognizing fc portion of IgG is called Fc gamma receptor (FcγR). Fc receptor recognizing C-terminal of IgA is called Fc alapha receptor (FcαR). Fc receptor recognizing C-terminal of IgE is called Fc epsilon receptor (FcεR).