Fc receptor is a protein belonging to immunoglobulin superfamily that contributes to the protective functions of the immune system. Fc receptor is found on the surface of certain cells - including B lymphocytes, natural killer cells, macrophages, neutrophils and mast cells. Its name is derived from its binding specificity for a part of an antibody known as the Fc portion. Fc receptors bind to antibodies that are attached to infected cells or invading pathogens. There are many kinds of Fc receptor based on the type of antibody that they recognize. Their activity stimulates phagocytic or cytotoxic cells to destroy microbes or infected cells by antibody-mediated phagocytosis or antibody-dependent cell-mediated cytotoxicity.
There are several types of Fc receptors based on the antibodies they recognize. For example, Fc receptor that bind IgG is called Fc gamma receptor (FcγR), Fc receptor that bind IgE is called Fc epsilon receptor (FcεR) and Fc receptor that bind IgA is called Fc alpha receptor (FcαR).
Fc gamma receptor (FcγR) is a receptor for the Fc portion of IgG. All of the Fc gamma receptors (FcγR) belong to the immunoglobulin superfamily. Fc gamma receptor is essential participant in many immune system effector functions, such as phagocytosis of opsonized, release of inflammatory mediators and antibody-dependent cellular cytotoxicity.
There are three major classes of Fc gamma receptor receptors depending on the affinity of receptor. Fc gamma receptor can be sorted as high-affinity receptor FcγRI (CD64) and low-affinity receptor FcγRII (CD32) and FcγRIII (CD16). The three classes of Fc gamma receptor contain highly conserved extracellular Ig domains.
Human IgG receptor expression pattern. + indicates expression; (+), inducible expression; ±, very low percentages or rare subsets express the receptor; −, no expression; and NA, not analyzed; Mono/Macro, monocytes, and/or macrophages. §Refer to the review by Guilliams et al. for specific expression on human DC subtypes. ♮In Fcgr2c-ORF persons. #Detectable and functional expression in non-conventional Fcgr2c-Stop persons
If your cells have many Fc-receptors on the cell surface (in particular monocytes, macrophages) or they have been cultured in serum free medium, it is advisable to block nonspecific binding of monoclonal antibodies by pre-incubation of cells with serum of same species of your cells, monoclonal anti-Fc receptor antibodies, or recombinant Fc protein, etc.. Note that for staining of whole blood this is not necessary, because serum in high concentration is present during staining. However, it's always be recommended to do Fc receptors blockade prior to sample staining if your sample contains the cell types mentioned above.