FcR is the receptor of immunoglobulin (Ig), which causes corresponding cell-specific immune response by binding to the specific region of the Fc segment of Ig, acting as a bridge between humoral immunity and cellular immunity. Gene polymorphisms of FcR enable it to induce various intracellular biological effects, which are closely related to the occurrence and development of various immune-related diseases such as autoimmune diseases SLE and RA. Fc receptor proteins are one of the most important protein families in the immune system, mediating antibody-dependent ADCP, ADCC and CDC effects, and playing a key role in immune system activation and antibody function.
Currently the most widely used are mainly IgG receptors including FcRn and FcγR. FcyRs can be divided into three classes: FcyRI, FcyRII and FcyRIII. FcγRI has high affinity for IgG (10-9M) and is mainly expressed in monocyte-macrophages. FcγRII, FcγRIII and IgG have low affinity (10-6M) and are widely distributed. FcγRII is divided into 3 types: FcγRIIa, FcγRIIb and FcγRIIc according to the structure of the cytoplasmic region. It exists in B cells, macrophages, polymorphonuclear cells, platelets and monocytes, and FcγRIIb is the only inhibitory receptor. FcγRIII is present in granulocytes, NK cells, macrophages and activated monocytes. The combination of FcγR and antibody can activate immune cells and produce endocytosis, phagocytosis, ADCC and other functions.