Region of the immunoglobulin molecule that binds to cells when the antigen-binding sites are occupied. Treatment of antibody with pepsin will release the Fc portion (fragment crystallizable) leaving the Fab2 fragment. Fc regions from the various antibody classes differ in their properties. Fc receptors are found on the surfaces of various cells involved in the immune response. There are five receptors for IgG: Fcγ-RI, -RII-A, -RII-B2, -RII-B1, and -RIII (CD16). FcγRII-B1 and FcγRII-B2 are inhibitory and their cytoplasmic domains have ITIM motifs. FcεRI binds IgE, FcαRI binds IgA. The consequences of receptor occupancy differ according to the receptor subtype.
Subjects: Medicine and Health.