FcRn complex consist of two subunits: IgG receptor FcRn large subunit p51（alpha chain) and Beta-2-microglobulin（Beta chain). The complexes is similar in structure to MHC class I-like heterodimer. Beta-2-microglobulin involved in the presentation of peptide antigens to the immune system. FcRn binds to the Fc region of monomeric immunoglobulins gamma, mediates the uptake of IgG from milk,Possible role in transfer of immunoglobulin G from mother to fetus. A principal component of antibody transport is the neonatal receptor for the Fc portion of immunoglobulin, a heterodimer of a MHC-1 alpha-chain homolog ( FcRn ) and beta-2-microglobulin ( B2M ).