Fc (Ig constant fragment) receptors ensure protection of the host against foreign antigens, such as microorganisms and pathogens, by removing Ig-coated antigen complexes from circulation. Fc receptors are present on lymphoid and myeloid derivatives, where they mediate endocytosis of Ig-antigen complexes, antibody production in B cells through T cell antigen presentation, cytotoxicity and the release of cytokines and reactive oxygen species. The Fc γ-binding protein (FCGBP) interacts with the Fc portion of IgG and MUC2 to mediate the maintenance of the mucosal structure. FCGBP is a 5,405 amino acid protein that contains twelve TIL (trypsin inhibitory-like) domains and thirteen VWFD domains. It is predominantly expressed in placenta and colon epithelium as well as in thyroid and serum. Patients with various autoimmune diseases seemingly have higher levels of FCGBP protein present in their serum.