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 α/μ receptor (FCAMR) functions as a receptor for the Fc fragment of IgA and IgM and mediates their endocytosis. FCAMR is a 532 amino acid protein that is expressed in mesangial cells and is upregulated by IFNG/IFN-γ. It is also expressed in secondary lymphoid organs, such as lymph node and appendix, kidney and intestine, suggesting an important role of the receptor for immunity in these organs.