Fc Receptor Homologs (FcRH)
Fc receptor homologs, also known as IRTA or IFGP (IgSF, FcR, gp42) proteins, are transmembrane proteins with sequence homology to classical Fc receptors. FcRH have from three to nine Ig-like domains in their extracellular region and variable combinations of cytoplasmic immunotyrosine activation or inhibitory motifs (ITAM or ITIM). FcRH function as activating or inhibitory receptors on discrete B cell populations and are involved in lymphocyte development and transformation. No ligands for these proteins have been identified.