FcRL5, also known as CD307e, CD307, IRTA2, FcRH5 and BXMAS1, is a 106kD type I transmembrane glycoprotein composed of 6-8 extracellular Ig like C2 domains and 2 cytoplasmic ITIM motifs. The FcRL5 gene is located on chromosome 1q21 and is normally expressed by tonsillar plasma cells and germinal center B cells. It has been suggested that FcRL5 contributes to B cell maturation and B cell receptor modulation. The identification of FcRL5 on a number of transformed cell types including hairy cell leukemia, mantle cell lymphoma, chronic lymphocytic lymphoma and Burkitt’s lymphoma has prompted interest in it as a potential biomarker or target for immunotherapy. FcRL5 binds all aggregated IgG isotypes.