Identification of a family of Fc receptor homologs with preferential B cell expression

Investigation of human genome sequences with a consensus sequence derived f rom receptors for the Fc region of Igs (FcR) led to the identification of a subfamily of five Ig superfamily members that we term the Fc receptor homo logs (FcRHs). The closely linked FcRH genes are located in a chromosome 1q2 1 region in the midst of previously recognized FcR genes. This report focus es on the FcRH1, FcRH2, and FcRH3 members of this gene family. Their cDNAs encode type I transmembrane glycoproteins with 3-6 Ig-like extracellular do mains and cytoplasmic domains containing consensus immunoreceptor tyrosine- based activating and/or inhibitory signaling motifs. The five FcRH genes ar e structurally related, and their protein products share 28-60% extracellul ar identity with each other. They also share 15-31% identity with their clo sest FcR relatives. The FcRH genes are expressed primarily, although not ex clusively, by mature B lineage cells. Their conserved structural features, patterns of cellular expression, and the inhibitory and activating signalin g potential of their transmembrane protein products suggest that the member s of this FcRH multigene family may serve important regulatory roles in nor mal and neoplastic B cell development.