Identification of a Family of Fc Receptor Homologs with Preferential B Cell Expression

Investigation of human genome sequences with a consensus sequence derived from 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 homologs (FcRHs). The closely linked FcRH genes are located in a chromosome 1q21 region in the midst of previously recognized FcR genes. This report focuses on the FcRH1, FcRH2, and FcRH3 members of this gene family. Their cDNAs encode type I transmembrane glycoproteins with 3-6 Ig-like extracellular domains and cytoplasmic domains containing consensus immunoreceptor tyrosine-based activating and/or inhibitory signaling motifs. The five FcRH genes are structurally related, and their protein products share 28-60% extracellular identity with each other. They also share 15-31% identity with their closest FcR relatives. The FcRH genes are expressed primarily, although not exclusively, by mature B lineage cells. Their conserved structural features, patterns of cellular expression, and the inhibitory and activating signaling potential of their transmembrane protein products suggest that the members of this FcRH multigene family may serve important regulatory roles in normal and neoplastic B cell development.