Molecular characterization of six variant Fc gamma receptor class I (CD64)transcripts

In humans, three distinct but closely related classes of receptors that bin d the Fe portion of IgG (Fc gamma RI, II, and III) have been identified. Fc gamma RI can bind monomeric IgG with high affinity and has a unique third extracellular domain (EC3). Three very similar genes have been characterize d for Fc gamma RI (A, B, C). Although the sequences are remarkably similar, a number of coding-region differences discriminate between the genes and a mongst their transcripts. Six distinct Fc gamma RI transcripts were analyse d. Three transcripts: one from each gene, contain all six exons. Only the g ene A transcript appears to encode a bona fide high affinity receptor, a th ree Ig-domain membrane spanning receptor that can bind monomeric IgG. Stop codons in the EC3 domains of the gene B and gene C isoforms would be predic ted to generate secreted receptors. Three transcripts are alternatively spl iced isoforms, one from gene A and two from gene B. One gene B transcript e ncodes a two Ig-domain transmembrane receptor which has structural characte ristics of a low affinity Fc gamma R. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.