And analysis of the gene encoding the human neonatal Fc receptor

The neonatal Fc receptor, FcRn, is expressed in human placental syncytiotro phoblast, capillary endothelium, intestinal epithelium, and other tissues. By analogy with its role in the mouse, human FcRn is expected to transport maternal IgG to the foetus, and protect circulating IgG from catabolism. Th e larger subunit of FcRn is homologous to the a chains of the major histoco mpatibility complex (MHC) class I proteins, but is encoded outside the MHC on chromosome 19. We report the isolation of clones encoding the a chain of human FcRn from chromosome 19-specific libraries. The sequence revealed a similar organization to classical and non-classical MHC, and MHC-related ge nes. Compared with classical MHC class I genes, the human FcRn a chain gene has expanded by acquiring many repetitive sequences in its introns, includ ing multiple Alu elements in the fourth intron. Primer extension analysis s howed that there are two transcription initiation sites in the upstream fla nking sequence.