FcRn: the MHC class I-related receptor that is more than an IgG transporter.

Recent data have indicated that the major histocompatibility complex (MHC) class I-related receptor FcRn plays a role in regulating serum IgG levels, in addition to transferring maternal IgGs across the rodent neonatal gut. The isolation of a human homolog of FcRn from placenta suggests that the studies in rodents have relevance to understanding similar processes in humans. This has implications for the engineering of improved antibodies for therapy.