Possible IgG transportation mechanism mediated by neonatal Fc receptor expressed in gingival epithelial cells

The neonatal Fc receptor (FcRn) for immunoglobulin G (IgG) expressed in intestinal epithelium has been shown to be responsible for IgG transport and to be involved in IgG catabolism (Simister, Vaccine 21:3365–3369, 2003; Ghetie and Ward, Immunol Res 25:97–113, 2002). In this study, we first examined the expression of FcRn in normal gingival epithelial cells (GECs) and then tested the possibility that IgG transportation is mediated by such FcRn expressed in GEC. To make these determinations, experiments were carried out to: (1) evaluate the expression pattern of FcRn using immunohistochemical staining of FcRn in human gingival tissue, (2) measure the expression of FcRn-mRNA in the cultured GEC, and (3) examine the transport of IgG via FcRn expressed in the GEC cultured in cell culture insert. Immunohistochemistry detected the expression of FcRn in human GEC. Primary culture of both GEC and human GEC line (OBA9) demonstrated the expression of FcRn-mRNA. Since RNAi-based inhibition of FcRn expression resulted in the diminished transportation of IgG, it was determined that FcRn expressed in GEC was responsible for the transport of IgG. Strikingly, the transport of IgG mediated by epithelial FcRn was pH-dependent. These results suggested that FcRn expressed in GEC may contribute to the recycling of IgG in the oral cavity.