Fcrn Expression in the Human Retinal Pigment Epithelium

Abstract

Purpose: : The neonatal Fc receptor (FcRn) protects immunoglobulin G (IgG) from catabolism and controls IgG transport between different cell layers. The FcRn extends the serum half-life of IgG by returning pinocytosed IgG back to the cell surface of vascular endothelial cells and into the bloodstream. IgG can also be found in the vitreous of the eye. How IgG is processed in or transported out of the vitreous is currently unknown, but the FcRn is a candidate molecule to regulate these processes. However, data on FcRn expression in the human eye are lacking. The main objective of this study was to examine FcRn expression in human retinal pigment epithelium (RPE) cells.

Methods: : RPE cell cultures were established from three donor eyes (harvested for cornea transplantation). In these RPE cultures and in human ARPE-19 cells FcRn and beta-2-microglobulin (β2M) mRNA levels were determined by real time quantitative PCR (RQ-PCR). FcRn protein expression was analysed by immunoprecipitation studies. Stimulation assays were performed with human TNF-alpha and recombinant human IFN-gamma. HT-29 and THP-1 cell lines were used as positive controls, HeLa cell line was used as negative control.

Results: : RQ-PCR revealed expression of FcRn mRNA in all three RPE cultures. FcRn mRNA was co-expressed with β2M mRNA. Western Blot analysis, using two different FcRn antibodies, demonstrated that the FcRn mRNA expression in all three RPE cultures co-existed with FcRn protein expression. FcRn expression in RPE cells is downregulated after stimulation with TNF-alpha and IFN-gamma, whereas FcRn expression in HT-29 and THP-1 cells is upregulated after stimulation with those cytokines.

Conclusions: : Human RPE cells express the FcRn. Proinflammatory cytokine TNF-alpha downregulates FcRn expression. We speculate that the FcRn may play a pivotal role in the immune privilege of the human eye.

Keywords: immune tolerance/privilege • retinal pigment epithelium • immunomodulation/immunoregulation