The neonatal Fc receptor is expressed by human retinal pigment epithelial cells and is downregulated by tumour necrosis factor-alpha

Background/aims The neonatal Fc receptor (FcRn) protects immunoglobulin G (IgG) from catabolism, controls its transport between cell layers and extends its serum half-life. In the human, vitreous IgG can be found, but how vitreous IgG is processed or transported is currently unknown. The FcRn is a candidate molecule to regulate these processes. The authors examined FcRn expression and regulation in human retinal pigment epithelium (RPE) cells. Methods In three primary RPE cell cultures (from three donor eyes) and in the human RPE cell line ARPE-19, FcRn and beta-2-microglobulin (beta 2M) mRNA levels were determined by real-time quantitative PCR. FcRn protein expression was analysed by western blot studies. Stimulation experiments were performed with recombinant human tumour necrosis factor (TNF)-alpha and interferon (IFN)-gamma. HT-29, THP-1 and HeLa cell lines were used as FcRn positive and negative non-ocular controls, respectively. Results Expression of FcRn mRNA and protein was demonstrated in all three RPE cultures. After stimulation with TNF-alpha, FcRn expression is downregulated in RPE cells and upregulated in HT-29 and THP-1 cells. IFN-gamma has no effect on FcRn expression in RPE cells. Conclusions Human RPE cells express FcRn. The proinflammatory cytokine TNF-alpha downregulates FcRn expression. The authors speculate that the FcRn may play a pivotal role in the immune privilege of the human eye.