Identification and characterization of GITRL (ligand for glucocorticoid induced TNF related receptor) in ocular tissues

Abstract

Abstract: : Purpose: Previous studies have shown that the expression of glucocorticoid induced TNF related receptor (GITR) on T helper cells correlates with the clinical activity of non–infectious uveitis. GITR has also been shown to be involved in regulating the function of CD4+CD25+ regulatory T cells, inhibition of T cell receptor–induced apoptosis and the up–regulation of inducible nitric oxide synthase (iNOS). We wanted to further investigate the expression of the ligand for GITR (GITRL) and its regulation by ocular tissues. Methods: Immunohistochemistry and confocal immunofluorescence microscopy were performed on ocular tissues to examine the in vivo expression of GITRL. The regulation of GITRL was also investigated by examining the response of retinal pigment epithelium (RPE) to pro–inflammatory cytokines by immunocytochemistry and reverse transcriptase PCR (RT–PCR). The in vivo mRNA expression of GITRL was further studied by RT–PCR on total RNA isolated from microdissected ocular tissues. Results:Both immunohistochemistry and confocal immunofluorescence microscopy demonstrated that GITRL was expressed constitutively on RPE and photoreceptor inner segments. Immunocytochemistry and RT–PCR demonstrated that in vitro stimulated RPE cells expressed GITRL at both the mRNA and protein levels. GITRL is up–regulated at 24 hrs by pro–inflammatory cytokines. RT–PCR on RNA from microdissected tissues confirmed constitutive GITRL mRNA expression in vivo. Conclusions:GITRL is expressed constitutively on RPE and photoreceptor inner segments. The up–regulation of GITRL by pro–inflammatory cytokines suggests that GITRL may play potentially important roles in ocular immunity. The high level of constitutive GITRL expression on photoreceptor inner segments suggests that photoreceptors participate in the regulation of ocular inflammation.

Keywords: autoimmune disease • inflammation • immunomodulation/immunoregulation