Inflammatory Modulators: Ocular Expression of PD–1 and PD–L1 During Active Uveitis

Abstract

Abstract: : Purpose: Program death–1 (PD–1), a CD28 family member, plays an important role in down–regulating active T cell responses and is typically observed on activated lymphocytes and myeloid cells. Expression of PD–1 ligands, PD–L1 and PD–L2, is observed in immune cells and in certain peripheral tissues leading to their putative roles in maintaining peripheral tolerance. The potential role for PD–1 and its ligands in maintaining ocular immune homeostasis is not yet described. The purpose of this study was to investigate expression of PD–1 and its ligands in eyes during active inflammation and in normal controls. Methods: Experimental autoimmune uveitis (EAU) was induced in B10RIII mice by immunization with interphotoreceptor retinoid–binding protein (IRBP)161–180. Eyes and thymus were harvested at two time points, one before development of and the second during active inflammation. These tissues were used for detection of PD–1, PD–L1, and PD–L2 by immunohistochemical analysis. Spleen was harvested for lymphocyte proliferation assays in order to measure T cell activation. RT–PCR was performed to detect PD–1 mRNA expression in the eye. Results: PD–1 was constitutively expressed in the normal mouse retina, both in the ganglion cell layer and inner nuclear layer. Although obvious changes in expression levels in the retina were not observed during active uveitis, PD–1 was expressed as anticipated by the invading inflammatory cells. Retinal expression of PD–1 was confirmed by predicted size after RT–PCR and by sequence analysis of the product. In contrast, PD–L1 and PD–L2 were not detected in the control retina but were minimally observed in the invading inflammatory cells during active uveitis. Conclusions: Constitutive expression of PD–1 in the retina was significant and its expression in neuronal cells has not been previously reported. This observation may indicate an important role in the ocular microenvironment. Expression of PD–1 and its ligands is observed in the inflammatory infiltrate during ocular inflammation induced by IRBP. PD–L1 expression is not observed in the uninflamed eye, but appears in the inflammatory infiltrate after the onset of uveitis.

Keywords: autoimmune disease • uveitis-clinical/animal model