OX40 ligand expression abrogates the immunosuppressive function of retinal pigment epithelium

Polymerase chain reaction confirmed the insertion of the OX40L gene into the fusion vector. Flow cytometry and fluorescence microscopy further confirmed surface expression of OX40L on ARPE cells after transfection. OX40L expression was induced in the RPE cells stimulated with pro-inflammatory cytokines. In the co-culture studies, there was a significant reversal (20% to 30%) of the RPE-induced suppression of activated PBMCs when the ARPE cells were transfected with OX40L. When both OX40L and GITRL were concomitantly transfected into ARPE cells, there was an additive reversal of RPE-mediated T cell suppression, when compared to the reversal caused by RPE cells expressing either OX40L alone or GITRL alone.Using an in vitro approach, we found that OX40L causes an abrogation of the RPE-mediated immunosuppression. OX40L appears to be regulated in the ARPE-19 cell line and may play an important role in the pathogenesis of various ocular inflammatory conditions.OX40 ligand (OX40L) is a member within the TNF ligand superfamily [1-4] and plays an important role in the induction of co-stimulatory signaling during T cell and antigen-presenting cell (APC) interactions [5-9]. Prior studies have demonstrated that OX40L is expressed predominantly on CD4+ T cells [10,11]. In addition to its role in co-stimulatory signaling, OX40/OX40L interaction is closely involved in effector functions [12-15]. OX40L expression has been observed on APCs including dendritic cells [16,17], B cells [12], and microglial cells [18], but has also been found on non-lymphoid cells (i.e., endothelial cells) [19].Recently, its potential role in the pathogenesis of immune-mediated ophthalmic diseases including uveitis, experimental allergic conjunctivitis, and corneal graft rejection has been investigated [20-23]. A recent study by Zhang et al. described the activation of ovalbumin-specific T cells with OX40-activating antibody and found that OX40-stimulated lymphocytes elicited more ocular inflammation com