Regulatory Role of TLR Ligands on the Activation of Autoreactive T Cells by Retinal Astrocytes

Abstract

To determine whether Toll-like receptor (TLR) ligands regulate the activation of retinal astrocytes (RACs) and the possible role of RACs in the polarization of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells. TLR expression on RACs isolated from C57BL/6 mice was examined using real-time PCR and flow cytometry. The ability of RACs before or after treatment with TLR ligands to interact with T cells was assessed by measuring major histocompatibility complex class II and costimulatory molecule expression and cytokine production. The stimulatory effect of RACs, with or without TLR stimulation, on responder IRBP-specific T cells was examined by T-cell proliferation, cytokine production, and disease-inducing ability. Cultured mouse RACs expressed TLR2, TLR3, and TLR4. Different TLR ligands had distinct stimulatory effects on RACs. PolyI:C (a TLR3 ligand) had the greatest effect in stimulating RACs to acquire antigen-presentation function, whereas BLP (a TLR2 ligand) had the lowest effect. TLR3 ligation increased the expression of MHC and costimulatory molecules and induced the production of IL-6, IL-12, and IL-23 by RACs. IRBP-specific T cells activated by polyI:C-treated RACs expanded vigorously, produced significant amounts of IFN-gamma and IL-17, and induced experimental autoimmune uveitis when injected into naive mice. The stimulatory effect of RACs on autoreactive T cells is regulated by TLR ligands. TLR3 had a marked effect on the ability of RACs to promote the activation of Th1 and Th17 IRBP-specific T cells. Thus, exposure to microbial antigen(s) may alter susceptibility to autoimmune uveitis by promoting the activation of autoreactive T cells.