Breakdown of Immune Privilege and Spontaneous Ocular Autoimmunity in IRBP-Specific T Cell Receptor Transgenic Mice

Abstract

Purpose: : To study effector and regulatory functions of autoreactive T cells in uveitis, we generated and analyzed transgenic (Tg) mice expressing a T cell receptor (TCR) specific to the uveitogenic retinal protein IRBP.

Methods: : IRBP TCR Tg mice were generated on the EAU-susceptible B10.RIII background. Rag2-/- mice and IRBP Tg mice were backcrossed onto the B10.RIII background and crossed to IRBP TCR Tg mice. The TCR repertoire was examined by quantitative real-time PCR, and the IRBP TCR Tg T cells were detected by binding of the IRBP161-180/I-Ar/IgG1 dimer. Leukocyte profiles in lymphoid tissues and eyes were examined by flow cytometry. Ocular pathology was evaluated by fundoscopy and histology.

Results: : IRBP TCR Tg mice on the conventional background as well as on the Rag2-/- background spontaneously developed uveitis and pinealitis. The former, but not the latter, mice showed presence of FoxP3+ natural T regulatory cells (Tregs) in the thymus, suggesting requirement for endogenous TCR chains to generate natural Treg. Most of the infiltrating T cells in uveitic eyes exhibited a memory phenotype and included Th1, Th17 and Tregs, as judged by intracellular staining for IFN-gamma, IL-17A and Foxp3. Tregs with IRBP-specific TCR were enriched in the eye compared to the periphery, implying retention and/or local conversion of conventional IRBP-specific T cells into Tregs. Interestingly, the proportion of IRBP TCR Tg T cells with memory phenotype was low in the periphery, suggesting limited extraocular availability of the priming antigens and limited egress of cells from the uveitic eye into the periphery. IRBP TCR Tg mice crossed to mice expressing IRBP extraocularly under the MHC class II promoter (IRBP TCR x IRBP double-Tg mice) had reduced frequency of IRBP-specific T cells in the thymus and in the periphery. Their remaining IRBP-specific cells were hyporesponsive to IRBP and the mice failed to develop spontaneous uveitis, indicating that extraocular expression of IRBP is tolerogenic and protects from disease.

Conclusions: : The IRBP TCR Tg mouse is a new model of spontaneous uveitis that provides a useful tool to understand basic mechanisms involved in ocular autoimmunity and to develop novel therapeutic strategies for uveitis.

Keywords: uveitis-clinical/animal model • immunomodulation/immunoregulation • inflammation