Abstract
Purpose:
Previously, we demonstrated that peripheral regulatory T cells (pTregs) can be generated within the retina and are protective against spontaneous and induced experimental autoimmune uveoretinitis (EAU). In this study we investigated the role of T cell anergy induced by endogenous retinal self-antigens as a mechanism retinal immune privilege.
Methods:
Transgenic (Tg) mice expressing beta-galactosidase (bgal mice) as a retinal neo-self antigen were used in conjunction with Tg mice expressing diphtheria toxin receptor (DTR) and green fluorescent protein (GFP) under control of the FoxP3 promoter (FDG mice) and bgal-specific T cell receptor Tg mice (BG2 mice). Tg mice expressing DTR and GFP under control of the CD11c promoter (CDG mice) were used assess the role of dendritic cells (DC) in the T cell response. Backcrossing was done to generate mice expressing two or more of these transgenes. Antigen specific retinal T cells responses were induced by posterior segment injection of bgal. At day three post-injection, retinal T cells were analyzed and sorted by FACS into three populations; Tregs (GFP+CD25+), candidate anergic T cells (GFP-CD25-), and activated effector T cells (GFP-CD25+). Analysis for expression of specific genes associated with each population was done by FACS and RT-PCR.
Results:
In response to bgal injection, retinal Treg numbers were reduced in bgal-FDG-BG2 mice compared to FDG-BG2 mice. Retinal effector T cells numbers were also reduced in bgal-FDG-BG2 mice even when existing Tregs were deleted by diphtheria toxin. The candidate anergic T cell population was increased in mice expressing retinal bgal. Analysis of gene expression in Tregs from bgal+ and bgal- retinas showed similar elevated levels of TGF-b, IL-10, and Helios compared to effector T cells. Analysis of candidate anergic T cells revealed a lack of markers associated with activated T cells (Ki-67, IL-2) and a lack of markers associated with Tregs (FoxP3, IL-10). In all cases the response to bgal was dependent on the presence of dendritic cells within the retina.
Conclusions:
Local expression of a retinal self-antigen alters the response to that antigen in the retina. The most significant difference is the appearance of cells that bear characteristics of anergic T cells. No evidence for local induction of anergic T cells by antigen presenting cells other than DC was found.