Mapping the generation and fate of Tregs associated with recovery of EAU

Abstract

Purpose : Experimental autoimmune uveitis (EAU) is used to gain a better understanding of human autoimmune uveitis. We and others have shown that the resolution of EAU is in part due to emergence of ocular antigen specific regulatory T cells (Post-EAU Tregs). These cells are identified in the spleen of mice that have recovered from EAU. However, the stability of these cells and in what tissues these cells migrate to suppress disease is not well understood. Therefore, we assessed the stability of the post-EAU Tregs and asked where these cells migrate to suppress disease.

Methods : We utilized FoxP3^GFP-Cre; Rosa26^{stopfl/fl-Tom} mice that allow for identification of Tregs that express FoxP3 (FoxP3, GFP⁺Tom⁺) or no longer express Foxp3 (exFoxP3, GFP^-Tom⁺). Using the fluorescent markers we determined when and where these Tregs emerge during the course of EAU. EAU was induced by immunizing mice with interphotoreceptor retinoid binding protein residues 1-20 (IRBP) emulsified with Complete Freund’s Adjuvant. The relative abundance of Tregs was assayed in the eyes and lymphoid tissues. Functional suppression of FoxP3 and exFoxP3 cells was determined by the adoptive transfer of these Tregs into recipient EAU mice.

Results : At the onset of EAU Tregs emerged in the eye and increased in frequency as EAU progressed to resolution. Also, the Tregs were found in different lymphoid tissues during the course of the EAU. Both FoxP3 and exFoxP3 cells emerged in the eye and were found in the lymphoid tissues during EAU. In contrast, the EAU-recovered mice, harbored both FoxP3 and exFoxP3 T cells in the lymphoid tissues but not the eye. Interestingly, the post-EAU Tregs capable of suppressing uveitis in the recipient mice had stable FoxP3 expression, but exFoxP3 cells did not suppress EAU, and the post-EAU Tregs trafficked to both the eye and lymphoid tissues at the onset of EAU.

Conclusions : Findings from this study elucidate a dynamic relationship of Treg migration from the eye to secondary lymphoid tissues that coincides with the resolution of EAU. Also, this study highlights that stability of FoxP3 transcription factor is a requirement for the suppressive function of post-EAU Tregs. Interestingly, these Tregs traffic to the eye to prevent a uveitic relapse but migrate out after resolution. This work suggests that unstable FoxP3 expression or aberrant tissue trafficking may provide an explanation for chronic and relapsing autoimmune uveitis.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.