Correlation of autoantigen-specific Treg frequency with development of spontaneous organ-specific autoimmunity in a mouse model of uveitis

Abstract About 50% of AireGW/+Lyn−/− mice developed autoimmune uveitis, and this was accompanied by the expansion of interphotoreceptor retinoid-binding protein (IRBP) specific CD4+T cells. Moreover, the response to IRBP was necessary for disease initiation, as deletion of IRBP prevented uveitis. Mass cytometry (CyTOF) analysis of CD4+T cells in the retina of the mice with uveitis identified activated T cell subsets characterized as Ly6Chi effectors, PD-1hi effectors, and Treg. To study cellular mechanisms that promoted development of uveitis, we did single-cell RNA sequencing (scRNA-seq) of eye-draining lymph node (LN) CD4+T cells that recognize the P2 epitope of IRBP (amino acid 271–290). Uniform manifold approximation and projection (UMAP) analysis showed that these CD4+T cells included distinct subsets that were Ly6c1hi , Pdcd1hi and Treg, with the Treg population being overrepresented in the mice without disease. Pseudotime analysis indicated that the Ly6c1hi T cell subset represented an earlier stage in activation, whereas the Pdcd1hi subset represented a later stage. Similar analysis of P2–specific CD4+T cells from the retina of mice with uveitis identified 6 subsets of P2-specific T cells, and was largely consistent with the CyTOF analysis of total CD4+ T cells from the retina. Pseudotime analysis indicated that toward the earlier time were cells characterized by being proliferative (Mki67hi), followed by a Lag3hi subset and at other end of the pseudotime axis by a Lag3hi / Pdcd1hi subset. Our results are consistent with the hypothesis that the fraction of Treg within the IRBP-specific CD4+ T cells in the draining LN determines whether these genetically susceptible mice develop eye-specific autoimmunity or are protected.