Targeted Deletion of STAT3 in CD4+ T Cells Prevents Development of Experimental Autoimmune Uveoretinitis (EAU) and Recruitment of Pathogenic ThIL17 and Th1 Cells into the Retina

Abstract

Purpose:: Th_IL17 cells have been implicated in etiology of multiple sclerosis, inflammatory bowel disease and rheumatoid arthritis. Recent reports have emphasized essential roles of IL-6 & TGFß1 in polarization of naive CD4⁺ cells into Th_IL17 lineage and a requirement of STAT3 for IL-17 expression. However, IL-6 is also a potent activator of STAT3, suggesting that STAT3 may also regulate development and pathogenic mechanisms of Th_IL17 cells. In this study we have examined whether Th_IL17 cells are involved in pathogenic mechanisms of experimental autoimmune uveoretinitis (EAU) and used a mouse with targeted deletion of STAT3 in CD4⁺ cells to investigate the role of STAT3 in Th_IL17 lineage commitment and in uveitis.

Methods:: Mice with targeted deletion of STAT3 in the CD4⁺ T cell compartment (STAT3 conditional KO) were generated by mating STAT3^fl/fl with CD4⁺-Cre mice. IRBP-induced EAU was characterized by histology, proliferation and DTH assays. Expression of transcription factors, lymphocyte effector molecules and cytokine secretion were assessed by Western blotting, RT-PCR, qRT-PCR or ELISA. Phenotype of lymph node or ocular pathogenic T-cells was analyzed by FACS and intracellular staining.

Results:: In contrast to wild type mice (WT), STAT3 conditional KO mice do not develop EAU. EAU in WT mice is characterized by infiltration of Th_IL17 and Th1 cells into the retina and the pathogenic T cells express high levels of VLA-4 and LFA-1 integrins. In contrast, naive STAT3 conditional KO T cells fail to differentiate into Th_IL17 phenotype, express low levels of VLA-4/LFA-1 integrins and do not enter the eye. Moreover, TGFß and IL-6 or IL-23 are unable to induce naive STAT3-deficient CD4 cells to differentiate into Th_IL17 cells.

Conclusions:: Accumulation of Th_IL17/Th1 cells in the retina of mice with EAU suggests that both T cell subsets may be involved in pathogenic mechanisms of EAU. Our data showing for the first time that TGFß and IL-6 or IL-23 are unable to induce naive STAT3-deficient CD4 cells to differentiate into Th_IL17 cells provides direct and compelling evidence that STAT3 regulates commitment of T cells into the Th_IL17 lineage. Our data showing that IRBP-primed STAT3-deficient T cells do not enter the eye and that STAT3 regulates expression of integrin receptors that guide activated effector T cells to leave blood and enter the CNS/retina, suggest that STAT3 maybe a target for therapeutic modulation of uveitis.

Keywords: autoimmune disease • inflammation • retina