Dissection of the microRNA transcriptomes of CD4 ⁺ T cell subsets in autoimmune inflammation identifies novel regulators of disease pathogenesis

MicroRNAs (miRNAs) are key regulators of CD4 ⁺ T cell differentiation, but how they contribute to the course of an autoimmune disease in vivo remains poorly studied. Given the known roles in autoimmunity of pro-inflammatory T helper 1 (Th)1 and Th17 cells, and anti-inflammatory Foxp3 ⁺ regulatory cells, we established a triple reporter mouse for Ifng , Il17 and Foxp3, and subjected it to experimental autoimmune encephalomyelitis (EAE) to characterize the miRNomes of the corresponding CD4 ⁺ T cell subsets. We identified 110 miRNAs differentially expressed between the pro-inflammatory (Th1 and Th17 cells) and the Treg cell subsets. Among these, we found novel functions for miR-122-5p and miR-1247 as regulators of Th17 cell proliferation and Th1 cell differentiation, thus impacting the course or severity of EAE, respectively. Importantly, their expression patterns suggest miR-122-5p and miR-1247 act as peripheral brakes to CD4 ⁺ T cell pathogenicity that are subverted in the inflamed central nervous system.