Regulatory T cells in skin are uniquely poised to suppress profibrotic immune responses

At the center of fibrosing diseases is the aberrant activation of tissue fibroblasts. The cellular and molecular mechanisms of how the immune system augments fibroblast activation have been described; however, little is known about how the immune system controls fibroblast function in tissues. Here, we identify regulatory T cells (T-regs) as important regulators of fibroblast activation in skin. Bulk cell and single-cell analysis of T-regs in murine skin and lungs revealed that T-regs in skin are transcriptionally distinct and skewed toward T helper 2 (T(H)2) differentiation. When compared with T-regs in lung, skin T-regs preferentially expressed high levels of GATA3, the master T(H)2 transcription factor. Genes regulated by GATA3 were highly enriched in skin T(H)2 T-reg subsets. In functional experiments, T-reg depletion resulted in a preferential increase in T(H)2 cytokine production in skin. Both acute depletion and chronic reduction of T-regs resulted in spontaneous skin fibroblast activation, profibrotic gene expression, and dermal fibrosis, all of which were exacerbated in a bleomycin-induced murine model of skin sclerosis. Lineage-specific deletion of Gata3 in T-regs resulted in an exacerbation of T(H)2 cytokine secretion that was preferential to skin, resulting in enhanced fibroblast activation and dermal fibrosis. Together, we demonstrate that T-regs play a critical role in regulating fibroblast activation in skin and do so by expressing a unique tissue-restricted transcriptional program that is mediated, at least in part, by GATA3.