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) as important regulators of fibroblast activation in skin. Bulk cell and single-cell analysis of T in murine skin and lungs revealed that T in skin are transcriptionally distinct and skewed toward T helper 2 (T2) differentiation. When compared with T in lung, skin T preferentially expressed high levels of GATA3, the master T2 transcription factor. Genes regulated by GATA3 were highly enriched in skin "T2 T" subsets. In functional experiments, T depletion resulted in a preferential increase in T2 cytokine production in skin. Both acute depletion and chronic reduction of T 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 in T resulted in an exacerbation of T2 cytokine secretion that was preferential to skin, resulting in enhanced fibroblast activation and dermal fibrosis. Together, we demonstrate that T 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.