Foxp3-expressing regulatory T cells (Tregs) reside in tissues where they control inflammation and mediate tissue-specific functions. The skin of mice and humans contain a large number of Tregs; however, the mechanisms of how these cells function in skin remain largely unknown. Here, we show that Tregs facilitate cutaneous wound healing. Highly activated Tregs accumulated in skin early after wounding and specific ablation of these cells resulted in delayed wound re-epithelialization and kinetics of wound closure. Tregs in wounded skin attenuated IFNγ production and pro-inflammatory macrophage accumulation. Upon wounding, Tregs induce expression of the epidermal growth factor receptor (EGFR). Lineage-specific deletion of EGFR in Tregs resulted in reduced Treg accumulation and activation in wounded skin, delayed wound closure and increased pro-inflammatory macrophage accumulation. Taken together, our results reveal a novel role for Tregs in facilitating skin wound repair and suggest that Tregs utilize the EGFR pathway to mediate these effects.

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 (Tregs) as important regulators of fibroblast activation in skin. Bulk cell and single-cell analysis of Tregs in murine skin and lungs revealed that Tregs in skin are transcriptionally distinct and skewed toward T helper 2 (TH2) differentiation. When compared with Tregs in lung, skin Tregs preferentially expressed high levels of GATA3, the master TH2 transcription factor. Genes regulated by GATA3 were highly enriched in skin “TH2 Treg” subsets. In functional experiments, Treg depletion resulted in a preferential increase in TH2 cytokine production in skin. Both acute depletion and chronic reduction of Tregs 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 Tregs resulted in an exacerbation of TH2 cytokine secretion that was preferential to skin, resulting in enhanced fibroblast activation and dermal fibrosis. Together, we demonstrate that Tregs 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.

ObjectiveSporadic inclusion body myositis (sIBM), the most frequent myositis in elderly patients, is characterized by the presence muscle inflammation and degeneration. We aimed at characterizing immune responses and regulatory T cells, considered key players in the maintenance of peripheral immune tolerance, in sIBM.MethodsSerum and muscle tissue levels of 25 cytokines and phenotype of circulating immune cells were measured in 22 sIBM patients and compared with 22 healthy subjects. Cytokine data were analysed by unsupervised hierarchical clustering and principal components analysis.ResultsCompared to healthy controls, sIBM patients had increased levels of Th-1 cytokines and chemokines such as IL-12 (261±138 pg/mL vs. 88±19 pg/mL; p<0.0001), CXCL-9 (186±12 pg/mL vs. 13±7 pg/mL; p<0.0001), and CXCL-10 (187±62 pg/mL vs. 13±6 pg/mL; p<0.0001). This was associated with an increased frequency of CD8+CD28− T cells (45.6±18.5% vs. 13.5±9.9%; p<0.0001), which were more prone to produce IFN-γ (45.6±18.5% vs. 13.5±9.9%; p<0.0001). sIBM patients also had a decreased frequency of circulating regulatory T cells (CD4+CD25+CD127lowFOXP3+, 6.9±1.7%; vs. 5.2±1.1%, p = 0.01), which displayed normal suppressor function and were also present in affected muscle.ConclusionsIBM patients present systemic immune activation with Th1 polarization involving the IFN-γ pathway and CD8+CD28− T cells associated with peripheral regulatory T cell deficiency.

IntroductionWe developed an experimental autoimmune myositis (EAM) mouse model of polymyositis where we outlined the role of regulatory T (Treg) cells. Rapamycin, this immunosuppressant drug used to prevent rejection in organ transplantation, is known to spare Treg. Our aim was to test the efficacy of rapamycin in vivo in this EAM model and to investigate the effects of the drug on different immune cell sub-populations.MethodsEAM is induced by 3 injections of myosin emulsified in CFA. Mice received rapamycin during 25 days starting one day before myosin immunization (preventive treatment), or during 10 days following the last myosin immunization (curative treatment).ResultsUnder preventive or curative treatment, an increase of muscle strength was observed with a parallel decrease of muscle inflammation, both being well correlated (R2 = −0.645, p<0.0001). Rapamycin induced a general decrease in muscle of CD4 and CD8 T cells in lymphoid tissues, but spared B cells. Among T cells, the frequency of Treg was increased in rapamycin treated mice in draining lymph nodes (16.9±2.2% vs. 9.3±1.4%, p<0.001), which were mostly activated regulatory T cells (CD62LlowCD44high: 58.1±5.78% vs. 33.1±7%, treated vs. untreated, p<0.001). In rapamycin treated mice, inhibition of proliferation (Ki-67+) is more important in effector T cells compared to Tregs cells (p<0.05). Furthermore, during preventive treatment, rapamycin increased the levels of KLF2 transcript in CD44low CD62Lhigh naive T cell and in CD62Llow CD44high activated T cell.ConclusionsRapamycin showed efficacy both as curative and preventive treatment in our murine model of experimental myositis, in which it induced an increase of muscle strength with a parallel decrease in muscle inflammation. Rapamycin administration was also associated with a decrease in the frequency of effector T cells, an increase in Tregs, and, when administered as preventive treatment, an upregulation of KFL2 in naive and activated T cells.