Regulatory T cells promote innate inflammation after skin barrier breach via TGF-β activation.

Regulatory T cells (Tregs) use multiple mechanisms to attenuate inflammation and prevent autoimmunity. Tregs residing in peripheral (i.e., nonlymphoid) tissues have specialized functions; specifically, skin Tregs promote wound healing, suppress dermal fibrosis, facilitate epidermal regeneration, and augment hair follicle cycling. Here, we demonstrated that skin Tregs were transcriptionally attuned to interact with their tissue environment through increased expression of integrin and TGF-β pathway genes that influence epithelial cell biology. We identified a molecular pathway where skin Tregs license keratinocytes to promote innate inflammation after skin barrier breach. Using a single-cell discovery approach, we identified preferential expression of the integrin αvβ8 on skin Tregs Upon skin injury, Tregs used this integrin to activate latent TGF-β, which acted directly on epithelial cells to promote CXCL5 production and neutrophil recruitment. Induction of this circuit delayed epidermal regeneration but provided protection from Staphylococcus aureus infection across a compromised barrier. Thus, αvβ8-expressing Tregs in the skin, somewhat paradoxical to their canonical immunosuppressive functions, facilitated inflammation acutely after loss of barrier integrity to promote host defense against infection.