Fibroblast-derived alarmin promotes oral wound healing by activating regulatory T cells that relay pro-angiogenic and anti-inflammatory responses.

Fibroblasts are abundant structural cells with an emerging immune-sentinel role in the wound healing process, though its functional significance remains incompletely explored. By utilizing an oral injury model that heals rapidly, we identify murine PI16(+) reticular fibroblasts to be enriched in interleukin-33 (IL-33), an alarmin cytokine, and demonstrate that Il33 deletion in fibroblasts impairs oral wound healing. Single-cell RNA sequencing analysis points to regulatory T (Treg) cells, which respond to IL-33 by upregulating the expression of macrophage migration-inhibitory factor (MIF) and transforming growth factor β1 (TGF-β1). Mechanistically, MIF promotes monocyte recruitment, which facilitates angiogenesis, whereas TGF-β1 is linked to early macrophage transition to a pro-resolving phenotype. Importantly, human oral mucosa harbors IL-33(+)PI16(+) fibroblasts in the reticular layer of connective tissue, and Treg cells express MIF and TGFB1 in regenerating human oral mucosa. These results unveil a crucial role of IL-33-expressing oral fibroblasts for modulating inflammation in healing wounds via Treg cell activation.