CD103 Regulates Dermal Regulatory T Cell Motility and Interactions with CD11c-Expressing Leukocytes to Control Skin Inflammation.

Dermal regulatory T cells (Tregs) are essential for maintenance of skin homeostasis and control of skin inflammatory responses. In mice, Tregs in the skin are characterized by high expression of CD103, the αE integrin. Evidence indicates that CD103 promotes Treg retention within the skin, although the mechanism underlying this effect is unknown. The main ligand of CD103, E-cadherin, is predominantly expressed by cells in the epidermis. However, because Tregs are predominantly located within the dermis, the nature of the interactions between E-cadherin and CD103-expressing Tregs is unclear. In this study, we used multiphoton intravital microscopy to examine the contribution of CD103 to Treg behavior in resting and inflamed skin of mice undergoing oxazolone-induced contact hypersensitivity. Inhibition of CD103 in uninflamed skin did not alter Treg behavior, whereas 48 h after inducing contact hypersensitivity by oxazolone challenge, CD103 inhibition increased Treg migration. This coincided with E-cadherin upregulation on infiltrating myeloid leukocytes in the dermis. Using CD11c-enhanced yellow fluorescent protein (EYFP) × Foxp3-GFP dual-reporter mice, inhibition of CD103 was found to reduce Treg interactions with dermal dendritic cells. CD103 inhibition also resulted in increased recruitment of effector CD4+ T cells and IFN-γ expression in challenged skin and resulted in reduced glucocorticoid-induced TNFR-related protein expression on Tregs. These results demonstrate that CD103 controls intradermal Treg migration, but only at later stages in the inflammatory response, when E-cadherin expression in the dermis is increased, and provide evidence that CD103-mediated interactions between Tregs and dermal dendritic cells support regulation of skin inflammation.