Tacrolimus attenuates Th17 cell-mediated allergic skin inflammation in mice

Tacrolimus, a topical calcineurin inhibitor, is used to treat atopic dermatitis (AD). AD is classically T helper type (Th) 2-driven, but Th17 cells are implicated in chronic AD, yet its efficacy against Th17-dependent pathology remains unclear. We investigated the effects of tacrolimus using a murine model of Th17-mediated allergic skin inflammation. In CD4⁺ T cells from DO11.10/Rag2^-/- mice, which express ovalbumin (OVA)-specific T cell receptor, tacrolimus differentially suppressed stimulation-induced cytokine expression by Th2 cells. At similar concentrations, tacrolimus suppressed Il21, but not Il17a or Il22, expression in Th17 cells. Subcutaneous OVA challenge elicited ear thickening in BALB/c mice after adoptive transfer of Th2 or Th17 cells, with a stronger response in Th17-transferred mice, but less than OVA-immunized controls. Topical tacrolimus reduced Th17-mediated ear swelling, corroborated by histopathology. In Th2-transferred mice, tacrolimus tended to reduce early skin thickening (day 3) but did not affect late responses (day 7). In Th17-transferred mice, tacrolimus significantly reduced allergen-specific T-cell accumulation in OVA-injected skin and tended to reduce Il21 expression, whereas Th2-cell accumulation and cytokine expression were unaffected. Tacrolimus exerts stronger inhibitory effects on Th17- than Th2-driven responses in this model, suggesting that suppression of Th17 pathways may contribute to its therapeutic benefit in AD.