IDO-expressing Fibroblasts Suppress the Development of Imiquimod-induced Psoriasis-like Dermatitis

Psoriasis is a chronic skin condition whose pathogenesis is reported to be due to the activation of the interleukin-23/interleukin-17 (IL-23/IL-17) pathway. Here, we report that indoleamine 2,3-dioxygenase (IDO)-expressing fibroblasts reduce the activity of this pathway in activated immune cells. The findings showed that intralesional injection of IDO-expressing fibroblasts in imiquimod-induced psoriasis-like dermatitis on the back and ear (Pso. ear group) in mice significantly improves the clinical lesional appearance by reducing the number of skin-infiltrated IL-17+ CD4+ T cells (1.9% +/- 0.3% vs. 6.9% +/- 0.6%, n = 3, P value < 0.01), IL-17+ gamma delta+ T cells (2.8% +/- 0.3% vs. 11.6% +/- 1.2%, n = 3, P value < 0.01), IL-23+ activated dendritic cells (7.6% +/- 0.9% vs. 14.0% +/- 0.5%, n = 3, P < 0.01), macrophages (4.3% +/- 0.1% vs.11.3% +/- 1.0%, n = 3, P value < 0.01), and granulocytes (2.5% +/- 0.4% vs. 4.5% +/- 0.3%, n = 3, P value < 0.01) as compared to untreated psoriatic mice. This finding suggests that IDO-expressing fibroblasts,and to a lesser extent, non-IDO primary fibroblasts suppress the psoriatic-like symptoms by inhibiting the infiltration of key immune cells involved in the development of psoriasis.