Fingolimod ameliorates imiquimod-induced psoriasiform dermatitis by sequestrating interleukin-17-producing ?d T cells in secondary lymph nodes

Background: Psoriasis is a chronic inflammatory skin disease. Interleukin (IL)-17A plays a key role in the pathogenesis of psoriasis. Fingolimod, which is available for the treatment of multiple sclerosis, exerts anti-inflammatory effects by sequestrating inflammatory lymphocytes in secondary lymphoid tissues and the thymus. The effect of fingolimod on psoriasis has not been reported yet. Objective: Our objectives were to investigate the effect of fingolimod on psoriasis utilizing mice with imiquimod (IMQ)-induced psoriasiform dermatitis, and explore the possibility of fingolimod as a therapeutic agent for psoriasis. Methods: Psoriasiform dermatitis was induced by imiquimod application on murine shaved back skin for six days. Fingolimod prepared in phosphate-buffered saline (PBS), or PBS alone as a control, was administered intraperitoneally daily from days 0 to 5. Results: Fingolimod ameliorated IMQ-induced psoriasis dermatitis clinically and histologically. On day 6, the mRNA expression level of IL-17A was lower in the skin of fingolimod-treated mice than in that of PBS-treated mice, whereas it was higher in the inguinal lymph nodes of fingolimod-treated mice than in those of PBS-treated mice. Flow cytometric analyses revealed that fingolimod reduced IL-17A-producing ?d T cells infiltrating into the skin, whereas it increased these cells in the inguinal lymph nodes. Fingolimod inhibited egress of Langerhans cells from the skin to lymph nodes. Conclusion: Our results demonstrated that fingolimod showed effectiveness for IMQ-induced psoriasiform dermatitis by hindering the emigration of IL-17A-producing ?d T cells from the lymph nodes to the skin, and suggest that fingolimod is a promising candidate for the treatment of psoriasis.