Imiquimod‐induced ex vivo model of psoriatic human skin via interleukin‐17A signalling of T cells and Langerhans cells

Several in vitro models have been developed to study the mechanisms involved in psoriasis and to screen new antipsoriatic drugs. However, most of them use single-cell or reconstructed human skin models that did not have complex anatomy of human skin. Thus, this study aimed to create a new model of psoriasis-like dermatitis using human skin under in vitro conditions. To perform this, human skin explants were topically treated with imiquimod (IMQ) or vehicle for 2, 3 or 6 consecutive days. Some explants were treated with an anti-psoriatic drug or antibody anti-interleukin-17A (IL-17A). Topical application of IMQ increased total epidermal area, epidermal proliferation and keratinocyte differentiation at 3, 4 or 7 days. The protein levels of CD3 were augmented in the IMQ-treated human skin explants at 7 days reflecting the activation of T cells. Topical IMQ promoted a higher protein and mRNA levels of IL-17A in human skin ex vivo. Immunofluorescence analysis showed CD207-positive Langerhans cells (LCs) and CD3-positive T cells expressing IL-17A in IMQ-treated human skin explants at 7 days. In addition, administration of antibody anti-IL-17A or an anti-psoriatic drug inhibited IMQ-induced increase in the epidermal thickness in ex vivo human skin at 7 days. In conclusion, topical IMQ application promotes epidermal changes in ex vivo human skin that resemble to human psoriatic skin lesions. Moreover, IMQ-induced production of IL-17 by LCs and T cells is critical to development of psoriasis-like inflammation in our model. This new model is suitable for in vitro screening of antipsoriatic drugs.