Experimentally induced psoriatic lesions associate with rapid but transient decrease in interleukin-33 immunostaining in epidermis.

A slight epidermal damage can induce the Köbner reaction in psoriasis, and the “alarmin”, interleukin-33 (IL-33), may be involved in this process. Therefore, the uninvolved psoriatic skin was tape-stripped, and skin biopsies were collected at 0 day, 2 h and 3 days or at 0 day, 1 day and 7 days for immunohistochemistry. Eight patients out of 18 with the positive Köbner reaction showed a decrease in epidermal thickness and revealed transient reduction in epidermal nuclear immunostaining of IL-33 in 2-h, 1-day, 3-day biopsies compared to the 10 Köbner-negative patients. In keratinocyte cultures, the full-length 32-kDa IL-33 was detected after damaging the cells with freeze-thawing. Interestingly, a very low concentration of rh-IL-33 (0.001–0.01 ng/ml) significantly stimulated (3)H-thymidine uptake by human LAD2 mast cells, but not by psoriatic peripheral blood mononuclear cells. The results show that epidermal IL-33 associates with positive Köbner response, and only a small amount of the IL-33 apparently released may induce proliferation in dermal mast cells.