Increased seum levels of IL-22 in patients with nickel contact dermatitis

Nickel can elicit both Th1-type and Th2-type responses in vitro in patients with nickel allergic contact dermatitis, but this complex cytokine cascade has still to be clarified. The recently discovered Th17 subset, which has crucial functions in host defence against infections and has been implicated in the development of autoimmune diseases, has been supposed to play an important role in some inflammatory and autoimmune skin disorders, Among TH17 cytokines, IL-22, has been demonstrated to have a crucial function in the development of dermal inflammation and epidermal acanthosis induced by IL-23 in mice. We measured the circulating levels of this cytokine in 31 patients with allergic nickel contact dermatitis and in 15 controls. IL-22 serum levels were significantly higher in patients affected by contact dermatitis compared with controls. It has been demonstrated that the injection of IL-23 (a Th17-inducing cytokine) into mice ears induces a model of psoriasis-like lesions mediated by IL-17 and IL-22. However, the histological features found in these murine models are not exclusively characteristic of psoriasis but of allergic contact dermatitis as well. Our data suggest a possible involvement of IL-22 in the pathogenesis of human allergic contact dermatitis. Therefore, as hypothesized for psoriasis, IL-22 could be of potential interest as a therapeutic target for the treatment of the disease.