A role for T cell‐derived interleukin 22 in psoriatic skin inflammation

Interleukin (IL)‐22 is a T cell‐derived cytokine that has been reported recently to induce cutaneous inflammation in an experimental murine model of psoriasis, and to induce in vitro an inflammatory‐like phenotype. In the present study, we assessed the presence of IL‐22 and the IL‐22 receptor 1 (IL‐22R1) in skin lesions, skin‐derived T cells, as well as IL‐22 levels in sera from patients with psoriasis. IL‐22R1 and IL‐10R2 transcripts are expressed at a similar level in psoriatic and healthy skin. In contrast, IL‐22 mRNA expression was up‐regulated in psoriatic skin lesions compared to normal skin, whereas IL‐22 mRNA levels in peripheral blood mononuclear cells from psoriatic patients and normal subjects were similar. Circulating IL‐22 levels were significantly higher in psoriatic patients than in normal subjects. T cells isolated from psoriatic skin produced higher levels of IL‐22 in comparison to peripheral T cells isolated from the same patients. IL‐10 was expressed at similar levels in skin biopsies and peripheral blood mononuclear cells of psoriatic patients and normal subjects. Finally, we show here that supernatants of lesional psoriatic skin‐infiltrating T cells induce an inflammatory response by normal human epidermal keratinocytes, resembling that observed in psoriatic lesions. Taken together, the results reported in this study indicate that IL‐22 is a cytokine produced by skin‐infiltrating lymphocytes that is potentially involved in initiation and/or maintenance of the pathogenesis of psoriasis.

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