Background: Interleukin (IL)- 20 and IL- 19 are recently discovered members of the IL- 10 family of cytokines. The skin of transgenic mice overexpressing IL- 20 shows histological changes resembling some of those seen in psoriasis, i.e. thickened epidermis, hyperkeratosis and a compact stratumcorneum. IL- 19 and IL- 20, as well as their receptor complexes, IL- 20Rα /IL- 20Rβ and IL- 22Rα /IL- 20Rβ , are expressed in human skin. Objectives: To study the dynamics of IL- 19 and IL- 20 gene expression as well as the expression of their receptor subunits in psoriatic skin lesions. Methods: Punch biopsies from patients with plaque- type psoriasis were collected before, during and after 28 days of treatment with either calcipotriol or ciclosporin (CsA). IL- 20, IL- 19, IL- 20Rα , IL- 20Rβ and IL- 22Rα mRNA expression were determined by quantitative reverse transcriptase- polymerase chain reaction. Results: We found IL- 19 and IL- 20 mRNA expression in lesional psoriatic skin to be strongly upregulated comparedwith nonlesional psoriatic skin by a factor of 65 and 22, respectively. In contrast to previous reports, IL- 20Rα and IL- 20Rβ mRNA levels showed a modest but statistically significant decrease in lesional psoriatic skin compared with nonlesional psoriatic skin. During treatment with calcipotriol or CsA, IL- 19 and IL- 20 mRNA levels decrease in accordance with the clinical improvement of psoriasis. Neither IL- 19, IL- 20, nor receptor subunit mRNA expression in lesional psoriatic skin reaches the levels of nonlesional skin during this short- term treatment. These findings are in line with the residual disease activity observed at the end of treatment. Conclusions: The increased IL- 19 and IL- 20 mRNA expression levels in lesional psoriatic skin suggest that these two cytokines play a role in the pathogenesis of psoriasis. An imbalance in the receptor complexes for IL- 19 and IL- 20 might contribute to their suspected pathogenic effects.
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