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a Department of Dermatology, Aarhus University Hospital, Aarhus, Denmark b Discovery, Novo Nordisk, Bagsvaerd, Denmark c Department of Dermatology, Roskilde Hospital, Roskilde, Denmark
Key Words: interleukin-20 • psoriasis • skin • human keratinocytes • PBMCs
Address for correspondence: Karin Stenderup, Ph.D., Department of Dermatology, Aarhus University Hospital, P.P. Oerumsgade 11, Bldg. 15, DK-8000 Aarhus, Denmark. Voice: +45-8949-1907; fax: +45-8949-1850. Karin.Stenderup{at}email.dk
Interleukin-20 (IL-20) is a new member of the IL-10 cytokine family discovered by a structural algorithm. IL-20 transgenic mice displayed skin abnormalities reminiscent of psoriasis, a finding that has prompted the investigation of this new interleukin in relation to this disease. This article reviews the role of IL-20 and its implication in psoriasis. It is shown that IL-20 and its receptors are found in human skin and that IL-20 is involved in proliferation, angiogenesis, and chemotaxis, all characteristics of psoriasis. We demonstrated that IL-20 induced the thickening of human epidermis in vivo; however, this thickening does not seem to be related to a direct effect of IL-20 on hyperproliferation since the growth of normal human epidermal keratinocytes (NHEKs) cultured in vitro was not affected by IL-20. On the other hand, in vitro, IL-20 stimulated human peripheral blood mononuclear cells (PBMCs) to produce proinflammatory cytokines and, in vivo, IL-20 in combination with PBMCs induced psoriasis. This may suggest that IL-20 indirectly exerts its proliferative effects on keratinocytes via immune cells present in the skin. Finally, we found that blocking IL-20 signaling in psoriasis improves psoriasis, suggesting that IL-20 is a potential target in psoriasis treatment.
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