Interleukin-20 as a Target in Psoriasis Treatment

: 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.