Interleukin 20 protein locates to distinct mononuclear cells in psoriatic skin.

We previously demonstrated that m RNA for the pro-inflammatory cytokine interleukin 20 ( IL-20) is expressed in suprapapillary keratinocytes of lesional psoriatic skin ( LS). Here, we describe the distribution of IL-20 protein and the identity of the IL-20-positive cells in LS. We found that the main part of IL-20 immunoreactivity is present in mononuclear cells of the dermal papillae, and that the IL-20-positive cells located in the papillae were langerin+, CD1a+, CD4+ and CD303+. These cells might be immature dendritic cell. In situ hybridization for IL-20 m RNA on non- LS, ex vivo stimulated with IL-1 β revealed a colocalization between IL-20 m RNA and the keratinocyte marker CK14. No IL-20 m RNA was detected in the dermal mononuclear cells. Our results suggest that IL-20 is produced by keratinocytes, released into the epidermis and then possibly taken up by papillary mononuclear cells. Our study supports that IL-20 is involved in the pathogenesis of psoriasis. [ABSTRACT FROM AUTHOR]