IL-17E (IL-25) and IL-17A Differentially Affect the Functions of Human Keratinocytes

Our group has recently shown that keratinocyte-derived IL-17E (IL-25), one of six members of the IL-17 family, is overexpressed in lesional psoriatic skin and is involved in its pathophysiology. We show here that IL-22 enhances IL-17E production in human keratinocytes and that these cells display a complete IL-17E receptor at their surface, the expression of which is further induced by IL-17A, indicating a potential autocrine effect of IL-17E. Therefore, we addressed the impact of IL-17E on the function of human primary keratinocytes. IL-17E promoted the proliferation of keratinocytes in two-dimensional and three-dimensional cultures and caused the concomitant upregulation of differentiation-associated gene transcripts (e.g., keratin 10), whereas their expression was either inhibited or not changed by IL-17A. Contrary to IL-17A, IL-17E was not involved in the induction of antimicrobial proteins. Time-lapse analysis of cell movement showed that IL-17E influences cell motility, increasing both cell speed and displacement. This was associated with specific changes in the actin cytoskeleton organization and the cell-substrate adhesion. No such effects were observed upon IL-17A stimulation. In summary, we identified effects of IL-17E clearly distinct from IL-17A, pointing toward an important role of IL-17E in the physiology and pathophysiology of the epidermis.