Interleukin-17 and interleukin-22 induced proinflammatory cytokine production in keratinocytes via inhibitor of nuclear factor-b kinase-a expression

The pathogenesis of psoriasis may involve the interleukin (IL)-23 and Th17-mediated immune responses. Th17 cells secret IL-17 and IL-22, which mediates dermal inflammation and acanthosis. Objective: As inhibitor of nuclear factor ?B kinase-a (IKKa) has been previously identified as a primary regulator of keratinocyte differentiation and proliferation, we proposed that IL-17 and IL-22 might affect keratinocyte differentiation by changing the expression of IKKa. Methods: We employed HaCaT cells maintained culture medium at a low calcium concentration (0.06 mM) and induced differentiation by switching to the high concentration (2.8 mM) media with IL-17 or IL-22, then compared the IKKa expression and the cell cycle. We employed reconstituted human epidermal skin (Neoderm) and mice ears for the in vivo studies. Results: Elevated calcium concentration induced IKKa expression and terminal differentiation with cell cycle arrest in HaCaT cell cultures. Moreover, IL-17 and IL-22 treatment also induced IKKa in HaCaT cells and reconstituted human epidermis. IKKa induction was also noted, following the injection of IL-17 and IL-22 into mice ears. Conclusion: Although the induction of IKKa was accompanied by keratinocyte differentiation, IL-17 and IL-22 did not affect calcium-mediated differentiation or the cell cycle. Rather, IL-17 and IL-22 appear to contribute to the inflammation occurring via the induction of IKKa from keratinocytes or skin layers.