Keratinocytes enriched for epidermal stem cells differ in their response to IFN-gamma from other proliferative...

The epidermis has a pool of adult stem cells [epidermal stem cells (ESC)]. Although the localization of ESC is well described, we lack a clear understanding of their role in perturbed conditions such as inflammation. One of the most important mediators in inflammatory skin diseases acting on keratinocytes (KCs) is interferon gamma (IFN-gamma). The assumption that ESC might generate a protected niche prompted us to investigate their response to the pro-inflammatory cytokine IFN-gamma. In this study, we isolated two populations of KCs according to their adherence ability. ESC enriched by adherence showed a higher CD29 and CD49f expression compared with other KCs. Surprisingly, surface expression of CD54 was more inducible upon IFN-gamma stimulation in short-term cultures of the ESC subpopulation. In contrary to that, a markedly lower induction of IL-18 and reduced basal production of CCL2 were observable in ESC. No differences in IFN-gamma-induced interleukin (IL)-10, CXCL10, CCL22 or transforming growth factor (TGF)beta1 secretion were detectable between the two keratinocyte subpopulations. These results suggest that ESC respond to IFN-gamma with a 'restricted' pattern of pro-inflammatory cytokines, and do not build up an anti-inflammatory microenvironment by means of TGF-beta or IL-10. Activated ESC possess the capability to interact with infiltrating lymphocytes via CD54. In conclusion, the ESC compartment might actively contribute to the immunological properties of the skin organ.