TH9 cells are considered to be a novel T cell subset, identified by the production of IL-9. These cells are mainly detected within the skin-homing TH population in peripheral blood and play a role in the pathogenesis of inflammatory skin diseases. As a better understanding of their biology may contribute to the development of novel therapeutic approaches, we adapted a skin T cell culture system to investigate the effects of IL-9 skewing cytokines on skin resident T cells. Healthy human skin biopsies were cultured on cell foam matrices (grids) either in the presence of IL-2 and IL-15 (standard condition) or IL-2, IL-4 and TGF-beta (TH9-promoting condition). Both culture conditions favored the proliferation of CD45RO+ T cells. TH9-promoting conditions yielded significantly higher numbers of CD4+ T cells as compared to standard conditions, while the frequency of Ki-67+ cells was similar under both conditions after 4 weeks. A differential expression of the skin-resident T cell markers CD69, CD103, and the skin homing receptors CLA and CCR4 was found on T cells using either culture condition. Paired analysis of T cells freshly isolated from skin and after 4 weeks under TH9-promoting culture conditions indicated drastic and significant downregulation of CD69 under both culture conditions and a trend towards upregulation of CD103 under TH9-promoting conditions. Significantly more T cells produced IL-9 under TH9-promoting conditions as compared to standard conditions upon CD3/CD28 stimulation and PMA/ionomycin restimulation. CD3+CD56+ cells were identified under standard conditions but not under TH9-promoting conditions. We show for the first time that IL-2, IL-4 and TGF-beta promote the expansion of IL-9-producing T cells from healthy human skin thus enabling further studies about their functional role in the skin.

IL-2, IL-4 and TGF-beta promote the differentiation of IL-9-producing T cells from healthy human skin