Stimulation of hair follicle stem cell proliferation through an IL-1 dependent activation of γδT-cells

The cutaneous wound-healing program is a product of a complex interplay among diverse cell types within the skin. One fundamental process that is mediated by these reciprocal interactions is the mobilization of local stem cell pools to promote tissue regeneration and repair. Using the ablation of epidermal caspase-8 as a model of wound healing in Mus musculus, we analyzed the signaling components responsible for epithelial stem cell proliferation. We found that IL-1 alpha and IL-7 secreted from keratinocytes work in tandem to expand the activated population of resident epidermal gamma delta T-cells. A downstream effect of activated gamma delta T-cells is the preferential proliferation of hair follicle stem cells. By contrast, IL-1 alpha-dependent stimulation of dermal fibroblasts optimally stimulates epidermal stem cell proliferation. These findings provide new mechanistic insights into the regulation and function of epidermal cellimmune cell interactions and into how components that are classically associated with inflammation can differentially influence distinct stem cell niches within a tissue.