IL-15 Is an Unexpected Guardian of Hair Follicle Immune Privilege and Promotes Human Hair Growth Ex Vivo

The document reports that interleukin-15 (IL-15) protects the immune privilege of hair follicles and stimulates hair growth in human hair follicles studied outside the body. In scalp hair follicles affected by alopecia areata (AA), there was an increase in IL-15+ cells and a decrease in IL-15 receptor alpha (IL-15Ra) protein expression compared to healthy scalp skin. Treatment with recombinant human IL-15 (rhlL-15) extended the growth phase of healthy hair follicles, reduced hair cell death, and modulated immune markers, including a 50-100 ng/mL increase in the immune privilege guardian a-MSH. Pre-treatment with rhlL-15 also prevented immune privilege collapse induced by IFNg. These findings suggest that enhancing IL-15Ra signaling could be a therapeutic strategy for AA and other inflammatory hair loss conditions.