SIRT1 downregulation provokes immune-inflammatory responses in hair follicle outer root sheath cells and may contribute to development of alopecia areata

•SIRT1 level is reduced in alopecia areata scalp compared to normal scalp.•SIRT1 downregulates NKG2D ligand expression in hair follicle ORS cells.•SIRT1 inhibition promotes Th1 cell-mediated immune response in hair follicle ORS cell.•The counteractive effect of SIRT1 is mediated by NF-κB and STAT3 pathway.