Maintenance of Hair Follicle Immune Privilege Is Linked to Prevention of NK Cell Attack

The study explored how hair follicles (HFs) maintain immune privilege (IP) to avoid natural killer (NK) cell attacks, which typically target cells with low MHC class I expression. It was found that HFs actively suppress NK cells, with the HF epithelium expressing the NK cell inhibitor macrophage migration inhibitory factor. In healthy individuals, fewer NK function-activating receptors and more inhibitory receptors were present compared to those with alopecia areata (AA), an autoimmune disease linked to a breakdown of HF-IP. AA patients showed increased NK cell activity around hair follicles, suggesting a defect in NK cell inhibition that contributes to the disease's pathogenesis. This defect was previously unreported and highlighted the need for considering NK cell activity in AA management.