Predominant Expression of Interleukin-17 in Chronic Alopecia Areata Compared to IFN-γ in Pathogenic Th17 Cells, Tissue-Resident Memory T Cells and Natural Killer Cells

This study involving 367 patients with chronic alopecia areata (AA) highlights the predominant role of IL-17 and Th17 cells in the disease's pathogenesis, particularly in the hair follicle bulge and bulb. IL-17 expression and CCR6+ pathogenic Th17 cells were found to increase with disease severity, while IFN-γ was only present in the mildest form of AA, indicating a limited role in chronic cases. The study also observed an increase in CD8+ T cells and CD8+ common-γ receptor+ NK cells with disease severity. Despite the promise of JAK inhibitors targeting IFN-γ pathways, IL-17 inhibitors like secukinumab were ineffective, suggesting the need for further research on IL-17's role and potential therapeutic interventions in chronic AA.