Disruption of Hair Follicle Immune Privilege in Alopecia Areata: Enigmatic Mechanisms and Emerging Concepts

Alopecia areata (AA) is characterized by the collapse of hair follicle immune privilege (HFIP), leading to an autoimmune attack on hair follicles. This breakdown involves increased antigen presentation, elevated expression of MHC molecules, and infiltration of autoreactive CD8+ T cells, particularly those with the NKG2D receptor. These cells, along with interferon-gamma (IFN-γ) and interleukin-15 (IL-15), activate the JAK-STAT pathway, promoting inflammation and follicular destruction. Other immune cells like natural killer cells, dendritic cells, and macrophages also contribute to the disease by enhancing antigen presentation. Restoring HFIP is a promising therapeutic strategy, and future research should focus on identifying molecular regulators to develop targeted treatments for AA.