Alopecia Areata: A Tissue-Specific Autoimmune Disease of the Hair Follicle

The 2006 review described alopecia areata (AA) as an autoimmune disease that specifically targets hair follicles, resulting in hair loss. It is associated with HLA-DQ3 and involves a T-lymphocyte response with a TH1 cytokine profile. The condition has a lifetime risk of 1.7% and can manifest before the age of 20 in 60% of cases. Genetic predisposition is indicated by a family history in 10% to 42% of patients and the association with certain HLA alleles. The loss of immune privilege in hair follicles, which normally prevents immune system attacks, is central to the disease's pathogenesis. This is evidenced by lymphocytic infiltration around affected follicles and the effectiveness of immunosuppressive treatments. The review also noted that pigmented hairs are more susceptible, and that emotional stress and neuropeptides may influence the disease. Animal models, particularly C3H/HeJ mice, are useful for studying AA, as they can develop the disease under the right genetic conditions. The review emphasized the importance of understanding the mechanisms leading to the loss of immune privilege to develop treatments for AA.