Objective: To identify the structures in hair follicles (HFs) targeted by alopecia areata (AA) antibodies and the role of antigen expression in the development or localization of AA lesions.
Design: The identity of HF structures targeted by AA antibodies was determined by indirect immunofluorescence and the level of antigen expression from the intensity of the staining.
Setting: A university medical center.
Patients: Ten patients with active AA and 8 control individuals.
Results: Antibodies to anagen HFs were present in up to 90% of patients with AA but in less than 37% of controls. The antibodies in patients with AA reacted to antigens present only in HFs. The structures most commonly targeted were the outer root sheath and, less often, the inner root sheath, matrix, and hair shaft. The same HF structure contained several immunologically distinct antigens reactive with AA antibodies. The expression of some AA antigens was much greater in the scalp of patients with AA than in normal individuals.
Conclusions: These findings indicate that the autoantibody responses to HFs in patients with AA are heterogeneous and target multiple structures in anagen HFs. The expression of some as-yet-unidentified HF antigens is increased in many patients with AA, suggesting that the initiation, localization, severity, and persistence of the disease may be related to the level of expression of some HF antigens.