Preferential Recognition of Hydroxyl Radical-Modified Superoxide Dismutase by Circulating Autoantibodies in Patients with Alopecia Areata

BACKGROUND: Alopecia areata (AA) is a common form of localized, non-scarring hair loss. The cause of AA is unknown but reports suggest an autoimmune etiology, where oxygen free radicals play an important role. OBJECTIVE: The aim of this study was to investigate the role of a hydroxyl radicals (·OH)-modified antioxidant enzyme, superoxide dismutase (SOD), in AA autoimmunity. METHODS: SOD was modified by ·OH radicals. Binding characteristics of autoantibodies in AA patients (n=26) against ·OH-modified SOD (·OH-SOD) were evaluated by immunoassays and the results were compared with those of healthy, age-matched controls (n=30). The effects of ·OH radicals on immunoglobulin G (IgG) isolated from AA patients were studied. RESULTS: Highly specific binding to ·OH-SOD was observed in 32% of the samples of patient sera, whereas normal human sera showed negligible binding with either antigen. Competitive inhibition immunoassays reiterated the results from direct binding. Protein-A-purified IgG from AA patients (AA-IgG) also showed strong binding to ·OH-SOD as compared to IgG from normal human controls (p<0.001). In addition, AA-IgG from patients with alopecia universalis recognized ·OH-SOD to a greater extent than did AA-IgG from patients with the patchy, persistent type of alopecia. Furthermore, sera from AA patients had lower levels of SOD activity as compared to control sera. CONCLUSION: This is the first report showing an association between ·OH-modified SOD and AA. These novel results demonstrate that ·OH radical-mediated changes in SOD present unique neo-epitopes that might contribute to antigen-driven antibody induction in AA.