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.