IgA basement membrane zone autoantibodies in bullous pemphigoid detect epidermal antigens of 270–280 kDa, 230 kDa, and 180 kDa molecular weight by immunoblotting

Bullous pemphigoid (BP) is an acquired subepidermal blistering disease characterized by circulating IgG autoantibodies binding to the 230 and 180 kDa hemidesmosomal proteins. Associated basement membrane zone (BMZ) autoantibodies of the IgA class have been reported in few BP patients. The incidence and clinical relevance of these IgA antibodies, as well as their target antigens are unknown. Sera of 26 patients with BP were analysed for circulating IgG- and IgA-anti-BMZ autoantibodies by indirect immunofluorescence on salt-split human skin. All of the patients had circulating IgG autoantibodies and, in addition, nine (35%) also had circulating anti-BMZ IgA antibodies, that bound to the epidermal side of salt-split skin. By immunoblotting, IgA antibodies in seven of nine sera recognized either the 180 kDa, the 230 kDa, or both BP antigens. Moreover, IgA anti-BMZ antibodies in seven sera also detected an epidermal protein of 270-280 kDa. IgA antibodies did not identify specific bands on immunoblots of dermal extracts. There was no clinical difference between BP patients with or without circulating anti-BMZ-IgA.