MAJOR ANTIGENIC EPITOPES OF BULLOUS PEMPHIGOID 230-KDA ANTIGEN MAP WITHIN THE C-TERMINAL END OF THE PROTEIN - EVIDENCE USING A 55-KDA RECOMBINANT PROTEIN

In order to obtain greater insight into the nature of B-cell epitopes in bullous pemphigoid (BP), we generated a BP recombinant protein of 5 5 kDa M(r) (rBP 55) from a cDNA sequence encoding for the carboxytermi nal region of the 230 kDa BP antigen, Serum IgG from guinea-pigs immun ized with rBP 55 stained the basement membrane zone of normal human sk in and immunoprecipitated the rBP 55 protein, and also the 230 kDa BP antigen recovered from extracts of cultured keratinocytes, thus confir ming that the rBP 55 amino acid sequence is present in native BP antig en. The reactivity of sera from 60 patients with BP was analysed using an immunoblot assay on epidermal protein extracts and on the rBP 55 p rotein, Forty of the 60 BP sera (66%) contained autoantibodies to the 230 kDa polypeptide in an epidermal extract, and 37 of these 40 sera ( 92%) recognized the rBP 55 protein. In contrast, no reactivity against rBP 55 was detected with 20 BP sera devoid of autoantibodies against the 230 kDa antigen, Likewise, sera from patients with autoimmune blis tering skin disorders other than BP (epidermolysis bullosa acquisita o r pemphigus vulgaris), and control sera, were unreactive to rBP 55. Th ese results clearly demonstrate the immunogenicity and antigenicity of the C-terminal end of the 230 kDa BP antigen. They confirm that this 555 amino acid segment, corresponding to rBP 55, contains major epitop es which can bind BP patients' autoantibodies, and suggest that the rB P 55 protein could be useful for further characterization of these B-c ell epitopes,