Immunoblotting studies of linear IgA disease.

Patients with linear IgA deposits at the basement membrane zone (BMZ) detected by direct immunofluorescence (IF) may show diverse clinical and laboratory findings. The aim of this study was to investigate the issue of target antigens for linear IgA disease (LAD) antibodies. We examined sera from 46 adults and children with exclusive IgA deposits at the BMZ, by both indirect IF on 1 M NaCl split human skin and immunoblotting. IgA anti-BMZ antibodies binding to the epidermal side of the split were found in 31 LAD sera. IgA anti-BMZ antibodies binding to the dermal side of the split were detected only in 4 LAD sera. No sera contained IgA anti-BMZ antibodies binding to both sides of the split. Immunoblotting revealed that 12 epidermal side-positive LAD sera reacted with the 97 kDa protein in the human epidermal extracts. Moreover, we found that 2 dermal side-positive LAD sera reacted with a protein of approximately 255 kDa on immunoblotting of the dermal extract. We conclude that there are at least two types of LAD. However, the nature of target antigens for LAD antibodies remains to be determined.