Clq binding substances in pemphigus and bullous pemphigoid

A modification of the [125I]Clq binding assay was developed to allow the estimation of Clq binding activity (Clq BA) in pemphigus and bullous pemphigoid sera. The modifications include lower final concentration of PEG 6000 (1.5%) which permitted the use of sera that had been stored at -200C for extended periods of time; use of 131I instead of 125I and an [131I]Clq concentration of 5 μg/ml rather than 1 μg/ml. EDTA was used at a final concentration of 0.13 M to obviate the need for heat inactivation of sera. Sera from seventy-one patients with pemphigus and from 142 patients with bullous pemphigoid were tested for Clq BA. Of these 40% of the pemphigus and 20% of the bullous pemphigoid patients showed elevated Clq BA. A relationship between elevated Clq BA in serum and active disease was noted. Sequential samples from forty patients with pemphigus and thirty-seven patients with bullous pemphigoid demonstrated two different types of relationship between serum antibody titres to cutaneous antigens and Clq BA. In some patients serum antibody titres and Clq BA increased and decreased simultaneously; in others, increase of Clq BA followed increase of antibody titre and coincided with its decrease. The latter relationship supports the hypothesis that Clq BA may represent at least in part antigen-antibody complexes containing cutaneous antigens. (author)