Studies on complement deposits in epidermolysis bullosa acquisita and bullous pemphigoid

Epidermolysis bullosa acquisita (EBA) is an inflammatory subepidermal blistering disease characterized by circulating and tissue-bound autoantibodies specific for type VII collagen of the basement membrane zone. The antibodies consist of both complement- and noncomplement-binding populations and belong to all four subclasses of IgG. We investigated the presence of the membrane attack complex C3b, C5, and S protein in EBA and compared C3b and C5 in EBA and bullous pemphigoid. In 10 patients with EBA, these components were detected at the basement membrane zone as follows: membrane attack complex, 90%; S protein, 90%; direct C5, 90%; C3b, 100%; and C5 binding, 90%. In the patients with bullous pemphigoid, the results were as follows: direct C5, 58%; C3b, 33%; and C5 binding, 19%. These results provide additional evidence for complement activation at the basement membrane zone in EBA, show that complement activation in EBA proceeds to activation of terminal complement components, and suggest that EBA antibodies are more potent activators of C5 than are bullous pemphigoid antibodies.