Linear IgA disease: a report of two dermal binding sera which recognize a pepsin-sensitive epitope (?NC-1 domain) of collagen type VII.

Linear IgA disease is a subepidermal blistering disease characterized by IgA autoantibody deposition at the basement membrane zone of skin and mucosa. The antigens targeted in linear IgA disease have been defined by their molecular weight and localization. It has been proposed that a minority of linear IgA disease sera that bind to the dermal aspect of salt-split skin target collagen type VII. We have identified two patients with linear IgA disease using dermal binding IgA autoantibodies on salt-split skin which recognize collagen type VII by immunoblot analysis. The reactive epitope was destroyed by the proteolytic enzymes pepsin, which destroys the NC-1 domain of collagen type VII, and protease type VIII. Localization studies compared the IgA autoantibodies from these patients with the monoclonal antibody LH7.2 to the NC-1 domain of collagen type VII and showed colocalization on a dermal cylindroma tumour tissue, and a similar distribution with immunogold electron microscopy, using purified blister fluid from one patient. We propose from these results that the IgA autoantibodies from these two patients recognize the NC-1 domain of collagen type VII, the classical immunodominant epitope for epidermolysis bullosa acquisita.