In mucous membrane pemphigoid (MMP), autoantibodies are directed against which component of the epithelial attachment?

Mucous membrane pemphigoid (cicatricial pemphigoid) is an autoimmune subepithelial blistering disease. Autoantibodies target hemidesmosomal proteins at the epithelial basement membrane zone, specifically BP180 (type XVII collagen) and BP230 — the same antigens as in bullous pemphigoid. The antibodies cause separation of the epithelium from the underlying connective tissue (subepithelial cleft), resulting in subepithelial blistering. This distinguishes MMP from pemphigus vulgaris, where antibodies target desmoglein 3 (a desmosomal protein), causing intraepithelial blistering. The Nikolsky sign is positive in pemphigus (intraepithelial cleavage) but negative or weakly positive in MMP (subepithelial cleavage).