Autoantibodies against the processed ectodomain of collagen XVII (BPAG2, BP180) define a canine homologue of linear IgA disease of humans

Linear IgA disease (LAD) is an acquired autoimmune subepidermal blistering dermatosis that affects human children and adults. In contrast to bullous p emphigoid, in which autoantibodies recognize transmembrane type XVII collag en (BP180, BPAG2), LAD is associated with skin-fixed and circulating IgA au toantibodies that target LAD-I, the processed extracellular form of type XV II collagen. An immunologic homologue of LAD in humans was identified in tw o dogs according to the following criteria: 1) erosive, ulcerative, and cru sted lesions seen on the face, in the oral cavity, and on the extremities, 2) dermoepidermal clefting present in the basement membrane lamina lucida w ithout inflammation or with mild neutrophilic infiltration, 3) basement mem brane-fixed IgG and/or IgA antibodies, and 4) circulating IgA and IgG autoa ntibodies that target the 120-kd soluble protein LAD-I. The present study e stablishes unequivocally the existence of a naturally occurring canine mode l of LAD of humans.