Identification of the target antigen in chronic bullous disease of childhood and linear IgA disease of adults.

Disease-associated autoantibodies to basement membrane proteins have been used to characterize structural components of the epidermal basement membrane such as bullous pemphigoid (BP) antigen and epidermolysis bullosa acquisita (EBA) antigen (type VII collagen). The autoimmune bullous diseases characterized by IgA autoantibodies to the basement membrane zone (BMZ), i.e. linear IgA disease of adults (LAD) and chronic bullous disease of childhood (CBDC) may have circulating antibodies. Previous studies of tissue distribution and ultrastructural binding have suggested that the LAD and CBDC antigens are similar, if not identical, and differ from the target antigens of the other bullous diseases. We present the molecular characterization of the LAD/CBDC antigens by Western blotting of a large series of antisera. Seven of 33 sera (21%) were positive on immunoblotting and bound to the same antigen which has a molecular weight (MW) of 285 kDa. Using both defined polyclonal antisera to BP and LH 7.2 monoclonal antibody to type VII collagen (carboxy terminal) we have shown that the LAD and CBDC antisera both bind to an identical molecular weight protein which clearly differs from both the BP and EBA (type VII collagen) antigens. Although detectable in dermal tissue extracts like EBA, the MW of 285 kDa is heavier than type VII collagen (250 kDa, in our system, using non-collagenous standards). This study confirms the identity of LAD and CBDC antigens to be the same and to differ from previously described basement membrane proteins.