Identification of a novel basement membrane antigen (p84) defined by sera with antibodies to both the epidermal and dermal side of split skin.

The diagnosis of autoimmune blistering skin disease is increasingly based on the skin antigen(s) that is the target of the autoimmune process. Some patients with bullous diseases have unusual basement membrane autoantibodies that react to antigens present in both the epidermal and dermal sides of skin split with 1 M NaCl. This combined staining pattern is due to antibodies directed in part to a 160-kilodalton (kD) basement membrane antigen present on the epidermal side of the split skin and to different antigen(s) present on the dermal side. The identity of the current antigen(s), and the significance of this unusual type of combined staining antibody response is not known. Sera of five patients with combined staining antibodies, 19 patients with other types of basement membrane antibodies (15 directed only to the epidermal and four only to the dermal side of split skin), and 23 patients without basement membrane antibodies were tested by Western immunoblot for reactivity to 4% sodium dodecyl sulfate+2 M urea extracts of dermal and epidermal side of salt-split skin. Three (60%) of the combined staining sera had antibodies to an 82-84-kD antigen (p84) reproducibly present in dermal, but not epidermal, extracts of normal human skin. Antibodies to this antigen were absent in the 42 control sera. Western blot affinity-purified antibody to p84 bound only to the basement membrane, on the dermal side of 1 molar salt-split skin. By co-migration experiments, p84 differed from other basement membrane antigens including the major and minor bullous pemphigoid, cicatrizing pemphigoid, and epidermolysis bullosa acquisita antigens, types III and IV collagen, laminin, and epiligrin. Thus, combined staining antibodies are directed in part to an 82-84-kD antigen (p84), a normal but previously underscribed component of the basement membrane of human skin. This antigen differs from the basement membrane antigens recognized by autoantibodies in other subepidermal bullous diseases. The antibody response to p84 provides a specific marker for a novel autoimmune subepidermal blistering skin disease.