Linear IgA disease: the IgA and IgG response to dermal antigens demonstrates a chiefly IgA response to LAD285 and a dermal 180‐kDa protein

Summary Background Linear IgA disease (LAD) of adults and children is mediated by IgA antibodies that target proteins of the epithelial adhesion complex. Most studies have concentrated on the epidermal‐associated antigens; the dermal antigens remain unresolved. Objectives  To determine the dermal antigen repertoire of IgA and IgG antibodies in LAD. Methods  Immunoblotting was carried out on salt‐split and urea‐extracted dermal skin extracts with IgA antibodies (63 adult and 34 childhood sera) and with IgG antibodies (49 adult and 18 childhood sera). Results  Antigens were identified by IgA (61%), IgG (27%) and by both antibody isotypes (19%). LAD285 and an antigen of 180 kDa were the major dermal antigens identified, and antigens of 230 kDa, collagen VII and a protein under 100 kDa were identified less commonly. IgA autoantibodies from adults bound single antigens more frequently than multiple antigens; from children they bound single and multiple antigens equally. The binding of multiple antigens was, however, more common in children than adults. The IgG response was weaker. The 180‐kDa antigen was the main IgG dermal target, and with a single exception, IgG autoantibodies targeted single antigens. Conclusions  There was an IgA and IgG response to dermal antigens in LAD; however, the dual antibody response was limited. The antibody response to LAD285 and a 180‐kDa antigen (probably BP180) suggests that intermolecular epitope spreading of the antigens associated with the extracellular matrix/dermal components of the basement membrane contributes to the immunopathology of the disease. The restricted IgG response suggests that dermal‐binding IgG autoantibodies are not pathologically significant.