Defining target antigens in linear IgA disease using skin from subjects with inherited epidermolysis bullosa as a substrate for indirect immunofluorescence microscopy

Identification of target antigens in immunobullous disorders usually involves laborious techniques such as immunoblotting and immunoprecipitation, which do not always provide conclusive data. This is particularly true of linear IgA disease (LAD) in which the target antigen has often proved difficult to identify. As an alternative means of antigen identification in five adult patients with LAD, we performed indirect immunofluorescence (IIF) microscopy on a panel of skin samples taken from subjects with different forms of inherited epidermolysis bullosa (EB). Skin samples were selected that showed a complete absence of immunostaining for a specific basement membrane zone (BMZ) molecule (type VII collagen, laminin 5 or the 180-kDa bullous pemphigoid antigen BP180). In each case, the underlying genetic mutations had been defined and shown to consist of premature termination codons on both alleles of the particular gene, resulting in total ablation of the encoded protein. Two epidermal-binding LAD sera showed BMZ fluorescence on all substrates except BP180-deficient skin, suggesting that the target antigen was BP180, or a closely related molecule. In contrast, two dermal-binding LAD sera were positive on all substrates except the type VII collagen-deficient skin, suggesting that the target antigen was likely to be type VII collagen. One LAD serum sample, which showed combined dermal and epidermal fluorescence on normal salt-split skin, was also positive on all substrates tested, suggesting a target antigen other than type VII collagen, laminin 5 or BP180. The study confirms that LAD is a heterogeneous disorder and illustrates that IIF using a panel of skin samples which lack specific BMZ molecules, taken from subjects with inherited EB, is a relatively simple and useful tool to help identify target antigens in immunobullous disorders.