Linear IgA disease: the IgA and IgG response to the epidermal antigens demonstrates that intermolecular epitope spreading is associated with IgA rather than IgG antibodies, and is more common in adults.

BACKGROUND

Linear IgA disease (LAD; adult and childhood) is a dapsone-responsive, acquired immunobullous disorder mediated by IgA antibodies directed at target antigens within the epithelial basement membrane. These antigens have not been completely characterized.

OBJECTIVES

To identify the target antigens in LAD, and to correlate these with the antibody isotype.

METHODS

We used 101 LAD sera without IgG antibodies detected by indirect immunofluorescence. The sera were analysed by immunoblotting for IgA (65 adults and 36 children) and IgG (61 adults and 34 children) autoantibodies, on salt-split, urea-extracted epidermal tissue extracts.

RESULTS

Antigens were targeted in LAD by IgA antibodies (54 adults and 23 children), IgG antibodies (34 adults and 19 children), and both isotypes (30 adults and 16 children). Three major antigens were recognized by IgA antibodies: LAD285 (22 adults and three children), BP230 (30 adults and eight children) and BP180 (collagen XVII), including the 97-kDa ectodomain (52 adults and 20 children). Seven 'minor' antigens were occasionally detected (18 adults and 13 children). IgA antibodies bound multiple antigens (33 adults and nine children) more frequently than single antigens (21 adults and 14 children), but the binding to multiple antigens was more restricted in children than in adults. IgG antibodies mainly bound a single antigen (29 adults and 16 children), predominantly BP180.

CONCLUSIONS

There was variation in the autoantibody response within the disease and the patient, with regard to target molecules and autoantibody class. The finding that IgG as well as IgA autoantibodies predominantly target BP180 supports a pivotal role for collagen XVII in adult and childhood LAD. The IgG response was very restricted compared with IgA autoantibodies (P < 0.01). Autoantibodies from children had a more restricted antigen repertoire than from adults (P < 0.05). Epitope spreading is common in LAD and is affected by the class of autoantibody and age of the patient.