The localization of target antigens and autoantibodies in linear IgA disease is variable: correlation of immunogold electron microscopy and immunoblotting

Abstract

Linear IgA disease (LAD) of adults and children is a dapsone-responsive, autoimmune subepidermal blistering disease characterized by linear IgA deposits at the basement membrane zone (BMZ) of the skin and mucosa. Circulating IgA antibodies to BMZ components are often present. In this study we investigated the ultrastructural localization of the antigens and autoantibodies in six patients with LAD (five adults and one child). Using a direct postembedding immunogold electron microscopy (EM) technique, three different patterns of IgA antibody deposition were seen in the skin of four patients with LAD. The IgA deposits localized within the uppermost part of the lamina lucida and to the basal surface of the hemidesmosome in two patients, to the lamina lucida in one, and to the lamina densa in the fourth patient. Using an indirect immunogold EM technique and serum or purified blister fluid from two additional LAD patients, we showed that the serum autoantibodies of one patient bound to the hemidesmosome of the BMZ, while the autoantibodies in the blister fluid of the other patient bound to the lamina densa and sublamina densa including the anchoring fibrils in a labelling pattern similar to that of the monoclonal antibody (LH7.2) to collagen VII. All the autoantibodies binding to the hemidesmosome or lamina lucida recognized a protein in epidermal extracts of molecular weight 180 kDa or its breakdown product of 97 kDa, 200 kDa or 230 kDa. The antibodies binding to the lamina densa recognized proteins of 180 and 285 kDa. The antibodies that bound to the lamina densa and anchoring fibrils recognized collagen VII. In this immunogold EM study we have shown four patterns of IgA labelling in six patients with LAD, associated with five different antigens as recognized by immunoblotting. These results, together with our previous immunofluorescence and immunoblotting findings add support to the contention that LAD is a heterogeneous disease as regards both the target antigens and epitopes.

Linear IgA disease with IgA antibodies directed against 200- and 280-kDa epidermal antigens

“…4,17 The epidermal 280-kDa protein has never previously been reported to be an antigen associated with LAD, but it could be identical to a protein reported as a 285-kDa epidermal protein, 12 because it is difficult to determine the MW of polypeptides with MW . As LAD has been reported to be a heterogeneous disease in respect of the localization and MWs of target autoantigens, we characterized the reactivity of this patient's autoantibodies by immunoblot analysis.…”

IgA Antibodies Recognizing LABD97 Are Predominantly IgA1 Subclass

“…We have shown that this LABD97 antigen is identical to a portion of the extracellular domain of the bullous pemphigoid antigen, BPAg2 (7). The IgA antibodies that bind LABD97 localize antigens in the lamina lucida between the NC16A and carboxyl terminal domains of BPAg2 by immunogold electron microscopy (8,9). It has been reported by immuno¯uorescent techniques that the BMZ antibodies in LABD are the IgA1 subtype (10).…”

Autoantibodies against the Processed Ectodomain of Collagen XVII (BPAG2, BP180) Define a Canine Homologue of Linear IgA Disease of Humans

“…In-depth immunologic investigations recently proved, however, that the antigens targeted by IgA autoantibodies were heterogeneous. 10,25,29 Circulating IgA autoantibodies were shown to target BP or EBA antigens or epidermal proteins of 120 or 97 kd. 30 Whereas the diagnosis of IgA BP or IgA EBA should be used when autoantibodies target BP or EBA antigens, the term LAD is now reserved for those human patients, either children or adult, who exhibit IgA and/or IgG autoantibodies that recognize the 120/97-kd processed extracellular segment of type XVII collagen.…”