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Linear IgA disease is an autoimmune subepidermal blistering disease characterized by IgA deposits at the cutaneous basement membrane zone. IgA antibodies from linear IgA disease sera react with antigens of 97 kDa (LABD97) and 120 kDa (LAD-1), both of which appear to be fragments of the extracellular domain of bullous pemphigoid 180 (type XVII collagen). The aim of this study was to determine whether linear IgA disease sera react with the immunodominant region of BP180 (NC16A domain), which is a major target of IgG autoantibodies produced by patients with bullous pemphigoid. Indeed, 11 of 50 linear IgA disease sera were found to contain IgA autoantibodies that recognized a recombinant form of NC16A by immunoblotting. The same sera also reacted with NC16A by enzyme-linked immunosorbent assay. An epitope mapping analysis uncovered four linear IgA disease-associated epitopes located within the 45 amino acid N-terminal stretch of NC16A, all of which were previously identified as antigenic sites targeted by bullous pemphigoid autoantibodies. Eight of the linear IgA disease sera that were reactive with NC16A also recognized LAD-1 secreted by the SCC-25 cell line, and five sera recognized BP180 extracted from keratinocytes. Linear IgA disease sera depleted of reactivity to NC16A by immunoadsorption continued to react with both the LAD-1 antigen and BP180 by immunoblotting and with the basement membrane zone by indirect immunofluorescence microscopy. Our results demonstrate that IgA autoantibodies from a subset of linear IgA disease patients react with the same sites on BP180 that are targeted by IgG autoantibodies in bullous pemphigoid.

Linear IgA disease (LAD) is an autoimmune subepidermal blistering skin disease characterized by the linear deposition of IgA at the dermoepidermal junction. Serum from patients with LAD most commonly contains autoantibodies that are directed against the hemidesmosomal transmembrane glycoprotein BP180 (type XVII collagen). Various antigenic sites on the extracellular domain of this anchoring filament protein have been shown to be targeted by autoantibodies in different autoimmune bullous skin diseases, including bullous pemphigoid and cicatricial pemphigoid (CP). However, little is known about epitopes on BP180 recognized by autoantibodies in LAD. In this study, we used three recombinant GST fusion proteins, together roughly covering the entire BP180 ectodomain, to characterize the autoimmune response in serum from patients with LAD. Interestingly, we found both IgA and IgG reactivity to all three portions of the BP180 ectodomain. The strongest reactivity was observed with the C-terminal portion of BP180. This is also the major region recognized by autoantibodies in patients with CP. This finding correlates with the observation that there may be significant overlap of the clinical and immunopathological findings in LAD and CP.

The dermal-epidermal junction contains a network of structural proteins that link epidermis and dermis. A central component of this complex is the cell membrane-associated hemidesmosomal plaque. Formation of autoantibodies against different components of this hemidesmosomal anchoring complex can lead to subepidermal blisters. Such autoantibodies have been frequently used to characterize the target antigens at the molecular level. Autoimmune subepidermal blistering diseases include bullous pemphigoid, pemphigoid gestationis, lichen planus pemphigoides, linear IgA disease, cicatricial pemphigoid, anti-p450-, anti-p200- and anti-p105-pemphigoid, epidermolysis bullosa acquisita, bullous systemic lupus erythematosus and dermatitis herpetiformis Duhring. Differences in the clinical picture of these diseases can be attributed, at least in part, to the different specificity of the autoantibodies involved. The autoimmune response is further modulated by inflammatory cells and other inflammatory mediators. Native and recombinant forms of the autoantigens are increasingly used for the diagnosis of these diseases.

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The increasing incidence of conditions associated with immune suppression, either as part of the illness or as the result of treatment, makes it necessary to investigate the possibility of fungus infections whenever there are broncho-pulmonary changes. In this respect, aspergillus is a common infection which produces more or less typical radiological changes. It often requires a variety of radiological procedures, including the use of CT and nuclear medicine. The latter can be useful in the allergic form of aspergillosis used for ventilation scintigraphy. The possibility of aspergillosis must be brought to the attention of the clinicians by the radiologist, even in cases that are not entirely typical.

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