Sensitivity of different assays for the serological diagnosis of epidermolysis bullosa acquisita: analysis of a cohort of 24 Italian patients.

Background: Epidermolysis bullosa acquisita (EBA) is an autoimmune blistering disease characterized by tissue-bound and circulating autoantibodies to the dermal-epidermal junction. The autoantibody target is type VII collagen (Col VII) which is involved in dermal-epidermal adhesion. Diagnosis is made by clinical and histopathological findings, linear deposition of autoantibodies at the dermal-epidermal junction detected by direct immunofluorescence, and binding to the dermal side of salt-split skin by indirect immunofluorescence (IIF). However, the detection of specific anti-Col VII reactivity has an important confirmatory value.

Methods: The humoral immune response in EBA sera was analysed by (i) IIF on human skin, (ii) a commercial Col VII ELISA, and (iii) immunoblotting on Col VII produced by an epithelial cell line.

Objective: The aim of this study was to compare the sensitivity of different approaches for the serological diagnosis of EBA.

Results: The vast majority of EBA sera (79.2%) bound to the Col VII non-collagenous domains by a commercial ELISA, while a small proportion of patients (12.5%) exclusively reacted to the collagenous domain by immunoblotting. Of note, the autoantibodies reactivity to Col VII was more frequently detected by IB (91.7%) than by IIF (83.3%) and ELISA (79.2%). Interestingly, 2 out of 24 sera recognized Col VII epitopes undetectable in the native secreted protein but present in the context of extracellular matrix proteins, as assessed by immunomapping on Col VII-deficient skin.

Conclusion: Our findings show that the use of multiple assays allows to improve diagnostic performance. An algorithm for efficient serological diagnosis of EBA is proposed.