Some Epidermolysis Bullosa Acquisita Sera React with Epitopes Within the Triple-helical Collagenous Domain As Indicated by Immunoelectron Microscopy

Background: Epidermolysis bullosa acquisita (EBA) autoantibodies recognize epitopes predominantly within the N-terminal noncollagenous (NC)-1 domain of type VII collagen. Recently, some EBA cases with reactivity to other domains, i.e. the triple-helical (T-H) collagenous domain and the NC-2 domain, have been reported.

Objectives: To investigate the ultrastructural localization of epitopes for sera from five patients with EBA that were unreactive by immunoblotting with the NC-1, NC-2 and collagenous domains of type VII collagen.

Methods: Immunogold postembedding indirect immunoelectron microscopy was performed using normal human skin and type VII collagen-deficient skin as substrates.

Results: Postembedding indirect immunoelectron microscopy revealed that the five EBA sera showed immunoreactivity in the dermis, mainly located 0-400 nm below the lamina densa. IgG labelling was not observed in type VII collagen-deficient skin from a patient with recessive dystrophic epidermolysis bullosa. The distribution histogram found in this study was different from those of sera that reacted with the NC-1 and/or NC-2 domains, and was similar to those of sera reacting with the T-H collagenous domain.

Conclusions: Our results suggest that epitopes within the T-H collagenous domain of type VII collagen are recognized by IgG antibodies from some EBA sera. These antibodies appear to be found in patients with inflammatory-type EBA.