Structural variations in anchoring fibrils in dystrophic epidermolysis bullosa: Correlation with type VII collagen expression

Dystrophic epidermolysis bullosa is characterized by various abnormalities of anchoring fibrils, which are mainly composed of type VII collagen, at the dermal-epidermal junction. To define these changes more clearly, we examined skin samples from 22 patients with different forms of dystrophic epidermolysis bullosa by pre-embedding immunoelectron microscopy using an antibody (LH 7:2) that binds to the NC-1 globular domain of type VII collagen, followed by 1 nm colloidal gold-labeled secondary antibodies and subsequent silver enhancement. In dominant dystrophic epidermolysis bullosa cases, there was only a slight but variable reduction in the immunolabeling density on anchoring fibrils and on the lamina densa, in parts similar to normal human skin. In localized recessive dystrophic epidermolysis bullosa skin, some fibrillar structures just below the lamina densa (and particularly subjacent to hemidesmosomes) had specific antibody labeling despite their lack of resemblance to definitive anchoring fibrils. Immunolabeling with LH 7:2 was also seen within basal keratinocyte endoplasmic reticulum and cytoplasmic vesicles in some dystrophic epidermolysis bullosa patients, usually with milder phenotypic features. Even in the most severe cases of generalized recessive dystrophic epidermolysis bullosa, occasional immunolabeling was found within the lamina densa and on scanty thin filamentous structures at sub-lamina densa sites usually occupied by anchoring fibrils. This study suggests that dystrophic epidermolysis bullosa patients express some type VII collagen NC-1 domain epitopes that may be variably reduced at the dermal-epidermal junction or retained within basal keratinocytes. The clinical heterogeneity in dystrophic epidermolysis bullosa is mirrored by a range of immunoelectron microscopy findings, indicating variability in completeness of anchoring fibril formation and a possible spectrum of underlying type VII collagen structural protein abnormalities.