Write short note on immunoelecton microscopy
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Immunoelectron microscopy has shown immunoglobulin deposits in patients with EBA localized to the lamina densa zone of the basement membrane, below the lamina lucida. Standard transmission electron microscopy of lesional skin of patients with EBA shows that the anchoring fibrils are decreased or absent. These findings may be relevant in the development of the clinically evident skin fragility, as anchoring fibrils are postulated to play a role in epidermal–dermal adherence via the linkage of the hemidesmosome through the basement membrane. The lack of an inflammatory infiltrate in many patients with EBA suggests that these autoantibodies may disrupt the interaction between anchoring fibrils and dermal matrix proteins.
The target antigen for the IgG autoantibodies present in the sera of patients with EBA is type VII collagen, a 300-kDa glycoprotein composed of a 145-kDa noncollagenous domain (NC1) at the amino-terminal end, an 18-kDa noncollagenous domain (NC2) at the carboxy-terminus, and a central collagenous domain. IgG antibodies from patients with EBA appear to be specific for epitopes within the NC1 noncollagenous domain of the protein. Type VII collagen is the major structural component of anchoring fibrils and is produced by both epithelial keratinocytes and dermal fibroblasts. Recently, passive transfer experiments using mice, as well as active immune models, have provided additional support for the critical role of antibodies directed against type VII collagen in the pathogenesis of EBA.31
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