97-kDa Linear IgA Bullous Dermatosis (LAD) Antigen Localizes to the Lamina Lucida of the Epidermal Basement Membrane

Abstract

Linear IgA bullous dermatosis (LAD) is an autoimmune blistering disease in which IgA autoantibodies develop against the epidermal basement membrane zone. Target antigens of the circulating autoantibodies are thought to be heterogeneous, and their ultrastructural localization has not been fully elucidated. Previous studies with immunoblotting have demonstrated that the 97-kDa autoantigen is detected most frequently in patients' sera and is thought to be a major LAD antigen. Although a recent report suggests that the 97-kDa antigen localized to the hemidesmosomal plaques and the adjacent lamina lucida, discrepancies still exist among previous immunoelectron microscopic findings. To identify the precise localization of the 97-kDa LAD antigen, we used two different low-temperature immunoelectron microscopic techniques. For immunolabeling, we selected five LAD sera that had a high titer of autoantibodies against the 97-kDa LAD antigen. A post-embedding method with cryofixation and freeze substitution failed to immunolabel the 97-kDa LAD antigen. Cryoultramicrotomy with immunoelectron microscopy succeeded in preserving the antigenicity of the 97-kDa LAD antigen. In all cases, the majority of labeling occurred in the lamina lucida beneath the hemidesmosomes. No specific labeling was observed in the hemidesmosomal attachment plaques or the lamina densa or sublamina densa region, including anchoring fibrils. These results indicate that the 97-kDa LAD antigen is a component of the lamina lucida.