Ubiquitinated cytokeratin inclusions in lichen amyloidosus: an immunohistochemical analysis

Eosinophilic hyaline inclusions were consistently seen in the perinuclear cytoplasm of suprabasal keratinocytes in lichen amyloidosus. The inclusions, negative with amyloid staining, were immunoreactive for ubiquitin and cytokeratin, and ultrastructurally showed aggregations of fine filaments of two sizes (central thin and peripheral thick). The thin filaments were the main component in the upper epidermal layer. Four monoclonal antibodies (AE1, AE3, KL1 and CAM5.2) and one antiserum (WSS) were used for characterizing cytokeratin expression. The AE1 antibody normally stained the basal cells, but in lichen amyloidosus basal staining mostly disappeared. Instead, groups of suprabasal keratinocytes were labeled, with AE1-reactive inclusions distributed therein. In contrast, the KL1 antibody, showing suprabasal staining, failed to react with the inclusions. The inclusions were weakly reactive with the AE3 and WSS antibodies, which stained all keratinocytes. The CAM5.2 antibody was unreactive. The subepidermal amyloid deposits were negative with all the antibodies. The inclusions were ubiquitinated especially in the granular layer. Immunoelectron microscopy disclosed that ubiquitin was more densely localized in the thin filaments than in the thick ones. This indicated that cytokeratin expression and metabolism are altered in the affected epidermis, and that ubiquitin functions in the process of degradation of abnormal cytokeratin filaments.