UBIQUITINATED CYTOKERATIN INCLUSIONS IN LICHEN AMYLOIDOSUS - AN IMMUNOHISTOCHEMICAL ANALYSIS

Eosinophilic hyaline inclusions were consistently seen in the perinucl ear cytoplasm of suprabasal keratinocytes in lichen amyloidosus. The i nclusions, negative with amyloid staining, were immunoreactive for ubi quitin and cytokeratin, and ultrastructurally showed aggregations of f ine filaments of two sizes (central thin and peripheral thick), The th in filaments were the main component in the upper epidermal layer, Fou r monoclonal antibodies (AE1, AE3, KL1 and CAM5.2) and one antiserum ( WSS) were used for characterizing cytokeratin expression. The AE1 anti body normally stained the basal cells, but in lichen amyloidosus basal staining mostly disappeared. Instead, groups of suprabasal keratinocy tes were labeled, with AE1-reactive inclusions distributed therein. In contrast, the KL1 antibody, showing suprabasal staining, failed to re act with the inclusions. The inclusions were weakly reactive with the AE3 and WSS antibodies, which stained all keratinocytes. The CAM5.2 an tibody 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 ubiqu itin was more densely localized in the thin filaments than in the thic k 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.