The immunohistochemical localization of intermediate filament proteins was studied in frozen sections of chemically fixed, nondecalcified adult human cochleas. Cytokeratins were found in all epithelial cells lining the cochlear duct (including most supporting cells of the organ of Corti) but were absent in the hair cells. Neurofilament proteins were present in the nerve endings at the hair cells, in the neural bundles, and in the ganglion cells. Vimentin staining occurred in most of the supporting structures and was roughly complementary to the regions showing cytokeratin staining and neurofilament staining. However, the region of the spiral prominence and outer sulcus, as well as the pillar cells and Deiters' cells in the organ of Corti, showed coexpression of vimentin and cytokeratins. No definite immunostaining was observed with antibodies to desmin and glial fibrillary acidic protein.

Epithelia can be characterized by the specific expression pattern of their cytokeratin components. Therefore, we investigated the immunohistochemical expression of different cytokeratin subunits in frozen sections of chemically fixed, non-decalcified, adult human cochleas. The organ of Corti and the marginal cells of the stria vascularis showed reactivity for cytokeratin subunits 8, 18 and 19, whereas the other cochlear epithelia in addition expressed cytokeratin 7. The expression of cytokeratins 7, 8, 18 and 19 by the epithelia of the adult human cochlea is typical of "simple" epithelia. The deviant cytokeratin pattern of the organ of Corti and marginal cells of the stria vascularis may well reflect their differences in functional state and/or differentiation as compared to the other cochlear epithelia.

The immunohistochemical detection of intermediate filament proteins, cytoskeletal constituents that allow the characterization of tissues, was investigated in frozen sections of the chemically fixed, nondecalcified, adult human vestibular labyrinth. Cytokeratins (CKs) were detected in all epithelia (including the sensory epithelia), although substantial differences in the degree of staining between individual cells occurred. The expression of CKs 7, 8, 18, and 19 as detected with our subunit-specific monoclonal antibodies in the vestibular epithelia is typical of "simple" epithelia and is identical to the CK subtypes found in the human cochlea. Although immunostaining for CK 7 was very weak and was limited to certain vestibular wall cells, the other CKs demonstrated a pronounced and rather uniform distribution throughout the different epithelia. All epithelia (including the sensory epithelia) displayed expression of vimentin, thus demonstrating co-expression with CKs. Vimentin was also present in the subepithelial connective tissue fibroblasts and mesothelial lining of the vestibular labyrinth. Neurofilament proteins were detected in all neuronal structures. The intense staining for CKs in the maculae and cristae implies that these sensory organs are rigid structures, a finding that may possibly be of importance in the mechanoelectrical transduction process for the sense of equilibrium.

Immunohistochemical detection of intermediate filament proteins and different subgroups of cytokeratins (Cks) was used to characterize the epithelium of the surgically removed adult human endolymphatic duct (ED) and sac (ES). The epithelium of the ED and ES demonstrated immunostaining for Cks 7, 8, 14, 17, 18 and 19, a pattern typical of so-called "complex" or "mixed" epithelia. This is a remarkable finding, since this pattern differs strikingly from previously reported data on the adult human cochlea and vestibular labyrinth that demonstrated a Ck pattern typical of "simple" (or single-layered) epithelia. Furthermore, the epithelium of the ED and ES demonstrated co-expression of Cks and vimentin. The present data indicate that the epithelium of the ED and ES exhibits another type of epithelial differentiation and demonstrates a higher degree of complexity than the other epithelia in the adult human inner ear.

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