The epithelium of the human endolymphatic sac: immunohistochemical characterization

Innate immune defense in the inner ear - mucines are expressed by the human endolymphatic sac

The human endolymphatic sac has been shown recently to have immunological capacities and has thus been proposed as the main entity protecting the inner ear from pathogen invasion, equivalent to mucosa-associated lymphoid tissue (MALT). Although the sac expresses molecules of the innate immune system, the potential expression of members of the important mucin family has not been detailed. Thus, this paper explores endolymphatic sac expression of a number of mucins and mucin precursors. Twelve fresh tissue samples from the human endolymphatic sac were obtained during translabyrinthine surgery. The expression of Mucin 1, 2, 5B/AC and 16, as well as the core structure elements (mucin precursors) T-antigen, Tn-antigen and Sialyl-Tn-antigen was investigated by immunohistochemistry. The endolymphatic sac epithelium expressed MUC1 (both apically towards the endolymphatic sac (ES) lumen and basally towards the capillary network), MUC 16 and Tn-antigen. There was no labeling after incubation with antibodies against T-antigen, sialyl-Tn-antigen, MUC2 and MUC5B/AC. We conclude that the human endolymphatic sac epithelium expresses a number of mucin molecules, which supports the hypothesis of the sac as the primary immunological tissue structure of the inner ear, equivalent to MALT in other organs. The mucins may also play a role in the formation and continuous homeostasis of the inner ear fluids, as well as the pathogenesis of Meniere's disease.

Expression of anion exchangers in cultured human endolymphatic sac epithelia

HYPOTHESIS

Pendrin acts as a Cl-/HCO3- exchanger and is responsible for endolymphatic fluid volume and pH homeostasis in human endolymphatic sac epithelial cells.

BACKGROUND

The endolymphatic sac (ES) is part of the membranous labyrinth in the inner ear that plays an important role in maintaining homeostasis of the endolymphatic fluid system. However, the exact mechanism of fluid volume and pH regulation is not fully understood yet. We aimed to demonstrate the expression of various anion exchangers (AEs), including pendrin, in cultured human endolymphatic sac epithelial (HESE) cells.

METHODS

Endolymphatic sac specimens were harvested during acoustic neuroma surgery (n = 24) using the translabyrinthine approach and then subcultured with high epidermal growth factor (EGF) (25 ng/ml) media and differentiated using low-EGF (0.5 ng/ml) media. The cultured cells were classified according to the morphology on TEM. The Cl-/HCO3- exchanger activity was assessed by pHi measurement using pH sensitive dye 2', 7'-bis (2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF/AM). We performed reverse transcriptase-polymerase chain reaction and immunohistochemical staining for AEs.

RESULTS

We determined that 7.3 ± 6.7% of cells differentiated into mitochodria-rich cells and 50.2 ± 15.1 of cells differentiated into ribosome-rich cells. bAE3, AE4, SLC26A4, SLC26A6, and SLC26A11 were also expressed in cultured HESE cells. The cultured cells had Cl-/HCO3- and Cl-/formate exchange activity on the luminal membrane, which is sensitive to anion channel inhibitors (DIDS 500 μM). Furthermore, we showed that pendrin (SLC26A4) was expressed in cultured HESE cell membranes.

CONCLUSION

Our results suggest that AEs, including pendrin, are expressed in epithelia of ES and may have role in maintaining ionic homeostasis, and the HESE culture system are useful for uncovering the functional role of ES epithelial cells.

In vitro growth of human endolymphatic sac cells: a transmission electron microscopic and immunohistochemical study in patients with vestibular schwannoma and Ménière's disease

HYPOTHESIS

Human endolymphatic sac cells have been notoriously difficult to maintain in culture. It was hypothesized that an in vitro environment intended for growth of keratinocytes would also be suitable for human endolymph sac cells.

BACKGROUND

Studies on cell physiology of human endolymphatic sac cells have been hampered by difficulties in maintaining them in culture.

METHODS

Human endolymphatic sac cells were taken from 10 patients during translabyrinthine skull base surgery for vestibular schwannoma, one of whom also had Ménière's disease. Cell lines of proliferating epithelial cells were obtained after trypsinization and growth in a 3:1 mixture of Dulbecco's modified Eagle medium and Ham's F12 medium supplemented with 10% fetal calf serum. Fibroblast overgrowth was counteracted by the use of so-called cloning rings. During various stages, cells were investigated with transmission electron microscopy and/or immunohistochemistry.

RESULTS

Proliferation took place after 2 to 3 days of primary cell culture. The cells were cytokeratin-positive and pleomorphic, and they had abundant polarized microvillus-like projections, numerous coated cytoplasmic pits and vesicles, and a well-developed rough endoplasmic reticulum.

CONCLUSION

Cell lines of proliferating human endolymphatic sac cells can be produced with the technique described here and may be a valid tool in studies of human endolymph sac physiology.

Oral vaccine in otosclerosis

Otosclerosis is a genetically based disease in which the development of autoimmune mechanisms can lead to its clinical expression. Anti-type II collagen antibodies have been found in otosclerotic patient serum. The first clinically unexpressive phase of the disease can be diagnosed from a family history and ON-OFF stapedial reflexes with evidence of an autoimmune disorder. The use of antigenic oral hyposensitization is accepted, based on autoimmune pathogenesis. Hyposensitization should be initiated during this subclinical period of otosclerosis with a type II collagen oral vaccine.

Endolymphatic sac tumours

This review article surveys clinical and pathological literature on endolymphatic sac tumours (ELST) and summarizes characteristics that describe the entity. ELST are rare neuroectodermal neoplasms in the petrous bone, originating from inner ear structures. They can be encountered sporadically or in von Hippel-Lindau disease. The most prominent symptom is sensorineural deafness. Historically, nomenclature of invasive adenoid tumours in the petrous bone has been divergent, the term papillary adenocarcinoma used most frequently. Histologically, they have a follicular or papillary and adenoid pattern that can be easily confused with various other neoplastic conditions including metastatic carcinoma. It remains to be verified whether similar tumours (papillary adenocarcinomas) can originate from the middle ear. Middle ear adenomas have a similar appearance but probably originate from neural crest cells in the middle ear. ELST can express a variety of epitopes (including cytokeratin and neuroectodermal markers) which can be detected immunohistochemically. In cases in von Hippel-Lindau disease the cerebello-pontine angle should be included in routine radiological examinations to detect ELST before the tumours lead to deafness. In apparently sporadic cases of ELST, genetic testing for von Hippel-Lindau disease should be considered. Correct distinction of ELST from metastatic carcinoma prevents futile searches for unknown primary tumours.

Measles virus in otosclerosis and the specific immune response of the inner ear

Histologic and immunohistochemical studies of otosclerotic lesions have shown that there is a chronic inflammatory reaction of the otic capsule with bone resorption resulting from vascular invasion accompanied by inflammatory cells. During the active lytic stage of otosclerosis, paramyxoviral structures have been identified by electron microscopy and measles virus antigen expression by immunohistochemistry. Recently, measles virus related sequences have been detected in tissue of otosclerotic lesions. Because the otosclerotic focus has a close relation to the perilymphatic space, the expression of measles virus antigens within it should represent an immunologic challenge to the immune system of the endolymphatic sac. In this study, measles virus specific antibodies were detected in all of the perilymph samples from 19 patients suffering from otosclerosis, and the relative amount of these IgG antibodies was much higher than in serum samples of the same patients or in perilymph of control patients. These findings support the hypothesis that measles viruses play an crucial role in the pathogenesis of otosclerosis.

Regeneration of the damaged endolymphatic sac epithelium

The regeneration of endolymphatic sac (ES) epithelium after epithelial damage was examined using 5-bromo-2'-deoxyuridine (BrdUrd). Guinea pigs and anti-BrdUrd, antikeratin, and anti-basement membrane (BM) component antibodies were used. Animals were sacrificed at 3, 7, and 14 days following an immune injury of the ES. The animals were sacrificed after an administration of BrdUrd at the designated times. Decalcified temporal bones were examined immunohistochemically. At day 3, epithelial loss without subepithelial BM was seen in the region of marked cell infiltration. BrdUrd-positive cells could be detected in the epithelium at the edge of the wound. At day 7, cell infiltration decreased, and the epithelial lining with BM was repaired. These results reveal that the epithelium of the ES can regenerate within 7 days after an immune injury.

Are papillary adenomas endolymphatic sac tumors?

Papillary adenomas of the temporal bone have been considered as originating from the endolymphatic sac. The radiologic, surgical, and pathologic findings in a patient suffering from von Hippel-Lindau disease with bilateral papillary adenomas of the temporal bone cast some doubt on this site of origin. Radiologically, the center of tumor growth was at the top of the jugular bulb. Intraoperatively, the tumor was found to have reached the lateral wall of the endolymphatic sac, but the lumen was tumor-free. Both ciliated and nonciliated tumor cells were found in the resected tumor, resembling the ultrastructure of normal epithelial lining in the human mastoid. A strong positive immunohistochemical reaction for keratin and negative reactions for vimentin, glial fibrillary acidic protein, and S-100 protein in the tumor tissue of this patient are typical for middle ear mucosa. Therefore, the described papillary adenoma originated from the mucosa of the pneumatic spaces surrounding the jugular bulb, and the theory that the endolymphatic sac is the origin of all papillary-cystic tumors (adenocarcinomas) should be questioned.

Endolymphatic sac tumors: histopathologic confirmation, clinical characterization, and implication in von Hippel-Lindau disease

The term "endolymphatic sac tumor" (ELST) was coined to identify the likely origin of aggressive papillary tumors of the temporal bone. To evaluate the validity of this designation, the temporal bone collection at the Massachusetts Eye and Ear Infirmary was accessed in an effort to determine the pathologic relationship between these tumors and the endolymphatic sac. The search resulted in the identification of a de-novo papillary epithelial lesion arising within the confines of the endolymphatic sac in a patient with von Hippel-Lindau (VHL) disease who harbored a large, destructive ELST in the opposite temporal bone. This finding provides the most substantial evidence to date regarding the origin of the ELST and the accuracy of its nomenclature. Seven additional clinical cases of ELST were identified and analyzed in order to define the natural history of these tumors. All patients had a history of sensorineural hearing loss diagnosed an average of 10.6 years prior to tumor discovery. The presence of a polypoid external auditory canal mass, facial paralysis, and evidence of a destructive mass arising on the posterior fossa surface of the temporal bone were common physical and radiographic findings. The management of these patients, as well as those who are probably prone to such tumors (i.e., VHL patients), is discussed.

Otosclerosis: a measles virus associated inflammatory disease

The etiology of otosclerosis is still unknown. Immunohistochemical studies have revealed the characteristics of chronic inflammation in the otospongiotic area. Paramyxoviral structures have been identified by electron microscopy and the expression of measles virus antigen has been observed by immunohistochemistry in active otosclerotic tissue. By use of the polymerase chain reaction, measles virus related sequences have been detected in otosclerotic bone tissue but not in control specimens. The aim of our study was i) to detect measles virus genome in affected patients using a more sensitive PCR system and ii) to search for anti-measles virus IgG in the perilymph. In 13 out of 14 specimens of bone fragments from surgically removed stapedes of patients suffering from otosclerosis, measles virus RNA sequences could be detected while other tissues from the same patients and from a negative control group lacked such sequences. Furthermore, IgG anti-measles virus antibodies were detected in the perilymph of 6 patients. Our results support our previously stated hypothesis that otosclerosis is a measles virus associated disease which provokes a local immune response within the inner ear.

The significance of the human endolymphatic sac and its possible role in Menière's disease

Modern immunohistochemical methods allow a functional characterization of the human endolymphatic sac (ES) and its associated cell populations. The currently available immunohistochemical data of the extraosseous part of the human ES support the assumption that the epithelium is metabolically active and capable of both secretion and adsorption. The reactivity of the epithelial cells with antibodies against neuroendocrine antigens imply a paracrine activity of the human ES. Further results provide evidence for a possible role of the human ES in inner ear immune defence and indicate a putative functional relationship of the human ES to the common mucosa-associated immune system (MALT).

Identification of substances in the endolymphatic sac

The composition of the contents of the endolymphatic sac (ES) has yet to be fully defined. Carbohydrates have been found in the ES of human fetuses and animals but not identified in the adult human ES. In the present study, celloidin was removed from previously prepared human temporal bone sections and a histochemical method was used to detect carbohydrates and protein in the ES. Six biotinylated lectins were used to identify specific carbohydrates in 15 ears: beta-D-N-acetylglucosamine, beta-D-galactose, D-galactose, alpha-D-mannose, D-N-acetylgalactosamine and alpha-L-fucose. The intensity of staining was graded qualitatively. A substance in the ES tubules that did not stain with any lectin was identified by the Millon reaction as containing protein. The carbohydrates and protein may exist in the different tubules or in the same tubule without mixing. This finding seems to support the idea that at least some of these substances are produced locally in the ES. Our observations support the hypothesis of the existence of a secretion and degradation system in the endolymphatic sac.

Papillary neoplasms (Heffner's tumors) of the endolymphatic sac

The sources of adenomatous neoplasms in the temporal bones are usually metastases or direct extensions from extratemporal lesions, or primary from the middle ear cleft. In 1989, Heffner added the endolymphatic sac's epithelium as another possible generative origin. In contrast to the adenomatous tumors of the middle ear or mastoid, the papillary cystic neoplasms of the endolymphatic sac are large and locally aggressive and often involve the middle and posterior cranial fossae and bone. These biologically low-grade adenocarcinomas have not been shown to be able to metastasize.

Immunohistochemical characterization of the human endolymphatic sac and its associated cell populations

The use of monoclonal and polyclonal antibodies as specific markers for the localization of tissue constituents in situ allows the characterization of cells according to their state of differentiation and the detection of cellular antigens related to the function of cells and tissues. Our studies focus on the immunohistochemical characterization of the human endolymphatic sac (ES) and its associated cell populations. A panel of 37 monoclonal and polyclonal antibodies were used on frozen sections and fixed material from 64 ES of 32 persons without any clinically known inner ear disorders. The ES were removed at the time of autopsy; case histories were available. The results of our studies on the extraosseous part of the human ES support the assumption that the epithelium is metabolically active and capable of both secretion and absorption. The reactivity of the epithelial cells with antibodies against neuron specific enolase, chromogranin and somatostatin, respectively, implies a paracrine activity of the ES. Further results obtained with antibodies specific for cells of the immune system indicate a possible role of the human ES in the inner ear immune defence and a functional relationship of the ES to the common mucosa-associated immune system.

Glycoconjugates in the human fetal endolymphatic sac as detected by lectins

The distribution of glycoconjugates in the 11 to 16 weeks old human fetal endolymphatic sac (ES) was analyzed using six biotinylated lectins; Wheat germ agglutinin (WGA), Abrus precatorius agglutinin (APA), Ulex europaeus agglutinin I (UEA-I), Ricinus communis agglutinin 120 (RCA120), Helix pomatia agglutinin (HPA), Concanavalin A (ConA). In the 11 week old human fetus, fluorescent reactions with WGA, APA, RCA120 and ConA were detected in the ES. There was almost no reaction with HPA and UEA-I. In the 14 week old human fetus, however fluorescent reactions with HPA and UEA-I appeared. This result suggests that the presence of glycoconjugates changes during the maturation process of the ES. Glycoconjugates detected with HPA were related to the epithelial cell elements of the ES epithelium. The reaction with UEA-I suggests that the stainable substance present in the ES lumen may be secreted locally by the ES itself.

Differential immunohistochemical detection of cytokeratins and vimentin in the surgically removed human endolymphatic duct and sac

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.