Homing of lymphocytes to the inner ear

Tracking Lymphatic Drainage Pathways Through Inner Ear Channels: A Systematic Review

The search for potential lymphatic routes through the cochlea, or membranous portions of the inner ear labyrinth, remains a significant challenge. Researchers often focus on lower mammals rather than humans to uncover these pathways. This review aims to delineate the speculated lymphatic routes within the inner ear to date. It follows the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines, conducting a comprehensive search of PubMed, Scopus, Crossref, and Google databases using the terms "inner ear" and "lymph." The problem, intervention, comparison, outcome (PICO) search strategy was employed, and analysis was performed using equation and scope metrics. Articles were screened and filtered using the CADIMA automation tool, resulting in 33 articles being reviewed, of which 23 were selected. Potential lymphatic drainage routes identified include the round window, oval window, scala tympani, spiral limbus, and lateral wall of the cochlea. The vestibular side of Reissner's membrane was noted as a key nodal point for lymphocytes within the inner ear. This review maps the proposed lymphatic networks in the inner ear and highlights existing gaps. It systematically gathers, evaluates, and synthesizes available evidence on the lymphatic pathways of the inner ear, offering valuable insights into their presence, structure, function, and clinical significance.

A mouse model of autoimmune inner ear disease without endolymphatic hydrops

Autoimmune inner ear disease (AIED) is an organ-specific disease characterized by irreversible, prolonged, and progressive hearing and equilibrium dysfunctions. The primary symptoms of AIED include asymmetric sensorineural hearing loss accompanied by vertigo, aural fullness, and tinnitus. AIED is divided into primary and secondary types. Research has been conducted using animal models of rheumatoid arthritis (RA), a cause of secondary AIED. However, current models are insufficient to accurately analyze vestibular function, and the mechanism underlying the onset of AIED has not yet been fully elucidated. Elucidation of the mechanism of AIED onset is urgently needed to develop effective treatments. In the present study, we analyzed the pathogenesis of vertigo in autoimmune diseases using a mouse model of type II collagen-induced RA. Auditory brain stem response analysis demonstrated that the RA mouse models exhibited hearing loss, which is the primary symptom of AIED. In addition, our vestibulo-oculomotor reflex analysis, which is an excellent vestibular function test, accurately captured vertigo symptoms in the RA mouse models. Moreover, our results revealed that the cause of hearing loss and vestibular dysfunction was not endolymphatic hydrops, but rather structural destruction of the organ of Corti and the lateral semicircular canal ampulla due to an autoimmune reaction against type II collagen. Overall, we were able to establish a mouse model of AIED without endolymphatic hydrops. Our findings will help elucidate the mechanisms of hearing loss and vertigo associated with AIED and facilitate the development of new therapeutic methods.

Temporal bone marrow of the rat and its connections to the inner ear

Calvarial bone marrow has been found to be central in the brain immune response, being connected to the dura through channels which allow leukocyte trafficking. Temporal bone marrow is thought to play important roles in relation to the inner ear, but is still largely uncharacterized, given this bone complex anatomy. We characterized the geometry and connectivity of rat temporal bone marrow using lightsheet imaging of cleared samples and microCT. Bone marrow was identified in cleared tissue by cellular content (and in particular by the presence of megakaryocytes); since air-filled cavities are absent in rodents, marrow clusters could be recognized in microCT scans by their geometry. In cleared petrosal bone, autofluorescence allowed delineation of the otic capsule layers. Within the endochondral layer, bone marrow was observed in association to the cochlear base and vestibule, and to the cochlear apex. Cochlear apex endochondral marrow (CAEM) was a separated cluster from the remaining endochondral marrow, which was therefore defined as "vestibular endochondral marrow" (VEM). A much larger marrow island (petrosal non-endochondral marrow, PNEM) extended outside the otic capsule surrounding semicircular canal arms. PNEM was mainly connected to the dura, through bone channels similar to those of calvarial bone, and only a few channels were directed toward the canal periosteum. On the contrary, endochondral bone marrow was well connected to the labyrinth through vascular loops (directed to the spiral ligament for CAEM and to the bony labyrinth periosteum for VEM), and to dural sinuses. In addition, CAEM was also connected to the tensor tympani fossa of the middle ear and VEM to the endolymphatic sac. Endochondral marrow was made up of small lobules connected to each other and to other structures by channels lined by elongated macrophages, whereas PNEM displayed larger lobules connected by channels with a sparse macrophage population. Our data suggest that the rat inner ear is surrounded by bone marrow at the junctions with middle ear and brain, most likely with "customs" role, restricting pathogen spread; a second marrow network with different structural features is found within the endochondral bone layer of the otic capsule and may play different functional roles.

Cochlear implantation in systemic autoimmune disease

PURPOSE OF REVIEW

Autoimmune inner ear disease (AIED) is a rare, but likely underrecognized cause of hearing loss. However, hearing loss is common in systemic autoimmune disease and it is important for the clinician to be familiar with the spectrum of disease. In this article, we will review the developments in diagnosis and management of AIED, with a focus on the outcomes and potential pitfalls of cochlear implantation.

RECENT FINDINGS

Hearing loss in AIED tends to be progressive and bilateral, but up to 40% can present as sudden hearing loss and one-third can present unilaterally. HSP-70 serology may help with diagnosis and may predict steroid response. Cochlear implantation provides excellent hearing and quality of life outcomes in patients deafened by AIED. Intracochlear fibrosis/ossification is found intraoperatively in the majority (54%) of patients undergoing cochlear implantation. A large percentage (32%) of patients has fluctuating impedances postimplantation, which may interfere with implant performance and mapping.

SUMMARY

Diagnosis of AIED is largely clinical, and a strong index of suspicion is required. Multidisciplinary care is crucial for optimal management. Cochlear implant outcomes are generally excellent, but the clinician needs to be cognizant of the pitfalls of encountering intracochlear fibrosis intraoperatively and likelihood of implant performance fluctuation related to ongoing inflammation in the cochlea.

Human Inner Ear Immune Activity: A Super-Resolution Immunohistochemistry Study

Background: Like the brain, the human inner ear was long thought to be devoid of immune activity. Only the endolymphatic sac (ES) was known to be endowed with white blood cells that could process antigens and serve as an immunologic defense organ for the entire inner ear. Unexpectedly, the cochlear and vestibular organs, including the eighth cranial nerve, were recently shown to contain macrophages whose functions and implication in ear disease are somewhat undefined. Here, we review recent inner ear findings in man and extend the analyses to the vestibular nerve using super-resolution structured illumination microscopy (SR-SIM).

Materials and Methods: Human ESs and cochleae were collected during surgery to treat patients with vestibular schwannoma and life-threatening petro-clival meningioma compressing the brainstem. The ESs and cochleae were placed in fixative, decalcified, and rapidly frozen and cryostat sectioned. Antibodies against ionized calcium-binding adaptor molecule 1-expressing cells (IBA1 cells), laminin β2 and type IV collagen TUJ1, cytokine fractalkine (CX3CL1), toll-like receptor 4 (TLR4), CD68, CD11b, CD4, CD8, the major histocompatibility complex type II (MHCII), and the microglial marker TEME119 were used.

Results: IBA1-positive cells were present in the ESs, the cochlea, central and peripheral axons of the cochlear nerve, and the vestibular nerve trunk. IBA1 cells were found in the cochlear lateral wall, spiral limbus, and spiral ganglion. Notable variants of IBA1 cells adhered to neurons with “synapse-like” specializations and cytoplasmic projections. Slender IBA1 cells occasionally protracted into the basal lamina of the Schwann cells and had intimate contact with surrounding axons.

Discussion: The human eighth nerve may be under the control of a well-developed macrophage cell system. A small number of CD4+ and CD8+ cells were found in the ES and occasionally in the cochlea, mostly located in the peripheral region of Rosenthal's canal. A neuro-immunologic axis may exist in the human inner ear that could play a role in the protection of the auditory nerve. The implication of the macrophage system during disease, surgical interventions, and cell-based transplantation should be further explored.

The Human Endolymphatic Sac and Inner Ear Immunity: Macrophage Interaction and Molecular Expression

Background: The endolymphatic sac (ES) is endowed with a multitude of white blood cells that may trap and process antigens that reach the inner ear from nearby infection-prone areas, it thus serves as an immunologic defense organ. The human ES, and unexpectedly the rest of the inner ear, has been recently shown to contain numerous resident macrophages. In this paper, we describe ES macrophages using super-resolution structured fluorescence microscopy (SR-SIM) and speculate on these macrophages' roles in human inner ear defense. Material and Methods: After ethical permission was obtained, human vestibular aqueducts were collected during trans-labyrinthine surgery for acoustic neuroma removal. Tissues were placed in fixative before being decalcified, rapidly frozen, and cryostat sectioned. Antibodies against IBA1, cytokine fractalkine (CX3CL1), toll-like receptor 4 (TLR4), cluster of differentiation (CD)68, CD11b, CD4, CD8, and the major histocompatibility complex type II (MHCII) were used for immunohistochemistry. Results: A large number of IBA1-positive cells with different morphologies were found to reside in the ES; the cells populated surrounding connective tissue and the epithelium. Macrophages interacted with other cells, showed migrant behavior, and expressed immune cell markers, all of which suggest their active role in the innate and adaptive inner ear defense and tolerance. Discussion: High-resolution immunohistochemistry shows that antigens reaching the ear may be trapped and processed by an immune cell machinery located in the ES. Thereby inflammatory activity may be evaded near the vulnerable inner ear sensory structures. We speculate on the immune defensive link between the ES and the rest of the inner ear.

The Role of Autoimmunity in the Pathogenesis of Sudden Sensorineural Hearing Loss

Sudden sensorineural hearing loss (SSHL) is a clinically common acute symptom in otolaryngology. Although the incidence of SSHL has increased around the world in recent years, the etiology of the disease is still unclear. It has been reported that infections, ototoxic drugs, membrane labyrinth rupture, carcinomas, circulatory system diseases, autoimmune diseases, brain lesions, mental diseases, congenital or inherited diseases, and so on, are all risk factors for SSHL. Here, we discuss the autoimmune mechanisms behind SSHL, which might be induced by type II–IV allergic reactions. We also introduce the main immunosuppressive medications that have been used to treat SSHL, which will help us to identify potential targets for immune therapy.

Current understanding of the pathogenesis of autoimmune inner ear disease: a review

BACKGROUND

Autoimmune inner ear disease (AIED) is a poorly understood form of sensorineural hearing loss that causes bilateral, asymmetric, progressive hearing loss, sometimes with vestibular symptoms, often associated with a systemic autoimmune disease, which is noteworthy as the only sensorineural loss responsive to medical therapy. Despite much research interest of the past 25 years, its aetiopathogenesis is still unproven.

OBJECTIVE OF REVIEW

To succinctly consolidate research and opinion regarding the pathogenesis of autoimmune inner ear disease, in ongoing efforts to elucidate the molecular and intracellular pathways that lead to inner ear damage, which may identify new targets for pharmacotherapy.

TYPE OF REVIEW

Systematic review

SEARCH STRATEGY

PubMed/MEDLINE search using key terms to identify articles published between January 1980 and Apr 2014. Additionally, any landmark works discussed in this body of literature were obtained and relevant information extracted as necessary.

EVALUATION METHOD

Inclusion criterion was any information from animal or human studies with information relevant to possible aetiopathogenesis of AIED. Studies that focused on diagnosis, ameliorating symptoms or treatment, without specific information relevant to mechanisms of immune-mediated injury were excluded from this work. Articles meeting the inclusion criteria were digested and summarised.

RESULTS

A proposed pathogenic mechanism of AIED involves inflammation and immune-mediated attack of specific inner ear structures, leading to an excessive Th1 immune response with vascular changes and tissue damage in the cochlea. Studies have identified self-reactive T cells and immunoglobulins, and have variously implicated immune-complex deposition, microthrombosis and electrochemical disturbances causing impaired neurosignalling in the pathogenesis of AIED. Research has also demonstrated abnormalities in the cytokine milieu in subjects with AIED, which may prove a target for therapy in the future.

CONCLUSION

Ongoing research is needed to further elucidate the aetiopathogenesis of AIED and discern between various mechanisms of tissue injury. Large-cohort clinical studies employing IL-1 receptor blockade are warranted to determine its potential for future therapy.

Measles Virus Prevalence in Otosclerotic Stapes Footplate Samples

HYPOTHESIS

The cause of otosclerosis is still unknown. Persistent measles virus infection of the otic capsule is supposed to be one of the etiologic factors in otosclerosis. Chronic viral antigen expression on the surface of infected cells can induce a secondary autoimmune reaction against the otic capsule.

BACKGROUND

In the past 15 years, some reports proposed the possible etiologic role of measles virus in otosclerosis. The presence of measles virus was shown in otosclerotic patients by reverse-transcriptase polymerase chain reaction amplification of the viral RNA, detecting the viral proteins by immunohistochemistry and detecting antimeasles immunoglobulin G in the perilymph samples. Many concerns were elicited by these results.

METHODS

Nucleic acid was extracted from pulverized, frozen stapes footplate samples of otosclerotic patients. Measles virus RNA was amplified by reverse-transcriptase polymerase chain reaction: reverse transcription and the first round polymerase chain reaction amplification was performed by heat stable recombinant Thermus thermophilus polymerase, whereas in the nested round, polymerase chain reaction Taq-polymerase was used. Measles virus nucleoprotein RNA-specific oligonucleotide primers were used in these reactions. An Edmonston-type measles virus served as a positive control and cortical bone fragments or stapes superstructures served as negative controls.

RESULTS

Among 34 otosclerotic patients, 20 stapes footplate samples contained measles virus RNA. Measles virus RNA was not detected in other bone specimens of the patients.

CONCLUSION

The etiologic role of measles virus in the pathogenesis of otosclerosis should be considered. The 14 negative samples may be genetically determined otosclerotic cases.

Autoimmune sensorineural hearing loss

Autoimmune sensorineural hearing loss has been increasingly recognized as a clinical entity since its description by McCabe in 1979. Recognition and proper management of this condition is important, as it is one of the very few forms of sensorineural hearing loss that can be successfully treated by medical therapy. Recent studies have provided experimental evidence to suggest that immune processes can cause sensorineural hearing loss in animals and humans. However, antigenic targets within the inner ear are diverse and as a result conclusive evidence for specific autoimmune damage to the inner ear has been elusive. This review focuses on the recent progress in understanding of the aetio-pathogenesis of autoimmune hearing loss along with a description of the various clinical conditions in which they occur. Recent advances in the laboratory diagnosis and management of this interesting condition are also described.

Cell proliferation in the endolymphatic sac in situ after the rat Waldeyer ring equivalent immunostimulation

OBJECTIVES/HYPOTHESIS

It has been recognized that immunological mechanisms could be involved in the pathogenesis of different inner ear disorders, such as progressive sensorineural hearing loss, Meniere's disease, and even sudden deafness. The endolymphatic sac acts as an immune control organ for the inner ear and has been considered as an effector site of the mucosa-associated lymphoid tissue. The purpose of the study was to determine the potentially immunological relationship between endolymphatic sac and Waldeyer ring equivalent, one of the most important affector organs in mucosa-associated lymphoid tissue.

STUDY DESIGN

Animal model.

METHODS

Thirty-six rats were employed. Two animals were killed for histological observation of Waldeyer ring equivalent, and another 34 animals were randomly divided into experimental and control groups and received bilateral intranasal immunizations with keyhole limpet hemocyanin or Freund adjuvant, respectively. The ears of immunized animals and control animals were examined for keyhole limpet hemocyanin-positive memory cells and immunoglobulin G-positive plasma cells with the technique of immunohistochemical analysis. The histopathological changes and cell proliferation in those ears were also assessed.

RESULTS

There were paired and organized lymphoid tissues in the lateral wall of the first choana in the rat. Keyhole limpet hemocyanin-positive lymphocytes appeared within the endolymphatic sac at 3 days after the first anti-genetic stimulus of the Waldeyer ring equivalent. Endolymphatic hydrops in the cochlea, elevated amounts of immunocompetent cells, and increased activity of cell proliferation within the endolymphatic sac were also considered after four intranasal injections of keyhole limpet hemocyanin.

CONCLUSION

Presumably, endolymphatic sac is supplied with immunocompetent cells from Waldeyer ring equivalent and has an ability of co-reaction with Waldeyer ring equivalent.

Ultrastructural analysis of [3H]thymidine-labeled cells in the rat utricular macula

Ototoxic drugs stimulate cell proliferation in adult rat vestibular sensory epithelia, as does the infusion of transforming growth factor alpha (TGFalpha) plus insulin. We sought to determine whether new hair cells can be regenerated by means of a mitotic pathway. Previously, studies have shown that the nuclei of some newly generated cells are located in the lumenal half of the sensory epithelium, suggesting that some may be newly generated sensory hair cells. The aim of this study was to examine the ultrastructural characteristics of newly proliferated cells after TGFalpha stimulation and/or aminoglycoside damage in the utricular sensory epithelium of the adult rat. The cell proliferation marker tritiated-thymidine was infused, with or without TGFalpha plus insulin, into the inner ears of normal or aminoglycoside-damaged rats for 3 or 7 days by means of osmotic pumps. Autoradiographic techniques and light microscopy were used to identify cells synthesizing DNA. Sections with labeled cells were re-embedded, processed for transmission electron microscopy, and the ultrastructural characteristics of the labeled cells were examined. The following five classes of tritiated-thymidine labeled cells were identified in the sensory epithelium: (1) labeled cells with synaptic specializations that appeared to be newly generated hair cells, (2) labeled supporting cells, (3) labeled leukocytes, (4) labeled cells that we have classified as "active cells" in that they are relatively nondescript but contain massive numbers of polyribosomes, and (5) labeled degenerating hair cells. These findings suggest that new hair cells can be generated in situ by means of a mitotic mechanism in the vestibular sensory epithelium of adult mammals.

[Immuno-pathogenesis in Meniere's disease]

Since the report of Duke in which an allergic etiology was considered to be the cause of Meniere's disease, the hypothesis that a certain type of Meniere's disease is generated through immuno-pathological mechanisms has been advocated for 70 years. During this period, another entity of immune-mediated inner ear disorders, i. e., autoimmune inner ear disease was introduced. Fundamental immunological phenomena of the inner ear have been rapidly elucidated since 1980. The endolymphatic sac is the only site which contains immuno-competent cells within the inner ear. The inner ear is capable of mounting active immune responses when appropriately stimulated and the endolymphatic sac plays an integral function for inner ear immune response. Actually, many reports have been published that link immunity and Meniere's disease with a variety of proposed immune-related etiologies from autoimmunity to non-autoimmunity. It is suggested that immune injury to the endolymphatic sac plays an important role in the pathogenesis of Meniere's disease. These functional and morphological circumstances strongly suggest that an immunological etiology of Meniere's disease is not theoretically unfounded.

Immune-mediated hearing loss: basic mechanisms and options for therapy

Immune responses are an important component of the defense of the inner ear against infection. However, immunity appears to be restricted in the labyrinth, as the inflammation associated with immune responses can damage the delicate cellular structures that mediate hearing and balance. When immunoregulation is compromised, either experimentally or through disease, immune-mediated inner ear damage and hearing loss can result. Because there are few resident leukocytes within the labyrinth, immunity and inflammation are mediated primarily by cells that enter the inner ear following the activation of post-capillary venules, which in the cochlea are the spiral modiolar veins. Activated lymphocytes are an important component of the infiltrating leukocytes, and their interactions with antigen mediate inner ear immunity. While evidence of autoimmunity specific to the inner ear is incomplete, an autoimmune origin is often suspected in idiopathic, bilateral, rapidly progressive hearing loss. Systemic immunosuppressive drugs can be effective in reversing such hearing loss, although at the cost of occasionally severe side-effects. Experimental evidence suggests that local therapy may be effective in treating this condition, if it were to target the infiltration of leukocytes into the labyrinth.

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.

Constitutive expression of GlyCAM-1 core protein in the rat cochlea

Glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1) is a mucin-like glycoprotein previously identified on high endothelial venules (HEV) of lymph nodes and also in lactating mammary glands. A specifically glycosilated form of GlyCAM-1 on HEV has been shown to be a ligand for a leukocyte L-selectin, which plays an important role in leukocyte rolling along the inflamed endothelium. Here we report that GlyCAM-1 is also expressed in the cochlea. Immunohistochemistry revealed the lateral wall of the cochlea, tectorial membrane, modiolus, organ of corti, and spiral modiolar vein (SMV) to be strongly stained with polyclonal anti-GlyCAM-1 antibody. Moreover, RT-PCR of the cochlear tissue by the use of specific oligonucleotide primers for rat GlyCAM-1 generated a 378 bp product which was then verified by nucleotide sequencing to represent GlyCAM-1. Electron microscopic investigation revealed the presence of GlyCAM-1 over the entire lumenal surface of the vessels, and the basolateral infoldings in stria vascularis. However, soluble L-selectin or mAb MECA-79 which recognizes a carbohydrate epitope on functional L-selectin ligands bound only to the spiral ligament, tectorial membrane and modiolus. These observations suggest that GlyCAM-1 expressed in the cochlear region is heterogenous in terms of its glycosylation.

T cells infiltrating from the systemic circulation proliferate in the endolymphatic sac

It has been reported that autoimmune mechanisms are involved in the development of inner ear disorders such as Meniere's disease and steroid-responsive sensorineural hearing loss. In the present study, using an animal model for graft-versus-host disease, we investigated the immune regulatory mechanism in the endolymphatic sac and demonstrated that donor T cells injected into the systemic circulation of recipients infiltrate and proliferate in the perisaccular region. These findings suggest that immunocompetent cells are supplied from the systemic circulation through blood-labyrinth and blood-endolymph barriers into the endolymphatic sac, and that the endolymphatic sac allows these cells to proliferate locally as a local immune defense. It therefore seems likely that the endolymphatic sac plays a crucial role in not only graft-versus-host disease but also autoimmune inner ear disorders.

Macrophage and microglia-like cells in the avian inner ear

Recent studies suggest that macrophages may influence early stages of the process of hair cell regeneration in lateral line neuromasts; numbers of macrophages were observed to increase prior to increases in hair cell progenitor proliferation, and macrophages have the potential to secrete mitogenic growth factors. We examined whether increases in the number of leukocytes present in the in vivo avian inner ear precede the proliferation of hair cell precursors following aminoglycoside insult. Bromodeoxyuridine (BrdU) immunohistochemistry was used to identify proliferating cells in chicken auditory and vestibular sensory receptor epithelia. LT40, an antibody to the avian homologue of common leukocyte antigen CD45, was used to label leukocytes within the receptor epithelia. Macrophages and, surprisingly, microglia-like cells are present in normal auditory and vestibular sensory epithelia. After hair cell loss caused by treatment with aminoglycosides, numbers of macrophage and microglia-like cells increase in the sensory epithelium. The increase in macrophage and microglia-like cell numbers precedes a significant increase in sensory epithelial cell proliferation. The results suggest that macrophage and microglia-like cells may play a role in releasing early signals for cell cycle progression in damaged inner ear sensory epithelium.

The endolymphatic sac receives antigenetic information from the organs of the mucosa-associated lymphatic system

The endolymphatic sac holds the entire arrangement of immunocompetent cells and functions as an immunological potent control organ for the inner ear. The evidence of secretory immunoglobulin A and other features of lymphocyte subtypes characterizes the endolymphatic sac as an organ of the mucosa-associated lymphatic system (MALT). In this system a permanent recirculation of sensitized memory lymphocytes from one organ to the other has been demonstrated experimentally as serving to dispose memory lymphocytes after renewed antigenetic stimulus. The aim of this study was to prove the possible recirculation of antigen-sensitized lymphocytes to the endolymphatic sac after antigenic stimulus of another part of the mucosa-associated lymphatic system. The results are evidence that the endolymphatic sac is provided with immunocompetent cells which derive from the lymphatic tissue of the nasopharynx. While the origin of immunocompetent cells in the endolymphatic sac still remains uncertain, this study underlines the role of lympho-epithelial tissue of the nasopharynx as a possible cell source for the endolymphatic sac. The results might explain the altered or disturbed function of the endolymphatic sac as a possible cause of certain inner ear diseases.

Evidence of cellular supplies to the endolymphatic sac from the systemic circulation

Donor T lymphocytes injected into the host systemic circulation were observed to infiltrate into the host endolymphatic sac in mice. These findings suggest that the endolymphatic sac, a major immune organ in the inner ear, is supplied with immunocompetent cells from the systemic circulation. This concept is consistent with clinical reports that inner ear disorders accompany certain systemic autoimmune diseases. Bone marrow transplantation to replace autoreactive immunocompetent cells with normal cells should be considered as a potential therapy for inner ear autoimmune diseases and an alternative to conventional treatments.

Cell proliferation in the endolymphatic sac in situ after inner ear immunostimulation

Cell proliferation in the endolymphatic sac (ES) after immunostimulation was assessed immunohistochemically. Guinea pigs were employed as experimental animals and keyhole limpet hemocyanin was used as the antigen. After i.p. injection of 5-bromo-2'-deoxyuridine (BrdUrd), the BrdUrd+ cells were counted to assess the number of proliferating cells. In the secondary immune reaction of the ES, the IgG+ cell count in the perisaccular region was markedly increased on days 7-14. An increased number of BrdUrd+ cells was detected, peaking on day 3, and the localization of these cells in the ES was similar to that of the IgG+ cells. This suggests that some BrdUrd+ cells may differentiate into IgG- cells within the ES.

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.

Adoptive transfer of an autoimmunological labyrinthitis in the guinea pig; animal model for a sympathetic cochleolabyrinthitis

Sensorineural hearing loss is a common problem in the otolaryngologist's practice, with autoimmune disease of the inner ear being one possible cause. The restoration of auditory function in some patients following immunosuppressive therapy has created a desire to define and understand this disease better. Because of the lack of a well defined detection method to identify this entity clinically, this study was undertaken in order to provide an animal model for autoimmune disease of the inner ear. Previous studies with guinea pigs have demonstrated that sensitized lymphocytes from the systemic circulation migrate to the labyrinth during an immune response in the inner ear. The aim of this study was to prove the capacity of sensitized lymphocytes to transfer autoimmune inner ear disease, and to describe the resulting morphological and physiological changes. Therefore two groups of sensitized lymphocytes partially labelled with a radioactive marker from inbred guinea pigs with an immune response within the inner ear were injected into the bloodstream of naive recipient animals. Most of the labelled cells were observed in the apical turn of the experimental cochlea, while only few cells were detectable in the control cochleas. In addition, the absence of otoacoustic emissions and the loss of outer hair cells observed by electron microscopy were interpreted as a sign of damage caused by the provoked immunopathologic mechanism. The results are discussed as a possible model for a sympathetic cochleolabyrinthitis.

Detection of cochlear dysfunction by the measurement of transiently evoked otoacoustic emissions in guinea pigs with autoimmune-induced labyrinthitis

For the evaluation of functional inner ear lesions caused by an autoimmune-induced labyrinthitis, transiently evoked otoacoustic emissions (TEOAEs) were detected in guinea pigs before and after transfer of sensitized lymphocytes from animals suffering from a labyrinthitis induced by the foreign protein keyhole limpet hemocyanin (KLH). Initially TEOAEs were detectable from 47 of 62 ears (76%) in healthy guinea pigs. These animals then were used as recipients for sensitized lymphocytes from donors exclusively. Three months after cell transfer the incidence of TEOAEs was reduced to 48% in animals receiving lymphocytes from donors sensitized with KLH intradermally and intracochlearly. In recipients of lymphocytes from donors sensitized only intradermally and in untreated animals no significant alteration of the TEOAE incidence was found. These findings showed strong correlation with those from scanning electron microscopy of the organ of Corti, indicating that the measurement of TEOAE is a useful, time-saving tool for the detection of cochlear dysfunction caused by sensitized lymphocytes in experimental animal. The present findings also show that the migration of sensitized lymphocytes actually leads to functional lesions in the cochlea.