Spontaneous remission in experimental autoimmune labyrinthitis

Controversies and Criticisms on Designs for Experimental Autoimmune Labyrinthitis

Although immune-mediated inner ear disease was reported around 25 years ago, numerous attempts to identify the inner ear antigens have been performed. Experimental animal models have been used to study the immune mechanisms involved in hearing loss and to develop new therapies. Because animal models of autoimmune labyrinthitis have been developed by means of different antigens, we cannot yet show a valid immunopathologic explanation. A critical analysis of the more relevant experimental models employed has been performed in order to validate the methodology. Comparison between these models and animals with spontaneous systemic autoimmune disease has raised more questions concerning the pathophysiology of autoimmune hearing loss. A new pathogenetic theory is suggested, involving the supporting cells of the organ of Corti.

High dose combination pertussis toxin induces autoimmune inner ear disease in Sprague-Dawley rats

CONCLUSION

A better animal model of autoimmune inner ear disease (AIED) in Sprague-Dawley rats has been developed by combination with high dose of pertussis toxin. This study also indicated that inner ear-specific antigens can be involved in autoimmune reactions. Cell-mediated immune injury can play an important role in the induction of AIED, at least in the earlier stage.

OBJECTIVES

The purpose of this study was to develop a more suitable rat model that demonstrated closer resemblance to the pathophysiological process in AIED.

METHODS

Ninety-six female Sprague-Dawley rats were divided into four groups. They were subcutaneously immunized with crude inner ear antigen/complete Freund's adjuvant (CIEAg/CFA), or intraperitoneal injection of 500 ng pertussis toxin (PT), or injection of CIEAg/CFA+PT, or phosphate-buffered saline (PBS) alone. The auditory function, histopathology of the inner ear, and autoantibodies were examined.

RESULTS

Significant differences in the time course of auditory brainstem response (ABR) threshold and mean score of cellular infiltration were demonstrated in the CIEAg/CFA+PT group of animals. Missing hair cells, degeneration of the spiral ganglion cells, endolymphatic hydrops, and autoantibodies were all noted after immunization. There were no significant differences in ABR threshold or histopathology in any other group of animals.

Immunosuppressive therapy for autoimmune inner ear disease

Autoimmune inner ear disease (AIED) is a rare disease that is diagnosed after clinical suspicion and response to corticosteroids. AIED manifests as progressive, bilateral, although often asynchronous, sensorineural hearing loss and can be associated with vestibular symptoms. Since its description as a defined disease entity in 1979, the initial mainstay of treatment remains high-dose corticosteroids. Several animal models have been developed to assist in determining efficacy of immunosuppression in AIED, and several clinical studies have also investigated the role of both steroid and steroid-sparing treatments. Here we discuss the basic science and clinical research surrounding the history of immunosuppressive therapy in AIED.

Murine autoimmune hearing loss mediated by CD4+ T cells specific for β-tubulin

Autoimmune inner ear disease is described as progressive, bilateral although asymmetric, sensorineural hearing loss and can be improved by immunosuppressive therapy. We showed that the inner ear autoantigen β-tubulin is capable of inducing experimental autoimmune hearing loss (EAHL) in mice. Immunization of BALB/c mice with β-tubulin resulted in hair cell loss and hearing loss, effects that were not seen in animals immunized with control peptide. Moreover, the EAHL model showed that β-tubulin responsiveness involved CD4(+) T cells producing IFN-γ, and T cell mediation of EAHL was determined by significantly increased auditory brainstem response after adoptive transfer of β-tubulin-activated CD4(+) T cells into naive BALB/c recipients. The potential mechanisms responsible for the observed pathology of EAHL can be attributed to decreased frequency and impaired suppressive function of regulatory T cells. Our study suggests that EAHL may be a T cell-mediated organ-specific autoimmune disorder of the inner ear.

Impaired CD4+CD25+ regulatory T cell activity in the peripheral blood of patients with autoimmune sensorineural hearing loss

CD4+CD25+ regulatory T cells exert an immune regulatory function and thus play an important role in the control of self-reactivity in the pathogenesis of autoimmune inflammatory conditions. The aim of the study presented here is to perform a quantitative and functional analyses of these cells in patients with autoimmune sensorineural hearing loss (ASNHL). T cell subsets (CD4+CD25+, CD4+CD25(high), CD4+, and CD8+) from the peripheral blood of 17 patients with ASNHL, 16 patients with noise induced hearing loss (NHL), and 100 normal controls were analyzed by flow cytometry. The CD4/CD8 ratio was also analyzed. In addition, the suppressive capability of CD4+CD25+ T cells was tested in vitro by measuring their ability to suppress the proliferation and IFN-gamma secretion of CD4+CD25- T cells. No significant difference was found in the T cell subsets of ASNHL patients compared to normal controls or NHL patients, except that the proportion of CD4+ T cells was elevated in ASNHL patients. However, we did observe defective regulatory function of CD4+CD25+ T cells in patients with ASNHL. Our data supported the idea that CD4+CD25+ regulatory T cells played an immunosuppressive function in the periphery. The impaired suppressive activity of these cells may be an important factor in the pathogenesis of ASNHL.

Surdités brusques idiopathiques

Idiopathic Sudden Sensorineural Hearing Loss (ISSHL) remains one of the major unsolved otologic emergencies. It is characterized by the onset of an unilateral sensorineural hearing loss developing within 24 hours, and averaging on pure tone audiogram at least 30 dB HL for three subsequent octave steps, with no marked vestibular symptoms and no identifiable cause. ISSHL is a syndrome covering several heterogeneous entities resulting from different pathogenetic mechanisms. At this time, the audiogram is the unique tool which may help clinicians to identify these entities and provide a classification based on 5 types of hearing loss. Numerous experimental and clinical studies have investigated the mechanisms by which infectious, ischemic, mechanic or immunologic insults may induce cochlear dysfunction. However, extrapolation to humans and rationale therapeutic approaches to ISSHL remain uncertain. SSHL being a diagnosis of exclusion, retrocochlear and neurologic etiologies should be eliminated. No argument allows to consider ISSHL a therapeutic emergency. More precisely, the experimental data presently available on cochlear physiology suggests that a treatment could have some chance to be effective if undertaken within minutes following the onset of ISSHL, a condition never encountered in daily practice. Conversely, it is not justifiable to impute the absence of hearing recovery to a delay in therapy. The various therapeutic strategies currently recommended are highly empirical and should be questionned in terms of cost-effectiveness, the most common being high-dose corticosteroids. New investigation tests are required for improving our approach to ISSHL.

Murine autoimmune hearing loss mediated by CD4+ T cells specific for inner ear peptides

Autoimmune sensorineural hearing loss (ASNHL) is characterized typically by bilateral, rapidly progressive hearing loss that responds therapeutically to corticosteroid treatment. Despite its name, data implicating autoimmunity in the etiopathogenesis of ASNHL have been limited, and targeted self-antigens have not been identified. In the current study we show that the inner ear-specific proteins cochlin and beta-tectorin are capable of targeting experimental autoimmune hearing loss (EAHL) in mice. Five weeks after immunization of SWXJ mice with either Coch 131-150 or beta-tectorin 71-90, auditory brainstem responses (ABR) showed significant hearing loss at all frequencies tested. Flow cytometry analysis showed that each peptide selectively activated CD4(+) T cells with a proinflammatory Th1-like phenotype. T cell mediation of EAHL was determined by showing significantly increased ABR thresholds 6 weeks after adoptive transfer of peptide-activated CD4(+) T cells into naive SWXJ recipients. Immunocytochemical analysis showed that leukocytic infiltration of inner ear tissues coincided with onset of hearing loss. Our study provides a contemporary mouse model for clarifying our understanding of ASNHL and facilitating the development of novel effective treatments for this clinical entity. Moreover, our data provide experimental confirmation that ASNHL may be a T cell-mediated organ-specific autoimmune disorder of the inner ear.

Autoimmune sensorineural hearing loss: an immunologic perspective

Autoimmune sensorineural hearing loss (ASNHL) typically produces a bilateral rapidly progressive loss of hearing that may occur suddenly. The diagnosis is made by excluding ototoxicity, systemic disease, and other factors that mimic ASNHL and by showing a therapeutic response to corticosteroid treatment. Although autoantibodies and autoreactive T cells have been implicated in the etiopathogenesis of ASNHL, several central issues remain unresolved, including the relative prominence of B cell or T cell autoimmunity in the initiation and progression of ASNHL, the identity of the putative inner ear self-antigen(s) that target ASNHL, and the development and application of immunosuppressive therapies for preventing the progressive hearing loss which may be profound and require cochlear implantation. In this review, we will examine the seminal human and animal studies that have led to our current views regarding the autoimmune etiopathogenesis of ASNHL. In addition, we will address the need for developing an inner ear-specific mouse model for ASNHL that may define the stages leading to the development of ASNHL and may also provide new diagnostic markers and help develop novel and effective treatments for preventing progressive hearing loss in ASNHL.

Th1: mediator lymphocytes in experimental autoimmune labyrinthitis

A previous study on experimental autoimmune labyrinthitis (EAL) consistently demonstrated transient infiltration of lymphocytes only into the inner ear of mice. To clarify the profile of lymphocytes in the initiation of EAL, the present study investigated cell surface antigens, as well as cytokines, from Day 4 to Day 35, using immunohistochemical techniques. Many CD4+ cells mainly infiltrated the endolymphatic sac as early as Day 4 and gradually spread to the rest of the inner ear. Infiltration peaked on Day 12 and persisted in most animals until Day 35, although the number of cells gradually decreased. In contrast, very few CD8+ cells were found to have appeared in the inner ear of all animals on Day 10, and the number of cells rapidly decreased. Many cells positive for IFN-gamma and IL-2 were identified in the endolymphatic sac on Day 4. These results suggest that helper T1 lymphocytes, rather than cytotoxic T lymphocytes, may play a central role in the initiation of EAL.

Experimental autoimmune inner ear disease: an electrocochleographic and histophysiologic study

Systemic immunization with swine inner ear antigens in complete Freund's adjuvant induces functional disturbances in the cochlea. Morphometric data indicate that an endolymphatic hydrops develops within 2 weeks. It diminishes 6 weeks after immunization. A progressive decrease in the compound action potential amplitude is observed from 2 to 6 weeks after immunization. Enhancement of the amplitude of the summating potential is present without a clear overall correlation to the presence of endolymphatic hydrops. The amplitude of the cochlear microphonics shows no significant changes after immunization. Western blot analysis of the sera performed 2 and 6 weeks after immunization shows enhanced reactivity at 68, 50, 45, and 27 kd molecular weights, as compared to controls. The same spectrum of cross-reacting antibodies is believed to be instrumental in immune-mediated sensorineural hearing loss in patients. Apparently, cross-reacting antibodies and released mediators disturb cochlear homeostasis, resulting in the observed changes in the electrophysiological responses. However, these changes are not clearly related to structural changes at the light and electron microscopic levels.

Experimental autoimmune labyrinthitis induced by cell-mediated immune reaction

This study was designed to establish an experimental cell-mediated autoimmune labyrinthitis model in C57BL/6 mice, which could exhibit high reproducibility and be adopted for precise immunological analysis. Inner ear antigen (IEA) was prepared from bovine membranous labyrinth. Following pretreatment with cyclophosphamide (CP) and primary sensitization with IEA/FCA, many inflammatory cells infiltrated transiently into the perilymphatic and endolymphatic regions of the cochlea, vestibule and the endolymphatic sac, but not into the kidney, lung, brain or liver. This reaction occurred from day 7 and peaked on day 12 in all animals, and then rapidly reduced. This reaction occurred in all experimental mice during day 10 to day 12. The control mice showed no cellular reaction in the inner ear. These results suggest that the inner ear may possess cross-species organ-specific antigen and that a cell-mediated immune reaction may play an important role in the induction of autoimmune labyrinthitis.

Immune-mediated sensorineural hearing loss

A review is given on the way our knowledge of pathways of immune responses inside and in the immediate vicinity of the inner ear has gradually developed over the past two decades. Immune reactivity plays a more important role in the etiopathogenesis and natural course of various inner ear disorders than was thought originally. They comprise certain forms of fluctuating or rapidly progressive sensorineural hearing loss (SNHL) with or without endolymphatic hydrops. Patients may present themselves clinically with symptoms resembling Ménière's disease or even with sudden deafness. Immune-mediated audio-vestibular dysfunctioning is either a separate disease entity or part of a more generalized (auto-) immune process. The various attempts which have been made to develop methods or tests to confirm the diagnosis of immune-mediated SNHL are critically reviewed, including the treatment responses to immunosuppressive therapy. Various animal models are furthermore presented.

Detection of inner ear disease autoantibodies by immunoblotting

To define further the character of autoantibodies against the inner ear in patients with inner ear disease, Autoantibodies in sera from 82 patients with inner ear disease were investigated by immunoblotting. The inner ear antigens were extracted from Hartley guinea pigs. Brain, kidney, lung, heart and liver extracts were also prepared. Antibodies against the inner ear were found in 32 of 82 (39%) patients with inner ear disease. These sera reacted with the 30 and 58 kDa bands of the inner ear extracts. The 30 kDa band was detected in sera from patients with various inner ear diseases, while the 58 kDa band reacted with sera of patients with idiopathic progressive sensorineural hearing loss. Only two of the 52 normal control sera had a very faint band at 30 kDa. Sixteen of 32 positive sera were then used to probe Western blots of the brain, kidney, lung heart and liver extracts. The 58 kDa band was also found in the protein extracts of the brain, the lung, and the liver. On the other hand, preliminary purification of the 30 and 58 kDa proteins from the inner ear extracts were achieved by anion exchange chromatography. These results show that antibodies in sera from patients with inner ear disease reacted with at least two polypeptide bands (30 and 58 kDa) of guinea pig inner ear extracts, and the 58 kDa antigenic epitope was not cochlea specific.

The localization and specificity of guinea pig inner ear antigenic epitopes

In this study, we investigated the relative localization of some antigenic epitopes in the inner ear. The inner ear protein antigens were extracted from various parts of the guinea pig inner ear. Brain, kidney, lung, heart and liver extracts were also obtained. We found by SDS-polyacrylamide gel electrophoresis that total inner ear extracts separated into three high concentration polypeptide bands with molecular weights of approximately 30, 42, 58 kd and three low density bands of 20, 25 and 35 kd. The 30 kd band was found mainly in the extract of the spiral ganglion and the acoustic nerve in the modiolus. The 42 and 58 kd bands were detected in the extract of the spiral ligament and the stria vascularis. The Organ of Corti and the basilar membrane extract gave rise to three bands of 30, 42 and 58 kd. Twenty-eight of the 75 sera from patients with inner ear disease reacted with the 30 and 58 kd bands of the inner ear protein extracts by immunoblotting. Sixteen of these 28 positive sera were then used to probe immunoblots of the brain, kidney, lung, heart and liver extracts. The 58 kd band was also found in protein extracts of the brain, the lung and the liver. This study suggests that the 30 kd antigenic epitope may be mainly related to the acoustic nerve and that the 58 kd antigenic epitope is not cochlear specific.

Extraction of inner ear antigens for studies in inner ear autoimmunity

The search for a diagnostic assay in patients with autoimmune inner ear disease has led to the preparation of antigens from the inner ear, a presumed target in this disorder. In order to standardize the antigen preparations currently being used in the Western blot immunoassay, we have examined several distinct extraction procedures that employ well-known solutions and detergents. Results of this investigation clearly show that antigens of interest (68 kd, 33 to 35 kd, and 32 kd) are optimally extracted with a detergent (0.5% sodium dodecyl sulfate) and that bovine serum albumin, a potential contaminant, can be removed in the water-soluble fractions. Purification of inner ear antigens by these methods will lead to more reproducible results in immunoblotting, as well as a greater opportunity to identify the mechanisms involved in autoimmune inner ear disease.