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

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.

Stress Reactivity, Susceptibility to Hypertension, and Differential Expression of Genes in Hypertensive Compared to Normotensive Patients

Although half of hypertensive patients have hypertensive parents, known hypertension-related human loci identified by genome-wide analysis explain only 3% of hypertension heredity. Therefore, mainstream transcriptome profiling of hypertensive subjects addresses differentially expressed genes (DEGs) specific to gender, age, and comorbidities in accordance with predictive preventive personalized participatory medicine treating patients according to their symptoms, individual lifestyle, and genetic background. Within this mainstream paradigm, here, we determined whether, among the known hypertension-related DEGs that we could find, there is any genome-wide hypertension theranostic molecular marker applicable to everyone, everywhere, anytime. Therefore, we sequenced the hippocampal transcriptome of tame and aggressive rats, corresponding to low and high stress reactivity, an increase of which raises hypertensive risk; we identified stress-reactivity-related rat DEGs and compared them with their known homologous hypertension-related animal DEGs. This yielded significant correlations between stress reactivity-related and hypertension-related fold changes (log2 values) of these DEG homologs. We found principal components, PC1 and PC2, corresponding to a half-difference and half-sum of these log2 values. Using the DEGs of hypertensive versus normotensive patients (as the control), we verified the correlations and principal components. This analysis highlighted downregulation of β-protocadherins and hemoglobin as whole-genome hypertension theranostic molecular markers associated with a wide vascular inner diameter and low blood viscosity, respectively.

The immune response after noise damage in the cochlea is characterized by a heterogeneous mix of adaptive and innate immune cells

Cells of the immune system are present in the adult cochlea and respond to damage caused by noise exposure. However, the types of immune cells involved and their locations within the cochlea are unclear. We used flow cytometry and immunostaining to reveal the heterogeneity of the immune cells in the cochlea and validated the presence of immune cell gene expression by analyzing existing single-cell RNA-sequencing (scRNAseq) data. We demonstrate that cell types of both the innate and adaptive immune system are present in the cochlea. In response to noise damage, immune cells increase in number. B, T, NK, and myeloid cells (macrophages and neutrophils) are the predominant immune cells present. Interestingly, immune cells appear to respond to noise damage by infiltrating the organ of Corti. Our studies highlight the need to further understand the role of these immune cells within the cochlea after noise exposure.

Autoimmune inner ear disease patient-associated 28-kDa proinflammatory IL-1β fragment results from caspase-7-mediated cleavage in vitro

Interleukin-1β (IL-1β) is a key proinflammatory cytokine involved in the progression of many autoinflammatory and autoimmune diseases, including autoimmune inner ear disease (AIED). IL-1β inhibition has been shown to result in clinical hearing improvement in a small cohort of corticosteroid-resistant patients with AIED. Canonical processing of pro-IL-1β by caspase-1 generates an active 17-kDa fragment, capable of instigating a proinflammatory microenvironment. However, in response to LPS, PBMCs from patients with AIED uniquely express a 28-kDa IL-1β fragment, as compared with PBMCs from control subjects. We synthesized and compared the biologic activity of the 28-kDa fragment to the 17-kDa IL-1β product and the pro-IL-1 31-kDa protein. The 28-kDa IL-1β fragment induces IL-6, TNF-α, and CCL3 in PBMCs. Uniquely, only caspase-7 treatment showed a dose- and time-dependent increase in 28-kDa band generation. Mass spectrometry confirmed the putative caspase-7 cleavage site of pro-IL-1β, which was used to generate the 28-kDa fragment used for PBMC stimulation studies. Collectively, these results provide insight into the function of a poorly understood, processed 28-kDa form of IL-1β in patients with AIED that is uniquely generated by caspase-7 and is capable of activating further downstream proinflammatory cytokines. Further investigation may provide novel pharmacologic targets for the treatment of this rare disease.

Super-resolution immunohistochemistry study on CD4 and CD8 cells and the relation to macrophages in human cochlea

Recently, the human cochlea has been shown to contain numerous resident macrophages under steady-state. The macrophages accumulate in the stria vascularis, among the auditory nerves, and are also spotted in the human organ of Corti. These macrophages may process antigens reaching the cochlea by invasion of pathogens and insertion of CI electrode. Thus, macrophages execute an innate, and possibly an adaptive immunity. Here, we describe the molecular markers CD4 and CD8 of T cells, macrophage markers MHCII and CD11b, as well as the microglial markers TEME119 and P2Y12, in the human cochlea. Immunohistochemistry and the advantageous super-resolution structured illumination microscopy (SR-SIM) were used in the study. CD4⁺ and CD8⁺ cells were found in the human cochleae. They were seen in the modiolus in a substantial number adjacent to the vessels, in the peripheral region of the Rosenthal's canal, and occasionally in the spiral ligament. While there are a surprisingly large number of macrophages in the stria vascularis as well as between the auditory neurons, CD4⁺ and CD8⁺ cells are hardly seen in these areas, and neither are seen in the organ of Corti. In the modiolus, macrophages, CD4⁺ and CD8⁺ cells appeared often in clusters. Interaction between these different cells was easily observed with SR-SIM, showing closely placed cell bodies, and the processes from macrophages reaching out and touching the lymphocytes. Otherwise the CD4⁺ and CD8⁺ cells in human cochlear tissue are discretely scattered. The possible roles of these immune cells are speculated.

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CD4⁺ and CD8⁺ cells were found in the human cochleae.

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They were seen in the modiolus in a substantial number adjacent to the vessels, in the peripheral region of the Rosenthal's canal, and occasionally in the spiral ligament.

Update on Vertigo in Autoimmune Disorders, from Diagnosis to Treatment

The prevalence of autoimmune diseases has been increasing over the last 20 years. The clinical presentation of this large and heterogeneous group of disorders depends on whether the involvement is organ-specific or non-organ-specific. Dizziness, vertigo, and disequilibrium are common symptoms reported by patients with vestibulocochlear involvement. The association of vertigo and autoimmune diseases has been largely documented, suggesting that autoimmune disorders could be overrepresented in patients with vertigo in comparison to the general population. The aim of this review is to present the recent literature findings in the field of autoimmune-mediated diseases with cochleovestibular involvement, focusing on the clinical presentation, diagnosis, and treatment of immune-mediated inner ear diseases including autoimmune inner ear disease (AIED), Meniere's disease, and bilateral vestibulopathy, as well as of systemic autoimmune diseases with audiovestibular disorders, namely, Behçet's disease, Cogan's syndrome, sarcoidosis, autoimmune thyroid disease, Vogt-Koyanagi-Harada syndrome, relapsing polychondritis, systemic lupus erythematosus, antiphospholipid syndrome, IgG4-related disease, and ANCA-associated vasculitides.

The Use of Human Mesenchymal Stem Cells as Therapeutic Agents for the in vivo Treatment of Immune-Related Diseases: A Systematic Review

Background: One of the greatest challenges for medicine is to find a safe and effective treatment for immune-related diseases. However, due to the low efficacy of the treatment available and the occurrence of serious adverse effects, many groups are currently searching for alternatives to the traditional therapy. In this regard, the use of human mesenchymal stem cells (hMSCs) represents a great promise for the treatment of a variety of immune-related diseases due to their potent immunomodulatory properties. The main objective of this study is, therefore, to present and summarize, through a systematic review of the literature, in vivo studies in which the efficacy of the administration of hMSCs for the treatment of immune-related diseases was evaluated. Methods: The article search was conducted in PubMed/MEDLINE, Scopus and Web of Science databases. Original research articles assessing the therapeutic potential of hMSCs administration for the in vivo treatment immune-related diseases, published from 1984 to December 2017, were selected and evaluated. Results: A total of 132 manuscripts formed the basis of this systematic review. Most of the studies analyzed reported positive results after hMSCs administration. Clinical effects commonly observed include an increase in the survival rates and a reduction in the severity and incidence of the immune-related diseases studied. In addition, hMSCs administration resulted in an inhibition in the proliferation and activation of CD19⁺ B cells, CD4⁺ Th1 and Th17 cells, CD8⁺ T cells, NK cells, macrophages, monocytes, and neutrophils. The clonal expansion of both Bregs and Tregs cells, however, was stimulated. Administration of hMSCs also resulted in a reduction in the levels of pro-inflammatory cytokines such as IFN-γ, TNF-α, IL-1, IL-2, IL-12, and IL-17 and in an increase in the levels of immunoregulatory cytokines such as IL-4, IL-10, and IL-13. Conclusions: The results obtained in this study open new avenues for the treatment of immune-related diseases through the administration of hMSCs and emphasize the importance of the conduction of further studies in this area.

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.

AAO: Autoimmune and Autoinflammatory (Disease) in Otology: What is New in Immune-Mediated Hearing Loss

OBJECTIVES

Autoinflammatory diseases are a family of immune-mediated, rare diseases, some of which, exhibit sensorineural hearing loss (SNHL), suggesting potentially similar mechanisms of molecular pathogenesis between autoinflammatory-mediated hearing loss and autoimmune inner ear disease (AIED) may exist. The purpose of this review is to compare the clinical features of autoimmune and autoinflammatory diseases that affect hearing, discuss the limitations of our knowledge, and highlight potential new disease mechanisms and therapeutics.

DATA SOURCES

Pubmed Literature Review; Google Scholar Literature review.

REVIEW METHODS

A focused comparison of AIED with a number of autoinflammatory diseases that manifest with sensorineural hearing loss was performed. The pathogenesis of these diseases is reviewed in the context of the innate and adaptive immune system, cytokine expression and genetic polymorphisms.

RESULTS

AIED, since first described by Cogan and Lehnhardt and first clinically characterized by McCabe, has remained an enigmatic disease, with limited advances in both new diagnostics and new therapeutics. Since the discovery of autoinflammatory diseases, a number of systemic autoimmune diseases have either been re-classed as autoinflammatory diseases or identified to have features of autoinflammatory disease.

CONCLUSION

AIED has clinical features of both autoimmune and autoinflammatory disease. It is critical that autoinflammatory diseases be correctly identified, as failure to do so may result in systemic amyloidosis and kidney damage.

Inflammatory and immune responses in the cochlea: potential therapeutic targets for sensorineural hearing loss

The inner ear was previously assumed to be an “immune-privileged” organ due to the existence of its tight junction-based blood-labyrinth barrier. However, studies performed during the past decade revealed that the mesenchymal region of the cochlea, including its lateral wall, is a common site of inflammation. Neutrophils do not enter this region, which is consistent with the old dogma; however, bone marrow-derived resident macrophages are always present in the spiral ligament of the lateral wall and are activated in response to various types of insults, including noise exposure, ischemia, mitochondrial damage, and surgical stress. Recent studies have also revealed another type of immune cell, called perivascular melanocyte-like macrophages (PVM/Ms), in the stria vascularis. These dedicated antigen-presenting cells also control vascular contraction and permeability. This review discusses a series of reports regarding inflammatory/immune cells in the cochlear lateral wall, the pathways involved in cochlear damage and their potential as therapeutic targets.

New prospects in the diagnosis and treatment of immune-mediated inner ear disease

Autoimmune inner ear disease (AIED) represents a very fertile research field and the advancements in the understanding of this disease have a direct application not only in patients affected with this condition but also in other inner ear disorders that share the same injury mechanism, damage to the inner ear hair cells. AIED also presents many challenges that have still to be overcome. Firstly, access to the inner ear is limited, as many interventions such as biopsies can result in great irreversible damage. Secondly, there are no completely specific markers for AIED. Lack of a definitive diagnosis can result in the treatment of patients not affected with the disease and, therefore, no response. Finally, some patients become refractory to glucocorticoids and new therapies are needed. This review offers an overview of the animal models that have contributed to the understanding of AIED pathophysiology, the value of currently available diagnostic tests, and therapeutic options, with a special focus on new therapies for non responders or patients refractory to glucocorticoids. Among these new options for therapy, biological agents have been tested recently, whereas gene and stem cell therapy may have a role in the future. The intratympanic route of administration avoids the systemic side effects associated with currently used drugs, and may become a more frequent approach in the future.

Uroplakin peptide-specific autoimmunity initiates interstitial cystitis/painful bladder syndrome in mice

The pathophysiology of interstitial cystitis/painful bladder syndrome (IC/PBS) is enigmatic. Autoimmunity and impaired urothelium might lead the underlying pathology. A major shortcoming in IC/PBS research has been the lack of an appropriate animal model. In this study, we show that the bladder specific uroplakin 3A-derived immunogenic peptide UPK3A 65–84, which contains the binding motif for IA^d MHC class II molecules expressed in BALB/c mice, is capable of inducing experimental autoimmune cystitis in female mice of that strain. A highly antigen-specific recall proliferative response of lymph node cells to UPK3A 65–84 was observed, characterized by selectively activated CD4+ T cells with a proinflammatory Th1-like phenotype, including enhanced production of interferon γ and interleukin-2. T cell infiltration of the bladder and bladder-specific increased gene expression of inflammatory cytokines were observed. Either active immunization with UPK3A 65–84 or adoptive transfer of peptide-activated CD4+ T cells induced all of the predominant IC/PBS phenotypic characteristics, including increased micturition frequency, decreased urine output per micturition, and increased pelvic pain responses to stimulation with von Frey filaments. Our study demonstrates the creation of a more specific experimental autoimmune cystitis model that is the first inducible model for IC/PBS that manifests all of the major symptoms of this debilitating condition.

A novel murine model of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) induced by immunization with a spermine binding protein (p25) peptide

The pathophysiology of chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is poorly understood. Inflammatory and autoimmune mechanisms may play a role. We developed a murine model of experimental autoimmune prostatitis (EAP) that mimics the human phenotype of CP/CPPS. Eight-week-old mice were immunized subcutaneously with prostate-specific peptides in an emulsion of complete Freund's adjuvant. Mice were euthanized 10 days after immunization, and lymph node cells were isolated and assessed for recall proliferation to each peptide. P25 99-118 was the most immunogenic peptide. T-cell and B-cell immunity and serum levels of C-reactive protein and nitrate/nitrite levels were evaluated over a 9-wk period. Morphometric studies of prostate, 24-h micturition frequencies, and urine volume per void were evaluated. Tactile referred hyperalgesia was measured using von Frey filaments to the pelvic region. The unpaired Student's t-test was used to analyze differences between EAP and control groups. Prostates from p25 99-118-immunized mice demonstrated elevated gene expression levels of TNF-α, IL-17A, IFN-γ, and IL-1β, not observed in control mice. Compared with controls, p25 99-118-immunized mice had significantly higher micturition frequency and decreased urine output per void, and they demonstrated elevated pelvic pain response. p25 99-118 immunization of male SWXJ mice induced prostate-specific autoimmunity characterized by prostate-confined inflammation, increased micturition frequency, and pelvic pain. This autoimmune prostatitis model provides a useful tool for exploring the pathophysiology and new treatments.

Vascular Pathophysiology in Hearing Disorders

The inner ear vasculature is responsible for maintenance of the blood-labyrinth barrier, transport of systemic hormones for ion homeostasis, and supplying nutrients for metabolic functions. Unfortunately, these blood vessels also expose the ear to circulating inflammatory factors resulting from systemic diseases. Thus, while the inner ear blood vessels are critical for normal function, they also are facilitating pathologic mechanisms that result in hearing and vestibular dysfunction. In spite of these numerous critical roles of inner ear vasculature, little is known of its normal homeostatic functions and how these are compromised in disease. The objective of this review is to discuss the current concepts of vascular biology, how blood vessels naturally respond to circulating inflammatory factors, and how such mechanisms of vascular pathophysiology may cause hearing loss.

The therapeutic efficacy of human adipose tissue-derived mesenchymal stem cells on experimental autoimmune hearing loss in mice

Autoimmune inner ear disease is characterized by progressive, bilateral although asymmetric, sensorineural hearing loss. Patients with autoimmune inner ear disease had higher frequencies of interferon-γ-producing T cells than did control subjects tested. Human adipose-derived mesenchymal stem cells (hASCs) were recently found to suppress effector T cells and inflammatory responses and therefore have beneficial effects in various autoimmune diseases. The aim of this study was to examine the immunosuppressive activity of hASCs on autoreactive T cells from the experimental autoimmune hearing loss (EAHL) murine model. Female BALB/c mice underwent β-tubulin immunization to develop EAHL; mice with EAHL were given hASCs or PBS intraperitoneally once a week for 6 consecutive weeks. Auditory brainstem responses were examined over time. The T helper type 1 (Th1)/Th17-mediated autoreactive responses were examined by determining the proliferative response and cytokine profile of splenocytes stimulated with β-tubulin. The frequency of regulatory T (Treg) cells and their suppressive capacity on autoreactive T cells were also determined. Systemic infusion of hASCs significantly improved hearing function and protected hair cells in established EAHL. The hASCs decreased the proliferation of antigen-specific Th1/Th17 cells and induced the production of anti-inflammatory cytokine interleukin-10 in splenocytes. They also induced the generation of antigen-specific CD4(+) CD25(+) Foxp3(+) Treg cells with the capacity to suppress autoantigen-specific T-cell responses. The experiment demonstrated that hASCs are one of the important regulators of immune tolerance with the capacity to suppress effector T cells and to induce the generation of antigen-specific Treg cells.

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.

IL-1β is overexpressed and aberrantly regulated in corticosteroid nonresponders with autoimmune inner ear disease

Autoimmune inner ear disease is an enigmatic disorder characterized by recurring episodes of sudden or progressive sensorineural hearing loss. Hearing loss can be improved by timely corticosteroid administration, but only half of those treated respond, and for many responders, that response is lost over time. The mechanisms that control corticosteroid responsiveness in this disorder are largely uncharacterized. We have previously identified that the induction by dexamethasone of IL-1R type II (IL-1R2) expression in PBMC predicts corticosteroid responsiveness in this disorder. In this study, we asked whether IL-1β was overexpressed, and whether clinical corticosteroid responders differentially regulated IL-1β expression or release in response to dexamethasone, as compared with nonresponders. IL-1β has been reported to induce matrix metalloproteinase-9 (MMP-9) expression. Given that metalloproteinases can cleave IL-1R2, we also asked whether MMP-9 expression was altered in this disorder. In this study, we demonstrate that corticosteroid nonresponders have elevated plasma levels of IL-1β and MMP-9 as compared with clinically responsive patients (p = 0.0008 and p = 0.037, respectively). Increasing MMP-9 expression correlated with increasing IL-1β concentration, suggesting that IL-1β expression regulates MMP-9 expression. As expected, monocytes were the predominant producers of IL-1β. In vitro exposure of PBMC to dexamethasone from clinical corticosteroid responders suppressed IL-1β release. PBMC of corticosteroid nonresponders have substantially higher release of IL-1β into the conditioned media, and when exposed to dexamethasone, failed to repress IL-1β release (p = 0.05). Treatment of PBMC from clinical corticosteroid nonresponders with anakinra resulted in repression of IL-1β release, suggesting that IL-1β blockade may be a viable therapy for these patients.

Proteomics, bioinformatics and targeted gene expression analysis reveals up-regulation of cochlin and identifies other potential biomarkers in the mouse model for deafness in Usher syndrome type 1F

Proteins and protein networks associated with cochlear pathogenesis in the Ames waltzer (av) mouse, a model for deafness in Usher syndrome 1F (USH1F), were identified. Cochlear protein from wild-type and av mice at postnatal day 30, a time point in which cochlear pathology is well established, was analyzed by quantitative 2D gel electrophoresis followed by mass spectrometry (MS). The analytic gel resolved 2270 spots; 69 spots showed significant changes in intensity in the av cochlea compared with the control. The cochlin protein was identified in 20 peptide spots, most of which were up-regulated, while a few were down-regulated. Analysis of MS sequence data showed that, in the av cochlea, a set of full-length isoforms of cochlin was up-regulated, while isoforms missing the N-terminal FCH/LCCL domain were down-regulated. Protein interaction network analysis of all differentially expressed proteins was performed with Metacore software. That analysis revealed a number of statistically significant candidate protein networks predicted to be altered in the affected cochlea. Quantitative PCR (qPCR) analysis of select candidates from the proteomic and bioinformatic investigations showed up-regulation of Coch mRNA and those of p53, Brn3a and Nrf2, transcription factors linked to stress response and survival. Increased mRNA of Brn3a and Nrf2 has previously been associated with increased expression of cochlin in human glaucomatous trabecular meshwork. Our report strongly suggests that increased level of cochlin is an important etiologic factor leading to the degeneration of cochlear neuroepithelia in the USH1F model.

Alternate splicing of interleukin-1 receptor type II (IL1R2) in vitro correlates with clinical glucocorticoid responsiveness in patients with AIED

Autoimmune Inner Ear Disease (AIED) is poorly characterized clinically, with no definitive laboratory test. All patients suspected of having AIED are given glucocorticoids during periods of acute hearing loss, however, only half initially respond, and still fewer respond over time.

We hypothesized that AIED is a systemic autoimmune disease characterized by dysfunctional peripheral blood mononuclear cells (PBMC) responses to a unique cochlear antigen(s). To test this hypothesis, we examined end-stage AIED patients undergoing cochlear implant surgery and compared autologous perilymph stimulated PBMC from AIED patients to controls. We determined that autologous perilymph from AIED patients was unable to induce expression of a long membrane-bound Interleukin-1 Receptor Type II (mIL1R2) transcript in PBMC as compared with controls, despite similar expression of the short soluble IL1R2 (sIL1R2) transcript (p<0.05). IL1R2 is a molecular decoy that traps interleukin-1β (IL-1β) and does not initiate subsequent signaling events, thereby suppressing an inflammatory response. IL1R2 transcript length is regulated by alternate splicing, and the major inhibitory function is attributed to the full-length mIL1R2. In addition, IL1R2 expression is induced by dexamethasone.

Separately, we prospectively examined patients with newer onset glucocorticoid-responsive AIED. Immediately prior to clinical treatment for acute deterioration of hearing thresholds, their PBMC demonstrated a robust induction of mIL1R2 in PBMC in response to dexamethasone in vitro that correlated with a clinical response to prednisone in vivo (p<0.0001) as measured by hearing restoration. In contrast, clinically steroid unresponsive patients demonstrated high basal levels of mIL1R2 in their PBMC and only minimally augmented expression in response to dexamethasone. Thus, induced expression of mIL1R2 appears to be a protective mechanism in hearing homeostasis and warrants further investigation in a large prospective clinical trial to determine if IL1R2 can be used as a specific biomarker for AIED.

Sudden deafness: is it viral?

A number of theories have been proposed to explain the etiopathogenesis of idiopathic sudden sensorineural hearing loss (ISSHL), including viral infection, vascular occlusion, breaks of labyrinthine membranes, immune-mediated mechanisms and abnormal cellular stress responses within the cochlea. In the present paper, we provide a critical review of the viral hypothesis of ISSHL. The evidence reviewed includes published reports of epidemiological and serological studies, clinical observations and results of antiviral therapy, morphological and histopathological studies, as well as results of animal experiments. The published evidence does not satisfy the majority of the Henle-Koch postulates for viral causation of an infectious disease. Possible explanations as to why these postulates remain unfulfilled are reviewed, and future studies that may provide more insight are described. We also discuss other mechanisms that have been postulated to explain ISSHL. Our review indicates that vascular occlusion, labyrinthine membrane breaks and immune-mediated mechanisms are unlikely to be common causes of ISSHL. Finally, we review our recently proposed theory that abnormal cellular stress responses within the cochlea may be responsible for ISSHL.

Cochlin isoforms and their interaction with CTL2 (SLC44A2) in the inner ear

Choline transporter-like protein 2 (CTL2) is a multi-transmembrane protein expressed on inner ear supporting cells that was discovered as a target of antibody-induced hearing loss. Its function is unknown. A 64 kDa band that consistently co-precipitates with CTL2 from inner ear extracts was identified by mass spectroscopy as cochlin. Cochlin is an abundant inner ear protein expressed as multiple isoforms. Its function is also unknown, but it is suspected to be an extracellular matrix component. Cochlin is mutated in individuals with DFNA9 hearing loss. To investigate the CTL2-cochlin interaction, antibodies were raised to a cochlin-specific peptide. The antibodies identify several cochlin polypeptides on western blots and are specific for cochlin. We show that the heterogeneity of the cochlin isoforms is caused, in part, by in vivo post-translational modification by N-glycosylation and, in part, caused by alternative splicing. We verified that antibody to CTL2 co-immunoprecipitates cochlin from the inner ear and antibody to cochlin co-immunoprecipitates CTL2. Using cochlear cross-sections, we show that CTL2 is more widely distributed than previously described, and its prominent expression on cells facing the scala media suggests a possible role in homeostasis. A prominent but previously unreported ribbon-like pattern of cochlin in the basilar membrane was demonstrated, suggesting an important role for cochlin in the structure of the basilar membrane. CTL2 and cochlin are expressed in close proximity in the inner sulcus, the spiral prominence, vessels, limbus, and spiral ligament. The possible functional significance of CTL2-cochlin interactions remains unknown.

Antibody reactivity to heat shock protein 70 and inner ear-specific proteins in patients with idiopathic sensorineural hearing loss

Deafness is attributable to autoimmunity in a subset of adult patients with sensorineural hearing loss (SNHL) of unknown aetiology. To determine the roles of self-antigens in the pathogenesis of idiopathic SNHL, we analysed antibody responses to the inner ear-specific proteins, cochlin and beta-tectorin as well as the non-specific heat shock protein 70 (HSP70). Recombinant cochlin and beta-tectorin proteins were used in a qualitative Western blot assay for the detection of antigen-specific IgG antibodies in 58 patients with idiopathic SNHL and 28 healthy blood donors. In the same study cohort, we also used a Western blot assay to assess IgG antibody responses to the recombinant human HSP70. Of the 58 patient samples analysed, 19 tested positive to the HSP70, eight to cochlin and one to beta-tectorin, giving a prevalence of 33, 14 and 2%, respectively. Only one patient sample was reactive for HSP70, cochlin and beta-tectorin, seven of the remaining eight cochlin IgG antibody-positive samples were monospecific. Thus, cochlin-specific antibodies were observed predominantly in HSP70 IgG-negative patients demonstrating an additive value for testing this antibody response in patients with idiopathic SNHL.

The inner ear and the neurologist

Inner ear disorders are common and patients with vestibular failure often present to a neurology clinic because of their dizziness, gait unsteadiness and oscillopsia. Vestibular disorders can be divided into peripheral and central vestibular disorders. Most of the peripheral vestibular disorders have a clinical diagnosis, and a thorough history and examination will often provide a clear direction as to the diagnosis. Correct diagnosis allows treatment for many of the peripheral and central vestibular disorders. As inner ear damage is generally irreversible, early diagnosis allowing prompt treatment is important. The aim of this review is to discuss some audiovestibular conditions that may well appear in a neurology clinic, and to discuss some recent advances within the audiovestibular field that may be of interest to neurologists. Some of the most common audiovestibular conditions will be discussed along side more uncommon conditions.

Experimental autoimmune hearing loss

Understanding of autoimmune sensorineural hearing loss (ASNHL) has been hindered by the inaccessibility of the inner ear to biopsy and the lack of workable animal models. A report in this issue of the JCI describes a mouse model of CD4(+) T cell-mediated ASNHL induced by immunization with peptides from the inner ear-specific proteins cochlin and beta-tectorin.