An experimental study of inner ear injury in an animal model of eosinophilic otitis media.

CONCLUSION: As the periods of intratympanic injection of ovalbumin (OVA) to the middle ear became longer, marked eosinophil infiltration in the perilymphatic space was observed. Moreover severe morphological damage of the organ of Corti was observed in the 28-day antigen-stimulation side. These results indicate that eosinophilic inflammation occurred in the inner ear and caused profound hearing loss. OBJECTIVE: The purpose of the present study was to elucidate the inner ear damage in a new animal model of eosinophilic otitis media (EOM) which we recently constructed. METHODS: We constructed the animal model of EOM by intraperitoneal and intratympanic injection of OVA. Infiltrating cells and the inner ear damage were examined by histological study. RESULTS: In the inner ear, a few eosinophils were seen in the scala tympani of the organ of Corti and the dilation of capillaries of the stria vascularis was observed in the 7-day stimulation side. In the 14-day antigen stimulation side, some eosinophils and macrophages were seen in not only the scala tympani but also the scala vestibule. In the 28-day antigen-stimulation side, severe morphological damage of the organ of Corti and many eosinophils, red blood cells, and plasma cells infiltrating the perilymph were observed.

The round window membrane in otitis media: effect of pneumococcal proteins.

OBJECTIVE: To determine whether mutants of Streptococcus pneumoniae that are deficient in pneumococcal surface protein A (PspA), pneumococcal surface antigen A (PsaA), or pneumolysin (Ply) are less virulent and less likely to penetrate the round window membrane (RWM). DESIGN: Histopathologic comparison of wild-type S. pneumoniae and its mutants deficient in PspA, PsaA, and Ply. SETTING: Otopathology Laboratory, Department of Otolaryngology, University of Minnesota Medical School, Minneapolis. PARTICIPANTS: Forty young chinchillas (weight, 250-350 g) with normal external auditory canals and tympanic membranes. INTERVENTION: Animals were divided into 3 groups and bullae inoculated with wild-type S. pneumoniae serotype 2, strain D39, or its mutants deficient in PspA, PsaA, or Ply. Two days after inoculation, bullae were processed for light microscopy and transmission electron microscopy. MAIN OUTCOME MEASURES: Comparison of inflammatory cell infiltration and penetration of bacteria into the round window membrane and adjacent scala tympani. RESULTS: Histopathologic findings using wild-type S. pneumoniae and Ply(-) mutant were similar and included otitis media and the presence of inflammatory cells and damage to and passage of bacteria through the RWM. Although otitis media was seen with the PspA(-) and PsaA(-) mutants, we observed no passage of bacteria through the RWM. CONCLUSIONS: Both PspA and PsaA affect the ability of S. pneumoniae to penetrate the RWM. Understanding the role of S. pneumoniae virulence proteins in the pathogenesis of the middle ear, RWM, and inner ear will provide new strategies for the prevention and treatment of otitis media and its complications.

Immunodefense of the round window.

A systematic analysis using serial sectioning of the round window membrane (RWM) in the cynomolgus monkey was performed. Light and transmission electron microscopy (LM and TEM) revealed that the RWM rim may be endowed with gland-like structures with glyco-protein material secernated into the window niche. This was detected in one third of the specimens. The secreted material displayed waste material and scavenger cells. There was also a rich network of capillaries, lymph channels, and sinusoidal veins containing leukocytes. Their abluminal surfaces displayed mature plasma cells and monocytes. These findings suggest that in certain primates the middle ear may have developed specific immunoprotective means for disposal of foreign and noxious substances before they reach the inner ear.

Interrelations between the middle and inner ear in otitis media.

This article reviews the importance of the round-window membrane in exposing the labyrinth to or protecting it from the toxic effects of otitis media. Characteristics of the immune system in the human middle ear and middle-ear mechanisms against bacteria are explained. The role of bacteria and bacterial products in inner-ear damage is detailed, and related pathological events are described. The hypothetical role of inflammatory mediators in bacteria-induced inner-ear toxicity is particularly emphasized. Clinical conditions causing these events are detailed, and the most frequently involved microorganisms are mentioned. Finally, round-window membrane macroscopic and microscopic anatomy is discussed, and considerations about the exact role of membrane inflammation--protection versus damage of the inner ear--are expressed.

Subepithelial fiber components of the round window membrane of the guinea pig: an ultrastructural and immunohistochemical study.

Subepithelial fiber components of the round window membrane (RWM) of the guinea pig were studied by the following methods: transmission electron microscopy (TEM), scanning electron microscopy (SEM) with NaOH treatment, high-voltage electron microscopy (HVEM) and immunohistochemical staining. SEM observation revealed intersecting collagen fibers and a vascular network in the middle layer. TEM observation showed that at the attachment region to the bone fibroblasts, collagen fibers and elastic fibers were intermingled with each other, and mesenchymal cells (bone-lining cells) were scattered on the surface of the bone. The cytoplasmic processes of fibroblasts and bone-lining cells were connected by interdigitations. HVEM demonstrated that collagen fibers of the RWM were directly linked to the fibers of the bone matrix. Immunohistochemically, the middle layer was positive for antibody to type I collagen. Immunoreaction for fibronectin was also positive at the middle layer and most intense in the region attached to the bone. Thus, the RWM is securely attached to the bone by type I collagen fibers together with the bone-lining cells and fibroblasts.

Inner ear inflammation and round window otosclerosis.

Recently, it has been suggested that otosclerosis represents the host's ongoing immunologic response to measles or other viral antigens. Documentation of past inflammation within the inner ear would serve as further evidence that this mechanism may be at play in the pathogenesis of the disease. Among the characteristic signs of prior inflammation in the inner ear is the presence of lamellar bone at the site of inflammation. This has been described in the temporal bone of a patient with immune-mediated deafness and with the temporal bones of experimental models of immune-mediated inner ear disease. Review of temporal bones with round window otosclerosis from the Eastern Temporal Bone Bank at the Massachusetts Eye and Ear Infirmary show that in four of ten cases there are characteristic signs of a prior severe inflammatory event centered in the scala tympani adjacent to the otosclerotic lesion. Otosclerosis, therefore, may have an inflammatory stage that is the consequence of a host response to an inciting event.

T cell subsets in round window membrane after middle ear immunostimulation.

In secondary middle ear immune response, kinetics of immunocytes, especially T cell subsets, was examined in the round window membrane (RWM) using immunohistochemical methods. Healthy BALB/c mice and keyhole limpet hemocyanin (KLH) antigen were employed in this study. The inflammatory responses of the RWM and middle ear were investigated after antigen challenge into the middle ear bulla. We used antibodies against murine macrophages and granulocytes (anti-Mac-1), murine helper/inducer T cells (anti-Lyt-1 and -L3T4), murine suppressor/cytotoxic T cells (anti-Lyt-2), murine interleukin-2 receptor (7D4), murine immunoglobulins (anti-IgG, -IgM and -IgA) and KLH. In the RWM and middle ear mucosa, inflammatory cells were observed at 6 hours, peaking on days 3-7, whereas these cells were rarely seen in the scala tympani of the basal turn. Luminal effusion with an enormous infiltration of inflammatory cells, which consisted mainly of Mac-1 cells, IgG cells and IgM cells, was observed in the middle ear cavity on days 1-7 post antigen challenge. In the inflamed RWM, Mac-1 cells were the predominant cell type followed by helper T cells, interleukin 2 receptor positive cells and IgG positive cells, though IgM, IgA and Lyt-2 positive cells were rarely observed after antigen challenge. Our results suggest that RWM has the ability to protect inner ear by cellular immune response through activated helper T cells and Mac-1 cells.

Round window membrane and perilymph in experimental otitis media with effusion.

To investigate the influence of middle ear effusion (MEE) on perilymph (PL), an experimental otitis media with effusion (OME) was manufactured in chinchillas by injecting the tympanic cavity with immune complexes. The presence of MEE lasted for up to 9 days after the injection of immune complexes. Perilymph was aspirated on the fourth, tenth, and 21st days after the inoculation. The mean concentrations of albumin, immunoglobulin G, histamine, and prostaglandin E2 (PGE2) were significantly greater in PL from ears with induced OME than in that from normal control ears. The 3H-PGE2 placed on the round window membrane of pathologically affected ears passed into PL in significantly greater amounts than in normal control ears. The findings indicate that the immune complexes placed in the middle ear cavity affect the biochemical milieu of PL, and that MEE is a result of immune complexes.