Macrophages and possible osteoclast differentiation in the rat bullar bone during experimental acute otitis media, with reference to tympanosclerosis

Large osteoclast-like cells, labeled by using monoclonal antibodies directed against macrophages, are participating in a bone remodeling process in the rat bullar bone after induced experimental acute otitis media, leading to tympanosclerosis. In humans, tympanosclerosis is a sequale of chronic otitis media. It causes hearing disability, especially if the ossicles or the inner ear are affected. No successful treatment is available. To evaluate the inflammatory stages that may lead to tympanosclerosis, the current study was performed. Sprague-Dawley rats were exposed to a pneumococcus Type 3 solution into the middle ear. The rats were killed at 3, 6, and 10 days after inoculation. Sections from the ear specimen were stained immunohistochemically. Antibodies used were directed against macrophages. Positive cells were seen in the tympanic membrane, in the middle ear mucosa, and close to the tympanic membrane insertion into the bone. Macrophages appeared to be linearized adjacent to the bullar bone, both on the inner and on the outer bullar wall. These cells had the appearance of osteoclasts. A differentiation of macrophages to osteoclasts is possible during induced otitis media in the rat, initiating a bone-remodeling process leading to tympanosclerosis.