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OBJECTIVE: Otitis media is one of the most common diseases among children. A well-known sequela of acute, chronic, and secretory otitis media is tympanosclerosis. With the exception of surgery, there is no causal treatment available for this condition, which may cause hearing disabilities. This study aimed to describe the localization of interleukin (IL)-6 mRNA and its gene product in the rat middle ear during pneumococcal otitis media. IL-6 is known to be involved in inflammatory and bone remodeling processes. METHODS: Using an experimental model of pneumococcal acute otitis media, the expression of interleukin IL-6, was analyzed. Sprague-Dawley rats were sacrificed at different time points varying from 1 h to 6 days intervals after inoculation. The middle ears were analyzed by messenger RNA in situ hybridization, and by immunohistochemistry with cell-type specific antibodies directed against IL-6. RESULTS: Transcripts of IL-6 were observed only on day 1 post-inoculation, whereas the final gene product was observed at all intervals after inoculation. IL-6 was localized in the bony part of the bulla nearest to the mucosa, around mucosal vessels, and in the ciliae of the mucosal epithelium. The results demonstrated that IL-6 was synthesized locally as early as 1 h after bacterial middle ear challenge, and that although transcription could not be detected after 24 h, the cytokine product persisted for at least 5 days after the infection was introduced. CONCLUSIONS: IL-6 was shown to be produced early in the inflammatory process during induced pneumococcal otitis media in the rat. No production was seen after 24 h although the protein remained in the tissue for at least 5 days. IL-6 could initiate a differentiation of macrophages to osteoclasts and thereby participate in a bone remodeling process leading to tympanosclerosis development.