Correlative mRNA and protein expression of middle and inner ear inflammatory cytokines during mouse acute otitis media

Although the inner ear has long been reported to be susceptible to middle ear disease, little is known of the inflammatory mechanisms that might cause permanent sensorineural hearing loss. Recent studies have shown inner ear tissues are capable of expressing inflammatory cytokines during otitis media. However, little quantitative information is available concerning cytokine gene expression in the inner ear and the protein products that result. Therefore, this study was conducted of mouse middle and inner ear during acute otitis media to measure the relationship between inflammatory cytokine genes and their protein products with quantitative RT-PCR and ELISA, respectively. Balb/c mice were inoculated transtympanically with heat-killed Haemophilus influenzae and middle and inner ear tissues collected for either quantitative RT-PCR microarrays or ELISA multiplex arrays. mRNA for several cytokine genes was significantly increased in both the middle and inner ear at 6h. In the inner ear, these included MIP-2 (448 fold), IL-6 (126 fold), IL-1β (7.8 fold), IL-10 (10.7 fold), TNFα (1.8 fold), and IL-1α (1.5 fold). The 24h samples showed a similar pattern of gene expression, although generally at lower levels. In parallel, the ELISA showed the related cytokines were present in the inner ear at concentrations higher by 2-122 fold higher at 18h, declining slightly from there at 24h. Immunohistochemistry with antibodies to a number of these cytokines demonstrated they occurred in greater amounts in the inner ear tissues. These findings demonstrate considerable inflammatory gene expression and gene products in the inner ear following acute otitis media. These higher cytokine levels suggest one potential mechanism for the permanent hearing loss seen in some cases of acute and chronic otitis media.