Upregulation of messenger RNA for inflammatory cytokines in middle ear mucosa in a rat model of acute otitis media

A rat model for acute otitis media has been established and was used to delineate the temporal expression of messenger RNA for key inflammatory cytokines. Inoculation with live Streptococcus pneumoniae induced a rapid expression of tumor necrosis factor a (within 6 hours) followed by upregulation of message for interleukin (IL)-6 (peak at 12 to 24 hours, remaining elevated through 120 hours) and IL-10 (peak at 24 hours). Inducible nitric oxide synthase message was also selectively increased following live bacterial inoculation (peak at 12 to 24 hours). Although there was a detectable inflammatory response to killed bacteria, it was minimal, was of short duration, and preceded the peak for live bacteria; only expression of IL-6 was significantly increased in this group (peak at 12 hours, remaining elevated through 72 hours). We interpret this to be due to an inflammatory response to bacterial products (such as lipopolysaccharide) in the heat-killed bacterial inoculum. The phosphate-buffered saline (PBS)-inoculated group exhibited a transient increase of IL-6 message, which indicates that this cytokine is a sensitive marker of the acute response to trauma. Otherwise, PBS invoked only a slight reaction in the mucosa with respect to the other inflammatory mediators being measured.