Interferon gamma levels in the sinus, ear, and airway in a rabbit sinusitis model induced by Bacteroides inoculation

Background: Previously, we found minimal bacterial dissemination and no evi dence of systemic inflammation in a rabbit sinusitis model in which the lef t maxillary sinus was inflamed by Bacteroides inoculation with the ostium c losed. However, we observed an increase in anti-Bacteroides IgG antibodies in the contralateral sinus, lower airway, and middle ear, with an apparent increase in interferon gamma (IFN-gamma) messenger RNA expression in the ea r and sinus mucosa. Objective: To evaluate how IFN-gamma production in the upper and lower airw ay is associated with localized bacterial sinusitis. Design: Interferon gamma levels were measured in lavage solutions from the sinus, airway, and middle ear and in serum at 1, 2, 3, and 4 weeks followin g bacterial inoculation. Subjects: The subjects were 6 rabbits at each time point. The controls were untreated (n = 5) and sham-operated (n = 4-5) rabbits at 2 and 4 weeks. Intervention: Bacteroides fragilis (10(8) plaque-forming units) was inocula ted into the left maxillary sinus. Results: Interferon gamma levels in the ear and sinus were less than 0.2 mu g/g protein in controls. Following bacterial inoculation into the left sin us, IFN-gamma levels increased up to 10-fold in both sinuses and even more in the middle ear at 3 weeks, independent of bacterial dissemination. Mean +/- SD IFN-gamma levels in the airway (0.3 +/- 0.28 mu g/g protein in contr ols) were not altered by bacterial inoculation into the sinus. Serum IFN-ga mma levels were very low (<0.05 mu g/g protein) in most rabbits and were un changed by bacterial inoculation. Conclusions: Interferon gamma levels increase in the ear and contralateral sinus in response to localized sinus inflammation, indicating concerted muc osal proinflammatory immune responses in the upper airway. Such responses m ay lead to the aseptic middle ear inflammation often observed in patients w ith chronic sinusitis.