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

Previously, we found minimal bacterial dissemination and no evidence of systemic inflammation in a rabbit sinusitis model in which the left maxillary sinus was inflamed by Bacteroides inoculation with the ostium closed. 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 ear and sinus mucosa.

To evaluate how IFN-gamma production in the upper and lower airway is associated with localized bacterial sinusitis.

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 following bacterial inoculation.

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.

Bacteroides fragilis (10(8) plaque-forming units) was inoculated into the left maxillary sinus.

Interferon gamma levels in the ear and sinus were less than 0.2 microg/g protein in controls. Following bacterial inoculation into the left sinus, 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 microg/g protein in controls) were not altered by bacterial inoculation into the sinus. Serum IFN-gamma levels were very low (<0.05 microg/g protein) in most rabbits and were unchanged by bacterial inoculation.

Interferon gamma levels increase in the ear and contralateral sinus in response to localized sinus inflammation, indicating concerted mucosal proinflammatory immune responses in the upper airway. Such responses may lead to the aseptic middle ear inflammation often observed in patients with chronic sinusitis.