IgG antibody levels in the sinus, ear, and airway in a rabbit model of sinusitis with Bacteroides.

Abstract

To evaluate distribution of IgG antibodies (Ab) in the airway, ear, and sinuses in association with inflammatory changes in a rabbit sinusitis model. We measured IgG Ab and lactate dehydrogenase levels in solutions from sinus, airway, and middle ear lavage and in serum, and determined interferon y messenger RNA expression in sinus and ear mucosa at 1, 2, 3, and 4 weeks after inoculation with Bacteroides fragilis. Six rabbits at each time point; controls were untreated (n=5) and sham-operated rabbits at 2 and 4 weeks (n=4-5). Bacteroides fragilis was inoculated into the left maxillary sinus with ostium closed. IgG Ab was undetectable in all controls. IgG Ab (>50 microg/g protein) was present at 2, 3, and 4 weeks in most bilateral sinus lavage samples and in 2 of 6, 5 of 6, and 6 of 10 ear lavage samples at 2, 3, and 4 weeks, respectively, following inoculation. Inflammatory changes (histological and lactate dehydrogenase) were much greater in the inflamed sinus. IgG Ab (>50 microg/g protein) was also detected in most bronchoalveolar lavage samples after 2 weeks. Interferon gamma mRNA was undetectable in all untreated and most sham-operated controls but was detected in the bilateral sinus mucosa at 1 to 2 weeks, and remained detectable up to 4 weeks in most rabbits. Serum IgG Ab levels positively correlated with those in lavage samples, with highest correlation with right sinus lavage IgG Ab levels (r=0.56, P<.001). IgG Ab levels in the upper airway mucosa likely increase within 2 weeks following bacterial inoculation as a part of mucosal immune responses independent of tissue necrosis.