Localized sinus inflammation in a rabbit sinusitis model induced by Bacteroides fragilis is accompanied by rigorous immune responses

We evaluated inflammatory and immune responses against Bacteroides fragilis in a rabbit sinusitis model. Bacteroides was inoculated into the left maxi llary sinus, and inflammatory (histology, cell number/cytology, lactose deh ydrogenase, and apoptosis) and immune responses in the sinus, airway, and p eripheral blood (PB) were determined for up to 4 weeks. In the inflamed sin us, the lactose dehydrogenase level was markedly elevated, with neutrophili c infiltration, severe tissue inflammation, and increased apoptosis. Low-gr ade tissue inflammation was present in the contralateral and sham-operated sinuses, but other parameters remained unchanged, and so did those in the a irway and PB in the inoculated rabbits. Serum IgG antibody levels increased rapidly, were highest at 3 weeks, and began to decline at 4 weeks. Cellula r immune responses (proliferation and interferon-gamma mRNA expression) aga inst Bacteroides were detected in the PB of all inoculated rabbits. Vigorou s immune responses against Bacteroides may have localized but failed to ter minate inflammation in the sinus, indicating importance of microenvironment al factors.