Middle ear pathologic changes associated with chronic anaerobic sinusitis in rabbits

Objective/Hypothesis: To study the histopathologic changes in association w ith the inflammatory/immune response present in the middle ears of a rabbit model of unilateral chronic anaerobic sinusitis. Study Design: New Zealand white rabbits, two at each experimental time point. Normal rabbits and sha m-operated animals served as controls. Methods: Left maxillary sinusitis wa s induced by inoculating Bacteroides fragilis surgically after closure of t he ostium. Cultures, lavages, and mucosa were harvested from bilateral midd le ear and sinus cavities at 1, 2, 3, and 4 weeks following inoculation. Pa rameters analyzed include tissue for histopathologic study, immunoglobulin G antibody (IgG Ab) against B fragilis, and lactate dehydrogenase (LDH) lev els in lavage samples, interferon gamma (IFN gamma) messenger RNA (mRNA) ex pression in mucosal tissue, and bacterial culture. Results: Despite closure of the ostium of the left sinus, mild to moderate dissemination of B fragi lis into the right sinus and left and light ears were observed in some but not all rabbits (2/8, 5/7, and 2/8, respectively). Histopathologic changes in the right sinus and middle ears were much less severe in contrast to the severe inflammatory changes in the left sinus. An immune response against B fragilis appeared to occur in the sinuses and ears bilaterally independen t of bacterial dissemination, as evidenced by a rise of IgG Ab in lavage fl uid and detection of IFNg mRNA Neither control nor sham-operated animals ha d detectable levels of IFNg mRNA or IgG Ab. In B fragilis-inoculated rabbit s, the magnitude of IgG Ab responses was equivalent in the right and left e ar, independent of B fragilis dissemination; IgG Ab levels in the middle ea r positively correlated to each other (P <.01) and to the levels in the sin uses (P <.01 and P <.01). LDH levels were closely associated with bacterial growth and degree of tissue inflammation. Conclusion: This reproducible mo del of chronic sinusitis provides an opportunity to study the middle ear in fection and inflammatory/immune responses occurring with sinusitis. Our res ults indicate bilateral middle ear mucosal immune responses to an elicited sinus infection, independent of B fragilis dissemination.