Middle ear pathologic changes associated with chronic anaerobic sinusitis in rabbits

Objective/Hypothesis: To study the histopathologic changes in association with 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 sham‐operated animals served as controls. Methods: Left maxillary sinusitis was induced by inoculating Bacteroides fragilis surgically after closure of the ostium. Cultures, lavages, and mucosa were harvested from bilateral middle ear and sinus cavities at 1, 2, 3, and 4 weeks following inoculation. Parameters analyzed include tissue for histopathologic study, immunoglobulin G antibody (IgG Ab) against B fragilis, and lactate dehydrogenase (LDH) levels in lavage samples, interferon gamma (IFNγ) messenger RNA (mRNA) expression in mucosal tissue, and bacterial culture. Results: Despite closure of the ostium of the left sinus, mild to moderate dissemination of B fragilis into the right sinus and left and right 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 independent of bacterial dissemination, as evidenced by a rise of IgG Ab in lavage fluid and detection of IFNg mRNA. Neither control nor sham‐operated animals had detectable levels of IFNg mRNA or IgG Ab. In B fragilis–inoculated rabbits, the magnitude of IgG Ab responses was equivalent in the right and left ear, independent of B fragilis dissemination; IgG Ab levels in the middle ear positively correlated to each other (P < .01) and to the levels in the sinuses (P < .01 and P < .01). LDH levels were closely associated with bacterial growth and degree of tissue inflammation. Conclusion: This reproducible model of chronic sinusitis provides an opportunity to study the middle ear infection and inflammatory/immune responses occurring with sinusitis. Our results indicate bilateral middle ear mucosal immune responses to an elicited sinus infection, independent of B fragilis dissemination.