Effect of genetic background on the response to bacterial sinusitis in mice

OBJECTIVE: To study the importance of ongoing allergen exposure and TH1/TH2 genetic background in augmented bacterial and inflammatory responses in allergic and infected mice. DESIGN: BALB/c and C57BL/6 mice were made allergic to ovalbumin. After 1 day of intranasal allergen exposure, they were inoculated intranasally with Streptococcus pneumoniae. The numbers of bacteria and inflammatory cells in the sinuses were determined, and nasal responsiveness to histamine was assessed. RESULTS: Infected BALB/c and C57BL/6 mice that received ongoing ovalbumin challenge following intraperitoneal sensitization showed significantly greater bacterial load and phagocyte level compared with the infected-only mice. Differences were diminished after the allergen challenge was stopped. Allergic and infected C57BL/6 mice showed fewer bacteria and phagocytes compared with the allergic and infected BALB/c mice. Surprisingly, in contrast to the nonallergenic C57BL/6 mice, the infected BALB/c mice showed a larger number of bacteria 28 days after infection. CONCLUSIONS: Ongoing allergic reaction augments bacterial load in both BALB/c and C57BL/6 mice and induces nasal hyperreactivity to histamine. Allergic and infected C57BL/6 mice show less allergic inflammation and bacterial load compared with allergic and infected BALB/c mice. Stopping allergen exposure reduces the response. Infected BALB/c mice, which favor a TH2 response, were less able to clear infection than C57BL/6 mice, which favor a TH1 response. Inflammation and bacterial load are affected by genetic background of mice and ongoing allergen stimulation.