Sensitivity to Ozone, Diesel Exhaust Particles, and Standardized Ambient Particulate Matter in Rats with a Listeria Monocytogenes-Induced Respiratory Infection

Ambient particulate matter may increase respiratory allergic skewing of the T-cell-mediated immune response toward a T-helper-2 (Th2) response, with the consequence that the Th1 response develops less well. Successful clearing of a respiratory bacterial infection depends on an adequate Th1 immune response; therefore, the subject would not control the infection as well if exposed to particulate matter. To substantiate this hypothesis, we examined the effect of exposure to diesel exhaust particles (DEP) and urban particulate matter (EHC-93, Ottawa dust) on rats with a Listeria monocytogenes respiratory infection. Since this hypothesis has been confirmed for ozone, we used it as a positive control. Wistar rats were exposed to ozone (2 mg/m3 for 24 h/day for 7 days) and to DEP or to EHC-93 (50 μg/rat intranasally daily for 7 consecutive days). Twenty-four hours after the last exposure, the rats were infected intratracheally with 1 × 106 L. monocytogenes bacteria. The number of L. monocytogenes was determined ...