In this study, we tested the hypothesis that exposure to DEP may impair lung defense against Listeria monocytogenes infection. Male Sprague-Dawley rats were dosed with either 5 mg/kg of DEP or saline intratracheally for 3 days, then intratracheally instilled with approximately 5,000 Listeria/rat. At 3, 5 and 7 days post-Listeria instillation, the rats were killed; the left lobe of lungs and the spleen were excised; and the numbers of Listeria in the tissues were determined. The remaining lung underwent bronchoalveolar lavage. Nitric oxide (NO) was measured in AM-conditioned supernatant. All rats survived and no significant lung inflammation and injury were noted in these rats. The pattern of Listeria clearance from the lungs was different between DEP and saline-pretreated rats. At 3 days post-Listeria exposure, the number of bacteria in the lungs of DEP-treated rats (approximately 55,000 Listeria/left lobe) was lower than that of saline-treated rats (approximately 110,000 Listeria/left lobe). In contrast, the number of Listeria in the lungs was significantly higher in the DEP-treated rats compared to the saline-treated rats at 5 and 7 days post-Listeria exposure (approximately 17,000 Listeria/left lobe vs approximately 8,500 at 5 days; approximately 7,000 vs approximately 1,500 at 7 days). Exposure to DEP alone resulted in increased NO production by AM. However, the NO production among Listeria-infected rats was not different. These results show that DEP exposure compromises the pulmonary clearance of Listeria and increases the susceptibility of hosts to this infectious pathogen. This decreased Listeria clearance in rats after DEP exposure does not seem to be dependent on reactive nitrogen intermediates.
The Toxicologist. Society of Toxicology 38th Annual Meeting, March 14-18, 1999, New Orleans, Louisiana