Inhalation of residual oil fly ash (ROFA) has been shown to increase pulmonary morbidity and impair lung defense mechanisms. The objective of this study was to evaluate the effect of ROFA exposure on the clearance of a bacterial pathogen from the lungs. Elemental analysis revealed the ROFA particles to be comprised of Al, Si, S, Ca, V, Fe, and Ni. Young adult male Sprague-Dawley rats were dosed intratracheally with saline (control) or ROFA at a dose of 1 mg/100 g b wt. Three days later, approximately 500,000 Listeria monocytogenes were intratracheally instilled into the ROFA-treated and saline control rats. Bronchoalveolar lavage was performed on the right lungs at 3,5, and 7 days after exposure to L. monocytogenes. The cells recovered were differentiated, and chemiluminescence, an index of macrophage activation, was measured. At the same time points, the left lung and spleen were removed, homogenized, and cultured on brain heart infusion agar at 37 C. Colony forming units were counted after an overnight incubation. Pre-exposure to ROFA significantly (p<0.05) delayed the pulmonary clearance of L. monocytogenes as compared to the saline control rats. ROFA had no effect on the influx of neutrophils into the lungs but caused a significant (p<0.05) decrease in macrophage chemiluminescence as compared to saline control rats. We have demonstrated that acute exposure to ROFA slowed the pulmonary clearance of L. monocytogenes. This is most likely due to a ROFA-induced suppression of macrophage activation, perhaps related to the elemental composition of the particles. Therefore, in an occupational setting, inhalation of ROFA may lead to increased susceptibility to pulmonary infection.
The Toxicologist. Society of Toxicology 39th Annual Meeting, March 19-23, 2000, Philadelphia, Pennsylvania