Exposure to silica activates macrophages and increases the pulmonary clearance of listeria monocytogenes in rats.
Yang-HM; Ma-JYC; Roberts-JR; Barger-MW; Butterworth-L; Castranova-V; Antonini-JM
Toxicologist 2000 Mar; 54(1):318
Alveolar macrophages (AM) play a crucial role in protecting the lungs from infectious agents. In this study, we evaluated the effect of silica on macrophage function using a rat Listeria monocytogenes (LM) infection model. Male Sprague-Dawley rats were instilled intratracheally with saline or silica (20 mg/rat). Thirty-five days later, the rats were then inoculated intratracheally with either approximately 5,000 or 500,000 LM. At 3, 5, and 7 days post-infection, the left lung was removed, homogenized and cultured on brain heart infusion agar at 37 degrees C. The numbers of viable LM were counted after an overnight incubation. Bronchoalveolar lavage (BAL) was performed on the right lungs and BAL cell differentials, acellular LDH activity and acellular albumin content were determined. Macrophage chemiluminescence (CL) and nitric oxide (NO) production were assessed as a measure of macrophage function. Pre-exposure to silica significantly increased the pulmonary clearance of LM as compared to saline controls. Exposure to silica caused significant increases in BAL neutrophils, LDH and albumin in non-infected rats. The generation of CL by AM was also enhanced in silica-treated rats. In summary, the results demonstrated that subchronic exposure of rats to silica increased neutrophil infiltration and macrophage activation. These enhanced activities may be responsible for increasing the pulmonary clearance of LM.
Silica-dusts; Exposure-levels; Silicates; Laboratory-animals; Animals; Animal-studies; Lung-disorders; Pulmonary-system-disorders; Respiratory-system-disorders
The Toxicologist. Society of Toxicology 39th Annual Meeting, March 19-23, 2000, Philadelphia, Pennsylvania