Pulmonary clearance of Pasteurella haemolytica and immune responses in mice following exposure to titanium dioxide.

The effects of dust inhalation on immune responses in mice to aerosolized Pasteurella haemolytica were investigated. Animals exposed to titanium dioxide dust (TiO2) at a respirable aerosol concentration of approximately 20 mg m-3 for 20 hr per day, before or after aerosol vaccination, had impaired pulmonary bacterial clearance relative to animals kept in clean air. Additionally, lymphocytes from the local (mediastinal) lymph nodes had depressed responses to bacterial antigen in vitro in mice exposed to dust immediately after vaccination. However, there were no differences in the splenic lymphocyte responses between groups, while serum antibody responses were low and variable. A second experiment showed that aerosol vaccinated and nonvaccinated animals, which were exposed to a respirable aerosol concentration of TiO2 at 20 mg m-3 immediately after inoculation with a bacterial aerosol, had impaired clearance compared to their respective controls maintained in clean air.