Modulation of Immune Function in Mice Exposed to 0.8 PPM Ozone

Abstract

Ozone has been shown to both enhance and suppress local and systemic immune responses, depending upon the experimental conditions and the immune parameters under investigation. To gain insight into this apparent immunomodulation, mice were continuously exposed to 0.8 ppm of 0, for 1, 3, 7, and 74 days prior to assessment of their immune function. Lymphocytes from the mediastinal lymph nodes (MLN) and the spleen were examined in order to distinguish local and systemic immune compartments, respectively. Ozone exposure resulted in an initial decrease in MLN cell numbers and spleenlbody weight ratios, which then returned to normal and increased above control values following more prolonged exposure. SirnilarlF the lymphocyte responses to mitogen and the splenocyte tumoricidal activity were initially decreased by exposure to 0.8 ppm ozone but later returned to control levels. To evaluate the effect of O₃ on the specific immune response, mice were immunized parenterally with ovalbumin (OA) followed by an aerosol boost with OA at 14 days. A week later the animals were assessed for specific immune responses. Exposure to 0.8 ppm O₃ for 14 days prior to assay resulted in an increased MLN lymphocyte response to specific antigen, while the splenic (systemic) response was decreased. Specific IgG and IgA antibody titers to the antigen in the bronchoalveolar lavage fluid were significantly suppressed following 7 and 14 days of exposure to O₃ but were unaltered in serum. These data, in part, explain the divergent responses observed by others. Ozone exposure initially suppresses local and systemic aspects of innate immunity, which recover or adapt over more prolonged exposure. Specific immune responses, however, can be either suppressed or enhanced following long-term exposure, depending upon the anatomical site and biological end point measured.