Ozone-induced modulation of cell-mediated immune responses in the lungs

Most pulmonary immunotoxicology studies of ambient pollutants have been broadly designed to discern if overall humoral or cell-mediated immunity (CMI) was altered; few have assessed effects on particular aspects of immune function. We hypothesized that effects from ozone (O3) exposure on pulmonary CMI are linked in part to changes in local immune cell capacities to form and/or to interact with immunoregulatory cytokines. Rats exposed to 0.1 or 0.3 ppm O3 4 h/day 5 days/week, for 1 or 3 weeks were assessed for resistance to, and pulmonary clearance of, a subsequent Listeria monocytogenes challenge. In situ cytokine release and immune cell profiles were also analyzed at different stages of the antilisterial response. Although O3 exposure modulated CMI, effects were not consistently concentration- or duration-dependent. Exposure did not effect cumulative mortality from infection, but induced concentration-related effects upon morbidity onset and persistence. All 1-week exposed rats had listeric burdens trending higher than controls; 0.3 ppm rats displayed continual burden increases rather than any onset of resolution. Rats exposed for 3 weeks had no O3-related changes in clearance. No exposure-related effect on neutrophil or pulmonary macrophage (PAM) numbers or percentages was noted. Bacterial burden analyses with respect to cell type showed that Listeria:PAM ratios in 0.3 ppm rats ultimately became greatest compared to all other rats. In situ IL-1alpha and TNFalpha levels were consistently higher in O3-exposed rats. All rats displayed increasing in situ IFNgamma levels as infection progressed, but no constant relationship was evident between IFNgamma and initial IL-1alpha/TNFalpha levels in O3-exposed hosts. It seems that short-term (i.e., 1 week) repeated O3 exposures imparted more effects upon CMI than a more prolonged (i.e., 3 week) regimen, with effects manifesting at the level of the PAM and in the cytokine network responsible for immunoactivation.