Susceptibility to Murine Respiratory Mycoplasmosis and Decreases Intrapulmonary Killing of Mycoplasma pulmonis 1 - 3

SUMMARY In C57BLl6N and C3H/HeN mice known to be free of allmurine pathogens and matched for age, sex, microbiologic, and environmental factors, exposure to NO, for 4 h prior to exposure to Infectious aerosols of Mycoplasma pulmonls resulted In potentiation of murine respiratory mycoplasmosis (MRM). In the C57BLl6N mice, NO, Increased the Incidence of death, incidence of gross lung lesions, and incidence of microscopic lung lesions, but did not Increase the Incidence of Infection in the lungs. Nitrogen dioxide affected the C3H/HeN mice (a strain known to be more susceptible than the C57BLl6N strain to MRM) similarly, with the exception that the incidence of death and microscopic lesions were not affected in this strain at the concentrations of M. pulmonls used. Exposure to the oxidant also Increased the severity of microscopic lesions and the numbers of Mycoplasma organisms In the lungs of both mouse strains. ThUS, NO, appeared to affact host lung defense mechanisms responsible for limiting the extent of Infection. The NO, exposure level required to produce potentiation varied witl1 the genetic background of the host, the number of Mycoplasma organisms administered, and the end point measured. In further experiments In C57BLl6N mice, exposure to 5 or 10 ppm of NO, for 4 h prior to Infection with aerosolized, radlola­ beled M. pu/monls reduced clearance of these organisms from the lungs over a 72-h time period. Nitrogen dioxide exposure did not change the rate of physical removal of Mycoplasma organisms from the lung. Reduced clearance was due to Impaired Intrapulmonary killing of Mycoplasma or­ ganisms In NO,-8xposed mice. In filtered-air control mice, there were no Increases In leukocytes recovered from mechanically dlsaggregated lungs within 72 h after infection. In contrast, by that time after Infection, NO,-8xposed mice showed a 400% increase Inneutrophil numbers, which oc­ curred after changes In mycoplasmacidalactivity. No differences_re found In the levels of specific anti-M. pulmonis IgM In the sera of NO,-8xposed and filtered-air control mice. These results directly link decreased pulmonary clearance after NO, exposure with Increased disease severity.