Spleen cellularity shifts from the inhalation of 0.25-0.35 PPM nitrogen dioxide.

The effects of ambient level (0.25-0.35 ppm)NO2 on percent spleen cell counts, relative percentages of spleen lymphocyte subpopulations, spleen lymphoid nodule size, and differential peripheral blood cell counts were investigated in 170 young adult male mice following various NO2 exposure periods. The total spleen cell counts, surface IgM-positive lymphocytes and spleen mean lymphoid nodule area were all significantly decreased in the groups exposed to NO2 following extended time periods. The relative percentages of peripheral blood lymphocytes were also significantly decreased in the groups exposed to NO2 for 8 weeks. The mechanism for these observed spleen changes following ambient level NO2 exposure remains unclear, but the results warrant further investigation and concern, especially since such changes may reflect altered immune responsiveness.