At 4 weeks after intraperitoneal (i.p.) injection of 0.21-LD50 (50% lethal dose) of murine cytomegalovirus (MCMV) in adult BALB/c mice, productive virus and the viral DNA were detected only in the salivary glands, but not in the lungs. A single i.p. injection of anti-CD3 mAb to these mice provoked pulmonary lesions, which included a thickening of the interstitium and peribronchiolar areas, accompanied with a cellular infiltration in those areas. As a result, half of the mice died. In a histochemical analysis with anti-nitrotyrosine polyclonal Ab, bronchiolar epithelial cells were stained with this Ab, thus demonstrating that peroxynitrite, which was biochemically derived from nitric oxide (NO), injured those cells. Similarly, when T cells of iNOS(+/)+ mice, which had been infected with MCMV 4 weeks before, were activated by a single injection of anti-CD3 mAb, 37.5% of the mice died. Nitrotyrosine was also detected in the bronchiolar epithelial cells in these mice. In contrast, none of MCMV-infected iNOS(-/-) mice died after the anti-CD3 injection. No pathological changes were noted in the histological findings of the lungs of those mice. An intranasal injection of bacterial superantigen, staphylococcal enterotoxin B (SEB), demonstrated the same histopathological changes in the lungs and mortality in BALB/c mice as those in mice i.p. injected with anti-CD3. Therefore, T-cell responsiveness to stimulation with anti-CD3 or a superantigen was presumably modified by MCMV infection. MCMV-associated pneumonitis in the present study was thus mediated not by a direct viral attack but by iNOS-derived NO, which can be induced by the cytokines from the T cells. In addition, it was demonstrated that the NO produced by the cytokine-mediated pathway targeted bronchiolar epithelial cells.
