We previously reported that congenic C57BL/6
inducible nitric oxide synthase(-/-) (iNOS(-/-)) mice infected with Mycoplasma pulmonis developed higher bacterial numbers and lung lesion scores than C57BL/6 iNOS(+/+) controls but had similar lung
nitrotyrosine levels. The present studies investigated the role of inflammatory cells in
nitrotyrosine formation during mycoplasmal
infection. iNOS(+/+) and iNOS(-/-) mice were injected with
cyclophosphamide (CYP) and inoculated with 10(7) CFU of M. pulmonis. CYP pretreatment of M. pulmonis-infected iNOS(+/+) and iNOS(-/-) mice reduced polymorphonuclear cells (PMNs) within bronchoalveolar lavages (BALs) by 88 and 72%, respectively, and whole-lung
myeloperoxidase levels by 80 and 78%, respectively, at 72 h postinfection but did not alter the number of alveolar macrophages (AMs) in BALs. CYP treatment also significantly decreased
nitrate and
nitrite (NOx) levels in BALs and plasma of infected iNOS(+/+) mice, whereas neither CYP nor mycoplasmal
infection altered NOx in iNOS(-/-) mice. CYP reduced lung
nitrotyrosine levels in both iNOS(+/+) and iNOS(-/-) mice to uninfected-control levels as shown by immunohistochemical staining and
enzyme-linked
immunosorbent assay and inhibited mycoplasmal killing by iNOS(+/+) mice in vivo. CYP inhibited the production of
gamma interferon-inducible NOx by iNOS(+/+) AMs in vitro but did not alter the number of iNOS-positive AMs, as detected by immunocytochemistry. In addition, AMs from CYP-treated iNOS(+/+) mice had significantly decreased ability to kill mycoplasmas in vitro. These results demonstrate that reactive species generated by inflammatory cells as well as PMN
myeloperoxidase are important contributors to
nitrotyrosine formation during mycoplasmal
infection and that treatment with CYP decreases NO* production by AMs and inhibits mycoplasmal killing.