Effects of oxidant stress on inflammation and survival of iNOS knockout mice after marrow transplantation

In a model of idiopathic pneumonia syndrome after bone marrow transplantati on (BMT), injection of allogeneic T cells induces nitric oxide (. NO), and the addition of cyclophosphamide (Cy) generates superoxide (O-2(radical ani on)) and a tissue-damaging nitrating oxidant. We hypothesized that . NO and O-2(radical anion) balance are major determinants of post-BMT survival and inflammation. Inducible nitric oxide synthase (iNOS) deletional mutant mic e (-/-) given donor bone marrow and spleen T cells (BMS) exhibited improved survival compared with matched BMS controls. Bronchoalveolar lavage fluids obtained on day 7 post-BMT from iNOS(-/-) BMS mice contained less tumor ne crosis factor-alpha and interferon-gamma, indicating that . NO stimulated t he production of proinflammatory cytokines. However, despite suppressed inf lammation and decreased nitrotyrosine staining, iNOS(-/-) mice given both d onor T cells and Cy (BMS + Cy) died earlier than iNOS-sufficient BMS + Cy m ice. Alveolar macrophages from iNOS(-/-) BMS + Cy mice did not produce . NO but persisted to generate strong oxidants as assessed by the oxidation of the intracellular fluorescent probe 2',7'-dichlorofluorescin. We concluded that . NO amplifies T cell-dependent inflammation and addition of Cy exacer bates . NO-dependent mortality. However, the lack of . NO during Cy-induced oxidant stress decreases survival of T cell-recipient mice, most likely by generation of . NO-independent toxic oxidants.