Activated Alveolar Macrophage-Derived Nitric Oxide Predicts the Development of Lung Damage After Marrow Transplantation in Mice

Abstract

A major complication of human bone marrow transplantation (BMT) is the development of noninfectious diffuse lung damage referred to as idiopathic pneumonia syndrome (IPS). We hypothesized that T cell-mediated immune responses are critical for the development of IPS. Alloresponsive donor T cells activate host alveolar macrophages (AMs) to release tissue-damaging reactive oxygen and nitrogen species such as nitric oxide (NO) and peroxynitrite. In a model of BMT in irradiated B10.BR mice, injection of C57BL/6 T cells at the time of BMT resulted in histologic evidence of lung injury associated with the following: (1) fivefold increase in lactate dehydrogenase and total protein detected in the BAL fluid measured at day 7; (2) increased systemic levels of interleukin-6, interferon-gamma, and tumor necrosis factor-alpha; and (3) lung infiltration with T cells co-localized with host macrophages, with an increase in major histocompatibility complex class II antigens expression as detected by monoclonal antibodies. Irradiated and transplanted mice not injected with T cells did not develop lung dysfunction, and their lactate dehydrogenase and protein levels in the BAL were at baseline values. AMs obtained from the BAL 7 days following BMT were cultured on IgG-plated wells (2 × 105 per well) for 48 h and the stable NO product, nitrite (Greiss reaction), in the supernant was measured. In contrast to cells obtained from irradiated animals that did not produce NO, AMs from mice injected with T cells expressed the inducible form of NO synthase protein, and spontaneously generated large amounts of NO (nitrite 20 μM; n = 6). Mice preconditioned with cyclophosphamide (120 mg/kg/d on days −3 and −2) and injected with T cells developed significantly worst lung dysfunction, and their AMs spontaneously produced maximal amounts of NO (nitrite 40.8 μM; n = 6). The inducible form of NO synthase messenger RNA was detected in lung tissue of mice injected with T cells. We conclude that T-cell responses are critical for the development of IPS. Activation of AM correlates with development of lung dysfunction and induction of NO generation.