Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract disease in infants and children worldwide. Intranasal infection of BALB/c mice with RSV strain A2, but not ultraviolet-inactivated RSV, for 2 or 4 days reduced basal alveolar fluid clearance (AFC), a seminal function of bronchoalveolar epithelium, and caused loss of AFC sensitivity to amiloride inhibition. Reduced AFC was temporally associated with increased lung water content but was not a consequence of increased epithelial permeability or cell death. Reduced AFC was also not due to decreased transcription of epithelial Na+ channel subunit genes in lung tissue. RSV-mediated inhibition of AFC 2 days after infection was rapidly prevented by addition to the instillate of P2Y receptor antagonists (suramin and XAMR-0721) or enzymes that degrade UTP, but not those that degrade ATP. After UTP degradation, AFC returned to control levels but was no longer sensitive to amiloride. UTP at nanomolar concentrations recapitulated the AFC inhibitory effect of RSV in normal mice and mice infected with RSV for 6 days, indicating that normalization of AFC at this time point is a consequence of cessation of UTP release, rather than P2Y receptor desensitization. We conclude that RSV infection of the bronchoalveolar epithelium results in reduced AFC as a consequence of autocrine feedback inhibition mediated by UTP. These studies are the first to demonstrate AFC inhibition by an important pulmonary viral pathogen. Reduced AFC may result in formation of an increased volume of fluid mucus, airway congestion, and rhinorrhea, all features of severe RSV disease.

We have previously shown that surfactant protein A (SP-A) mediates in vitro killing of mycoplasmas by alveolar macrophages (AMs) from resistant C57BL/6 mice through a nitric oxide (⅐NO)-dependent mechanism. Herein, SP-A-deficient [SP-A(؊/؊)] and inducible ⅐NO synthasedeficient [iNOS(؊/؊)] mice were infected intranasally with 10 5 or 10 7 colony-forming units of Mycoplasma pulmonis. SP-A(؊/؊) mice were as susceptible to mycoplasmal infection as highly susceptible C3H/He mice, and far more susceptible than resistant C57BL/6 mice. iNOS(؊/؊) mice had significantly greater numbers of mycoplasmas and severity of lung lesions than iNOS(؉/؉) controls. In vitro, AMs isolated from C57BL/6 mice, activated with IFN-␥, incubated with SP-A (25 g/ml), and infected with 10 10 colony-forming units of M. pulmonis, killed mycoplasmas within 6 h. Mycoplasmal killing was abrogated by 1,000 units/ml of copper-zinc superoxide dismutase. In the absence of AMs, incubation of M. pulmonis with the peroxynitrite generator 3-morpholinosynodiomine⅐HCl (SIN-1) effected complete killing of mycoplasmas by 90 min in a dose-dependent manner. Addition of copper-zinc superoxide dismutase (3,000 units/ml), which converts SIN-1 to a ⅐NO donor, prevented this killing. Neither of the reactive oxygen species generated by xanthine oxidase (10 milliunits/ ml, plus 500 M xanthine and 100 M FeCl 3 ), nor ⅐NO generated by 1-propanamine-3-(2-hydroxy-2-nitroso-1-propylhydrazine (PAPA NONOate) (100 M) killed mycoplasmas. These data establish that peroxynitrite generation by AMs is necessary for the killing of a pathogen in vitro and in vivo.

Oxidative stress may impair alveolar macrophage function in patients with inflammatory lung diseases or those exposed to high concentrations of oxygen. We investigated putative mechanisms of injury to macrophages by oxidative stress, using RAW 264.7 cells exposed to 95% oxygen for 48 h. Hyperoxia-exposed macrophages were less able to phagocytose and kill Klebsiella pneumoniae than normoxic controls, despite increased production of nitric oxide, a free radical important in pathogen killing. Exposure of macrophages to hyperoxia had marked effects on the actin cytoskeleton, including increased actin polymerization, loss of cortical actin, formation of stress fibers, de novo synthesis of actin, and actin oxidation. Hyperoxia induced changes in cell morphology, with increased cell size and pseudopod formation. Exposure of macrophages to jasplakinolide, an agent that increases actin polymerization, also impaired their ability to phagocytose Klebsiella. Alveolar macrophages isolated from mice exposed to 100% oxygen for 84 h also demonstrated impaired phagocytic function, as well as similar effects on the actin cytoskeleton and cell morphology to macrophages exposed to hyperoxia in vitro. We conclude that oxidative stress in vitro and in vivo impairs macrophage antibacterial function through effects on actin.

Rationale: Previously, we demonstrated that intranasal infection of BALB/c mice with respiratory syncytial virus (RSV) resulted in an early 40% reduction in alveolar fluid clearance (AFC), an effect mediated via P2Y purinergic receptors. Objectives: To confirm that RSV-induced inhibition of AFC is mediated by uridine triphosphate (UTP), and to demonstrate that inhibition of de novo pyrimidine synthesis with leflunomide prevents increased UTP release after RSV infection, and thereby also prevents inhibition of AFC by RSV. Methods: BALB/c mice were infected intranasally with RSV strain A2. AFC was measured in anesthetized, ventilated mice by instillation of 5% bovine serum albumin into the dependent lung. Some mice were pretreated with leflunomide or 6-mercaptopurine. Measurements and Main Results: RSV-mediated inhibition of AFC is associated temporally with a 20-nM increase in UTP and ATP content of bronchoalveolar lavage fluid, hypoxemia, and altered nasal potential difference. RSV-mediated nucleotide release, AFC inhibition, and physiologic sequelae thereof can be prevented by pretreatment of mice with the de novo pyrimidine synthesis inhibitor leflunomide, which is not toxic to the mice, and which does not affect RSV replication in the lungs. In contrast, pretreatment of mice with 6-mercaptopurine, an inhibitor of de novo purine synthesis, has no beneficial effect on AFC or other indicators of disease progression. Finally, RSV-mediated inhibition of AFC is prevented by volumeregulated anion channel inhibitors. Conclusion: Pyrimidine synthesis or release pathways may provide novel therapeutic targets to counter the pathophysiologic sequelae of impaired AFC in RSV disease.Keywords: ion transport; paramyxovirus infections; pneumonia, viral; pulmonary edemaThe dominant ion transport process of the alveolar epithelium is active movement of Na ϩ ions from the airspace lining fluid to the interstitium (1). This creates an osmotic gradient, causing water to follow passively. This process of alveolar fluid clearance (AFC) is crucial to efficient gas exchange. Importantly, patients with acute lung injury with intact AFC have lower morbidity and mortality than those with compromised AFC (2).Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract disease in infants and children worldwide (3), but its pathogenesis remains poorly understood. Previously, we demonstrated that infection of BALB/c mice with RSV results in reduced AFC at early time points after infection, and inferred that RSV-mediated inhibition of AFC 2 d after infection was mediated by uridine triphosphate (UTP), acting on P2Y receptors (P2YRs) on lung epithelial cells (4). The aim of the current study was to confirm the central role of UTP in mediating the inhibitory effects of RSV on AFC, and to demonstrate that pharmacologic inhibition of de novo pyrimidine synthesis with leflunomide prevents increased UTP release after RSV infection, and thereby also prevents inhibition of AFC by RSV. Furthermore, we demonstrated that blockag...

Mycoplasma pneumoniae is a leading cause of pneumonia and exacerbates other respiratory diseases in humans. We investigated the potential role of surfactant protein (SP) A in antimycoplasmal defense using alveolar macrophages (AMs) from C57BL/6NCr (C57BL) mice, which are highly resistant to infections of Mycoplasma pulmonis. C57BL AMs, activated with interferon (IFN)-γ and incubated with SP-A (25 μg/ml) at 37°C, produced significant amounts of nitric oxide (⋅ NO; nitrate and nitrite production = 1.1 μM ⋅ h−1 ⋅ 105AMs−1) and effected an 83% decrease in mycoplasma colony-forming units (CFUs) by 6 h postinfection. Preincubation of AMs with the inducible nitric oxide synthase inhibitor N G-monomethyl-l-arginine abolished ⋅ NO production and SP-A-mediated killing of mycoplasmas. No decrease in CFUs was seen when IFN-γ-activated macrophages were infected with mycoplasmas in the absence of SP-A despite significant ⋅ NO production (nitrate and nitrite production = 0.6 μM ⋅ h−1 ⋅ 105AMs−1). These results demonstrate that SP-A mediates killing of mycoplasmas by AMs, possibly through an ⋅ NO-dependent mechanism.