Human metapneumovirus (HMPV) has emerged as an important human respiratory pathogen causing upper and lower respiratory tract infections in young children and older adults. Recent epidemiological evidence indicates that HMPV may cocirculate with respiratory syncytial virus, and HMPV infection has been associated with other respiratory diseases. In this study, we show that BALB/c mice are susceptible to HMPV infection, the virus replicates in the lungs with biphasic growth kinetics in which peak titers occur at days 7 and 14 postinfection (p.i.), and infectious HMPV can be recovered from lungs up to day 60 p.i. In addition, we show that genomic HMPV RNA can be detected in the lungs for >180 days p.i. by reverse transcription-PCR; however, neither HMPV RNA nor infectious virus can be detected in serum, spleen, kidneys, heart, trachea, and brain tissue. Lung histopathology revealed prevalent mononuclear cell infiltration in the interstitium beginning at day 2 p.i. and peaking at day 4 p.i. which decreased by day 14 p.i. and was associated with airway remodeling. Increased mucus production evident at day 2 p.i. was concordant with increased bronchial and bronchiolar inflammation. HMPV-specific antibodies were detected by day 14 p.i., neutralizing antibody titers reached >6.46 log 2 end-point titers by day 28 p. i., and depletion of T cells or NK cells resulted in increased HMPV titers in the lungs, suggesting some immune control of viral persistence. This study shows that BALB/c mice are amenable for HMPV studies and indicates that HMPV persists as infectious virus in the lungs of normal mice for several weeks postinfection.Human metapneumovirus (HMPV) is tentatively a member of the Metapneumovirus genus based on genetic sequence similarity to the type species avian metapneumovirus (46). HMPV was first identified in respiratory specimens from young children hospitalized with mild to severe lower respiratory tract illness (46), and recent studies indicate that HMPV may cause upper and lower respiratory tract illness in patients between the ages of 2 months and 87 years (5,6,8,23,49,50). The disease burden associated with HMPV infection is not well known and may be complicated by the ability of HMPV to cocirculate with respiratory syncytial virus (RSV) in the community (28,37,50). A recent prospective study of young and older adults hospitalized for respiratory infections during the RSV season showed that HMPV was associated with approx-

Intratracheal infection of mice with adenovirus is associated with subsequent pulmonary inflammation and edema. Water movement through the air space-capillary barrier in the distal lung is facilitated by aquaporins (AQPs). To investigate the possibility that distal lung AQPs undergo altered regulation under conditions of aberrant fluid handling in the lung, we analyzed messenger RNA (mRNA) and protein expression of AQPs 1 and 5 in the lungs of mice 7 and 14 d after infection with adenovirus. Here, we demonstrate that AQP1 and AQP5 show decreased expression following adenoviral infection. Northern blot analysis showed significantly decreased mRNA levels of AQP1, which is expressed in the capillary endothelium, and AQP5, which is expressed in alveolar epithelium, in the lungs of mice both 7 and 14 d after infection. Immunoblotting studies demonstrated significantly reduced levels of AQP1 and AQP5 protein after infection as well. In addition, mRNA expression of the alpha subunit of the epithelial sodium channel was reduced in the lungs of mice 7 and 14 d after adenoviral infection. In contrast, mRNA expression of the alpha1 subunit of the Na,K-adenosine triphosphatase in the lung was unaltered. Immunohistochemical analysis demonstrated that the decreases in AQP1 and AQP5 expression were not localized to regions of overt inflammation but were found throughout the lung. Thus, this study provides the first report of AQP gene regulation in an in vivo model of pulmonary inflammation and edema. Decreased AQP1 and AQP5 levels during adenoviral infection suggest a role for AQP1 and AQP5 in the abnormal fluid fluxes detected during pulmonary inflammation.

Although epidemiologic data strongly suggest a role for inhaled environmental pollutants in modulating the susceptibility to respiratory infection in humans, the underlying cellular and molecular mechanisms have not been well studied in experimental systems. The current study assessed the impact of inhaled diesel engine emissions (DEE) on the host response in vivo to a common pediatric respiratory pathogen, respiratory syncytial virus (RSV). Using a relatively resistant mouse model of RSV infection, prior exposure to either 30 microg/m3 particulate matter (PM) or 1,000 microg/m3 PM of inhaled DEE (6 h/d for seven consecutive days) increased lung inflammation to RSV infection as compared with air-exposed RSV-infected C57Bl/6 mice. Inflammatory cells in bronchoalveolar lavage fluid were increased in a dose-dependent manner with regard to the level of DEE exposure, concomitant with increased levels of inflammatory mediators. Lung histology analysis indicated pronounced peribronchial and peribronchiolar inflammation concordant with the level of DEE exposure during infection. Mucous cell metaplasia was markedly increased in the airway epithelium of DEE-exposed mice following RSV infection. Interestingly, both airway and alveolar host defense and immunomodulatory proteins were attenuated during RSV infection by prior DEE exposure. DEE-induced changes in inflammatory and lung epithelial responses to infection were associated with increased RSV gene expression in the lungs following DEE exposure. These findings are consistent with the concept that DEE exposure modulates the lung host defense to respiratory viral infections and may alter the susceptibility to respiratory infections leading to increased lung disease.

Replication-deficient adenovirus vectors (Avs) have shown high-efficiency gene transfer in a variety of animal models, but demonstrated lower than expected efficiency in the intensely inflammatory milieu of the respiratory tract of individuals with cystic fibrosis (CF). Specific acquired immune responses directed at adenovirus capsid proteins are known to limit the duration of transgene expression and the effectiveness of vector readministration. In these models, however, nonspecific inflammation is also frequently noted to accompany specific immune responses. Because inflammation can occur early after Av administration, we hypothesized that inflammation may block Av-mediated gene transfer in the lung independent of specific immune responses. To evaluate this hypothesis, we measured pulmonary gene transfer and expression in the absence or presence of the potent antiinflammatory agent dexamethasone. To address and eliminate concerns over the potentially confounding effects of systemic, vector-specific acquired immune responses, evaluations were confined to a 3-day period following Av administration and were carried out, in parallel, in normal and immunodeficient (athymic) mice. Dexamethasone significantly reduced Av-associated inflammation in all animals as measured by a significant reduction of blinded, quantitative lung histopathology scores and by reduced proinflammatory cytokine release. Concomitant with reduced inflammation, gene transfer efficiency was significantly increased in both normal and immunodeficient animals as measured by transgene product activity (beta-galactosidase) in total lung homogenates 3 days after vector administration. This finding could not be explained by a direct effect of dexamethasone on transgene specific activity. To begin to understand the molecular mechanisms of Av-induced inflammatory responses, lung levels of the chemoattractive chemokines MIP-2, MIP-1alpha, and MCP-1 were quantified. All were elevated significantly in Av-exposed animals. Dexamethasone reduced levels of MCP-1 and MIP-1alpha, but not MIP-2, consistent with the observed pattern of inflammatory cell changes. Expression of several proinflammatory cytokines including TNF-alpha, IL-6, IL-1beta, and IFN-gamma were also elevated in Av-exposed animals and modulated by dexamethasone. These observations demonstrate that nonspecific inflammation is an important determinant of the efficiency of in vivo pulmonary gene transfer and expression independent of specific immune responses and may have important implications for human gene therapy for diseases of the lung.