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Viral respiratory infections are a common cause of severe disease, especially in infants, people who are immunocompromised, and in the elderly. Neutrophils, an important innate immune cell, infiltrate the lungs rapidly after an inflammatory insult. The most well-characterized effector mechanisms by which neutrophils contribute to host defense are largely extracellular and the involvement of neutrophils in protection from numerous bacterial and fungal infections is well established. However, the role of neutrophils in responses to viruses, which replicate intracellularly, has been less studied. It remains unclear whether and, by which underlying immunological mechanisms, neutrophils contribute to viral control or confer protection against an intracellular pathogen. Furthermore, neutrophils need to be tightly regulated to avoid bystander damage to host tissues. This is especially relevant in the lung where damage to delicate alveolar structures can compromise gas exchange with life-threatening consequences. It is inherently less clear how neutrophils can contribute to host immunity to viruses without causing immunopathology and/or exacerbating disease severity. In this review, we summarize and discuss the current understanding of how neutrophils in the lung direct immune responses to viruses, control viral replication and spread, and cause pathology during respiratory viral infections.

The three-dimensional structure of the haemagglutinin-neuraminidase (HN) from a human parainfluenza virus is described at ca 2.0 A resolution, both in native form and in complex with three substrate analogues. In support of earlier work on the structure of the homologous protein from the avian pathogen Newcastle disease virus (NDV), we observe a dimer of beta-propellers and find no evidence for spatially separated sites performing the receptor-binding and neuraminidase functions of the protein. As with the NDV HN, the active site of the HN of parainfluenza viruses is structurally flexible, suggesting that it may be able to switch between a receptor-binding state and a catalytic state. However, in contrast to the NDV structures, we observe no ligand-induced structural changes that extend beyond the active site and modify the dimer interface.

Background: Recently, we observed that the severity of glomerulonephritis in an experimental model of immunoglobulin A nephropathy (IgAN) induced by Sendai virus differs between C57BL/6 and BALB/c mouse strains. The determinants of differing renal insufficiency are not understood. In the present study, we examine the capacity for mesangial cells to support Sendai viral replication and assess the direct effects of Sendai virus on the production of selected cytokines, chemokines, and eicosanoids by mesangial cells, comparing C57BL/6 to BALB/c mouse strains., Methods: Sendai virus replication was measured by viral plaque assay using LLCMK2 cells. Production of cytokines [interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha)], chemokines (JE and KC), and eicosanoids [prostaglandin E2 (PGE2) and thromboxane B2 (TxB2)] in culture medium was evaluated by sandwich enzyme-linked immunosorbent assay (ELISA) or competitive enzyme immunoassay (EIA) after 48 hours' incubation with infectious or inactivated Sendai virus., Results: Sendai virus replicates equally well in mesangial cells from both strains, and infection evokes increased IL-6, JE, KC, and PGE2 production in relation to viral dose. BALB/c mesangial cells produce significantly more IL-6 and JE than those from C57BL/6, and the dose response for KC is steeper in BALB/c mesangial cells than those from C57BL/6. Synthesis of PGE2 in BALB/c mesangial cells is higher than that of C57BL/6 mesangial cells, both under basal conditions and in response to infectious Sendai virus, again in a dose-dependent manner. There is no TNF-alpha or thromboxane response to viral stimulation., Conclusion: We conclude that different mesangial cell responses to this common mucosal viral pathogen might influence the severity of IgAN in our model system.

To elucidate molecular mechanisms underlying the association between respiratory viral infection and predisposition to subsequent bacterial infection, we used in vivo and in vitro models and human samples to characterize respiratory virus-induced changes in airway epithelial cell morphology, gene expression, and mucociliary function. Mouse paramyxoviral bronchitis resulted in airway epithelial cell infection and a distinct pattern of epithelial cell morphology changes and altered expression of the differentiation markers beta-tubulin-IV, Clara cell secretory protein, and Foxj1. Furthermore, changes in gene expression were recapitulated using an in vitro epithelial cell culture system and progressed independent of the host inflammatory response. Restoration of mature airway epithelium occurred in a pattern similar to epithelial cell differentiation and ciliogenesis in embryonic lung development characterized by sequential proliferation of undifferentiated cells, basal body production, Foxj1 expression, and beta-tubulin-IV expression. The effects of virus-induced alterations in morphology and gene expression on epithelial cell function were illustrated by decreased airway mucociliary velocity and impaired bacterial clearance. Similar changes in epithelial cell Foxj1 expression were also observed in human paramyxoviral respiratory infection. Taken together, these model systems of paramyxoviral respiratory infection mimic human pathology and identify epithelial cell Foxj1 expression as an early marker of epithelial cell differentiation, recovery, and function.

This study was performed to evaluate the effect of ozone (O3) exposure at 1 ppm for 2 hr on the susceptibility/resistance of adult human alveolar macrophages (AM) to infection with respiratory syncytial virus (RSV) in vitro and on RSV-induced cytokine production by the AM. AM were first exposed to O3 or to filtered air and then infected with RSV at multiplicities of infection (m.o.i.) of 0.1, 1.0, and 10. The percentage RSV-infected AM and the amount of infectious virus released by the cells were determined at Days 2 and 4 after infection. Interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF) levels in the supernatants were determined on Day 2. No difference in the percentage infected AM or in the amount of infectious RSV produced was found between control and O3-exposed cultures. However, O3-exposed AM infected with RSV at m.o.i. 1 produced less IL-1 in response to RSV infection than control AM: 63.6 pg/ml compared with 98.5 pg/ml. No difference in IL-1 was seen with m.o.i. 10. IL-6 levels were also decreased, but only after infection with m.o.i. 0.1. At this level of infection 830 pg/ml was produced by control AM as compared to 468.2 pg/ml by O3-exposed AM. TNF production was unaffected by O3 at all multiplicities of infection. Statistical analysis of the O3 effect on AM cytokine production induced by the different multiplicities, however, revealed no significant effect of O3. Based on these observations it appears unlikely that O3 alters susceptibility of AM to infection with RSV, nor does O3 dramatically alter cytokine production in response to RSV since effects on IL-1 and IL-6 secretion were only found with the lowest levels of infection which induced cytokine release.