Effect of diesel exhaust on the host response to respiratory viral infection: involvement of toll-like receptor 3

Adverse effects resulting from exposure to air pollutants have become an increasing problem worldwide. Particularly levels of air pollutants have been associated with increases in the susceptibility and response to many respiratory diseases. Of the numerous air pollutants, diesel exhaust (DE) has become a major concern since it can account for a significant amount of the pollutants generated by motor vehicles in many areas. Previous results in our laboratory have demonstrated that prior exposure of respiratory epithelial cells to DE enhances the susceptibility to influenza infections. In this work, these results were confirmed and expanded upon both in vitro and in vivo. The effects of DE on the expression and signaling of toll-like receptor 3 (TLR3), which has previously shown to be needed for a complete innate immune response to influenza infections as well as other respiratory viral infections, were examined as well as mechanistic aspects involved in the observed effects. Increased expression and signaling of TLR3 was observed in respiratory epithelial cells exposed to DE prior to infection with influenza, resulting in an enhancement of the influenza-induced inflammatory and interferon (IFN) responses. A positive-feedback loop involving type I IFNs and DE-induced effects on epithelial cell tight junctional complexes played a role in the observed effects. In vivo exposure of mice to DE enhanced the susceptibility to influenza infections and decreased expression of surfactant proteins A and D, which are an important part of the innate immune defense against influenza and other respiratory viruses. Together, these results demonstrate that exposure to an oxidant air pollutant, such as diesel exhaust, can enhance the susceptibility and response to respiratory viral infection and elucidate potential mechanisms behind some of these effects

Localization of Type I Interferon Receptor Limits Interferon-Induced TLR3 in Epithelial Cells

Previous studies have shown that influenza infections increase Toll-like receptor 3 (TLR3) expression and that type I interferons (IFNs) may play a role in this response. This study aimed to expand on the role of type I IFNs in the influenza-induced upregulation of TLR3 and determine whether and how the localization of the IFN-α/β receptor (IFNAR) in respiratory epithelial cells could modify IFN-induced responses. Using differentiated primary human airway epithelial cells this study demonstrates that soluble mediators secreted in response to influenza infection upregulate TLR3 expression in naive cells. This response was associated with an upregulation of type I IFNs and stimulation with type I, but not type II, IFNs enhanced TLR3 expression. Interestingly, although influenza infection results in IFN-β release both toward the apical and basolateral sides of the epithelium, TLR3 expression is only enhanced in cells stimulated with IFN-β from the basolateral side. Immunohistochemical analysis demonstrates that IFNAR expression is limited to the basolateral side of differentiated human airway epithelial cells. However, non- or poorly differentiated epithelial cells express IFNAR more toward the apical side. These data demonstrate that restricted expression of the IFNAR in the differentiated airway epithelium presents a potential mechanism of regulating type I IFN-induced TLR3 expression

Determinants of host susceptibility to murine respiratory syncytial virus (RSV) disease identify a role for the innate immunity scavenger receptor MARCO gene in human infants

AbstractBackgroundRespiratory syncytial virus (RSV) is the global leading cause of lower respiratory tract infection in infants. Nearly 30% of all infected infants develop severe disease including bronchiolitis, but susceptibility mechanisms remain unclear.MethodsWe infected a panel of 30 inbred strains of mice with RSV and measured changes in lung disease parameters 1 and 5days post-infection and they were used in genome-wide association (GWA) studies to identify quantitative trait loci (QTL) and susceptibility gene candidates.FindingsGWA identified QTLs for RSV disease phenotypes, and the innate immunity scavenger receptor Marco was a candidate susceptibility gene; targeted deletion of Marco worsened murine RSV disease. We characterized a human MARCO promoter SNP that caused loss of gene expression, increased in vitro cellular response to RSV infection, and associated with increased risk of disease severity in two independent populations of children infected with RSV.InterpretationTranslational integration of a genetic animal model and in vitro human studies identified a role for MARCO in human RSV disease severity. Because no RSV vaccines are approved for clinical use, genetic studies have implications for diagnosing individuals who are at risk for severe RSV disease, and disease prevention strategies (e.g. RSV antibodies)

Localization of Type I Interferon Receptor Limits Interferon-Induced TLR3 in Epithelial Cells

Previous studies have shown that influenza infections increase Toll-like receptor 3 (TLR3) expression and that type I interferons (IFNs) may play a role in this response. This study aimed to expand on the role of type I IFNs in the influenza-induced upregulation of TLR3 and determine whether and how the localization of the IFN-α/β receptor (IFNAR) in respiratory epithelial cells could modify IFN-induced responses. Using differentiated primary human airway epithelial cells this study demonstrates that soluble mediators secreted in response to influenza infection upregulate TLR3 expression in naive cells. This response was associated with an upregulation of type I IFNs and stimulation with type I, but not type II, IFNs enhanced TLR3 expression. Interestingly, although influenza infection results in IFN-β release both toward the apical and basolateral sides of the epithelium, TLR3 expression is only enhanced in cells stimulated with IFN-β from the basolateral side. Immunohistochemical analysis demonstrates that IFNAR expression is limited to the basolateral side of differentiated human airway epithelial cells. However, non- or poorly differentiated epithelial cells express IFNAR more toward the apical side. These data demonstrate that restricted expression of the IFNAR in the differentiated airway epithelium presents a potential mechanism of regulating type I IFN-induced TLR3 expression

Determinants of host susceptibility to murine respiratory syncytial virus (RSV) disease identify a role for the innate immunity scavenger receptor MARCO gene in human infants

Background: Respiratory syncytial virus (RSV) is the global leading cause of lower respiratory tract infection in infants. Nearly 30% of all infected infants develop severe disease including bronchiolitis, but susceptibility mechanisms remain unclear. Methods: We infected a panel of 30 inbred strains of mice with RSV and measured changes in lung disease parameters 1 and 5 days post-infection and they were used in genome-wide association (GWA) studies to identify quantitative trait loci (QTL) and susceptibility gene candidates. Findings: GWA identified QTLs for RSV disease phenotypes, and the innate immunity scavenger receptor Marco was a candidate susceptibility gene; targeted deletion of Marco worsened murine RSV disease. We characterized a human MARCO promoter SNP that caused loss of gene expression, increased in vitro cellular response to RSV infection, and associated with increased risk of disease severity in two independent populations of children infected with RSV. Interpretation Translational integration of a genetic animal model and in vitro human studies identified a role for MARCO in human RSV disease severity. Because no RSV vaccines are approved for clinical use, genetic studies have implications for diagnosing individuals who are at risk for severe RSV disease, and disease prevention strategies (e.g. RSV antibodies)