Impaired wound healing predisposes obese mice to severe influenza virus infection.

For the first time, obesity appeared as a risk factor for developing severe 2009 pandemic influenza infection. Given the increase in obesity, there is a need to understand the mechanisms underlying poor outcomes in this population. In these studies, we examined the severity of pandemic influenza virus in obese mice and evaluated antiviral effectiveness. We found that genetically and diet-induced obese mice challenged with either 2009 influenza A virus subtype H1N1 or 1968 subtype H3N2 strains were more likely to have increased mortality and lung pathology associated with impaired wound repair and subsequent pulmonary edema. Antiviral treatment with oseltamivir enhanced survival of obese mice. Overall, these studies demonstrate that impaired wound lung repair in the lungs of obese animals may result in severe influenza virus infection. Alternative approaches to prevention and control of influenza may be needed in the setting of obesity.

Parasite-mediated upregulation of NK cell-derived gamma interferon protects against severe highly pathogenic H5N1 influenza virus infection.

Outbreaks of influenza A viruses are associated with significant human morbidity worldwide. Given the increasing resistance to the available influenza drugs, new therapies for the treatment of influenza virus infection are needed. An alternative approach is to identify products that enhance a protective immune response. In these studies, we demonstrate that infecting mice with the Th1-inducing parasite Toxoplasma gondii prior to highly pathogenic avian H5N1 influenza virus infection led to decreased lung viral titers and enhanced survival. A noninfectious fraction of T. gondii soluble antigens (STAg) elicited an immune response similar to that elicited by live parasites, and administration of STAg 2 days after H5N1 influenza virus infection enhanced survival, lowered viral titers, and reduced clinical disease. STAg administration protected H5N1 virus-infected mice lacking lymphocytes, suggesting that while the adaptive immune response was not required for enhanced survival, it was necessary for STAg-mediated viral clearance. Mechanistically, we found that administration of STAg led to increased production of gamma interferon (IFN-γ) from natural killer (NK) cells, which were both necessary and sufficient for survival. Further, administration of exogenous IFN-γ alone enhanced survival from H5N1 influenza virus infection, although not to the same level as STAg treatment. These studies demonstrate that a noninfectious T. gondii extract enhances the protective immune response against severe H5N1 influenza virus infections even when a single dose is administered 2 days postinfection.

A protective role for complement C3 protein during pandemic 2009 H1N1 and H5N1 influenza A virus infection.

Highly pathogenic H5N1 influenza infections are associated with enhanced inflammatory and cytokine responses, severe lung damage, and an overall dysregulation of innate immunity. C3, a member of the complement system of serum proteins, is a major component of the innate immune and inflammatory responses. However, the role of this protein in the pathogenesis of H5N1 infection is unknown. Here we demonstrate that H5N1 influenza virus infected mice had increased levels of C5a and C3 activation byproducts as compared to mice infected with either seasonal or pandemic 2009 H1N1 influenza viruses. We hypothesized that the increased complement was associated with the enhanced disease associated with the H5N1 infection. However, studies in knockout mice demonstrated that C3 was required for protection from influenza infection, proper viral clearance, and associated with changes in cellular infiltration. These studies suggest that although the levels of complement activation may differ depending on the influenza virus subtype, complement is an important host defense mechanism.

Transforming growth factor-ß: activation by neuraminidase and role in highly pathogenic H5N1 influenza pathogenesis.

Transforming growth factor-beta (TGF-ß), a multifunctional cytokine regulating several immunologic processes, is expressed by virtually all cells as a biologically inactive molecule termed latent TGF-ß (LTGF-ß). We have previously shown that TGF-ß activity increases during influenza virus infection in mice and suggested that the neuraminidase (NA) protein mediates this activation. In the current study, we determined the mechanism of activation of LTGF-ß by NA from the influenza virus A/Gray Teal/Australia/2/1979 by mobility shift and enzyme inhibition assays. We also investigated whether exogenous TGF-ß administered via a replication-deficient adenovirus vector provides protection from H5N1 influenza pathogenesis and whether depletion of TGF-ß during virus infection increases morbidity in mice. We found that both the influenza and bacterial NA activate LTGF-ß by removing sialic acid motifs from LTGF-ß, each NA being specific for the sialic acid linkages cleaved. Further, NA likely activates LTGF-ß primarily via its enzymatic activity, but proteases might also play a role in this process. Several influenza A virus subtypes (H1N1, H1N2, H3N2, H5N9, H6N1, and H7N3) except the highly pathogenic H5N1 strains activated LTGF-ß in vitro and in vivo. Addition of exogenous TGF-ß to H5N1 influenza virus-infected mice delayed mortality and reduced viral titers whereas neutralization of TGF-ß during H5N1 and pandemic 2009 H1N1 infection increased morbidity. Together, these data show that microbe-associated NAs can directly activate LTGF-ß and that TGF-ß plays a pivotal role protecting the host from influenza pathogenesis.