The PB1-F2 protein of influenza A virus modulates the early immune response leading to increased pathogenesis in the mouse model.

Session IV – Conenello, Young Investigator Applicant

The PB1-F2 protein of influenza A virus modulates the early immune response leading to increased pathogenesis in the mouse model. 

Gina M. Conenello1 and Peter Palese1,2
1Department of Microbiology, 2Department of Medicine Mount Sinai School of Medicine, New York, NY 10029, USA

    The PB1-F2 protein has been shown to be a pathogenicity factor in the mouse model.  The presence of PB1-F2 from highly virulent viruses containing an N66S mutation in the amino acid sequence causes increased morbidity, mortality, lung titer and cytokine dysregulation.  The mechanism of increased virulence as a result of the N66S mutation is currently unknown.  After eliminating the adaptive immune response as a significant contributor to increased virulence in previous experiments, we chose to focus on the early cellular immune response.  In this study we characterized the lung cell population at early time points during infection.  Mouse lungs were analyzed via flow cytometry for macrophage, natural killer cell and dendritic cell markers, as well as T-cell markers.  Additionally, ex-vivo lung cells were analyzed for production of seven different cytokines and chemokines.  Lungs were also harvested for processing of histological sections to visualize lung inflammation, cell recruitment and localization of infection.  All assays were conducted on days 2 through 5 and day 7 post-inoculation and plaque assays were done in parallel to confirm the fitness of the viruses used.  The data shows that there is a dysregulation of the cytokine and chemokine response in the presence of a virus containing a PB1-F2 with the mutation N66S as compared to a wt virus.  Additionally there is an upregulation of inflammatory cells, specifically neutrophils and macrophages in the lungs starting at day 3 and continuing throughout infection until death.  Together these results indicate that the PB1-F2 protein with the N66S mutation interferes with the initial anti-viral cytokine response while also causing unchecked infiltration of cells into the lung.  These results correlate with previous data from other laboratories showing that highly pathogenic infections are characterized by large numbers of neutrophils and macrophages in the lung.  Our data supports a hypothesis that the PB1-F2 protein could be a major inducer of this observed immune dysregulation