Graduate student Tufts Univerisity, Graduate School of Biomedical Sciences Madison, Wisconsin, United States
Disclosure(s):
Alessandra Setaro: No financial relationships to disclose
Introduction/Rationale: Influenza A virus can evade detection by the adaptive immune system, as evidenced by low vaccine efficacy and reinfections during human challenge studies. Like all successful viruses, influenza A virus regulates host antiviral responses, and it encodes multiple immunomodulatory proteins for this purpose. One such viral protein, PA-X, is an endoribonuclease that suppresses host gene expression during infection. Here we investigate the impact of PA-X on MHC I antigen presentation, a key process for host detection of intracellular pathogens.
Methods: To investigate PA-X dependent changes during infection, we infected primary human donor air liquid interface (ALI) cultures of airway epithelial cells with wild type (WT) or PA-X deficient H3N2 influenza A virus. Using single cell RNA sequencing, we detected changes in gene expression of antigen processing and presentation. We then investigated surface and intracellular MHC I protein levels using flow cytometry and MHC I trafficking to the cell surface using an acid strip time course.
Results: The influenza A viral protein PA-X significantly reduced expression of antigen processing and presentation genes in infected epithelial cells. Both surface and intracellular MHC I levels were significantly reduced in WT influenza-infected ALI cultures compared to mock-infected cultures or cultures infected with PA-X deficient virus. Furthermore, PA-X activity halved the rate of MHC I trafficking to the surface during infection.
Conclusion: Through regulation of MHC I gene expression, PA-X decreases the rate of MHC I trafficking during infection. This likely delays detection by antigen-specific T cells, allowing the virus to replicate and spread, particularly in hosts with prior immunity to influenza A virus, and contributing to the continued success of this virus. Future work will investigate the functional impacts of PA-X disruption of MHC I using immunopeptidomics and in vivo studies.
