HLA class I molecules reflect an altered host proteome after influenza virus infection.

Class I HLA sample and display peptides from thousands of endogenous proteins at the cell surface. During infection, the influenza virus modifies the host cell proteome by triggering host antiviral responses, hijacking host processes, and inhibiting host mRNA processing. In turn, the catalog of HLA class I peptides that decorate the surface of an infected cell is positioned to reflect an altered host cell proteome. To understand the host-encoded peptides presented by class I molecules after influenza infection, we compared by mass spectrometry (MS) the peptides eluted from the HLA of naive and infected cells. We identified 20 peptide ligands unique to infected cells and 347 peptides with increased presentation after infection. Infection with different influenza strains demonstrated that proteome changes are predominantly strain-specific, with few individual cellular interactions observed for multiple viral strains. Modeling by pathway analysis, however, revealed that strain specific host peptide changes represent different routes to the same destination; host changes mediated by influenza are found predominantly clustered around HLA-B, ACTB, HSP90AB1, CDK2, and ANXA2. The class I HLA proteome scanning of influenza-infected cells therefore indicates how divergent strains of influenza pursue alternate routes to access the same host cell processes.