Anti-IAV Polyclonal antibody

Influenza A virus (IAV) is a seasonal pathogen with the potential to cause devastating pandemics. IAV infects multiple epithelial cell subsets in the respiratory tract, eliciting damage to the lungs. Clearance of IAV is primarily dependent on CD8(+) T cells, which must balance control of the infection with immunopathology. Using a virus expressing Cre recombinase to permanently label infected cells in a Cre-inducible reporter mouse, we previously discovered infected club cells that survive both lytic virus replication and CD8(+) T cell-mediated clearance. In this study, we demonstrate that ciliated epithelial cells, type I and type II alveolar cells can also become survivor cells. Survivor cells are stable in the lung long-term and demonstrate enhanced proliferation compared to uninfected cells. When we investigated how survivor cells evade CD8(+) T cell killing we observed that survivor cells upregulated the inhibitory ligand PD-L1, but survivor cells did not use PD-L1 to evade CD8(+) T cell killing. Instead our data suggest that survivor cells are not inherently resistant to CD8(+) T cell killing, but instead no longer present IAV antigen and cannot be detected by CD8(+) T cells. Finally, we evaluate the failure of CD8(+) T cells to kill these previously infected cells. This work demonstrates that additional cell types can survive IAV infection and that these cells robustly proliferate and are stable long term. By sparing previously infected cells, the adaptive immune system may be minimizing pathology associated with IAV infection. Author summary Influenza A virus is a seasonal respiratory pathogen that can cause severe lung damage and death. We previously made the discovery that cells infected with influenza virus do not have a death sentence. An infected cell can survive both influenza virus infection and the immune response to eliminate the virus, specifically CD8(+) T cells which are required for virus clearance. Here, we investigated how an infected cell could survive the CD8(+) T cell immune response. We used an influenza virus expressing a recombinant protein that permanently labels infected cells in inducible reporter mice. This system allowed us to detect actively infected cells, as well as cells that had survived influenza virus infection and CD8(+) T cell-mediated killing, called survivor cells. We demonstrate that survivor cells do not actively block CD8(+) T cell effector function and are not inherently resistant to CD8(+) T cell-mediated killing. Our data suggest that survivor cells have lost influenza virus antigen and are rendered invisible to virus-specific CD8(+) T cells. Our research provides important new insight into the mechanism of how survivor cells can be generated. This could be a mechanism by which the host is protecting the lung from greater pathology during influenza virus infection.

Influenza A virus (IAV) is a leading cause of respiratory infections, with increased risk of severe illness and death in the very young, aged, and immunocompromised individuals. In both mice and humans, IAV-specific T cell responses are protective during primary as well as homologous and heterologous challenge infections. Many mouse studies have focused on CD4 T cells specific for a single, known model or IAV antigen. However, studies have demonstrated that the IAV-specific CD4 T cell response comprises many epitopes spread across multiple viral proteins. Therefore, herein we track the antigen-experienced CD4 T cell response using the surrogate markers CD49d and CD11a. This novel surrogate marker method allows us to characterize the full IAV-specific CD4 T cell response without the potential bias that could occur when examining an individual Ag-specificity. Our findings demonstrate that the immunodominant I-A(b)-binding NP311-325 epitope often used in studies of IAV-specific CD4 T cells represents only about 5% of the total IAV-specific CD4 T cell response. Further, we find that the kinetics of the full pulmonary CD4 T cell response is similar to that of NP311-specific T cells and that the full CD4 T cell response in the lungs is predominantly composed of cells expressing the Th1 transcription factor T-bet, with smaller but significant portions of the response expressing the Treg and Tfh associated transcription factors Foxp3 and Bcl-6, respectively. Interestingly, although Th1 cells are the most abundant Th subset in the lungs of both BALB/c and C57Bl/6 mice following IAV, the relative abundance of Treg and Tfh is reversed in the different mouse strains. In BALB/c mice, Foxp3(+) cells are more abundant than Bcl6(+) cells, whereas in C57Bl/6 mice, there are more Bcl6(+) cells. As a whole, these data highlight the diversity of the endogenous CD4 T cell response to a primary IAV infection, providing an important context for past and future studies of the IAV-specific CD4 T cell response.