Dendritic cell-Natural Killer cell Crosstalk Modulates T cell activation in Response to Influenza A Viral Infection

Influenza viruses lead to substantial morbidity and mortality including ~3-5 million cases of severe illness and ~290,000-650,000 deaths annually. One of the major hurdles regarding influenza vaccine efficacy is generating a durable, robust cellular immune response. Appropriate stimulation of the innate immune system is key to generating cellular immunity. Crosstalk between innate dendritic cells (DC) and natural killer (NK) cells plays a key role in activating virus-specific T cells, yet the mechanisms used by influenza A viruses (IAV) to govern this process remain incompletely understood. Here, we used an ex vivo autologous human primary immune cell culture system to evaluate the impact of genetically distinct IAV strains on DC-NK cell crosstalk and subsequent T cell activation. We report that the addition of NK cells to cultures containing both DCs and naïve T cells led to an increase in the frequency of CD69 + and CD25 + T cells and elevated levels of IFN-γ, TNF, and IL-10. However, upon IAV infection of DCs, the addition of NK cells to cultures no longer increased the frequency of CD25 + T cells nor elevated IFN-γ, TNF, and IL-10 cytokine levels. Investigation of the impact of IAV infection on DC-NK crosstalk revealed that exposure of DCs to influenza virus in co-culture led to an increased frequency of HLA-DR + and a decreased frequency of CD83 + and CD86 + cells–molecules involved in stimulating T cell activation. An expansion of an HLA-DR + NK cell subset was observed following culture with influenza-infected DCs in a contact-dependent and cytokine independent-manner. Overall, our results indicate a role for DC-NK cell crosstalk in T cell priming in the context of influenza infection, informing the immunological mechanisms that could be manipulated for the next generation influenza vaccine or immunotherapeutic.