All cells are immune cells: the impact of endothelial-T cell crosstalk on protective pulmonary immune responses 2333504

Abstract Introduction Not all natural infections or vaccines elicit long-lived, protective immune responses. The mechanism(s) responsible for waning immunity to pulmonary bacterial infections are poorly understood. We previously found that poor prognosis after virulent Francisella tularensis challenge was associated with rapid IFN-γ production by lung-resident T cells, endothelial IDO1 up-regulation, lung tryptophan depletion, and poor T cell proliferation. We are now studying the crosstalk between T cells and endothelial cells during primary infection with attenuated F. tularensis to understand how cellular communication educates both populations prior to challenge. Methods We utilized single-cell RNA sequencing to identify gene expression changes in pulmonary endothelial cells following F. tularensis infection. Key findings were validated at the protein level using flow cytometry. We are also employing a Cre-lox system to specifically remove IFN-γ signaling from endothelial cells to determine the importance of these pathways during infection. Results Following infection, endothelial cells respond to IFN-γ by up-regulating genes associated with cellular recruitment, T cell activation, and metabolism. Flow cytometry validation confirmed increased protein expression as early as day 5 post-infection suggesting a non-T cell source of IFN-γ, likely NK cells, is responsible for the initial reprogramming of endothelial cells. Indeed, depletion of NK cells attenuated the response in endothelial cells. Finally, elimination of IFN-γ signaling in endothelial cells leads to increased susceptibility to F. tularensis. Conclusion We predict that poor immunity against tularemia results from reprogramming of the endothelial compartment by current live vaccine strategies. Our findings underscore how the pulmonary milieu impacts T cell function and leads to subpar immune responses. These results should inform the development of improved vaccines and vaccination strategies for difficult-to-target pulmonary pathogens like F. tularensis. Funding Source This work was supported by the Intramural Research Program of the National Institute of Allergy and Infectious Disease, National Institutes of Health Topic Categories Microbial, Parasitic, and Fungal Immunology (MPF)