The anatomy of T-cell mediated neutrophil recruitment during lung infection

Abstract Pneumonia is a leading cause of morbidity and mortality worldwide. Microbes that cause respiratory infections are encountered by virtually everyone, but effective immunity in healthy individuals typically prevents such exposures from progressing to pneumonia. Yet, host signals guiding lung defense constitute a major knowledge gap, limiting opportunities for clinical intervention in patients at risk for pneumonia. A goal of our research is to delineate when, where, and how prior experience with respiratory pathogens influences pneumonia susceptibility thereafter. Recovery from lung infections elicits strong and rapid protection in response to a subsequent challenge with related but distinct organisms (e.g., different strains/serotypes). We and others have demonstrated that this heterotypic protection is location-dependent, restricted to the previously exposed region and independent of circulating factors. Moreover, accelerated immunity in experienced lungs requires lung CD4+ resident memory T (TRM) cells, which accumulate in the interstitium near bronchovascular bundles and pulmonary veins. CD4+ T cells are required for the rapid and protective neutrophil response observed in experienced lungs, and our pilot studies, using a novel crystal ribcage approach to connect experienced lungs to the circulation of naïve mice, indicate that this is specifically driven by lung-localized CD4+ TRM cells. Excitingly, this same approach revealed neutrophil recruitment as remote as subpleural alveoli in as few as 4hrs in the experienced lung, demanding a better understanding of the multi- cellular signaling network tethering CD4+ TRM cells to enhanced neutrophilic defense. The primary objectives of this proposal are to determine the spatiotemporal relationship between centrally concentrated CD4+ TRM cells and emigrated neutrophils during pneumonia, while developing a transcriptional atlas of key immune processes corresponding with enhanced defense in the experienced lung. To do so, we will test the hypotheses that: 1) Infection of the experienced lung activates CD4+ T cells in the interstitium of bronchovascular bundles and pulmonary veins, coinciding with diffusely parenchymal neutrophil recruitment; and 2) CD4+ T cells in the experienced lung trigger rapid, diffuse, and heterogeneous transcriptome changes across diverse distal lung and immune cells. This will be accomplished using state-of-the-art approaches for imaging, cytometry, and spatial transcriptomics, leveraging expertise and resources across two neighboring institutions. Results from this study will provide key insights about the cells and signals dictating host immunity. Furthermore, data from the proposed experiments will provide a foundation for future investigations by our groups and others, having a lasting impact on the field.