Interleukin-11 (IL-11) is an interleukin-6 (IL-6) family cytokine shown to play a protective role in acute inflammatory settings including systemic infection. In this study we addressed the role of IL-11 in acute bacterial pneumonia using a mouse model of E. coli pneumonia. Compared with other related cytokines, IL-11 protein was maintained at high levels in the lung at baseline, with only mild alterations in whole lung and BALF levels during acute infection. The primary source of IL-11 in the lung was the epithelium, but steady state production was not dependent on the inflammatory transcription factor nuclear factor kappa B in cells of either myeloid or epithelial lineage. Blockade of IL-11 with neutralizing antibodies resulted in a mild but significant decrease in neutrophil recruitment and increase in pulmonary edema during pneumonia, without detectable alterations in bacterial clearance. Exogenous IL-11 administration, however, had no effect at baseline or during infection. Overall, we conclude that maintenance of lung IL-11 concentrations may influence acute pulmonary inflammation during infection, albeit modestly.

Identifying host factors that contribute to pneumonia incidence and severity are of utmost importance to guiding the development of more effective therapies. Lectin-like oxidized lowdensity lipoprotein receptor-1 (LOX-1) is a scavenger receptor known to promote vascular injury and inflammation, but it is unknown whether and how LOX-1 functions in the lung. Here, we provide evidence of substantial accumulation of LOX-1 in the lungs of ARDS patients and in mice with pneumonia. Unlike previously described injurious contributions of LOX-1, we found that LOX-1 is uniquely protective in the pulmonary airspaces, limiting proteinaceous edema and inflammation. We also identified alveolar macrophages and recruited neutrophils as two prominent sites of LOX-1 expression in the lungs, whereby macrophages are capable of further induction during pneumonia and neutrophils exhibit a rapid, but heterogenous elevation of LOX-1 in the infected lung. Blockade of LOX-1 led to dysregulated immune signaling in alveolar macrophages, marked by alterations in activation markers and a concomitant elevation of inflammatory gene networks. However, bone marrow chimeras also suggested a prominent role for neutrophils in LOX-1-mediated lung protection, further supported by LOX-1+ neutrophils exhibiting transcriptional changes consistent with reparative processes. Taken together, this work establishes LOX-1 as a tissue-protective factor in the lungs during pneumonia, possibly mediated by its influence on immune signaling in alveolar macrophages (AMs) and LOX-1+ airspace neutrophils.

Pneumonia is a major public health concern, causing significant morbidity and mortality annually, despite broad use of antimicrobial agents. Underlying many of the severe sequelae of acute lung infections is dysfunction of the immune response, which remains incompletely understood, yet is an attractive target of adjunct therapy in pneumonia. Here, we investigate the role of Oncostatin M (OSM), a pleiotropic cytokine of the IL-6 family, and how its signaling modulates multiple innate immune pathways during pneumonia. Previously, we have shown that OSM is necessary for neutrophil recruitment to the lungs during pneumonia by stimulating STAT3-driven CXCL5 expression. In this study, transcriptional profiling of whole lung pneumonia with OSM neutralization revealed 241 differentially expressed genes following only 6 hours of infection. Many downregulated genes are associated with STAT1, STAT3, and interferon signaling, suggesting these pathways are induced by OSM early in pneumonia. Interestingly, STAT1 and STAT3 activation was subsequently upregulated with OSM neutralization by 24 hours, suggesting that OSM interruption dysregulates these central signaling pathways. When we investigated the source of OSM in pneumonia, neutrophils, and to a lesser extent, macrophages, appear to be primary sources, suggesting a positive feedback loop of OSM production by neutrophils. From these studies we conclude that OSM produced by recruited neutrophils tunes early innate immune signaling pathways, improving pneumonia outcome.

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Neutrophils are transcriptionally dynamic during acute pneumonia. Our prior work demonstrated that 1733 genes were differentially expressed between peripheral blood and alveolar neutrophils during pneumococcal pneumonia. In multiple settings of chronic inflammation or malignancy, functionally distinct neutrophil subsets have been defined. This current study was designed to test the hypothesis that acute pulmonary infection leads to the development of multiple functionally distinct neutrophil subsets in the alveolar space. METHODS: Neutrophils were isolated from blood and BAL fluid from two C57BL/6 mice infected with S. pneumoniae for 24 hours. Single cell RNA sequencing was performed, utilizing the 10x Genomic Chromium and Illumina NextSeq 500 systems. Clusters were generated using Celda and visualized using tSNE dimensionally reduction. Gene expression patterns were analyzed within and between Celda-defined cell clusters. RESULTS AND CONCLUSIONS: Sequences were obtained from an average of 3200 cells per sample and 30k reads per cell, resulting in 28,692 features, aligned to 3,481 genes among 12,790 cells. Non-neutrophils were identified by known sequence markers and excluded from further analysis. Peripheral blood neutrophils had a distinct transcriptome from BAL neutrophils, consistent with prior bulk transcriptomic data. The peripheral blood neutrophil transcriptome was largely uniform, whereas subsets of alveolar neutrophils demonstrated significant transcriptomic diversity. Variable genes included central regulators of inflammation and apoptosis, and secreted chemokines and cytokines.