Single-cell RNA-sequence of the resolution phase of lung inflammation in LPS-induced ARDS model

Acute respiratory distress syndrome (ARDS) is a serious lung failure with a high mortality rate and no effective pharmacological therapies. While the cellular and molecular mechanisms underlying the induction of ARDS have been extensively studied, those controlling its resolution remain poorly understood. Recent human cohort studies have implied the correlation between the severity of ARDS and the paucity of blood basophils. To examine the causative relationships between basophils and the pathogenesis of ARDS, we assessed the effect of basophil depletion in an LPS-induced mouse model of ARDS and explored the possible role for basophils in the induction and resolution of ARDS by using genetically engineered mice and single-cell RNA-sequencing (scRNA-seq) analyses. Intratracheal LPS administration induced severe lung inflammation with massive neutrophil accumulation, followed by the recovery to homeostatic conditions. Basophil depletion impaired the recovery but not induction of lung inflammation, demonstrating the crucial role for basophils in the resolution phase of ARDS. scRNA-seq analysis identified that basophils accumulating in the lung were predominant sources of cytokine IL-4. Mice with basophil-specific IL-4 deficiency failed to resolve the lung inflammation. This was also the case in mice with neutrophil-specific IL-4 receptor deficiency. scRNA-seq analysis suggested that basophil-derived IL-4 acts on neutrophils to suppress their expression of anti-apoptotic genes and pro-inflammatory mediators. Thus, the present study demonstrated that basophils play a crucial role in the resolution phase of a mouse model of ARDS through the production of IL-4 which in turn acts on neutrophils to restrict lung inflammation. Overall design: Cells isolated from inflamed lungs of WT and IL-4 KO mice on day 6 post-LPS inhalation were analyzed by scRNA-seq.