Potential role of extracellular vesicles in bacterial phagocytosis during Escherichia coli pneumonia in ex vivo perfused human lungs

Abstract Background Plasma extracellular vesicles (EV) play an inflammatory role in bacterial pneumonia. This study aimed to determine if plasma EVs could be manipulated to reduce lung injury. We hypothesized that inhibition of multidrug resistance-associated protein (MRP) 1 on EVs would increase total leukotriene (LT) B4 and lipoxin (LX) A4 levels and, when incubated with immune cells, would increase bacterial phagocytosis and decrease cytokines secreted by the cells. Results Plasma EVs released from ex vivo perfused human lungs injured with E.coli bacteria (E.coli EV) or from control lungs (nEV) were incubated with LPS and Reversan, a MRP1 inhibitor, and the effect of EVs on bacterial phagocytosis and inflammation was studied using a macrophage cell line. In addition, the therapeutic effects of Reversan were studied in perfused human lungs injured with E.coli pneumonia. Levels of LTB4 and LXA4 were lower in E.coli EVs compared to nEVs. E.coli EVs were less capable than nEVs to stimulate bacterial phagocytosis by macrophages in vitro. Pretreatment of E.coli EVs with LPS and Reversan increased both total LTB4 and LXA4 levels, and, when incubated with Raw264.7 cells, bacterial phagocytosis was increased and TNFα levels secretion was decreased by the cells. Intravenous administration of Reversan to human lungs injured with E.coli bacterial pneumonia significantly restored alveolar fluid clearance rate and reduced bacterial levels in the injured alveolus at 6 h. Conclusion Administration of a MRP1 inhibitor to plasma EVs increased its LTB4 content, which, when incubated with macrophages, further increased phagocytosis of bacteria by the cells.