Abstract
Extracellular vesicles (EVs) have now been recognized as important mediators of cellular communication during injury and repair. We previously found that plasma EVs isolated from ex vivo perfused human lungs injured with Escherichia coli bacterial pneumonia were inflammatory, and exogenous administration of high molecular weight (HMW) hyaluronic acid (HA) as therapy bound to these EVs, decreasing inflammation and injury. In the current study, we studied the role of EVs released during severe Pseudomonas aeruginosa (PA) pneumonia in mice and determined whether intravenous administration of exogenous HMW HA would have therapeutic effects against the bacterial pneumonia. EVs were collected from the bronchoalveolar lavage fluid (BALF) of mice infected with PA103 by ultracentrifugation and analyzed by NanoSight and flow cytometry. In a cytotoxicity assay, administration of EVs released from infected mice (I-EVs) decreased the viability of A549 cells compared to EV isolated from sham control mice (C-EVs). Either exogenous HMW HA or an anti-CD44 antibody, when co-incubated with I-EVs, significantly improved the viability of the A549 cells. In mice with PA103 pneumonia, administration of HMW HA improved pulmonary edema and bacterial count in the lungs and decreased TNF-α and caspase-3 levels in the supernatant of lung homogenates. In conclusion, EVs isolated from BALF of mice with P. aeruginosa pneumonia were cytotoxic and inflammatory, and intravenous HMW HA administration was protective against P. aeruginosa pneumonia.