Fig. 1

M2-Exos reduce lung injury and improve the survival of septic mice. a Electron micrograph of exosomes derived from the supernatant of polarized mouse Raw264.7 macrophages. Scale bar, 100 nm. b Exosome size distribution was measured by NanoSight tracking analysis. c CD63, CD9 and TSG101 protein expression in exosomes loaded with equal amounts of exosome protein (40 μg) was quantified by Western blotting. d–j WT C57BL/6 mice were intraperitoneally administered M0-Exos or M2-Exos (300 μg/mouse) derived from mouse Raw264.7 macrophages 1 h after CLP. d Schematic design for M0-Exo/M2-Exo treatment in the CLP model. e Representative images of direct immunofluorescence staining of DNA (blue), Ly6G (green), and Dil (red) in lung sections following intraperitoneal injection of Dil-labelled exosomes; white arrows indicate Dil-positive neutrophils. Scale bar, 50 μm. f Ex vivo fluorescent signals in the lungs of mice intraperitoneally injected with Dil-labelled exosomes. g Evaluation of lung histology by H&E staining (magnification × 400). Red arrows indicate neutrophils in the alveolar and interstitial space, blue arrows indicate alveolar macrophages, green arrows indicate proteinaceous debris filling, and black arrows indicate thickening of the alveolar walls. Scale bar, 40 μm. Lung injury scores were assessed. h Detection of inflammatory cytokine mRNA (IL-1β, IL-6, TNF-α) expression in lung tissues by RT‒qPCR. i Survival rate of CLP mice with M0-Exo or M2-Exo treatment (n = 8) and log-rank test was used for the analysis. j Lung tissues were harvested at 24 h after CLP. The supernatant was collected after homogenization and centrifugation. An equal amount of the supernatant was spread on agar plates for colony formation. The number of bacterial colonies was assessed. CFU, colony-forming unit. One-way analysis of variance with Tukey’s multiple comparisons test was used for the analysis. Graphs represent means ± standard deviations, n ≥ 3; *P < 0.05, **P < 0.01 compared within two groups; NS, not significant