Human KITs from SM-EVs are taken up by HSCs when injected into mice, and SM-EVs induce activation markers of HSCs. (A) Groups of three mice were injected with equal amounts of EVs (100 µg) pooled from four HVs randomly chosen (HV-EVs), a pool of SMs with tryptase<110 ng/mL (four patients) and SMs with tryptase>110 ng/mL (four patients) (ISM-EVs), or a pool of the four patients with SSM (SSM-EVs). (B) Liver lysates showing expression of α-SMA and human KIT 24 h after the last injection of the indicated EVs. The numbers underneath each blot in B represent average fold changes in fluorescence intensity normalized to actin and compared with the band intensity in mouse 1 of the untreated group. (C) Tyrosine kinase activity of KIT in liver lysates was determined following KIT immunoprecipitation. **P < 0.01; n.s., not significant. (D) Immunostaining of liver sections of recipient mice injected with the indicated types of EVs. Confocal images show staining of α-SMA (red) around hepatic portal areas identifying HSCs and increased intensity of α-SMA staining in recipient mice treated with SM-EVs. Human KIT is shown in green and nuclei from cells in blue following DAPI staining. Arrows indicate examples of seemingly membrane locations. Images were obtained using a 60× objective, and the width of each panel corresponds to 315 μm. (Scale bar, 50 nm.) (E) Schematic representation of the data demonstrating increased numbers of circulating EVs with a mast cell signature in patients with SM and their potential contribution to hepatic pathology with HSC proliferation and activation.