Porcine milk exosomes modulate the immune functions of CD14+ monocytes in vitro

Exosomes mediate near and long-distance intercellular communication by transferring their molecular cargo to recipient cells, altering their biological response. Milk exosomes (MEx) are internalized by immune cells and exert immunomodulatory functions in vitro. Porcine MEx can accumulate in the small intestine, rich in macrophages. No information is available on the immunomodulatory ability of porcine MEx on porcine monocytes, which are known precursors of gut macrophages. Therefore, this study aims at (1) assessing the in vitro uptake of porcine MEx by porcine monocytes (CD14+), and (2) evaluating the in vitro impact of porcine MEx on porcine monocytes immune functions. MEx were purified by ultracentrifugation and size exclusion chromatography. The monocytes’ internalization of PKH26-labeled MEx was examined using fluorescence microscopy. Monocytes were incubated with increasing exosome concentrations and their apoptosis and viability were measured. Lastly, the ability of MEx to modulate the cells’ immune activities was evaluated by measuring monocytes’ phagocytosis, the capacity of killing bacteria, chemotaxis, and reactive oxygen species (ROS) production. MEx were internalized by porcine monocytes in vitro. They also decreased their chemotaxis and phagocytosis, and increased ROS production. Altogether, this study provides insights into the role that MEx might play in pigs’ immunity by demonstrating that MEx are internalized by porcine monocytes in vitro and exert immunomodulatory effects on inflammatory functions.