Extracellular Vesicle-Associated IL4 Displays Enhanced Anti-Inflammatory Properties in Microglial Cells

Neuroinflammation and neurodegeneration are strictly related phenomena, characterized by dysregulation of microglia, central nervous system (CNS) resident immune cells. Interleukin-4 (IL4) has shown beneficial abilities to re-establish microglial homeostasis in experimental models of CNS traumatic injury, stroke and multiple sclerosis, but its optimal administration system remains uncertain. Here, we show that extracellular vesicles (EVs) released by engineered murine microglia BV2 cells constitutively expressing IL4 induced a faster and enhanced anti-inflammatory phenotype in wild type BV2 cells (as assessed by IL4R downstream signalling), compared with soluble IL4. This effect was blunted by an anti-IL4 antibody, while it was not dampened by knocking out the IL4 receptor α subunit in EV-releasing BV2 cells, suggesting that IL4 was localized on the EV surface and did not necessitate to be co-conveyed with the receptor to exert its function. BV2 cells treated with EV-associated IL4, compared with soluble IL4, demonstrated delayed permanence of IL4R in the early endosome, suggesting amplified signalling effects. In conclusion, we here show that the association of IL4 with microglia-derived EVs improve its anti-inflammatory effect in an in vitro murine microglial model, which may inform on novel therapeutic opportunities to restore microglia in human disorders marked by neuroinflammation.