Differential responses of liver versus lymphoid tissue DC to small extracellular vesicles generated by hepatic ischemia-reperfusion injury

Abstract Hepatic ischemia-reperfusion (I/R) injury triggers release of small extracellular vesicles (sEVs) that can function as systemic conveyors of inflammatory signals. While sEV-mediated immune cell modulation has been studied extensively in vitro, knowledge is based largely on sEVs derived from cultured cells, rather than injured tissues. Consequently, the immunological impact of liver I/R-sEVs is poorly understood. Here, we combined in vitro and in vivo approaches with sEVs purified from mouse livers subjected to I/R to define their influence on dendritic cells (DCs). In vitro, in contrast to sham-sEVs, I/R-sEVs activated syngeneic bone marrow-derived DCs (BMDCs), inducing upregulation of costimulatory molecules and enhancing their capacity to stimulate naive allogeneic T-cells. In contrast, liver DCs (LDCs) were refractory to liver I/R-sEV-mediated activation. This differential responsiveness may in part reflect greater I/R-sEV internalization by BMDCs. To assess in vivo relevance, labeled sham or I/R-sEVs were administered intravenously. Following systemic delivery, syngeneic I/R-sEVs, but not sham-sEVs, accumulated in liver and spleen of otherwise naive mice exhibiting different patterns of uptake by immune cell populations. In the spleen, macrophages and B-cells were the principal I/R-sEV-acquiring populations, whereas in the liver, sEV uptake was dominated by macrophages and neutrophils. Additionally, while splenic DCs showed increased expression of activation markers and T-cell stimulatory activity following exposure to I/R-sEVs, LDCs were unresponsive. These findings identify liver-I/R-sEVs as promotors of extra-hepatic DC maturation/activation, whereas liver-resident DCs were refractory to I/R-sEV stimulation. The findings have implications for regulation of inflammatory responses following liver I/R injury.