A microphysiological system of sterile injury demonstrates neutrophil reverse migration via macrophage-derived...

Persistent neutrophilic inflammation can lead to tissue damage and chronic inflammation, contributing to non-healing wounds. The resolution phase of neutrophilic inflammation is critical to preventing tissue damage, as observed in diseases characterized by influx of neutrophils such as atherosclerosis and non-healing wounds. Animal models have provided insight into resolution of neutrophilic inflammation via efferocytosis and reverse migration (rM); however, species-specific differences and complexity of innate immune responses make translation to humans challenging. Thus, there is a need for in vitro systems that can elucidate mechanisms of resolution of human neutrophilic inflammation. Here, we developed a human microphysiological system (MPS) to mimic an inflammatory sterile injury (SI) microenvironment to study the role of macrophage derived extracellular vesicles (M-EVs) in determining the resolution of inflammation via neutrophil rM. The MPS integrates a human umbilical vein endothelial cell (HUVEC) lined lumen, injury site spheroid, human neutrophils, macrophages and macrophage derived EVs to investigate the role of M-EVs in neutrophil rM in vitro . The key features of the MPS enabled us to demonstrate that EVs derived from macrophage subsets modulate migratory behavior in primary neutrophils differently in specific inflammatory microenvironments. Importantly, we identified a new mechanism underlying neutrophil rM via M-EV, where neutrophils exposed to M2-EV-derived IL-8 migrate away from the SI site upon reaching the site, using the SI MPS. Overall, our SI MPS system demonstrates a reverse migratory pattern in human primary neutrophils, advancing the study of the resolution of inflammation via M-EVs.