Huang, F. Y. | bioRxiv Science

bioRxiv2026

Megakaryocyte emperipolesis arms neutrophils via intracellular provisioning

Neutrophils are phenotypically heterogenous cells that mediate host defense and tissue homeostasis. Here, we identify emperipolesis - the evolutionarily conserved process by which neutrophils pass through megakaryocytes - as a phenotypically transformative route of egress from bone marrow. By intravital microscopy and 3-D histology, we show that the rapid form emperipolesis is markedly enhanced under inflammatory conditions. Neutrophils exit from megakaryocytes directly to the blood, acquiring exosomes enriched in proteins related to metabolism, migration, and immune function. This transfer induces a distinct neutrophil phenotype characterized by enhanced glycolysis, oxidative phosphorylation, cytokine release, and longevity. Correspondingly, emperipolesis-educated neutrophils display accelerated migration in vitro and in vivo. Disrupting emperipolesis does not alter circulating neutrophil abundance but impairs neutrophil infiltration into inflamed tissues, including Pseudomonas aeruginosa-infected lung. These findings establish emperipolesis as a mechanism by which megakaryocytes amplify neutrophil-mediated immunity.

immunology↗

bioRxiv2021

Neutrophil transit time and localization within the megakaryocyte define morphologically distinct forms of emperipolesis

In emperipolesis, neutrophils transit through megakaryocytes, but it is unknown whether this interaction represents a single type of cell-in-cell interaction or a set of distinct processes. Using an in vitro model of murine emperipolesis, we characterized neutrophils entering megakaryocytes using live-cell spinning disk microscopy and electron microscopy. Approximately half of neutrophils exited the megakaryocyte rapidly, typically in 10 minutes or less, displaying ameboid morphology as they passed through the host cell (fast emperipolesis). The remaining neutrophils assumed a sessile morphology, most remaining within the megakaryocyte for at least 60 minutes (slow emperipolesis). These neutrophils typically localized near the megakaryocyte nucleus. By ultrastructural assessment, all internalized neutrophils remained morphologically intact. Most neutrophils resided within emperisomes, but some could be visualized exiting the emperisome into the cell cytoplasm. Neutrophils in the cytoplasm assumed close contact with the platelet-forming demarcation membrane system or with the perinuclear endoplasmic reticulum, as confirmed by immunofluorescence microscopy. Together, these findings reveal that megakaryocyte emperipolesis reflects at least two processes, fast and slow emperipolesis, each with its own characteristic transit time, morphology, and intracellular localization, suggesting distinct functions. Key PointsO_LINeutrophil passage through megakaryocytes, termed emperipolesis, diverges into fast and slow forms that differ in transit time, morphology, and intracellular localization C_LIO_LIDuring emperipolesis, neutrophils can reside in vacuoles (emperisomes) or escape into the cell cytoplasm to assume positions near the megakaryocytes demarcation membrane system, endoplasmic reticulum, or nucleus. C_LI

cell biology↗