Hijacked Immune Cells Traverse Microenvironmental Barriers by Positioning and Pushing their Intracellular Parasite Cargo

Intracellular pathogens hijack the cytoskeletal networks of their host cells to facilitate their uptake, drive their intracellular motility, or prevent their degradation. While many underlying principles have been explored during host cell infections by intracellular bacteria like Listeria, Chlamydia , or Shigella , it remains less well understood how large eukaryotic intracellular parasites like Toxoplasma gondii exploit the host cytoskeleton. In particular, how Toxoplasma achieves its transport within highly motile immune cells remains largely unknown despite its large intracellular size. Here, we discover that Toxoplasma gondii hijacks host myosin forces for translocation through microenvironmental barriers along immune cell migration paths. Using highly defined micro-engineered migration paths and dendritic cells as a highly motile immune cell model, we reveal that large parasitic cargos acquire a surprising intracellular position frontward of the host nucleus and microtubule-organizing center. This frontward localization of parasitic cargos depends on microenvironmental confinement and host myosin activity. We identify that the parasite cargos cause high contractility within their motile host cells mediated by host myosin-II, thereby facilitating their squeezing and deformation to enable transversal through confining microenvironments. Our findings establish parasitic hijacking of myosin forces as a novel principle of how parasites exploit host cytoskeletal networks.