Intracellular Leishmania major parasites drive host cell death and cell-to-cell transfer depending on the parasite proliferation rate (Exit WS)

Abstract text

Introduction: The virulence of the intracellular pathogens relies largely on the ability to survive and replicate within phagocytes, but also to be released and transferred into new host cells. Recent findings suggest that release of Leishmania parasites from infected host cells is strictly regulated, with the mechanisms involved still to be determined.

Objectives: To study Leishmania major (L. major) transmission from infected monocytes to newly recruited cells in the context of infected host cell death.

Materials & methods: We quantified L. major transfer and uptake of host cell material together with the parasite into adoptively transferred cells in vivo using intravital 2-photon microscopy analysis and flow cytometry analysis of CD11c-YFP reporter mice. Also, we visualized cell death by live cell imaging, and by intravital 2-photon imaging of a fluorescence resonance energy transfer-based (FRET-based) cell-death-biosensor.

Results: We observed increased original host cell material uptake in infected as compared to uninfected cells. This suggests that original host cells can be phagocytosed by new cells together with the parasites. Also, infected host cells show signs of cell death before parasite transfer in vitro and show more Caspase-3 activity, indicating apoptosis, compared to uninfected cells in vivo. Lastly, we detected higher L. major proliferation in TUNEL+ compared to TUNEL- murine intraperitoneal macrophages using a photoconversion-based proliferation biosensor in vitro. In addition, our data indicate that high parasite proliferation is associated to shorter infection time of the infected host in vitro.

Conclusion: These data suggest that a high L. major proliferation rate induces cell death and thereby drives the dissemination of the pathogen to new phagocytes.