Effect of Nramp1 on maturation of phagosomes containing Leishmania donovani

Nramp1 is a membrane transporter that is essential for mouse resistance to infection with intracellular pathogens Mycobacterium, Salmonella and Leishmania. It is expressed in the lysosomal compartment of macrophages and is recruited to the phagosomal membrane after phagocytosis with kinetics similar to the lysosomal protein Lamp1. The Nramp1 effect on resistance/susceptibility to Leishmania infection is observed by counting the number of parasites in livers from infected mice. The mechanism by which Nramp1 limits liver replication of Leishmania is still unknown. The goal of the work presented was to explore the effect of Nramp1 on maturation of Leishmania parasitophorous vacuoles in macrophages ex vivo using primary macrophages isolated from Nramp1+/+ or isogenic Nramp1-/- mice infected with Leishmania. Immunofluorescence was used to monitor the kinetics of association of markers for different intracellular compartments with Leishmania vacuoles. The markers Lamp1, cathepsin D and M6PR were used together with Nramp1. No difference in the maturation kinetics of Leishmania vacuole was observed between Nramp1+/+ and Nramp1-/- macrophages for all markers and all times post-infection. In addition, the infection rate and multiplication of Leishmania monitored in infected macrophages ex vivo were not significantly different between Nramp1+/+ and Nramp1-/- cells in contrast to infected livers. Thus, the mechanism by which Nramp1 suppresses Leishmania replication should be further studied directly in vivo in infected livers from Nramp1+/+ and Nramp1-/- mice