In vivo fusion of lysosomes with parasitophorous vacuoles of Leishmania-infected macrophages.

The in vivo infection of murine peritoneal macrophages by promastigotes of infective and non-infective isolates of Leishmaniasis mexicana ssp. was studied. Ultrastructural observations showed that lysosomes fuse with phagosomes containing Leishmania parasites. Intracellular parasites always occurred within phagosomes and there was no evidence of direct contact with host cytoplasm. The behaviour of infective parasites within macrophages resembled that described for a non-infective isolate. The presence of lysosomal marker in the phagosomes confirms previous findings in vitro.