INHIBITION OF EARLY ENDOSOME FUSION BY TRYPANOSOMA CRUZI-INFECTED MACROPHAGE CYTOSOL

Trypanosoma cruzi trypomastigotes survive inside macrophages by promot ing fusion between the parasitophorous vacuole and mature host lysosom es upon internalization. Since trypomastigotes can evade the lytic pat hway, the earliest steps of endocytosis, such as early endosome fusion , may be affected. To test this hypothesis, we used an in vitro early endosome fusion assay. Our results show that trypomastigote-infected m acrophage cytosols cannot promote fusion between early endosomes, comp ared to mock-infected cytosols (heat-killed trypomastigotes were used in the parasite-macrophage interaction assay). GTP gamma S addition po tentiates the fusogenic activity driven by trypomastigote-infected mac rophage cytosol-mediated assays, unlike the biphasic fusogenic effect obtained with GTP gamma S treatment of macrophage cytosol controls. Ca lcium-stimulated early endosome fusogenic processes are not affected i n the assays mediated by infected macrophage cytosol. We conclude that GTP-regulated factors, and not calcium-regulated elements, are involv ed in the inhibition of the early endosome fusogenic process by the tr ypomastigote infected macrophage cytosol. This primary impediment to t he progress of a normal endocytosis may be a relevant step required fo r the lysosomal recruitment-fusion of the host lysosomes upon trypomas tigote infection and further survival of the parasite within its host.