Toxoplasma gondii resides in a vacuole that avoids fusion with host cell endocytic and exocytic vesicular trafficking pathways

Toxoplasma gondii actively penetrates its vertebrate host cell to establish a nonfusigenic compartment called the parasitophorous vacuole (PV) that ha s previously been characterized primarily in phagocytic cells. To determine the fate of this unique compartment in nonphagocytic cells, we examined th e trafficking of host cell proteins and lipids in Toxoplasma-infected fibro blasts using quantitative immunofluorescence and immunoelectron microscopy. Toxoplasma-containing vacuoles remained segregated from all levels of the endocytic pathway, as shown by the absence of delivery of transferrin recep tors, mannose phosphate receptors, and the lysosomal-associated protein LAM P1 to the vacuole. The PV was also inaccessible to lipids (DiIC(16), and GM 1) that were internalized from the plasma membrane via the endocytic system . In contrast, vacuoles containing dead parasites or zymosan sequentially a cquired both endosomal and lysosomal protein markers and host lipids, refle cting the competency of fibroblasts to process phagocytic vacuoles. The mat ure PV often lies adjacent to the host cell Golgi, suggesting that it may i ntersect with vesicles from the exocytic pathway. Despite this proximity, t he PV was inaccessible to nitrobenzadiazole-labeled sphingolipids exported from the Golgi and did not contain the host protein markers API or beta-COP . Our results demonstrate that Toxoplasma resides in a compartment that exc ludes delivery of protein and lipid components from the host cell endocytic and exocytic pathways. (C) 1999 Academic Press.