Host cells: mobilizable lipid resources for the intracellular parasite Toxoplasma gondii

Successful replication of the intracellular parasite Toxoplasma gondii within its parasitophorous vacuole necessitates a substantial increase in membrane mass. The possible diversion and metabolism of host cell lipids and lipid precursors by Toxoplasma was therefore investigated using radioisotopic and fluorophore-conjugated compounds. Confocal microscopic analyses demonstrated that Toxoplasma is selective with regards to both the acquisition and compartmentalization of host cell lipids. Lipids were compartmentalized into parasite endomembranes and, in some cases, were apparently integrated into the surrounding vacuolar membrane. Additionally, some labels became concentrated in discrete lipid bodies that were biochemically and morphologically distinct from the parasite apical secretory organelles. Thin layer chromatography established that parasites readily scavenged long-chain fatty acids as well as cholesterol, and in certain cases modified the host-derived lipids. When provided with radiolabeled phospholipid precursors, including polar head groups, phosphatidic acid and small fatty acids, intracellular parasites preferentially accrued phosphatidylcholine (PtdCho) over other phospholipids. Moreover, Toxoplasma was found to be competent to synthesize PtdCho from radiolabeled precursors obtained from its environment. Together, these studies underscore the ability of Toxoplasma gondii to divert and use lipid resources from its host, a process that may contribute to the biogenesis of parasite membranes.