Freeze-fracture study of the dynamics of Toxoplasma gondii parasitophorous vacuole development

Toxoplasma gondii resides in a nonfusogenic parasitophorous vacuole (PV), which provides a safe environment for parasite survival and replication. In this work, we used the freeze-fracture technique to analyze the PV during different times of T. gondii infection in an epithelial cell line. After a short time of interaction with host cell, T. gondii PV membrane already showed a significant quantity of intramembranous particles (IMPs)—293 IMPs/μm2. The IMP density evaluated did not vary until 6 h of interaction. As the PV area enlarged with the progression of infection, the density of these particles increased, reaching a stable quantity in the order of 1100 particles/μm2. The IMPs were heterogeneous in size and were found distributed without any special pattern throughout the time of infection studied. The membrane lining the PV presented circular figures, which resembled vesicle fusion areas or attachments of the membranous tubular network, regions free from particles and small depressions, demonstrating to be a dynamic structure. IMPs were found in tubulo-vesicular structures present in the intravacuolar matrix, although rarely observed in elements of the intravacuolar network