Keywords: Toxoplasma go«d///parasite-host cell interaction/parasitophorous vacuole/fluorescence microscopy ABSTRACT. The initial association of tachyzoites of Toxoplasma gondii with a host cell induces an endocytic process which leads to the formation of a vacuole known as the parasitophorous vacuole (PV). Weanalyzed the parasite-host cell interaction process using either parasites or host cells whose membranewas previously labeled with probes specific for proteins, sialoglycoconjugates and lipids, and then allowed to interact for periods varying from 5 minutes to 24 hours. The fate of the fluorscents probes was followed by con focal laser scanning microscopy. In host cells previously labeled with PKH26, FITC-Thiosemicarbazide or DTAF, which label membraneproteins, siloglycoconjugates and lipids, respectively, a uniform labeling of the cell surface was observed before interaction.When allowed to interact with T. gondii, labeling for PKH26and DTAF, but not for FITC-Thiosemicarbazide, was observed initially at the region of contact between the two cells and subsequently on the membrane lining the PV and the intravacuolar parasites. These observations show that some, but not all, membranecomponents contribute to the formation of the PVmembrane. Previously labeled parasites attach to the host cell surface but lose the fluorescent probes during the invasion process so that no labeled parasites were seen within the PV. These observations point to the existence of a dynamic process of membraneassociated components of the parasite and host cell during the interaction process.

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Tachyzoites of Toxoplasma gondii attach to the macrophage surface and are internalized either by a phagocytic process, which can be inhibited by cytochalasin D, or by an active process, independent of host cell actin. Previous studies have shown that parasite attachment induces the secretion of macromolecules found in the apical organelles (micronemes and rhoptries) and subsequent/concomitant parasite internalization with the formation of a membrane-bound vacuole known as the parasitophorous vacuole. In the present study we labeled the macrophage surface with fluorescent probes that bind to proteins (DiIC16) and lipids (DTAF) and then allowed control or cytochalasin-D-treated cells to interact with untreated or antibody-coated tachyzoites of T. gondii. The interaction was interrupted at different time points by fixation and the distribution of the probes was analyzed by confocal laser scanning microscopy. Following attachment of the parasites to the macrophage surface, intense labeling of the parasite surface was observed, suggesting transfer of components of the macrophage surface to the parasite surface. Nonadherent parasites were not labeled. Immediately after attachment, most of the parasites were internalized and labeling of the internalized parasites as well as of the parasitophorous vacuole, probably of its membrane, was evident, indicating that surface components of the macrophage are involved in the formation of the parasitophorous vacuole.

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Tritrichomonas foetus is a flagellate protozoan and the etiological agent of bovine genital tri-chomoniasis [1], which is an infectious vene- real disease. This parasite is usually found as- sociated with the mucosal surface of the uro- genital tract in females or the male preputial and penile membranes. In females, the clinical ma-nifestations may include abortion, with repe- tition of estrus at irregular intervals, vaginitis, cervicitis, endometritis, and pyometra. Parasi- tized males may have a discharge with small nodules in the preputial membrane. After that, the bulls have no clinical symptoms, and are thus an asymptomatic carrier that may spread the infection. Considering that a bull could cover up to twenty females [2], bovine genital trichomoniasis is a serious medical and veteri- nary problem, with economical repercussion for beef and milk production. As T. foetus is an amitochondrial and aerotolerant organism, en- ergy production under low O2 tension in the protozoan is done via hydrogenosome, which, as the name suggests, is the organelle where H2 is generated [3,4,5]. The molecular machinery of mitochondrial cell death is, therefore, absent in this parasite and the mechanism that activates of cell death program is not clear. This review seeks to understand the characteristics of the protozoan parasite T. foetus in order to propose new therapies for animals suffering from this infectious and contagious agent