Molecular basis of host epithelial cell recognition by Trichomonas vaginalis

Multiple double-stranded RNA segments are associated with virus particles infecting Trichomonas vaginalis

Previous studies demonstrated that some isolates of the sexually transmitted protozoan Trichomonas vaginalis are infected with a nonsegmented, double-stranded RNA (dsRNA) virus. A reexamination of the total dsRNA extracted from several virus-harboring isolates indicated the presence of at least three dsRNAs with sizes ranging from 4.8 to 4.3 kbp. The double-stranded nature of each of the three segments was determined by hybridization experiments using riboprobes of opposite polarities obtained from cDNA generated to each of the segments. All three segments were present in agar clones originating from single organisms of T. vaginalis isolates, suggesting that the three segments were not the result of a mixed population of trichomonads harboring different sizes of dsRNA. The three segments were associated with CsCl-purified virus particles, as evidenced by electron microscopy, and RNAse treatment of the preparation containing virus particles did not destroy the dsRNAs. Finally, the individual dsRNA segments were purified for use as probes to determine whether the three dsRNAs shared any sequence homology. Each end-labeled dsRNA segment did not cross-hybridize to any of the other two segments, a finding consistent with the hybridization of labeled cDNAs to only the segments from which they were derived. These results show that the coding capacity of the dsRNA virus may be at least three times greater than that estimated earlier and illustrates further the complexity of this virus-parasite interrelationship.

Trichomonas vaginalis haemolysis: evidence of functional pores formation on red cell membranes

We have investigated the mechanisms used by Trichomonas vaginalis to damage cellular membranes, using human erythrocytes as target cells. Haemolysis is a contact- and temperature-dependent phenomenon, and is inhibited in 4 mM EGTA. Osmotic protection experiments using carbohydrates with different molecular diameters as protectants demonstrated that the cytolytic activity of T. vaginalis is inhibited in 75 mM stachyose. On the basis of our data, we hypothesize a cytopathic mechanism mediated by the formation of functional pores into the target membrane. Some of the Trichomonas protein involved in haemolysis have been immunologically characterized.

Signalling of Trichomonas vaginalis for amoeboid transformation and adhesion synthesis follows cytoadherence

The cytoadherence of Trichomonas vaginalis, the sexually transmitted flagellated protozoan, to vaginal epithelial cells (VECs) is the key to infection. Electron microscopy revealed that in vitro-grown parasites having typical globular shape transformed rapidly after contact with VECs into thin, flat, amoeboid cells, maximizing the area of adhesion to the surface of VECs. Amoebic trichomonads formed filopodia and pseudopodia, which interdigitated at distinct sites on the plasma membrane of target cells. In contrast, the amoeboid transformation did not occur for T. vaginalis interacting with HeLa cells, the previously used in vitro host model cell. Initial parasitism of VECs by a single organism was followed by establishment of a monolayer of trichomonads on the host cell. Finally, parasites adhering to either VECs or HeLa cells were induced to synthesize greater amounts of the four previously described adhesins. Therefore, distinct signals after contact with either epithelial cell type leads to the morphological transformation and/or induction of adhesion synthesis by T. vaginalis.

Analysis of adhesion and cytotoxicity of Tritrichomonas foetus to mammalian cells by use of monoclonal antibodies

The relationship of Tritrichomonas foetus adhesion to mammalian cells and cytotoxicity to these targets was investigated. High-adherence and low-adherence lines of T. foetus, derived by repeated adhesion to HeLa cells, showed high and low cytotoxicity, respectively, to HeLa cells. When parasites were separated from targets by membranes (0.4-microns pore size), no cytotoxicity was detectable. Monoclonal antibodies elicited against T. foetus that lowered adhesion also lowered parasite-mediated cytotoxicity. Flow cytometry experiments revealed that the levels of an adhesion- and cytotoxicity-blocking antibody bound to the surface of high-adherence clones of T. foetus were higher than those in low-adherence clones. Western blots of parasite extracts separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis were probed with an anti-T. foetus antibody. A molecule with a molecular weight of approximately 190,000 composed of subunits with molecular weights of approximately 140,000 to 150,000 and approximately 65,000 was identified. Immunoprecipitation experiments with metabolically labeled T. foetus and the same antibody confirmed that similar subunits were synthesized by the parasite. These results indicate that adhesion of T. foetus to mammalian cells is an important step in cytotoxic damage of these targets and that a surface adhesin on the parasite is involved in the adhesion mechanism.