Research & Interests
Trichomonas vaginalis, the number one, non-viral sexually transmitted organism, is the focus of our research program. The study of parasite and host cell-tissue interactions is focused on the identification of surface proteins that contribute to infection and disease pathogenesis.
We have studied several important properties of the biology of the parasite and the host-parasite interaction. These include antigenic diversity, cytoadherence, immune evasion, iron acquisition, and the dsRNA virus infection. The highly evolved and complex nature of the interrelationship between host and parasite is evidenced by the dynamics of the protein-antigen phenotypic variations and the various important protein repertoires, which have been defined. The phenotypic variation of trichomonad protein repertoires can either be coordinated, such as for the immunogens and adhesins, or be independent of one another, as seen for the proteinases. DNA sequence and the other data have been used to determine that an important phenotypically varying immunogen (P270) contains only one immunodominant epitope repeated many times, and the number of repeats varies among clinical isolates. Among most isolate trichomonads, this tandemly-repeated sequence was further found to comprise one-half of the total protein size, illustrating the complexity of the immunogen in terms of silent versus active antibody-generating domains.
The fact that trichomonads survive during phenotypic variation (without surface expression of major immunogens) does not suggest an absence of an important biofunctionality for these molecules. Biofunctional proteins, such as the epithelial cell- and erythrocyte-binding adhesins, also undergo phenotypic variation that is modulated by iron. More recently, we obtained evidence that the phenotypically varying protein plays a role in lipoprotein uptake, an important property given that trichomonads cannot synthesize lipids.
The studies on the immune evasion strategies of T. vaginalis are important for our understanding of the mechanisms of parasite survival during a host antibody response, especially when antibody readily kills the parasite in a complement-independent manner. This information may also lead to interference strategies apart from the development of vaccines to trichomonad proteins, like the adhesins. The future for pharmacologic targeting appears possible with the recent, exciting observation that proteinase activity, apart from degrading immunoglobulins and complement, is necessary for initial and sustained host parasitism.
The importance of a holistic, multidisciplinary approach to dissecting and understanding the complex host-parasite interaction is evidenced by several recent findings. Iron both up- and down-regulates transcription of genes, including adhesins and immunogens. Further, iron modulates compartmentalization and surface expression of the adhesins. Importantly, the adhesins have sequence identity to hydrogenosome metabolic enzymes, thereby invoking molecular mimicry, gene sharing, and functional diversity as important features for surface proteins of this parasite. Finally, the double-stranded RNA virus and satellite dsRNAs infecting T. vaginalis influence expression of many parasite proteins and directly correlate with the property of phenotypic variation.
Several recent new discoveries are the following: 1) There is a relationship between polyamine metabolism and the properties of cytoadherence and cytotoxicity. There is a direct relationship between polyamine depletion and enhanced adherence coupled with complete absence of host cell killing. Moreover, polyamine depletion down-regulates transcription of the cysteine proteinase known to be involved in cytotoxicity. 2) We have established an efficient transfection system that has permitted us to inhibit expression of trichomonad genes, thereby establishing a genetic approach to confirm the function of the adhesins and other virulence genes. 3) We have performed heterologous expression of functional T. vaginalis virulence genes in the bovine trichomonad Tritrichomonas foetus, and this opens exciting new approaches for examining virulence factors in a related organism. 4) We have demonstrated the up-regulation of gene expression in vaginal epithelial cells and in T. vaginalis that result immediately upon contact, showing that there are signaling events taking place in both parasites and host cells. 5) Adhesins and other trichomonad ligands for binding host molecules are among numerous metabolic enzymes of the secretome that become associated with the parasite surface for expression of function, properties that are also found among other microbial pathogens.
6) Finally, a noteworthy new finding is the relationship between seropositivity of men to T. vaginalis and prostate cancer, a finding that will establish a new paradigm for a microbial pathogen—this STD agent—as a causative agent for carcinogenesis.
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|Trichomonads have an ellipsoid morphology when grown in batch culture and when adherent to the HeLa epithelial cells (a transformed cell line). Note the flagella and undulating membranes are on the side opposite adherent to the epithelial cells. ||This is a cross-section electron photomicrograph showing the parasite (dark cell) intimacy with the vaginal epithelial cell (light cell). The vaginal epithelial cell is the tropic cell during colonization of the vaginal epithelium following infection. The membrane-membrane, parasite-host cell interaction is indicative of very specific ligand-receptor binding reactions. |
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|: After attachment of a single parasite to the host cell, there appears to be signaling by the parasite to attract other parasites to the parasitized cell. This leads to numerous organisms arriving and attaching to the epithelial cell. ||Unlike attachment to HeLa epithelial cells, adherence to vaginal epithelial cells leads to dramatic morphologic transformation from ellipsoid to amoeboid with many filopodia and pseudopodia (the membrane extensions). The fact that this change in morphology occurs only with vaginal epithelial cells is indicative of specific signaling by the host cell to the parasite. |
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