Vaccination strategies against Tritrichomonas foetus

Repurposing the open access malaria box reveals compounds with activity against Tritrichomonas foetus trophozoites

The protozoan parasite Tritrichomonas foetus causes early embryonic death in cattle which results in severe economic loss. In the United States, there are no drugs are approved for treatment of this pathogen. In this study, we evaluated in vitro anti-protozoal effects of compounds from an open access chemical library against T. foetus trophozoites. An initial high-throughput screen identified 16 compounds of interest. Further investigation revealed 12 compounds that inhibited parasite growth and 4 compounds with lethal effects. For lethal compounds, dose-response curves were constructed and the LD₅₀ was calculated for laboratory and field strains of T. foetus. Our experiments revealed chemical scaffolds that were parasiticidal in the micromolar range, and these scaffolds provide a starting point for drug discovery efforts. Further investigation is still needed to investigate suitability of these scaffolds and related compounds in food animals. Importantly, open access chemical libraries can be useful for identifying compounds with activity against protozoan pathogens of veterinary importance.

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No legal treatments are available for bovine trichomoniasis in the United States.

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The open access malaria box was screened for compounds with activity against T. foetus trophozoites.

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Identification of several scaffolds meriting further investigation for suitability in food animals.

Current therapeutics, their problems, and sulfur-containing-amino-acid metabolism as a novel target against infections by "amitochondriate" protozoan parasites

The "amitochondriate" protozoan parasites of humans Entamoeba histolytica, Giardia intestinalis, and Trichomonas vaginalis share many biochemical features, e.g., energy and amino acid metabolism, a spectrum of drugs for their treatment, and the occurrence of drug resistance. These parasites possess metabolic pathways that are divergent from those of their mammalian hosts and are often considered to be good targets for drug development. Sulfur-containing-amino-acid metabolism represents one such divergent metabolic pathway, namely, the cysteine biosynthetic pathway and methionine gamma-lyase-mediated catabolism of sulfur-containing amino acids, which are present in T. vaginalis and E. histolytica but absent in G. intestinalis. These pathways are potentially exploitable for development of drugs against amoebiasis and trichomoniasis. For instance, L-trifluoromethionine, which is catalyzed by methionine gamma-lyase and produces a toxic product, is effective against T. vaginalis and E. histolytica parasites in vitro and in vivo and may represent a good lead compound. In this review, we summarize the biology of these microaerophilic parasites, their clinical manifestation and epidemiology of disease, chemotherapeutics, the modes of action of representative drugs, and problems related to these drugs, including drug resistance. We further discuss our approach to exploit unique sulfur-containing-amino-acid metabolism, focusing on development of drugs against E. histolytica.

An improved molecular assay for Tritrichomonas foetus

Tritrichomonas foetus (T. foetus) is the causative agent of bovine trichomonosis, a sexually transmitted disease leading to abortion (from 1 to 8 months gestation), infertility, and occasional pyometra. The annual losses to the U.S. beef industry are estimated to be in the hundreds of millions of dollars. Currently, the "gold standard" diagnostic test for trichomonosis in most countries is the cultivation of live organisms from reproductive secretions. The cultured organisms can then be followed by PCR assays with primers that amplify T. foetus to the exclusion of all other trichomonad species. Thus, negative results present as null data, indistinguishable from failed PCR amplification during T. foetus specific amplification. Our newly developed assay improves previously developed PCR based techniques by using diagnostic size variants from within the internal transcribed spacer 1 (ITS1) region that is between the 18S rRNA and 5.8S rRNA subunits. This new PCR assay amplifies trichomonad DNA from a variety of genera and positively identifies the causative agent in the bovine trichomonad infection. This approach eliminates false negatives found in some current assays as well as identifying the causative agent of trichomonad infection. Additionally, our assay incorporates a fluorescently labeled primer enabling high sensitivity and rapid assessment of the specific trichomonad species. Moreover, electrophoretic separation of amplified samples can be outsourced, thus eliminating the need for diagnostic laboratories to purchase expensive analysis equipment.

Immunological and biochemical analysis of glycosylated surface antigens and lipophosphoglycan of Tritrichomonas foetus

Immunoaffinity-purified TF1.17 adhesin antigen was compared biochemically and antigenically to Tritrichomonas foetus (TF) lipophosphoglycan (LPG) and a soluble glycosylated antigen (SGA) released from T. foetus and implicated in pathogenesis and immunity. The monoclonal antibodies (Mabs TF1.15 and TF1.17) specific for a glycosylated TF1.17 antigen were previously shown to prevent adhesion of the T. foetus parasites to bovine vaginal epithelial cells and to mediate killing by bovine complement. SGA was isolated from T. foetus-conditioned buffer and purified by octyl-Sepharose hydrophobic column chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of SGA showed a major SGA1 component (approximately 190 kDa) and a minor SGA2 component (50-70 kDa), which migrated close to TF-LPG and TF1.17. The carbohydrate and lipid compositional analyses of affinity-purified TF1.17 and SGA2 by high-performance liquid chromatography (HPLC) and gas-liquid chromatography revealed the presence of monosaccharides and fatty acids as found in TF-LPG. All antigens contained terminal fucose as determined by alpha-fucosidase digestion followed by HPLC. ELISA and western blots were used to further characterize these glycosylated antigens and to analyze their relationships. The Mabs TF1.15 and TF1.17 reacted very strongly to TF-LPG and SGA2. as well as TF1.17 antigen, indicating that these molecules share common epitopes. These Mabs did not react with the SGA1 component either in ELISA and western blot analyses. Also, the monosaccharide composition of SGA1 was very different from the other three antigen, suggesting SGA1 was different from LPG, SGA2 and TF1.17. Although LPG reacted with Mabs to native TF1.17 antigen, LPG did not induce an immune response in cattle with the same route and adjuvant used to produce strong antibody responses to the native antigen. The latter response suggests that the tightly bound peptide present in the immunoaffinity-purified antigen is necessary for induction of a response to (an) epitope(s) in TF-LPG and TF1.17. Furthermore, vaginal fluid from T. foetus-infected heifers and serum from a cow with a T. foetus-associated pyometra recognized both TF1.17 and TF-LPG in western blots. These results suggest that T. foetus LPG and SGA2 are related to TF1.17 antigen, which was previously shown to play an important role in the pathogenesis and host response in bovine trichomoniasis.

Drug targets and mechanisms of resistance in the anaerobic protozoa

The anaerobic protozoa Giardia duodenalis, Trichomonas vaginalis, and Entamoeba histolytica infect up to a billion people each year. G. duodenalis and E. histolytica are primarily pathogens of the intestinal tract, although E. histolytica can form abscesses and invade other organs, where it can be fatal if left untreated. T. vaginalis infection is a sexually transmitted infection causing vaginitis and acute inflammatory disease of the genital mucosa. T. vaginalis has also been reported in the urinary tract, fallopian tubes, and pelvis and can cause pneumonia, bronchitis, and oral lesions. Respiratory infections can be acquired perinatally. T. vaginalis infections have been associated with preterm delivery, low birth weight, and increased mortality as well as predisposing to human immunodeficiency virus infection, AIDS, and cervical cancer. All three organisms lack mitochondria and are susceptible to the nitroimidazole metronidazole because of similar low-redox-potential anaerobic metabolic pathways. Resistance to metronidazole and other drugs has been observed clinically and in the laboratory. Laboratory studies have identified the enzyme that activates metronidazole, pyruvate:ferredoxin oxidoreductase, to its nitroso form and distinct mechanisms of decreasing drug susceptibility that are induced in each organism. Although the nitroimidazoles have been the drug family of choice for treating the anaerobic protozoa, G. duodenalis is less susceptible to other antiparasitic drugs, such as furazolidone, albendazole, and quinacrine. Resistance has been demonstrated for each agent, and the mechanism of resistance has been investigated. Metronidazole resistance in T. vaginalis is well documented, and the principal mechanisms have been defined. Bypass metabolism, such as alternative oxidoreductases, have been discovered in both organisms. Aerobic versus anaerobic resistance in T. vaginalis is discussed. Mechanisms of metronidazole resistance in E. histolytica have recently been investigated using laboratory-induced resistant isolates. Instead of downregulation of the pyruvate:ferredoxin oxidoreductase and ferredoxin pathway as seen in G. duodenalis and T. vaginalis, E. histolytica induces oxidative stress mechanisms, including superoxide dismutase and peroxiredoxin. The review examines the value of investigating both clinical and laboratory-induced syngeneic drug-resistant isolates and dissection of the complementary data obtained. Comparison of resistance mechanisms in anaerobic bacteria and the parasitic protozoa is discussed as well as the value of studies of the epidemiology of resistance.

Effect of the antimicrobial peptide, D-hecate, on trichomonads

Tritrichomonas foetus and Trichomonas vaginalis are protozoan parasites that cause sexually transmitted diseases in cattle and humans, respectively. There is a need for new antimicrobial agents to treat or prevent trichomoniasis because there are currently no approved chemotherapeutic agents against T. foetus and resistance of T. vaginalis to metronidazole does occur. Therefore, we evaluated the effect of a novel antimicrobial peptide, D-hecate, on the viability of 6 isolates of T. foetus and T. vaginalis in vitro. Tritrichomonas foetus and T. vaginalis were grown to mid log phase (24 hr) or late log/stationary phase (48 hr). Parasites at 10(6)/ml were mixed with equal volumes of D-hecate to final concentrations of 10 microM, 20 microM. and 40 microM of D-hecate. Controls had minimal essential medium (MEM) alone. The numbers of viable parasites were determined microscopically after 10, 20, and 30 min of incubation at 37 C with D-hecate or MEM. Our results show that D-hecate killed all 6 isolates of T. foetus and T. vaginalis evaluated. The killing effect was dependent on the concentration of the peptide, incubation time, and phase of growth of the parasites. Ultrastructural studies of parasites treated with 10 microM of D-hecate revealed extensive damage to the plasma membrane of most T. foetus and T. vaginalis cells, while a few cells were distorted but remained intact. D-Hecate may be a useful chemotherapeutic agent for the treatment of trichomoniasis.

Host-parasite interaction in bovine infection with Tritrichomonas foetus

Tritrichomonas foetus is a parasite of particular veterinary importance causing bovine tritrichomonosis, a sexually transmitted disease leading to infertility and abortion. The present review summarizes the current knowledge on potential mechanisms of pathogenicity of T. foetus, the immunology of host-parasite interaction in bovine tritrichomonosis, and the experimental model systems of this parasitic disease.

Adhesion of Tritrichomonas foetus to bovine vaginal epithelial cells

An in vitro culture system of bovine vaginal epithelial cells (BVECs) was developed to study the cytopathogenic effects of Tritrichomonas foetus and the role of lipophosphoglycan (LPG)-like cell surface glycoconjugates in adhesion of parasites to host cells. Exposure of BVEC monolayers to T. foetus resulted in extensive damage of monolayers. Host cell disruption was measured quantitatively by a trypan blue exclusion assay and by release of (3)H from [(3)H]thymidine-labeled host cells. Results indicated contact-dependent cytotoxicity of host cells by T. foetus. The cytopathogenic effect was a function of T. foetus density. Metronidazole- or periodate-treated T. foetus showed no damage to BVEC monolayers. A related human trichomonad, Trichomonas vaginalis, showed no cytotoxic effects, indicating species-specific host-parasite interactions. A direct binding assay was developed and used to investigate the role of a major cell surface LPG-like molecule in host-parasite adhesion. The results of competition experiments showed that the binding to BVECs was displaceable, was saturable, and yielded a typical binding curve, suggesting that specific receptor-ligand interactions mediate the attachment of T. foetus to BVECs. Progesterone-treated BVECs showed enhanced parasite binding. T. foetus LPG inhibited the binding of T. foetus to BVECs; the LPG from T. vaginalis and a variety of other glycoconjugates did not. These data imply specificity of LPG on host-parasite adhesion. Periodate-treated parasites showed no adherence to host cells, indicating the involvement of carbohydrate containing molecules in the adhesion process.

Sialic acid-specific lectin from Tritrichomonas foetus

A novel sialic acid-specific lectin (TFL) was isolated from Tritrichomonas foetus culture supernatant and purified by erythrocyte adsorption followed by fetuin-agarose affinity chromatography. According to gel filtration TFL is a protein of 728 kDa, different from the two sialidases of 853 and 254 kDa, secreted by T. foetus into the medium. The lectin is formed by multimeric complexes of 66 kDa subunit according to SDS-PAGE under reducing conditions. TFL is glycosylated with 4.2% of carbohydrates, half of which is represented by glucose. The lectin reacts equally with N-acetyl and N-glycolyl neuraminic acid, free, in alpha2,3- or alpha2,6-linkage. TFL has 7-fold weaker affinity to alpha2,8-linked N-acetylneuraminic acid (Neu5Ac) in colominic acid. Horse erythrocytes containing 4-O-acetyl Neu5Ac are agglutinated equally as compared to the human cells. TFL affinity to 9-O-acetyl Neu5Ac is 4-fold weaker as documented by hemagglutination inhibition with de-O-acetylated bovine submaxillary mucin, and ovine submaxillary mucin. A panel of mono- and oligosaccharides other than Neu5Ac do not inhibit TFL activity at 200 mM. The lectin does not require bivalent cations for activity, shows optimal reactivity at neutral pH and is stable at 4 degrees C. Anti-TFL antibodies identify membrane positivity on T. foetus, suggesting that the lectin functions in adhesion of the parasites. These findings, together with good stability and immunogenicity, make TFL a prospective candidate for further studies, especially in searching for efficient diagnostics and prevention of bovine trichomoniasis.

Immunoglobulin G, plasma cells, and lymphocytes in the murine vagina after vaginal or parenteral immunization with attenuated herpes simplex virus type 2

This investigation evaluated immunity to vaginal herpes simplex virus type 2 (HSV-2) infection after local or parenteral immunization with attenuated HSV-2. Vaginal immunization induced sterilizing immunity against challenge with a high dose of wild-type virus, whereas parenteral immunizations protected against neurologic disease but did not entirely prevent infection of the vagina. Vaginal immunization caused 86- and 31-fold increases in the numbers of immunoglobulin G (IgG) plasma cells in the vagina at 6 weeks and 10 months after immunization, whereas parenteral immunizations did not increase plasma cell numbers in the vagina. Vaginal secretion/serum titer ratios and specific antibody activities in vaginal secretions and serum indicated that IgG viral antibody was produced in the vagina and released into vaginal secretions at 6 weeks and 10 months after vaginal immunization but not after parenteral immunizations. In contrast to the case for plasma cells, the numbers of T and B lymphocytes in the vagina were similar in vaginally and parenterally immunized mice. Also, lymphocyte numbers in the vagina were markedly but similarly increased by vaginal challenge with HSV-2 in both vaginally and parenterally immunized mice. Lymphocyte recruitment to the vagina after virus challenge appeared to involve memory lymphocytes, because it was not observed in nonimmunized mice. Thus, local vaginal immunization with attenuated HSV-2 increased the number of IgG plasma cells in the vagina and increased vaginal secretion/serum titer ratios to 3.0- to 4.7-fold higher than in parenterally immunized groups but caused little if any selective homing of T and B lymphocytes to the vagina.

Purification and expression of the Tf190 adhesin in Tritrichomonas foetus

Bovine trichomoniasis is a sexually transmitted disease caused by Tritrichomonas foetus and characterized by early embryo loss. The mechanism of this loss is not known, although the parasite is known to cause inflammation and to have the ability to kill host cells by a contact-dependent cytotoxic mechanism. Antibody specific for a 190,000-Da surface complex (Tf190) was previously shown to inhibit this adhesion. In this study we used immunoaffinity chromatography to purify Tf190 from T. foetus in order to analyze its composition and examine its expression. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified Tf190 followed by silver staining revealed three components of Tf190. Western blotting and antibody-binding experiments showed that the 140- and 60-kDa bands were immunogenic. By using a battery of monoclonal antibodies (MAbs) periodate-sensitive epitopes were identified on Tf190, suggesting that these epitopes contained carbohydrate structures. Analyses of affinity-purified Tf190 by high-performance liquid chromatography and gas-liquid chromatography demonstrated the presence of the monosaccharides and lipids known to be prominent constituents of the lipophosphoglycan (LPG) of T. foetus. Flow cytometry experiments on several isolates of T. foetus with Tf190-specific antibodies revealed that Tf190 was present on subpopulations of all isolates but that not all epitopes were present on every isolate. This pattern of reactivities on the different parasite isolates was confirmed by Western blots of whole-parasite extracts probed with MAbs and antiserum. These results suggest that although variation in the expression of epitopes of Tf190 occurs in different strains of T. foetus, the Tf190 adhesion complex is widespread in different populations of the parasite. The data further suggest that immunogenic structures, important in the adhesion of T. foetus to mammalian cells, are located in the LPG-like component of Tf190.

Detection of Tritrichomonas foetus by PCR and DNA enzyme immunoassay based on rRNA gene unit sequences

Tritrichomonas foetus is the causative agent of bovine tritrichomonosis, a sexually transmitted disease leading to infertility and abortion. Diagnosis is hampered by putative contamination of samples with intestinal or coprophilic trichomonadid protozoa which might be mistaken for T. foetus. Therefore, we developed a PCR test optimized for applicability in routine diagnosis. Amplification is based upon primers TFR3 and TFR4 directed to the rRNA gene units of T. foetus. In order to avoid potential carryover contamination by products of previous amplification reactions, conditions were adapted to the use of the uracil DNA glycosylase system. Furthermore, documentation and interpretation of results were facilitated by including a DNA enzyme immunoassay for the detection of amplification products. Specificity was confirmed with genomic material from different related trichomonadid protozoa. The high sensitivity of the test allowed the detection of a single T. foetus organism in diagnostic culture medium or about 50 parasites per ml of preputial washing fluid. The present methods are thus proposed as (i) confirmatory tests for microscopic diagnosis following diagnostic in vitro cultivation and (ii) a direct T. foetus screening test with diagnostic samples.

Protective immunity against HSV-2 in the mouse vagina

Herpes simplex virus type 2 (HSV-2) is a sexually transmitted pathogen that infects the genital tract. The high prevalence of HSV-2 in humans underscores the need to develop an effective vaccine. Efforts to develop vaccines to protect women against this and other sexually transmitted pathogens would be facilitated by a better understanding of the immune mechanisms that protect the female reproductive tract against infections in animal models. Such information would be invaluable in developing vaccine strategies to promote the type and magnitude of immune responses in the genital tract that would effectively protect against infection. This review focuses on recent studies using a progestin-treated adult mouse model to explore mucosal immunity to HSV-2 in the vagina. Evidence indicating a major role for both humoral and T cell immunity is presented.

Immunoglobulin G is the main protective antibody in mouse vaginal secretions after vaginal immunization with attenuated herpes simplex virus type 2

We investigated the protective role of antibodies in vaginal secretions of mice that were immune to vaginal challenge with herpes simplex virus type 2 (HSV-2). Unfractionated vaginal immunoglobulins from immune and nonimmune mice and affinity-purified immunoglobulin G (IgG) and secretory IgA (S-IgA) from immune secretions were adjusted to their concentrations in vivo. Wild-type HSV-2 was incubated in the immunoglobulin preparations for 15 min in vitro, followed by inoculation into vaginae of nonimmune mice. HSV-2 was neutralized by unfractionated antibody and purified IgG from immune secretions but not by unfractionated nonimmune antibody or by purified immune S-IgA. The protective effect of IgG in vivo was investigated by passively transferring purified serum IgG from immune and nonimmune donors to nonimmune recipients before vaginal challenge infection. Immune IgG significantly reduced the percentage of vaginal epithelium infected, concentrations of shed virus protein in the vaginal lumen, and illness scores, even though the viral antibody titers in serum and vaginal secretions of recipient mice at the time of challenge were only 29 and 8%, respectively, of those in actively immunized mice. Additionally, removal of vaginal secretions from immune mice 10 min before vaginal challenge with HSV-2 significantly increased the concentration of shed virus protein in the vaginal lumen after challenge. Collectively, the data indicate that IgG antibody in vaginal secretions of immune mice provides early protection against vaginal challenge infection, probably by neutralizing virus in the vaginal lumen. In contrast, S-IgA antibody contributed relatively little to immune protection of the vagina.

Identification of a neutrophil chemotactic factor from Tritrichomonas foetus as superoxide dismutase

Antibodies to a neutrophil chemotactic factor from Tritrichomonas foetus were used to screen a T. foetus cDNA expression library in lambda gt11. All positive clones were identified as homologs of iron-containing superoxide dismutase (SOD). Native gel electrophoresis showed that the antibodies indeed recognized T. foetus antigens with SOD activity. Two SOD genes were found in T. foetus, and cloned and sequenced as parts of larger genomic segments of 3844 and 4089 base pairs. Transcription initiated between the first and second methionine codons of each genomic open reading frame, generating mRNAs with 5' untranslated regions of 11-15 bases, and encoding proteins of 195 amino acids. The two SOD coding sequences lacked obvious introns. They were 79% identical at both the nucleotide and amino acid levels. Both SOD genes were inserted into a eukaryotic expression vector and stably expressed in mammalian cells; both proteins were recognized by the antibodies, and both assumed a cytosolic, extranuclear distribution in these cells. Histidine-tagged forms of both T. foetus SODs were expressed in E. coli and after purification, found to have neutrophil chemotactic activity similar to the non-recombinant factor purified from T. foetus. Identification of this neutrophil chemotactic factor as SOD provides additional insight into the host-parasite interaction.

Pathogenesis, diagnosis, and management of trichomoniasis in cattle

Trichomoniasis is a disease of the pregnancy, but apparently not of either the cow or the bull, except in the case of postcoital pyometra. Its self-limiting nature in the cow and chronic nature in the bull mean that a positive diagnosis for the herd can more easily be obtained from bulls than from cows. Incubation of preputial scrapings or washings (or pyometritic fluid, if available) in a selective growth medium such as the InPouch system is the diagnostic method of choice. The diagnosis is based on identification of the morphology and characteristic rolling motility of the trichomonad. "High tech" molecular approaches may eventually offer greater diagnostic sensitivity than can culture methods, but currently they are no more accurate. In addition, serologic screening of the female herd (but interestingly, not the bulls) may become possible and may allow the practitioner to at least determine whether exposure has occurred in an unvaccinated herd. Control in an infected herd involves no pharmacologic treatment but rather culling of infected bulls, retention of younger, culture-negative bulls, and segregation of the female herd by reproductive status.

Lesions of experimental genital Tritrichomonas foetus infections in estrogenized BALB/c mice

Ninety-seven BALB/c mice were inoculated intravaginally with 8.0 x 10(5) Tritrichomonas foetus organisms, using either isolate ATCC 30003 or field isolate MU Y22 2 days after estrogenization with 15 micrograms 17 beta-estradiol. Reproductive tracts were examined at several time points post-inoculation to determine gross and histologic responses to trichomonad infection as compared to estrogenized, uninfected control animals. The two isolates varied greatly in ability to maintain chronic infection; no ATCC 30003-inoculated animals remained culture-positive beyond 7 weeks post-inoculation, whereas MU Y22-inoculated animals were infected for greater than 26 weeks. Lesions were seen in 40-60% of animals prior to 10 weeks post-inoculation and included moderate uterine dilation and glandular atrophy, uterine gland abscesses, pyometra, intramural perivascular lymphoid infiltrates, and ovarian bursitis. The severity of lesions was independent of the T. foetus isolate. Lesions became more severe at 10 weeks post-inoculation, and at 10 and 26 weeks post-inoculation, lesions were seen in 60% and 75% of animals, respectively. In addition to lesions described above, epithelial changes were marked at these late necropsies, including ulceration, flattening, hypertrophy, and squamous metaplasia. The lesions seen in these mice closely resemble those described in natural bovine infection, suggesting that the estrogenized BALB/c mouse is an excellent model for study of bovine trichomoniasis.