In Silico Analysis of the ROP29 Protein as a Vaccine Candidate Against Toxoplasma gondii

The progression of Toxoplasma gondii (T. gondii) invasion is aided by rhoptry proteins (ROPs), which are also crucial for the parasite's survival in host cells. In this study, in silico analysis was performed to examine the various aspects of the ROP29 protein, such as physicochemical properties, potential T- and B-cell epitopes, and other significant features. The research revealed that there were 55 possible sites for posttranslational modification in the ROP29 protein. The secondary structure of the ROP29 protein consists of a random coil, an alpha-helix, and an extended strand, which account for 49.69%, 36.81%, and 13.50%, respectively. Moreover, a number of putative T- and B-cell epitopes for ROP29 were found. The Ramachandran plot showed that 88.91% (crude model) and 97.54% (refine model) of the amino acid residues were located in the favored regions. Also, the testing of this protein's antigenicity and allergenicity showed that it was nonallergenic and immunogenic. Our results suggested that employing in silico tools to apply structural and functional predictions to the ROP29 protein can lower the likelihood that laboratory investigations will fail. This research served as a crucial foundation for further research. More research is required in the future in suitable animal model employing ROP29 alone or in combination with other antigens.

Protective effect against toxoplasmosis in BALB/C mice vaccinated with recombinant Toxoplasma gondii CDPK3, GRA35, and ROP46 protein cocktail vaccine

Toxoplasma gondii (T. gondii) is one of the most common pathogenic protozoa in the world, and causes toxoplasmosis, which in varying degrees causes significant economic losses and poses a serious public health challenge globally. To date, the development of an effective vaccine for human toxoplasmosis remains a challenge. Given that T.gondii calcium-dependent protein kinase 3 (CDPK3), dense granule protein 35 (GRA35) and rhoptry organelle protein 46 (ROP46) play key roles during Toxoplasma gondii invasion of host cells, we developed a protein vaccine cocktail including these proteins and validated its protective efficacy. The specific protective effects of vaccine on mice were analyzed by measuring serum antibodies, cytokines, splenocyte proliferation, the percentage of CD4+ and CD8+ T-lymphocytes, survival rate, and parasite cyst burden. The results showed that mice vaccinated with a three-protein cocktail produced the highest levels of immune protein antibodies to IgG, and high levels of IFN-γ, IL-2, IL-4, and IL-10 compared to other mice vaccinated with two proteins. In addition, CD4+ and CD8+ T cell percentages were significantly elevated. Compared to the control groups, mice vaccinated with the three-protein cocktail survived significantly longer after acute infection with T. gondii and had significantly fewer cysts after chronic infection. These results demonstrated that a cocktail vaccine of TgCDPK3, TgGRA35, and TgROP46 can effectively induce cellular and humoral immune responses with good protective effects in mice, indicating its potential as vaccine candidates for toxoplasmosis.

Mineralization Reduces the Toxicity and Improves Stability and Protective Immune Response Induced by Toxoplasma gondii

Vaccination is an ideal strategy for the control and prevention of toxoplasmosis. However, the thermostability and effectiveness of vaccines limit their application. Here, calcium mineralization was used to fabricate Toxoplasma gondii tachyzoites as immunogenic core-shell particles with improved immune response and thermostability. In the current study, T. gondii RH particles coated with mineralized shells were fabricated by calcium mineralization. The mineralized shells could maintain the T. gondii tachyzoites structural integrity for at least 12 months and weaken the virulence. Immunization of mice with mineralized tachyzoites induced high levels of T. gondii-specific antibodies and cytokines. The immunized mice were protected with a 100% survival rate in acute and chronic infection, and brain cyst burdens were significantly reduced. This study reported for the first time the strategy of calcium mineralization on T. gondii and proved that mineralized tachyzoites could play an immune protective role, thus expanding the application of biomineralization in T. gondii vaccine delivery.

CD4+ T Cell Responses to Toxoplasma gondii Are a Double-Edged Sword

CD4+ T cells have been found to play critical roles in the control of both acute and chronic Toxoplasma infection. Previous studies identified a protective role for the Toxoplasma CD4+ T cell-eliciting peptide AS15 (AVEIHRPVPGTAPPS) in C57BL/6J mice. Herein, we found that immunizing mice with AS15 combined with GLA-SE, a TLR-4 agonist in emulsion adjuvant, can be either helpful in protecting male and female mice at early stages against Type I and Type II Toxoplasma parasites or harmful (lethal with intestinal, hepatic, and spleen pathology associated with a storm of IL6). Introducing the universal CD4+ T cell epitope PADRE abrogates the harmful phenotype of AS15. Our findings demonstrate quantitative and qualitative features of an effective Toxoplasma-specific CD4+ T cell response that should be considered in testing next-generation vaccines against toxoplasmosis. Our results also are cautionary that individual vaccine constituents can cause severe harm depending on the company they keep.

Bioinformatics-based prediction and screening of immunogenic epitopes of Toxoplasma gondii rhoptry proteins 7, 21 and 22 as candidate vaccine target

Introduction

Toxoplasmosis is a well-known zoonotic disease caused by Toxoplasma gondii. The main causes of the disease range from eating undercooked or contaminated meat and shellfish to cleaning litter trays into which cats that excreted toxoplasma via faeces. This pathogen can live for a very long time, possibly a lifetime, within the bodies of humans and other animals.

Aims and objectives

This study aimed to predict and analyse candidate immunogenic epitopes for vaccine development by evaluating the physio-chemical properties, multiple sequence alignment, secondary and tertiary structures, phosphorylation sites, transmembrane domains, and signal peptides, of T. gondii rhoptry proteins ROP7, ROP21, and ROP22 using bioinformatics tools.

Methods

To find immunogenic epitopes of rhoptry proteins, numerous bioinformatics web servers were used containing multiple sequence alignment, physiochemical properties, antigenicity and allergenicity, post-translational modification sites (PTMs), signal peptides, transmembrane domains, secondary and tertiary structures, and screening of predicted epitopes. We evaluated immunogenic linear B-cell epitopes as candidate proteins for vaccine development.

Results

Nine epitopes were identified for each protein, and analysis of immunogenicity, revealed three candidate epitopes for ROP7, one for ROP21, and four for ROP22. Among all candidate epitopes, ROP22 contained the most immunogenic epitopes with immunogenicity score of 0.50575.

Conclusion

We acquired detailed information on predicted immunogenic epitopes using in-silico methods. The results provide a foundation for further experimental analysis of toxoplasmosis, and potential vaccine development.

Vaccination of squirrel monkeys (Saimiri spp.) with nanoparticle based-Toxoplasma gondii antigens: new hope for captive susceptible species

Squirrel monkeys (Saimiri spp.), new world primates from South America, are very susceptible to toxoplasmosis. Numerous outbreaks of fatal toxoplasmosis in zoos have been identified around the world, resulting in acute respiratory distress and sudden death. To date, preventive hygiene measures or available treatments are not able to significantly reduce this mortality in zoos. Therefore, vaccination seems to be the best long-term solution to control acute toxoplasmosis. Recently, we developed a nasal vaccine composed of total extract of soluble proteins of Toxoplasma gondii associated with muco-adhesive maltodextrin-nanoparticles. The vaccine, which generated specific cellular immune responses, demonstrated efficacy against toxoplasmosis in murine and ovine experimental models. In collaboration with six French zoos, our vaccine was used as a last resort in 48 squirrel monkeys to prevent toxoplasmosis. The full protocol of vaccination includes two intranasal sprays followed by combined intranasal and s.c. administration. No local or systemic side-effects were observed irrespective of the route of administration. Blood samples were collected to study systemic humoral and cellular immune responses up to 1 year after the last vaccination. Vaccination induced a strong and lasting systemic cellular immune response mediated by specific IFN-γ secretion by peripheral blood mononuclear cells. Since the introduction of vaccination, no deaths of squirrel monkeys due to T. gondii has been observed for more than 4 years suggesting the promising usage of our vaccine. Moreover, to explain the high susceptibility of naive squirrel monkeys to toxoplasmosis, their innate immune sensors were investigated. It was observed that Toll-like and Nod-like receptors appear to be functional following T. gondii recognition suggesting that the extreme susceptibility to toxoplasmosis may not be linked to innate detection of the parasite.

Insight into the current Toxoplasma gondii DNA vaccine: a review article

INTRODUCTION

Toxoplasma gondii (T.gondii) is a widespread protozoan with significant economic losses and public health importance. But so far, the protective effect of reported DNA-based vaccines fluctuates widely, and no study has demonstrated complete protection.

AREAS COVERED

This review provides an inclusive summary of T. gondii DNA vaccine antigens, adjuvants, and some other parameters. A total of 140 articles from 2000 to 2021 were collected from five databases. By contrasting the outcomes of acute and chronic challenges, we aimed to investigate and identify viable immunological strategies for optimum protection. Furthermore, we evaluated and discussed the impact of several parameters on challenge outcomes in the hopes of developing some recommendations to assist better future horizontal comparisons among research.

EXPERT OPINION

In the coming five years of research, the exploration of vaccine cocktails combining invasion antigens and metabolic antigens with genetic adjuvants or novel DNA delivery methods may offer us desirable protection against this multiple stage of life parasite. In addition to finding a better immune strategy, developing better in silico prediction methods, solving problems posed by variables in practical applications, and gaining a more profound knowledge of T.gondii-host molecular interaction is also crucial towards a successful vaccine.

Enhancement of immune responses by vaccine potential of three antigens, including ROP18, MIC4, and SAG1 against acute toxoplasmosis in mice

Toxoplasma gondii (T. gondii) causes considerable financial losses in the livestock industry and can present serious threats to pregnant women, as well as immunocompromised patients. Therefore, it is required to design and produce an efficient vaccine for controlling toxoplasmosis. The present study aimed to evaluate the protective immunity induced by RMS protein (ROP18, MIC4, and SAG1) with Freund adjuvant, calcium phosphate nanoparticles (CaPNs), and chitosan nanoparticles (CNs) in BALB/c mice. The RMS protein was expressed in Escherichia coli (E. coli) and purified using a HisTrap HP column. Thereafter, cellular and humoral immunity was assessed by injecting RMS protein on days 0, 21, and 35 into four groups [RMS, RMS-chitosan nanoparticles (RMS-CNs), RMS-calcium phosphate nanoparticles (RMS-CaPNs), and RMS-Freund]. Phosphate buffered saline (PBS), CNs, CaPNs, and Freund served as the four control groups. The results displayed that vaccination with RMS protein and adjuvants significantly elicited the levels of specific IgG antibodies and cytokines against toxoplasmosis. There were high levels of total IgG, IgG2a, and IFN-γ in vaccinated mice, compared to those in the control groups, especially in the RMS-Freund, indicating a Th-1 type response. The vaccinated and control mice were challenged intraperitoneally with 1 × 10³ tachyzoites of the T. gondii RH strain four weeks after the last injection, and in RMS-Freund and RMS-CaPNs groups, the highest increase in survival time was observed (15 days). The RMS can significantly increase Th1 and Th2 responses; moreover, multi-epitope vaccines with adjuvants can be a promising strategy for the production of a vaccine against toxoplasmosis.

Development of multistage recombinant protein vaccine formulations against toxoplasmosis using a new chitosan and porin based adjuvant system

Toxoplasmosis is a global health problem affecting both human and animal populations. The lack of effective treatment makes the development of a vaccine against toxoplasmosis one of the main goals in the management of this disease. In our study, vaccine formulations containing the multistage recombinant antigens, rBAG1 + rGRA1 were developed with a combined adjuvant system consisting of chitosan and Salmonella Typhi porins in micro (MicroAS) and nanoparticulate (NanoAS) forms. BALB/c mice were immunized intraperitoneally with vaccine formulations two times at three-week intervals. Three weeks after the second vaccination, mice were challenged with 7-8 live tissue cysts of the virulent T. gondii PRU strain by oral gavage. Higher cellular uptake by macrophages and enhanced cellular (IFN-γ and I-4 in stimulated spleen cells) and humoral (IgG, IgG1, IgG2a) responses were obtained with the adjuvanted formulation, higher with microsystem when compared to that of nanosystem. Microsystem was found to stimulate Th1-polarized immune responses, whereasnon-adjuvanted antigens stimulated Th2-polarized immune response. The highest survival rate and reduction in cysts numbers and T. gondii DNA were obtained with the adjuvanted antigens.Our study showed that adjuvanted multistage recombinant vaccine systems increase theimmune response with strong protection againstT. gondii, more profoundly in microparticulate form.

Protective immunity induced with a DNA vaccine encoding B- and T-cells multi-epitope SAG1, ROP16, MIC4, GRA12, M2AP, and multi-epitope ROP8 against acute and chronic toxoplasmosis in BALB/c mice

BACKGROUND

T. gondii infection is characterized by a high global prevalence. Nearly, 16-40% of people have been infected by T. gondii. Although T. gondii often causes subclinical infection, it may cause severe complications in newborns with congenital infection and immunocompromised individuals. Constant attempts of scientists have made valuable findings in the development of T. gondii candidate vaccines. However, an effective vaccine has not been successfully developed yet. In this study, multi-epitope SAG1, MIC4, ROP16, M2AP, GRA12, and multi-epitope ROP8 were injected into BALB/c mice intramuscularly, as cocktailed plasmids or as single-gene plasmids to assess the immune response against chronic and acute Toxoplasma infection.

METHODS

BALB/c mice were immunized on days 0, 21, and 42. The immune responses of both vaccinated and control groups were evaluated using cytokine and antibody measurements, lymphocyte proliferation assay, survival time, and average number of cysts in each brain.

RESULTS

The results indicated that DNA vaccination using multi-epitope ROP8 and multi-epitope SAG1, ROP16, MIC4, GRA12, M2AP could elicit both cellular and humoral immune responses, and enhanced the survival time in BALB/c mice. Also, the administration of multi-epitope ROP8 plus multi-epitope SAG1, ROP16, MIC4, GRA12, M2AP could enhance the concentrations of IgG antibody, elicit a mixed IgG1/IgG2a reaction with the predominance of the IgG2a, increase the release of IFN-γ cytokine, prolonge the survival time, and reduce the brain cysts.

CONCLUSIONS

Here, we report that vaccination using cocktailed plasmids could induce better protective immunity compared to single plasmid for acute and chronic T. gondii infection.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Recombinant Toxoplasma gondii MIF, CDPK3, and 14-3-3 Protein Cocktail Vaccine

Toxoplasma gondii can infect almost all endotherm organisms including humans and cause life-threatening toxoplasmosis in immunocompromised individuals, which leads to serious public health problems. Developing an excellent vaccine against this disease is impending. In present study, we formulated a cocktail protein vaccine including the TgMIF, TgCDPK3, and Tg14-3-3 proteins, which play critical roles in T. gondii infection. The recombinant protein vaccines were constructed and assessed by vaccination in BALB/c mice. We organized the mice in various protein combination groups of vaccines, and all mice were immunized with corresponding proteins at 0, 2, and 4 weeks. The specific protective effects of the vaccines on mice against T. gondii were analyzed by the mensuration of cytokines, serum antibodies, splenocyte proliferation assay, survival time, and parasite cyst burden of mice after the challenge. The study indicated that mice immunized with all three multicomponent proteins vaccine triggered a strong immune response with highest levels of IFN-γ production and IgG antibody compared with the other two protein combinations and controls. Moreover, there was an increase in IL-4 production and antigen-specific lymphocyte proliferation. The parasite cysts were significantly reduced (resulting in an 82.7% reduction), and survival time was longer in immunized mice with three multicomponent proteins compared with the other groups of mice. The enhanced humoral and cell-mediated immunity indicated that the protein cocktail vaccine containing three antigens provided effective protection for mice. These results indicated that recombinant TgMIF, TgCDPK3, and Tg14-3-3 multicomponent proteins were potential candidates for vaccine against toxoplasmosis.

A Novel Combined DNA Vaccine Encoding Toxoplasma gondii SAG1 and ROP18 Provokes Protective Immunity Against a Lethal Challenge in Mice

PURPOSE

Antigens expressed by Toxoplasma gondii (T. gondii) during its life cycle trigger various immune responses in the host. Recently, toxoplasma vaccine research focused on T. gondii surface antigen 1 (SAG1) and Rhoptry Protein 18 (ROP18) to establish a safe and efficacious DNA vaccine.

METHOD

We constructed two eukaryotic expression plasmids: p3 × FLAG-Myc-CMV™-24-SAG1 and p3 × FLAG-Myc-CMV™-24-ROP18. BALB/c mice were randomly divided into six groups and immunized with these DNA vaccines either separately or in combination. The combination vaccine was administered at either the full dose or at half-strength dose. Control mice were immunized with empty vector or with phosphate-buffered saline.

RESULTS

The frequency of CD4⁺ cells in the spleen was consistent among all groups, whereas that of CD8⁺ T cells was the highest in the group immunized with the combination vaccine at half-strength dose (p < 0.05). Importantly, the mRNA expression levels of interleukin-12 (IL-12) and interferon-gamma (INF-γ) were closely correlated (r = 0.6, p < 0.0001) and both were upregulated in the group that was immunized with the combination vaccine at half-strength dose (p < 0.0001). The survival time of the mice subjected to a lethal dose of toxoplasma was significantly extended by prior immunization with DNA vaccines expressing either SAG1 or ROP18 or a combination of both (p < 0.05). The group that was immunized with the combination vaccine at half-strength dose demonstrated the best efficacy (p < 0.05).

CONCLUSION

These results showed that the combination DNA vaccine provided better immune protection than the single gene vaccines, and that optimizing the dosing of the vaccine can improve the immune response.

Unravelling Toxoplasma treatment: conventional drugs toward nanomedicine

Toxoplasma gondii is a worldwide protozoan parasite that infects almost all warm-blooded animals. Although human toxoplasmosis is mostly latent, pregnant women and immunocompromised patients need effective treatment. There are drugs of choice for treatment of toxoplasmosis; however, due to their side effects and/or their disease stage-specificity, prescription of them is limited. During recent years, nanomedicine has been employed to overcome limitations of conventional drugs. Here, we provided a state-of-the-art review of experimental toxoplasmosis treatment using nanotechnology.

Epitope Analysis and Efficacy Evaluation of Phosphatase 2C (PP2C) DNA Vaccine Against Toxoplasma gondii Infection

Toxoplasma gondii infects almost all warm-blooded animals and negatively affects the health of a wide range of these animals, including humans. Protein phosphatase 2C (PP2C) is a T. gondii protein secreted by rhoptry organelles during host cell invasion. However, very little is known about whether this protein can induce protective immunity against T. gondii. In this study, bioinformatics analysis of PP2C revealed some useful information in the context of anti-toxoplasmosis treatments and vaccine research. In addition, the PP2C gene was amplified, and a eukaryotic expression vector (pEGFP-PP2C) was successfully constructed to express PP2C. Finally, the constructed pEGFP-PP2C was injected into mice to evaluate whether it could induce immunoprotection. Compared with the control groups, we found that immunizations with the pEGFP-PP2C plasmid could elicit specific IgG antibodies and cytokines against T. gondii infection. The survival of mice immunized with the pEGFP-PP2C plasmid was significantly prolonged compared with that of the control group mice. Based on the ability of pEGFP-PP2C to induce specific immune responses against T. gondii, we propose that PP2C merits consideration as a potential vaccine candidate against toxoplasmosis.

Curcumin@metal organic frameworks nano-composite for treatment of chronic toxoplasmosis

Toxoplasmosis is a zoonotic protozoal disease caused by Toxoplasma gondii, an intracellular opportunistic protozoan parasite that can infect any warm-blooded vertebrate cell. In this study, zirconium, and iron-based metal-organic framework was prepared according to the solvothermal method. New nanocomposite (Curcumin@MOFs) was prepared by reacting curcumin with amino-functionalized metal-organic frameworks (Fe-MOF and UiO-66-NH₂). Besides characterizations of the composite by powder X-ray diffraction and scanning electron microscope, nano-Curcumin@MOFs was used as a new novel structure as atrial for treatment of chronic toxoplasmosis. Results showed a reduced number of brain cysts, high levels of serum Toxo IgG, and normal histo-morphology with preserved parenchymal, and stromal tissues in rats groups treated with curcumin and Curcumin@MOFs nanocomposite.

Toxoplasma gondii ROP38 protein: Bioinformatics analysis for vaccine design improvement against toxoplasmosis

Rhoptry proteins (ROPs) play a significant role in various stages of Toxoplasma gondii (T. gondii) life cycle, being critical for both invasion and intracellular survival. ROP38 is a key manipulator of host gene expression and has a function in tachyzoite to bradyzoite conversion. In this study, we've employed various bioinformatics online tools for immunogenicity prediction of ROP38 protein, comprising physico-chemical, antigenic and allergenic profiles, transmembrane domain, subcellular localization, post-translational modification (PTM) sites, secondary and 3D structure, B-cell, MHC-binding and cytotoxic T-lymphocyte (CTL) epitopes. The findings showed 54 PTM sites without a transmembrane domain. Also, ROP38 was proved a non-allergenic and antigenic protein. The protein had Sec signal peptide (Sec/SPI) with 0.8762 likelihood. The secondary structure included 52.68% random coil, 29.57% alpha helix and 17.74% extended strand. Based on Ramachandran plot output for refined model, 95.3%, 3.4%, and 1.4% of amino acid residues were incorporated in the favored, allowed, and outlier regions, respectively. B-cell epitopes TFPGDDIQTSS (67-72) and KAKNKWGRTRYTLQG (207-221) as well as T-cell epitope LSPVGFFTAL (6-15) possessed the highest antigenic index in the protein sequence. This paper is a premise for further researches, and provides insights for the development of a suitable vaccine against toxoplasmosis. More empirical studies are required using the ROP38 alone or in combination with other antigens/epitopes in the future.

Effective Nanoparticle-Based Nasal Vaccine Against Latent and Congenital Toxoplasmosis in Sheep

Toxoplasma gondii is a parasitic protozoan of worldwide distribution, able to infect all warm-blooded animals, but particularly sheep. Primary infection in pregnant sheep leads to millions of abortions and significant economic losses for the livestock industry. Moreover, infected animals constitute the main parasitic reservoir for humans. Therefore, the development of a One-health vaccine seems the best prevention strategy. Following earlier work, a vaccine constituted of total extract of Toxoplasma gondii proteins (TE) associated with maltodextrin nanoparticles (DGNP) was developed in rodents. In this study we evaluated the ability of this vaccine candidate to protect against latent and congenital toxoplasmosis in sheep. After two immunizations by either intranasal or intradermal route, DGNP/TE vaccine generated specific Th1-cellular immune response, mediated by APC-secretion of IFN-γ and IL-12. Secretion of IL-10 appeared to regulate this Th1 response for intradermally vaccinated sheep but was absent in intranasally-vaccinated animals. Finally, protection against latent toxoplasmosis and transplacental transmission were explored. Intranasal vaccination led to a marked decrease of brain cysts compared with the non-vaccinated group. This DGNP/TE vaccine administered intranasally conferred a high level of protection against latent toxoplasmosis and its transplacental transmission in sheep, highlighting the potential for development of such a vaccine for studies in other species.

Protective immunity induced by a DNA vaccine cocktail expressing TgSAG1, TgROP2, and the genetic adjuvant HBsAg against Toxoplasma gondii infection

Toxoplasma gondii is an intracellular obligate parasitic protozoon that can infect all warm-blooded animals, causing zoonotic toxoplasmosis. So far, there is no commercial toxoplasmosis vaccine for human use. In the present study, we constructed a DNA vaccine cocktail which includes the surface protein (SAG1) and the rhoptry protein ROP2 denoted as pEGFP-N1-SAG1-ROP2. In order to improve the efficacy, HBsAg was used as a genetic adjuvant to construct pEGFP-N1-HBsAg-SAG1-ROP2. Two eukaryotic plasmids were transiently transfected into HEK293T cells and the expression was examined using fluorescence microscopy and western blotting. We then immunized Kunming mice intramuscularly with the DNA vaccine. After three immunizations, the immune response was evaluated by measuring antibody levels, cytokine production, percentages of CD4⁺ and CD8⁺ T lymphocytes, and the survival times of the T. gondii RH strain challenged mice. The results showed that the two DNA vaccines stimulated Th1 responses, and had a higher antibody titer, IL-2, IL-12, and IFN-γ levels, and percentage of CD4⁺ and CD8⁺ T lymphocytes than the control group. In addition, mice immunized with the pEGFP-N1-HBsAg-SAG1-ROP2 vaccine showed increased survival times compared with pEGFP-N1-SAG1-ROP2.

Identification of Toxoplasma Gondii Tyrosine Hydroxylase (TH) Activity and Molecular Immunoprotection against Toxoplasmosis

The neurotropic parasite Toxoplasma gondii (T. gondii) infection can change the behavior of rodents and cause neuropsychological symptoms in humans, which may be related to the change in neurotransmitter dopamine in the host brain caused by T. gondii infection. T. gondii tyrosine hydroxylase (TgTH) is an important factor in increasing the neurotransmitter dopamine in the host brain. In this study, the enzyme activity of TgTH catalytic substrate for dopamine production and the molecular characteristics of TgTH were identified. In order to amplify the open reading frame (ORF), the designing of the specific primers for polymerase chain reaction (PCR) was on the basis of the TgTH sequence (GenBank Accession No. EU481510.1), which was inserted into pET-32a (+) for the expression of recombined TgTH (rTgTH). The sequence analysis indicated that the gene of TgTH directed the encoding of a 62.4-kDa protein consisting of 565 amino acid residues, which was predicted to have a high antigen index. The enzyme activity test showed that rTgTH and the soluble proteins extracted separately from T. gondii RH strain and PRU strain could catalyze the substrate to produce dopamine in a dose-dependent manner, and the optimum catalytic temperature was 37 °C. The result of the Western Blotting assay revealed that the rTgTH and the native TgTH extracted from somatic of T. gondii RH tachyzoite were successfully detected by the sera of mice infected with T. gondii and the rat serum after rTgTH immune, respectively. Immunofluorescence analysis using antibody against rTgTH demonstrated that the protein was expressed and located on the surface of T. gondii RH tachyzoite. Freund’s adjuvant was used to emulsify the rTgTH, which was subsequently applied to BALB/c mouse immune thrice on week 0, week 2, and week 4, respectively. The result of the animal challenge experiments showed an integral increase in IgG, IgG2a, IgG1, and IFN-γ, IL-4, and IL17 were as well significantly increased, and that the rTgTH vaccinated animals apparently had a prolonged survival time (14.30 ± 2.41) after infection with the RH strain of T. gondii compared with that of the non-vaccinated control animals, which died within 11 days. Additionally, in the rTgTH vaccination group, the number of brain cysts (1275 ± 224) significantly decreased (p < 0.05) compared to the blank control group (2375 ± 883), and the size of the brain cysts in the animals immunized with rTgTH vaccination was remarkably smaller than that of the control mice. All the findings prove that TgTH played an important role in increasing the neurotransmitter dopamine in the host brain and could be used as a vaccine candidate antigen to mediate cell-mediated and humoral immunity.

Structural predication and antigenic analysis of ROP16 protein utilizing immunoinformatics methods in order to identification of a vaccine against Toxoplasma gondii: An in silico approach

Toxoplasmosis, caused by Toxoplasma gondii, is a common parasitic disease, affecting almost one-third of the world's population. Currently, there are no effective treatments for inhibiting the formation of chronic tissue cysts in infected hosts. Thus, the production of appropriate vaccines against this pathogen is an important goal to avoid toxoplasmosis. considering the role of rhoptry antigens like ROP16 in virulence and satisfactory immunogenicity, they can be used as promising vaccine candidates against T. gondii. In the present study, an in silico approach was used to analyze various aspects of the ROP16 protein, including physicochemical characteristics, the potential epitopes of B and T-cells, the secondary and tertiary structure, the subcellular localization, the transmembrane domain, and other important features of this protein using several bioinformatics tools to design a proper vaccine against T. gondii. The results showed that ROP16 protein includes 93 potential post-translational modification sites. The secondary structure of the ROP16 protein comprises 34.23% alpha-helix, 54.46% random coil, and 11.32% extended strand. Moreover, several potential B- and T-cell epitopes were identified for ROP16. Based on the results of Ramachandran plot, 84.64% of the amino acid residues were located in the favored, 10.34% in allowed, and 5.02% in outlier regions. Furthermore, the results of the antigenicity and allergenicity assessment noted that this protein was immunogenic and non-allergenic. Our findings suggested that structural and functional predictions applied to ROP16 protein using in silico tools can reduce the failure risk of the laboratory studies. This research provided an important basis for further studies and also developed an effective vaccine against acute and chronic toxoplasmosis by various strategies. Further studies are needed on the development of vaccines in vivo using ROP16 alone or in combination with other antigens in the future.

Vaccination with recombinant Toxoplasma gondii CDPK3 induces protective immunity against experimental toxoplasmosis

Toxoplasma gondii, a ubiquitous and obligate intracellular pathogen, belonging to the phylum Apicomplexa, is capable of infecting a broad range of warm-blooded hosts including birds and mammals that is nearly worldwide. Preventive measures for toxoplasmosis are currently lacking and as such, development of novel vaccines is of urgent need. The plant-like calcium-dependent protein kinases (CDPKs) expressed by T. gondii, play important roles in cell invasion, gliding motility, egress and some other developmental processes, in which T. gondii CDPK3 (TgCDPK3) has been implicated as an important virulence factor. In this study, the immune protective function of recombinant TgCDPK3 (rTgCDPK3) against experimental toxoplasmosis in BALB/c were evaluated. We divided the mice into different dose groups of vaccines and all immunizations with purified rTgCDPK3 protein were injected by intramuscular at weeks 0, 2, and 4 in BALB/c mice. The rTgCDPK3 vaccine provided protection was correlated with the development of humoral and cellular immune responses demonstrated through the antigen-specific spleen cell proliferation, release of Th1 cytokines IFN-γ, and the production of the high titers of IgG antibody with a predominance of IgG2a over IgG1. Vaccination with rTgCDPK3 conferred partial protection against acute toxoplasmosis, as demonstrated by prolonged survival rate after lethal challenge. Additionally, the amount of brain tissues cysts in vaccinated mice led to 46.5% reduction compared with non-vaccinated ones. These data demonstrated that rTgCDPK3 inoculation prevents or attenuates the harmful influence of T. gondii infection, and it is a potential vaccine candidate against toxoplasmosis.

QuilA-Adjuvanted T. gondii Lysate Antigens Trigger Robust Antibody and IFNγ+ T Cell Responses in Pigs Leading to Reduction in Parasite DNA in Tissues Upon Challenge Infection

Toxoplasma gondii is an intracellular parasite of all mammals and birds, responsible for toxoplasmosis. In healthy individuals T. gondii infections mostly remain asymptomatic, however this parasite causes severe morbidity and mortality in immunocompromised patients and congenital toxoplasmosis in pregnant women. The consumption of raw or undercooked pork is considered as an important risk factor to develop toxoplasmosis in humans. Since effective therapeutic interventions to treat toxoplasmosis are scarce, vaccination of meat producing animals may prevent T. gondii transmission to humans. Here, we evaluated the elicited immune responses and the efficacy of a potential vaccine candidate, generated by size fractionation of T. gondii lysate proteins, to reduce the parasite burden in tissues from experimentally T. gondii infected pigs as compared to vaccination with total lysate antigens (TLA). Our results show that both the vaccine candidate and the TLA immunization elicited strong serum IgG responses and elevated percentages of CD4+CD8+IFNγ+ T cells in T. gondii infected pigs. However, the TLA vaccine induced the strongest immune response and reduced the parasite DNA load below the detection limit in brain and skeletal muscle tissue in most animals. These findings might inform the development of novel vaccines to prevent T. gondii infections in livestock species and humans.

Assessment of the immunogenicity and protective efficiency of a novel dual-promoter DNA vaccine, harboring SAG1 and GRA7 genes, from RH strain of Toxoplasma gondii in BALB/c mice

BACKGROUND

Toxoplasmosis, a protozoan parasitic disease caused by Toxoplasma gondii, has been a serious human and veterinary medicine problem with global distribution. In the current study, we assessed immunogenicity and protective efficiency of a novel dual-promoter DNA vaccine, harboring SAG1 and GRA7 genes, from RH strain of Toxoplasma gondii (T. gondii) with or without CpG-ODN as adjuvant in a murine model.

METHODS

BALB/c mice were immunized intramuscularly with pVitro-SAG1-GRA7 alone and pVitro-SAG1-GRA7 with CpG-ODN three times at three-week intervals. Enzyme-linked immunosorbent assay (ELISA) was used to assess total IgG, IgG1 and IgG2a antibodies and gamma interferon (IFN-γ) and interleukin-10 (IL-10) cytokines in mice sera. Four weeks post final vaccination, MTT assay and lethal challenge-infection with 1×103 tachyzoites of T. gondii RH strain were carried out to assess stimulation index (SI) and mice survival time, respectively.

RESULTS

The IgG levels in mice immunized with multicomponent vaccines, including pVitro-SAG1-GRA7 alone and pVitro-SAG1-GRA7 with CpG-ODN, were significantly higher than those in control mice or single-gene DNA-vaccinated ones (P<0.05). Furthermore, level of IgG2a in mice receiving pVitro-SAG1-GRA7 with CpG-ODN was significantly higher than that in mice receiving pVitro-SAG1-GRA7 alone (P<0.05). The Toxoplasma lysate antigen (TLA)-stimulated lymphocytes from pVitro-SAG1-GRA7 with CpG-ODN group responded more dramatically than those from control groups or single-gene DNA-vaccinated groups (P<0.001). The pVitro-SAG1-GRA7 with CpG-ODN-vaccinated mice developed high levels of IgG2a and IFN-γ (P<0.001) and low levels of IgG1 and IL-10, compared to control groups, suggesting a modulated immune response type Th1. In addition, survival time of the mice immunized with pVitro-SAG1-GRA7 with CpG-ODN was significantly extended, compared to controls (P<0.05); however, all mice died.

CONCLUSION

The multivalent pVitro-SAG1-GRA7 DNA vaccine with CpG-ODN adjuvant is a promising vaccine candidate against toxoplasmosis.

Immunization With a Live-Attenuated RH:ΔNPT1 Strain of Toxoplasma gondii Induces Strong Protective Immunity Against Toxoplasmosis in Mice

Toxoplasmosis, one of the most important health-threatening diseases worldwide, is caused by Toxoplasma gondii, which infects a wide range of warm-blooded animals and humans, leading to enormous health and socioeconomic concerns. T. gondii can establish chronic infection to evade the immune response in hosts. Once a chronic infection has been established, the available treatments cannot efficiently control this stage of T. gondii efficiently. Moreover, the available treatments rely only on a few drugs, such as sulfapyridine and pyrimethamine, that tend to have severe side effects. Given these factors, vaccination has been considered to be the most efficient method to prevent and control this disease. However, there is currently lack of effective vaccine available for use to prevent toxoplasmosis apart form Toxovax®, the only available vaccine, which is used in sheep to prevent abortion. To address this problem, we knocked out the NPT1 gene of the type I T. gondii strain using the CRISPR-Cas9 system, constructed a live-attenuated vaccine and evaluated its protective efficacy in a mouse model. Immunization of mice with RH:ΔNPT1 induced a high level of Toxoplasma-specific IgG1, IgG2a and total IgG 42 days after immunization. There was a significant increase in the levels of cytokines in the splenocyte suspensions of RH:ΔNPT1-infected mice, and a mixed Th1/Th2 response was induced in the mice. Remarkably, after heterologous challenges with tachyzoites of the RH, PYS and Pru strains and cysts of the Pru strain by different infection routes, the immunized animals were protected from toxoplasmosis with a 100% survival rate, in both acute and chronic infection. In addition, compared with control mice, the Pru cyst load was clearly reduced in the brains of RH:ΔNPT1-infected immunization-mice. Our study demonstrated that the RH:ΔNPT1 strain was able to evoke strong anti-Toxoplasma immune responses and provide effective protection against parasite strains with different levels of virulence, suggesting that the RH:ΔNPT1 strain may represent a promising live-attenuated vaccine against toxoplasmosis, which is worthy of further evaluation in food-producing animals and in definitive feline host.

Rhomboid antigens are promising targets in the vaccine development against Toxoplasma gondii

Toxoplasma gondii (T. gondii) is an obligate intracellular parasite with worldwide distribution. It is estimated that near one-third of the people around the globe are latently seropositive for the parasite. Since the current common drugs are incapable in the elimination of parasites within tissue cysts, the development of an effective vaccine has high priority for researchers to limit the infection. During recent years, non-stop efforts of scientists have made great progress in the identification and development of T. gondii candidate vaccines. However, there is a lack of a commercially licensed vaccine for human application yet. Rhomboid proteases (ROMs) are a class of serine proteases that have an important role in the invasion of the parasites that can be considered as a new target for vaccine strategy. They also play critical roles in mitochondrial fusion and growth factor signaling, allowing the parasite to completely enter into the host cell. In the current review, we have summarized the recent progress regarding the development of ROM-based vaccines against acute and chronic T. gondii infection in animal models.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Toxoplasma gondii Macrophage Migration Inhibitory Factor

Toxoplasma gondii is an obligate intracellular parasite responsible for toxoplasmosis, which can cause severe disease in the fetus and immunocompromised individuals. Developing an effective vaccine is crucial to control this disease. Macrophage migration inhibitory factor (MIF) has gained substantial attention as a pivotal upstream cytokine to mediate innate and adaptive immune responses. Homologs of MIF have been discovered in many parasitic species, and one homolog of MIF has been isolated from the parasite Toxoplasma gondii. In this study, the recombinant Toxoplasma gondii MIF (rTgMIF) as a protein vaccine was expressed and evaluated by intramuscular injection in BALB/c mice. We divided the mice into different dose groups of vaccines, and all immunizations with purified rTgMIF protein were performed at 0, 2, and 4 weeks. The protective efficacy of vaccination was analyzed by antibody assays, cytokine measurements and lymphoproliferative assays, respectively. The results obtained indicated that the rTgMIF vaccine elicited strong humoral and cellular immune responses with high levels of IgG antibody and IFN-γ production compared to those of the controls, in addition to slight higher levels of IL-4 production. After vaccination, a stronger lymphoproliferative response was also noted. Additionally, the survival time of mice immunized with rTgMIF was longer than that of the mice in control groups after challenge infection with virulent T. gondii RH tachyzoites. Moreover, the number of brain tissue cysts in vaccinated mice was reduced by 62.26% compared with the control group. These findings demonstrated that recombinant TgMIF protein is a potential candidate for vaccine development against toxoplasmosis.

GRA24-Based DNA Vaccine Prolongs Survival in Mice Challenged With a Virulent Toxoplasma gondii Strain

Toxoplasma gondii causes infections in a wide range of intermediate hosts and remains a threatening disease worldwide because of the lack of effective drugs and vaccines. Dense granule protein 24 (GRA24) is a novel essential virulence factor that is transferred into the nucleus of host cells from the parasitophorous vacuole to regulate gene expression. In the present study, bioinformatic analysis showed that GRA24 had a high score for B-cell and T-cell epitopes compared with surface antigen 1 (SAG1), which has been studied as a promising vaccine candidate. As a DNA vaccine, pVAX1-GRA24 was injected intramuscularly into BALB/c mice and the induced immune response was evaluated. pVAX1-GRA24 induced high levels of a mixed Th1/Th2 cytokines at 6 weeks after immunization. Antibody determinations, cytokines [interferon gamma (IFN-γ), interleukin (IL)-12, IL-4, IL-10], antigen-specific lymphocyte proliferation, CD4+ and CD8+ T lymphocytes, and cytotoxic T lymphocyte activity showed that mice immunized with pVAX1-GRA24 produced specific humoral and cellular immune responses. The expression levels of interferon regulatory factor 8 (IRF8), nuclear factor kappa B (NF-κB), and T-Box 21 (T-bet) were significantly higher in the pVAX1-GRA24 immunization group than in the control groups. Survival times were prolonged significantly (24.6 ± 5.5 days) in the mice immunized with pVAX1-GRA24 compared with the mice in the control groups, which died within 7 days of T. gondii challenge (p < 0.05). The results of the present study showed that pVAX1-GRA24 induced a T. gondii-specific immune response and thus represents a promising candidate vaccine to treat toxoplasmosis.

Toxoplasma gondii and Other Zoonotic Protozoans in Mediterranean Mussel ( Mytilus galloprovincialis) and Blue Mussel ( Mytilus edulis): A Food Safety Concern?

Mediterranean mussels ( Mytilus galloprovincialis) and blue mussels ( Mytilus edulis) are among the most consumed fishery products, but they are frequent vehicles of foodborne infection worldwide. In this study, we investigated the occurrence and seasonality of zoonotic protozoans in mussels farmed or sold at retail outlets in Italy. We collected and tested 1,440 M. galloprovincialis and 180 M. edulis. Pooled samples were molecularly tested for Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii and then sequenced. Sixty-two (45.9%; 95% confidence interval, 37.5 to 54.3%) mussel pools tested positive for one or more of the investigated pathogens. Both Mytilus species and samples from all the investigated areas harbored pathogens. Mussels were statistically more contaminated by Cryptosporidium spp., followed by T. gondii and G. duodenalis assemblage A, and M. galloprovincialis was more contaminated than M. edulis ( P < 0.01). Contamination was more likely in mussels at retail outlets ( P < 0.05) than in those from farms and in mussels collected in spring ( P < 0.01) than in other seasons. This is the first report of T. gondii found in M. galloprovincialis in Italy and in M. edulis in Europe. The detection of zoonotic protozoans in a widely consumed food source indicates the need for a more detailed microbiological risk analysis, especially considering that bivalve mollusks are often consumed raw worldwide.

A systematic review of Toxoplasma gondii antigens to find the best vaccine candidates for immunization

At present, there is not any available accepted vaccine for prevention of Toxoplasma gondii (T. gondii) in human and animals. We conducted literature search through English (Google Scholar, PubMed, Science Direct, Scopus, EBSCO, ISI Web of Science) scientific paper databases to find the best vaccine candidates against toxoplasmosis among T. gondii antigens. Articles with information on infective stage, pathogenicity, immunogenicity and characterization of antigens were selected. We considered that the ideal and significant vaccines should include different antigens and been expressed in all infective stages of the parasite with a high pathogenicity and immunogenicity. Evaluation within this systematic review indicates that MIC 3, 4, 13, ROP 2, RON 5, GRA 1, 6, 8, 14 are expressed in all three infective stages and have pathogenicity and immunogenicity. MIC 5, ROM 4, GRA 2, 4, 15, ROP 5, 16, 17, 38, RON 4, MIC 1, GRA 10, 12, 16, SAG 3 are expressed in only tachyzoites and bradyzoites stages of T. gondii with pathogenicity/immunogenicity. Some antigens appeared to be expressed in a single stage (tachyzoites) but have high pathogenicity and induce immune response. They include enolase2 (ENO2), SAG 1, SAG5D, HSP 70, ROM 1, ROM 5, AMA 1, ROP 18, RON2 and GRA 24. In conclusion, current vaccination against T. gondii infection is not satisfactory, and with the increasing number of high-risk individuals, the development of an effective and safe specific vaccine is greatly valuable for toxoplasmosis prevention. This systematic review reveals prepare candidates for immunization studies.

A Gene-Based Positive Selection Detection Approach to Identify Vaccine Candidates Using Toxoplasma gondii as a Test Case Protozoan Pathogen

Over the last two decades, various in silico approaches have been developed and refined that attempt to identify protein and/or peptide vaccines candidates from informative signals encoded in protein sequences of a target pathogen. As to date, no signal has been identified that clearly indicates a protein will effectively contribute to a protective immune response in a host. The premise for this study is that proteins under positive selection from the immune system are more likely suitable vaccine candidates than proteins exposed to other selection pressures. Furthermore, our expectation is that protein sequence regions encoding major histocompatibility complexes (MHC) binding peptides will contain consecutive positive selection sites. Using freely available data and bioinformatic tools, we present a high-throughput approach through a pipeline that predicts positive selection sites, protein subcellular locations, and sequence locations of medium to high T-Cell MHC class I binding peptides. Positive selection sites are estimated from a sequence alignment by comparing rates of synonymous (dS) and non-synonymous (dN) substitutions among protein coding sequences of orthologous genes in a phylogeny. The main pipeline output is a list of protein vaccine candidates predicted to be naturally exposed to the immune system and containing sites under positive selection. Candidates are ranked with respect to the number of consecutive sites located on protein sequence regions encoding MHCI-binding peptides. Results are constrained by the reliability of prediction programs and quality of input data. Protein sequences from Toxoplasma gondii ME49 strain (TGME49) were used as a case study. Surface antigen (SAG), dense granules (GRA), microneme (MIC), and rhoptry (ROP) proteins are considered worthy T. gondii candidates. Given 8263 TGME49 protein sequences processed anonymously, the top 10 predicted candidates were all worthy candidates. In particular, the top ten included ROP5 and ROP18, which are T. gondii virulence determinants. The chance of randomly selecting a ROP protein was 0.2% given 8263 sequences. We conclude that the approach described is a valuable addition to other in silico approaches to identify vaccines candidates worthy of laboratory validation and could be adapted for other apicomplexan parasite species (with appropriate data).

Recent progress in microneme-based vaccines development against Toxoplasma gondii

Toxoplasmosis is a cosmopolitan zoonotic disease, which infect several warm-blooded mammals. More than one-third of the human population are seropositive worldwide. Due to the high seroprevalence of Toxoplasma gondii infection worldwide, the resulting clinical, mental, and economical complications, as well as incapability of current drugs in the elimination of parasites within tissue cysts, the development of a vaccine against T. gondii would be critical. In the past decades, valuable advances have been achieved in order to identification of vaccine candidates against T. gondii infection. Microneme proteins (MICs) secreted by the micronemes play a critical role in the initial stages of host cell invasion by parasites. In this review, we have summarized the recent progress for MIC-based vaccines development, such as DNA vaccines, recombinant protein vaccines, vaccines based on live-attenuated vectors, and prime-boost strategy in different mouse models. In conclusion, the use of live-attenuated vectors as vehicles to deliver and express the target gene and prime-boost regimens showed excellent outcomes in the development of vaccines against toxoplasmosis, which need more attention in the future studies.

Immune Responses Induced by HSP60 DNA Vaccine against Toxoplasma gondii Infection in Kunming Mice

Toxoplasma gondii can infect all the vertebrates including human, and leads to serious toxoplasmosis and considerable veterinary problems. T. gondii heat shock protein 60 (HSP60) is associated with the activation of antigen presenting cells by inducing initial immune responses and releasing inflammatory cytokines. It might be a potential DNA vaccine candidate for this parasite. A pVAX-HSP60 DNA vaccine was constructed and immune responses was evaluated in Kunming mice in this study. Our data indicated that the innate and adaptive immune responses was elicited by successive immunizations with pVAX-HSP60 DNA, showing apparent increases of CD3e+CD4+ and CD3e+CD8a+ T cells in spleen tissues of the HSP60 DNA-immunized mice (24.70±1.23% and 10.90±0.89%, P<0.05) and higher levels of specific antibodies in sera. Furthermore, the survival period of the immunized mice (10.53±4.78 day) were significantly prolonged during the acute T. gondii infection. Decrease of brain cysts was significant in the experimental group during the chronic infection (P<0.01). Taken together, TgHSP60 DNA can be as a vaccine candidate to prevent the acute and chronic T. gondii infections.

Induction of Th1 type-oriented humoral response through intranasal immunization of mice with SAG1-Toxoplasma gondii polymeric nanospheres

About one-third of the world population is prone to have infection with T. gondii, which can cause toxoplasmosis in the developing fetus and in people whose immune system is compromised through disease or chemotherapy. Surface antigen-1 (SAG1) is the candidate of vaccine against toxoplasmosis. Recent advances in biotechnology and nano-pharmaceuticals have made possible to formulate nanospheres of recombinant protein, which are suitable for sub-unit vaccine delivery. In current study, the local strain was obtained from cat feces as toxoplasma oocysts. Amplified 957 bp of SAG1 was cloned into pGEM-T and further sub-cloned into pET28-SAG1. BL21 bacteria were induced at different concentrations of isopropyl β-d-1-thiogalactopyranoside for the expression of rSAG1 protein. An immunoblot was developed for the confirmation of recombinant protein expression at 35 kDa that was actually recognized by anti-HIS antibodies and sera were collected from infected mice. PLGA encapsulated nanospheres of recombinant SAG1 were characterized through scanning electron microscopy. Experimental mice were intraperitoneally immunized with rSAG1 protein and intra-nasally immunized with nanosphere. The immune response was evaluated by indirect ELISA. In results intra-nasally administered rSAG1 in nanospheres appeared to elicit elevated responses of specific IgA and IgG2a than in control. Nanospheres of rSAG1 are found to be a bio-compatible candidate for the development of vaccine against T. gondii.

Immune Protection of Rhoptry Protein 21 (ROP21) of Toxoplasma gondii as a DNA Vaccine Against Toxoplasmosis

Toxoplasma gondii rhoptry proteins (TgROPs) are the major targets as key molecules for immunodiagnosis as well as immunoprophylaxis because of their initial presentation to the host immune system. In this work, it was aimed at evaluating the protection effect of TgROP21 DNA vaccine on experimental mice subjected to T. gondii challenge. The gene sequence encoding TgROP21 was inserted into the eukaryotic expression vector pVAX I, and western blotting indicates that the lysate of BHK cells transfected with pVAX-TgROP21 was specifically recognized as a band of about 82.6 kDa by serum obtained from a T. gondii infected chicken. The efficacy of intramuscular vaccination of BALB/c mice three times at weeks 0, 2, and 4 with pVAX-ROP21 was analyzed. The levels of IgG, IgG1, and IgG2a among pVAX-ROP21 vaccinated animals were integrally increased. It was uncovered by cytokine profile analyses that IFN-γ was significantly increased, while no significant changes were detected in interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-10 (IL-10). Additionally, we found that immunization with pVAX-ROP21 significantly prolonged survival time (13.50 ± 1.65 days) after challenge infection with the virulent T. gondii RH strain, in comparison to those of control animals (died within 10 days). Moreover, the number of brain cysts (1475 ± 163) in the animals subjected to pVAX-TgROP21 vaccination decreased remarkably (P < 0.05) compared to the blank control mice (2333 ± 473), and the size of brain cysts in pVAX-TgROP21 group was significantly smaller than the groups of blank, PBS and pVAXI. It was indicated that intense cell-mediated and humoral immunity was triggered and defense against T. gondii was partially induced after vaccination by TgROP21.

Evaluation of potential anti-toxoplasmosis efficiency of combined traditional herbs in a mouse model

Toxoplasma gondii is a worldwide spread protozoan and is able to infect almost all warm-blood animals. No effective drugs are available clinically on toxoplasmosis. Chinese traditional herbal medicines have provided remedies for many health problems. There exists a possibility that Chinese herbs may provide protection against T. gondii. This work aims to assess the protective efficacy of combined Chinese herbs against T. gondii. We screened five herbal medicines that have different pharmacological effects and combined them into a prescription according to the traditional Chinese medicine compatibility principle. The drug potential and protective efficacy were evaluated through a mouse model by determining the survival time, the parasite load in blood and tissues, the change of cell proportions in blood and histological detection. The results showed that the survival time of mice in the 500 mg Chinese herbs group and sulfadiazine group was significantly longer than that of the PBS control group. Also the parasite load in blood and tissues of 500 mg Chinese herbs and sulfadiazine groups was significantly lower than that of PBS group at 7 days post infection (dpi), which was in accordance with the result of histological detection. Monocyte and neutrophil of infected mice were remarkably increased while lymphocyte was dramatically decreased compared to that of blank group at 7 dpi. The results demonstrated that the 500 mg dosage of our Chinese herbs could slow down the replication of T. gondii and prolong the survival time of mice and could be considered as possible candidate drug against toxoplasmosis.

Calcium-dependent protein kinases are potential targets for Toxoplasma gondii vaccine

Toxoplasma gondii belongs to the Apicomplexa phylum that caused a widespread zoonotic infection in wide range of intermediate hosts. Over one-third of the world's population are latently infected with T. gondii and carry it. The complex life cycle of T. gondii indicates the presence of a plurality of antigenic epitopes. During the recent years, continuous efforts of scientists have made precious advances to elucidate the different aspects of the cell and molecular biology of T. gondii. Despite of great progresses, the development of vaccine candidates for preventing of T. gondii infection in men and animals is still remains a challenge. The calcium-dependent protein kinases (CDPKs) belongs to the superfamily of kinases, which restricted to the apicomplexans, ciliates, and plants. It has been documented that they contribute several functions in the life cycle of T. gondii such as gliding motility, cell invasion, and egress as well as some other critical developmental processes. In current paper, we reviewed the recent progress concerning the development of CDPK-based vaccines against acute and chronic T. gondii.

Moving towards improved vaccines for Toxoplasma gondii

INTRODUCTION

Toxoplasma gondii is an intracellular parasitic protozoan that infects almost all warm-blooded animals and humans, resulting in threats to public health and economic losses. Despite continuous research efforts, there are still very few effective strategies against toxoplasmosis. In the past few years, numerous vaccination experiments have been performed to control T. gondii infection.

AREAS COVERED

In this review, the authors summarize the development of T. gondii vaccines with proper adjuvants, ranging from live or live-attenuated vaccines to protein vaccines, DNA vaccines, epitope vaccines and novel vaccines. They also highlight the challenges involved in the development of T. gondii vaccines, including specific impediments and shortcomings.

EXPERT OPINION

Moving towards the development of effective vaccines against T. gondii is not only a tedious mission but also a difficult challenge. Future studies should consider new approaches and strategies for vaccine development, particularly novel vaccines and genetic adjuvants, as well as optimizing immunization protocols and evaluation criteria.

Vaccination with a DNA vaccine encoding Toxoplasma gondii ROP54 induces protective immunity against toxoplasmosis in mice

Toxoplasma gondii is an obligatory intracellular protozoan, which infects most of the warm-blooded animals, causing serious public health problems and enormous economic losses worldwide. The rhoptry effector protein 54 (ROP54) has been indicated as a virulence factor that promotes Toxoplasma infection by modulating GBP2 loading onto parasite-containing vacuoles, which can modulate some aspects of the host immune response. In order to evaluate the immuno-protective value of ROP54, we constructed a eukaryotic recombinant plasmid expressing T. gondii ROP54 and intramuscularly immunized Kunming mice with this recombinant plasmid against acute and chronic toxoplasmosis. All mice immunized with pVAX-ROP54 elicited a high level of specific antibody responses, a significant increase of lymphocyte proliferation, and a significant level of Th1-type cytokines (IFN-γ, IL-2 and IL-12p70), in addition to an increased production of Th2-type cytokines (IL-4 and IL-10). These results demonstrated that pVAX-ROP54 induced significant cellular and humoral (Th1/Th2) immune responses, which extended the survival time (13.0±1.15days for pVAX-ROP54 vs 6.7±0.48days for pVAX I, 6.8±0.42days for PBS and 6.5±0.53 for blank control) and significantly reduced cyst burden (35.9% for pVAX-ROP54, 1% for pVAX I and 2% for PBS, compared with blank control) of immunized mice. These results indicate that the recombinant ROP54 plasmid can provide partial protection and might be a potential vaccine candidate against acute and chronic toxoplasmosis.

A comprehensive analysis of direct and photosensitized attenuation of Toxoplasma gondii tachyzoites

In the present work, we have evaluated the effect of three different types of radiation: UVC (254±5nm), UVA (365±20nm) and visible (420±20nm) on different morphological and biological functions of Toxoplasma gondii tachyzoites. Briefly, UVC and UVA showed an inhibitory effect on parasite invasion in a dose-dependent manner. UVC showed the strongest effect inducing both structural damage (antigens) and functional inhibition (i.e., invasion and replication). On its own, visible light induces a quite distinctive and selective pattern of parasite-attenuation. This type of incident radiation inhibits the replication of the parasite affecting neither the capability of invasion/attachment nor the native structure of proteins (antigens) on parasites. Such effects are a consequence of photosensitized processes where phenol red might act as the active photosensitizer. The potential uses of the methodologies investigated herein are discussed.

SAG4 DNA and Peptide Vaccination Provides Partial Protection against T. gondii Infection in BALB/c Mice

Toxoplasma gondii can lead to congenital infections in human. Surface antigen protein 4 (SAG4) of T. gondii is a potential stimulator for humoral and cellular immune responses. In the present study, a DNA vaccine encoding SAG4 from T. gondii was constructed and used to immunize BALB/c mice with peptide to evaluate the protective efficacy of the vaccine. The productions of IgG antibodies and cytokines (gamma interferon) from the vaccine (pSAG4/peptide) group were significantly higher than pSAG4 or peptide groups. After a lethal challenge by 1 × 10⁴ tachyzoites from the I strain (RH), the survival time of mice immunized by pSAG4/peptide was longer than that of pSAG4 or peptide immunized mice or control mice. Moreover, after challenging by 20 cysts of the II strain (PRU) of T. gondii, the number of brain cysts from pSAG4/peptide vaccinated mice was only 31% of the number in PBS injected mice. The findings suggested the SAG4 DNA vaccine with peptide led significant immune responses and improved the protection against T. gondii challenges.