Evaluation of the immune response in BALB/c mice induced by a novel DNA vaccine expressing GRA14 againstToxoplasma gondii

Protective efficacy of Toxoplasma gondii bivalent MAG1 and SAG1 DNA vaccine against acute toxoplasmosis in BALB/c mice

Toxoplasma gondii can infect a wide range of warm-blooded animals, causing a global toxoplasmosis zoonotic epidemic. Surface antigen 1 (SAG1) protein is expressed at the proliferative tachyzoite stage, whereas matrix antigen 1 (MAG1) is expressed at the bradyzoite and tachyzoite stages. These two proteins were found to perform protective roles in previous studies; however, their synergetic protective efficacy as a DNA vaccine against toxoplasmosis has not been clarified. In this study, we constructed recombinant pcDNA3.1( +)-TgMAG1 (pMAG1), pcDNA3.1( +)-TgSAG1 (pSAG1), and pcDNA3.1( +)-TgMAG1-TgSAG1 (pMAG1-SAG1) plasmids and administered them intramuscularly to immunize mice. The levels of anti-T. gondii IgG in serum and cytokines, such as Interleukin (IL)-4, IL-10, and Interferon (IFN)-γ, in splenocytes were measured using ELISA and the respective culture supernatants. Lethal doses of T. gondii (type I) RH strain tachyzoites were administered to immunized mice, and mortality was assessed. Conversely, mice infected with low doses of tachyzoites were monitored to determine their survival rates, and parasite burden analyses of the brains and livers were conducted. The bivalent TgMAG1 and TgSAG1 DNA vaccines exhibited excellent protective immunity against toxoplasmosis in mice, with higher serum IgG and splenocyte IFN-γ release levels, longer survival days, and reduced parasite burden in the brain and liver tissues (p < 0.05). These findings provide a new perspective for the development of T. gondii vaccines.

Immunological evaluation of a novel multi-antigenic DNA vaccine encoding SAG1, SAG3, MIC4, GRA5, GRA7, AMA1and BAG1 against Toxoplasma gondii in BALB/c mice

Many recent studies have been conducted to find new DNA vaccines based on Toxoplasma gondii antigens. DNA vaccines encoding complex of different antigens showed better immune responses compared to single antigen vaccine. In this study, we constructed a DNA vaccine encoding SAG1, SAG3, MIC4, GRA5, GRA7, AMA1 and BAG1 against T. gondii, and evaluated the immune response it induced in BALB/c mice. For this purposes, thirty BALB/c mice were randomly divided into three groups containing tenmice each. There were two negative control groups (PBSand pVAX1 vector) and one vaccination group (pVAX1-MAF, Multantigenic Fragment). On days 0, 14 and 28, the mice were immunized intramuscularly, and 5 weeks later they were challenged with T. gondii RH strain. The immune responses were evaluated using lymphocyte proliferation assay, T-cell subsets detection, and measurement of antibody and cytokine levels. The results showed that mice immunized with pVAX1-MAF developed high levels of IL-2, IL-12, IgG and IFN- γ as well as CD3+CD4+ T cells. In addition, the survival time of mice immunized by pVAX1-MAF was longer than that control mice. In conclusion, our results show that the multiple DNA vaccine encodingSAG1, SAG3, mic4, GRA5, GRA7, AMA and BAG1effectively enhanced humoral and cellular immune responses, and prolonged the survival time. Together this would suggest that further investigation may result in a promising candidate vaccine to treat toxoplasmosis.

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.

Comparative Performance of Recombinant GRA6, GRA7, and GRA14 for the Serodetection of T. gondii Infection and Analysis of IgG Subclasses in Human Sera from the Philippines

Highly specific and sensitive diagnostic methods are vital for the effective control and treatment of toxoplasmosis. Routine diagnosis is primarily serological because T. gondii infections stimulate persistently high IgG antibody responses. The sensitivity and specificity of methods are crucial factors for the proper diagnosis of toxoplasmosis, primarily dependent on the antigens used in different assays. In the present study, we compared the serodiagnostic performances of three recombinant dense granule antigens, namely, the GRA6, GRA7, and GRA14, to detect IgG antibodies against T. gondii in human sera from the Philippines. Moreover, we evaluated the IgG1, IgG2, IgG3, and IgG4 responses against the different recombinant antigens, which has not been performed previously. Our results revealed that the TgGRA7 has consistently displayed superior diagnostic capability, while TgGRA6 can be a satisfactory alternative antigen among the GRA proteins. Furthermore, IgG1 is the predominant subclass stimulated by the different recombinant antigens. This study's results provide options to researchers and manufacturers to choose recombinant antigens suitable for their purpose.

Evaluation of Th17 immune responses of recombinant DNA vaccine encoding GRA14 and ROP13 genes against Toxoplasma gondii in BALB/c mice

Toxoplasma gondii, a worldwide opportunistic parasite, causes serious diseases in both humans and fetuses with defective immune systems. The development of an effective vaccine is urgently required to prevent and control the spread of toxoplasmosis, caused by the apicomplexan parasite Toxoplasma gondii which is one of the most damaging zoonotic diseases of global importance. Plasmid DNA vaccination is a promising procedure for vaccine development and following the previous studies, pcROP13 + pcGRA14 cocktail DNA vaccine was evaluated for Th17 immune responses. Four groups of BALB/c mice were immunized intramuscularly three times at 2-week intervals. Subsequently, the production of anti- T. gondii antibodies and serum levels of cytokines IL-17, and IL-22 were evaluated against the RH strain of T. gondii. In addition, both the reactive oxygen species (ROS) and parasite load were assessed using ELISA and Q-PCR, respectively. The results of this study showed that high levels of IgG were found in mice immunized with cocktail DNA vaccine (p < 0.05). The cytokines level of Th17, IL-17, and IL-22, increased remarkably in the immunized mice (p < 0.05). Also, significant induction (p < 0.05) was observed in ROS. In addition, immunization with pcROP13 + GRA14 resulted in a considerable decrease in parasite load compared to the control groups (p < 0.05). Based on the results, the pcROP13 + GRA14 cocktail DNA vaccine induced Th17 related cytokines and decreased the parasite load in spleen and brain tissues. Hence, pcGRA14 + pcROP13 cocktails are suitable candidates for DNA-based vaccines and due to the development of protective immune responses against T. gondii infection, future studies may yield promising results using these antigens in vaccine design.

REVIEW OF DNA VACCINE APPROACHES AGAINST THE PARASITE TOXOPLASMA GONDII

Toxoplasma gondii is an apicomplexan parasite that affects both humans and livestock. Transmitted to humans through ingestion, it is the second-leading cause of foodborne illness-related death. Currently, there exists no approved vaccine for humans or most livestock against the parasite. DNA vaccines, a type of subunit vaccine which uses segments of the pathogen's DNA to generate immunity, have shown varying degrees of experimental efficacy against infection caused by the parasite. This review compiles DNA vaccine efforts against Toxoplasma gondii, segmenting the analysis by parasite antigen, as well as a review of concomitant adjuvant usage. No single antigenic group was consistently more effective within in vivo trials relative to others.

Advances in Toxoplasma gondii Vaccines: Current Strategies and Challenges for Vaccine Development

Toxoplasmosis, caused by the apicomplexan parasite Toxoplasma gondii, is one of the most damaging parasite-borne zoonotic diseases of global importance. While approximately one-third of the entire world’s population is estimated to be infected with T. gondii, an effective vaccine for human use remains unavailable. Global efforts in pursuit of developing a T. gondii vaccine have been ongoing for decades, and novel innovative approaches have been introduced to aid this process. A wide array of vaccination strategies have been conducted to date including, but not limited to, nucleic acids, protein subunits, attenuated vaccines, and nanoparticles, which have been assessed in rodents with promising results. Yet, translation of these in vivo results into clinical studies remains a major obstacle that needs to be overcome. In this review, we will aim to summarize the current advances in T. gondii vaccine strategies and address the challenges hindering vaccine development.

Immunogenicity of in-silico designed multi-epitope DNA vaccine encoding SAG1, SAG3 and SAG5 of Toxoplasma gondii adjuvanted with CpG-ODN against acute toxoplasmosis in BALB/c mice

The causative agent of toxoplasmosis, Toxoplasma gondii (T. gondii), is able to influence the health of humans and other vertebrates. Toxoplasma may cause severe illness in the fetus and immunocompromised individuals. The high incidence and intense damages of Toxoplasma infection clearly shows the need to achieve the safe and suitable vaccine. In this study, an immunoinformatics approach was employed to design a multi-epitope DNA vaccine encoding the T. gondii SAG1, SAG3 and SAG5. The bioinformatic outputs supported the immunogenic and non-allergic natures of multi-epitope vaccine. Thereafter, the protective efficacy of the vaccine was evaluated with/without CpG-ODN adjuvant in a laboratory animal model. BALB/c mice were immunized subcutaneously with multi-epitope DNA vaccine. The in vivo findings indicated that the multi-epitope DNA vaccine elicited significant production of IgG antibodies (472.90 ± 2.74 ng/ml) as well as IFN-γ (173.71 ± 26.39 pg/ml) (p < 0.001). Moreover, a significant reduced parasite-burden (17,470 per mg of spleen) and prolonged survival time (9 days) were observed in the immunized groups compared to the controls (p < 0.05). The low values of IL-4 (22.5 ± 0.16 pg/ml) were detected in vaccinated mice compared to the control (PBS) (p > 0.05). In addition, CpG-ODN as an adjuvant increased the immune efficacy of the multi-epitope DNA vaccine. In multi-epitope vaccine+CpG-ODN group, the values of IgG antibodies (535.90 ±7.29 ng/ml) and IFN-γ (358.21 ± 32.70 pg/ml) were significanly higher than the multi-epitope vaccine group. Meanwhile, an increased survival time (10 days) and fewer parasite load (15,485 per mg of spleen) were observed in multi-epitope vaccine+CpG-ODN group. The results revealed that the DNA vaccine containing epitopes of SAG1, SAG3 and SAG5 adjuvanted with CpG-ODN might be a new model for further investigations against acute T. gondii infection.

Immune Protective Evaluation Elicited by DNA Vaccination With Neospora caninum Dense Granules Proteins in Mice

Neospora caninum, an obligate intracellular protozoan, is the major cause for neosporosis and brings serious economic losses to cattle breeding industries worldwide. After invasion, dense granules proteins are abundantly secreted and being important components of parasitophorous vacuole and intravacuolar network where N. caninum survives and replicates. The aim of the present study was to evaluate the protective immunity induced by DNA vaccines with genes encoding dense granules proteins 1 (GRA1), GRA4, GRA9, GRA14, GRA17, and GRA23 against N. caninum tachyzoites in BALB/C mice. Eukaryotic expressing plasmids of pcNcGRAs were constructed and the mice were intramuscularly immunized with pcNcGRAs followed by challenging infection with lethal doses of N. caninum. Immune responses were evaluated through monitoring the levels of serum antibodies, measurement of lymphocyte proliferation, and secretion of cytokines. Immune protection assays were carried out through monitoring survival time, body weight, and parasite burden in the brains. Results showed that all the pcNcGRA DNA vaccines could trigger remarkably specific humoral and cellular responses, with higher levels of IgG and IgG2a antibodies as well as obviously increased secretion of Th1-type IFN-γ cytokines. The immune protective efficacy revealed that pcNcGRA4, pcNcGRA14, and pcNcGRA17 DNA vaccines could individually increase the survival rate to 50, 37.5, and 25% in comparison with 0% in the control group; prolong the survival time more than 20.88 ± 11.12, 18.88 ± 10.83, and 16.63 ± 10.66 days compared with the control group of 4 ± 1.31 days; and decrease parasite burden in the brains to 297.63 ± 83.77, 471.5 ± 110.74, and 592.13 ± 102.2 parasites/100 ng comparing with 1221.36 ± 269.59 parasites/100 ng in the control group. These findings indicated that NcGRA4, NcGRA14, and NcGRA17 are potential vaccine candidates; NcGRA4 displayed better performance in immune protective efficacy and could be further combined with other advantageous antigens applied to the development of safe and effective DNA vaccines against N. caninum.

Protective effect of a DNA vaccine cocktail encoding ROP13 and GRA14 with Alum nano-adjuvant against Toxoplasma gondii infection in mice

Toxoplasma gondii is an obligate intracellular protozoan parasite that can cause serious public health problems. The development of a safe and effective vaccine against T. gondii is urgently needed to prevent and control the spread of toxoplasmosis. The aim of this study was to evaluate the immune responses induced by a pcGRA14 + pcROP13 vaccine cocktail in BALB/c mice. All groups were immunized intramuscularly three times at two-week intervals. The production of anti-Toxoplasma gondii lysate antigen (TLA) antibodies, lymphocyte proliferation, serum levels of IFN-γ and IL-4 cytokines and the survival time were monitored after vaccination and challenged with the virulent RH strain of T. gondii. The results showed that immunization with the pcGRA14 + pcROP13 DNA vaccine significantly increased the production of specific IgG antibodies and cytokines against toxoplasmosis. Interestingly, high levels of IgG2a and IFN-γ were found in animals vaccinated with DNA vaccine cocktail. Furthermore, immunized mice challenged with the RH strain of T. gondii showed prolonged survival time when compared to control groups (P <0.05). The present study demonstrates the potential of a DNA cocktail vaccine expressing pcGRA14 and pcROP13 in developing specific immune responses and providing effective protection against T. gondii infection.

Enhancing immune responses by a novel multi-epitope ROP8 DNA vaccine plus interleukin-12 plasmid as a genetic adjuvant against acute Toxoplasma gondii infection in BALB/c mice

BACKGROUND

Toxoplasmosis is a widespread zoonotic infection, caused by an obligate intracellular protozoan. The infection is often asymptomatic in immunocompetent individuals, although in persons with impaired immune system may lead to severe and progressive complications. Constant attempts of scientists have made valuable findings in the development of Toxoplasma gondii (T. gondii) candidate vaccines. However, an effective vaccine has not been successfully developed yet. In the current study, we tested the co-delivery of a novel multi-epitope pcROP8 DNA vaccine with a plasmid encoding IL-12 (pcIL-12) to assess the immune responses in BALB/c mice against acute T. gondii 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, and survival time.

RESULTS

The findings demonstrated that immunization with multi-epitope pcROP8 significantly enhanced the level of anti-T. gondii antibodies, TH1-type cellular immune responses, lymphocyte proliferation, and prolonged survival time, compared to control groups (P < 0.05). Furthermore, the use of pcIL-12 as a genetic adjuvant led to enhancements of the above-mentioned immune responses in BALB/c mice (P < 0.05).

CONCLUSIONS

The co-administration of pcIL-12 with multi-epitope pcROP8 vaccine, could successfully enhance the level of protection. Thus, this immunization regimen may represent an effective vaccine strategy against acute T. gondii infection.

Toxoplasma gondii Dense Granule Proteins 7, 14, and 15 Are Involved in Modification and Control of the Immune Response Mediated via NF-κB Pathway

Toxoplasma gondii infects almost all warm-blooded animals, including humans, leading to both cellular and humoral immune responses in the host. The virulence of T. gondii is strain specific and is defined by secreted effector proteins that disturb host immunity. Here, we focus on nuclear factor-kappa B (NFκB) signaling, which regulates the induction of T-helper type 1 immunity. A luciferase assay for screening effector proteins, including ROPs and GRAs that have biological activity against an NFκB-dependent reporter plasmid, found that overexpression of GRA7, 14, and 15 of a type II strain resulted in a strong activity. Thus, our study was aimed at understanding the involvement of NFκB in the pathogenesis of toxoplasmosis through a comparative analysis of these three molecules. We found that GRA7 and GRA14 were partially involved in the activation of NFκB, whereas GRA15 was essential for NFκB activation. The deletion of GRA7, GRA14, and GRA15 in the type II Prugniaud (Pru) strain resulted in a defect in the nuclear translocation of RelA. Cells infected with the PruΔgra15 parasite showed reduced phosphorylation of inhibitor-κBα. GRA7, GRA14, and GRA15 deficiency decreased the levels of interleukin-6 in RAW246.7 cells, and RNA-seq analysis revealed that GRA7, GRA14, and GRA15 deficiency predominantly resulted in downregulation of gene expression mediated by NFκB. The virulence of all mutant strains increased, but PruΔgra14 only showed a slight increase in virulence. However, the intra-footpad injection of the highly-virulent type I RHΔgra14 parasites in mice resulted in increased virulence. This study shows that GRA7, 14, and 15-induced host immunity via NFκB limits parasite expansion.

Evaluation of immune protection against Toxoplasma gondii infection in mice induced by a multi-antigenic DNA vaccine containing TgGRA24, TgGRA25 and TgMIC6

Toxoplasma gondii infection is prevalent in humans and animals worldwide. In this study, recombinant eukaryotic expression plasmids (pVAX-GRA24, pVAX-GRA25 and pVAX-MIC6) were constructed, and then injected into Kunming mice intramuscularly, as cocktailed plasmids or as single-gene plasmids. We evaluated immune protective responses by detecting the titer of antibodies and cytokine production of IFN-γ, IL-2, IL-4, IL-10, IL-12 and IL-23, the percentages of the subclasses of T lymphocytes, as well as the records of the survival time and cyst decrement in the brain of the mouse model after challenge with the T. gondii RH and Pru strains, respectively. Compared with the control groups, antibody and cytokine production were significantly increased, while the survival times of mice in all immunized groups were also prolonged, and the number of T. gondii cysts in their brains were decreased significantly (29.03% for pVAX-GRA24; 40.88% for pVAX-GRA25; 37.70% for pVAX-MIC6; 48.06% for pVAX-GRA24 + pVAX-GRA25; and 55.37% for pVAX-GRA24 + pVAX-GRA25 + pVAX-MIC6). The mouse group immunized with the three-gene cocktail (TgGRA24 + TgGRA25 + TgMIC6) had better performance in each detection index than the mouse groups immunized with the two-gene cocktail of TgGRA24 + TgGRA25, which was better than that in the group immunized with the single gene vaccine of TgGRA24, TgMIC6 or TgGRA25. In conclusion, TgGRA24 or TgGRA25 may be good vaccine candidates against T. gondii infection, but the three-gene cocktail of TgGRA24, TgMIC6 and TgGRA25 may induce the strongest protective immunity. Further studies of multi-antigenic DNA vaccines or cocktailed vaccines against T. gondii infection are necessary.

Anti-Toxoplasma Activities of Zea Mays and Eryngium Caucasicum Extracts, In Vitro and In Vivo

OBJECTIVES

Toxoplasmosis is a worldwide health problem that caused by intracellular apicomplexan parasite, Toxoplasma gondii (T. gondii). Considering that the available drugs for toxoplasmosis have serious host toxicity, the aim of the current study was to survey the in vitro and in vivo anti-Toxoplasma activity of Zea mays (Z. mays) and Eryngium caucasicum (E. caucasicum) extracts.

METHODS

Four concentrations (5, 10, 25, and 50 mg mL-1) of Z. mays and E. caucasicum methanolic extracts for 30, 60, 120, and 180 min were incubated with infected macrophages and then the viability of RH strain of T. gondii tachyzoites was evaluated by trypan blue staining method. Also, we evaluated the survival rate of acutely infected mice with the extracts (100 and 200 mg kg-1 day-1) intraperitoneally for 5 days after infection with 2× 104 tachyzoites of T. gondii.

RESULTS

The anti-Toxoplasma effect of the methanolic extracts were extremely significant compared to the negative control group in all exposure times (P < 0.05). The Z. mays (10, 25 and 50 mg mL-1) killed 100% of the parasites after 180 and 120 min exposure, respectively. Also, high toxoplasmacidal activity was observed with E. caucasicum extract. Furthermore, treatment of experimentally infected mice with the Z. mays (100, 200 mg kg-1 day-1) and E. caucasicum (100 mg kg-1 day-1) significantly increased their survival rate compared to untreated infected control (P < 0.05).

CONCLUSION

These extracts are promising candidates for further medicine development on toxoplasmosis. However, further investigations are necessary to clarify effective fractions of the Z. mays and E. caucasicum extracts and the mechanisms of action.

Antigenic Epitope Analysis and Efficacy Evaluation of GRA41 DNA Vaccine Against T. gondii Infection

BACKGROUND

Toxoplasma gondii has a comprehensive impact on a great range of warm-blood mammals, in which one-third of the population all over the world is involved. Dense granular proteins, regarded as GRA family, mediating substantial interface between host cell cytoplasm and parasite, are widely studied for preventing the infection of T. gondii.

PURPOSE

As is handled in our study, the effect of intramuscularly injecting the genetic vaccine pEGFP-C1/GRA41 encoding a novel dense granule protein, GRA41, was evaluated.

METHODS

At the beginning, bioinformatics analysis was used to evaluate epitopes of both B cells and T cells on the GRA41 protein of T. gondii. Afterwards, recombinant plasmids (pEGFP-C1/GRA41) were injected into BALB/c mice and the quantity of IgG and its subclass IgG2a remarkably increased. IFN-γ, distinctive from the other cytokines (IL-4, and IL-10), was significant in growth. Afterwards, the intraperitoneal challenge was executed for recording survival time with tachyzoites with high virulence (in RH strain) and counting the number of brain cysts was carried out after the infection of PRU strain (low virulence).

RESULTS

In pEGFP-C1/GRA41 group, the survival period was significantly longer (13.3 ± 3.37 days) after tachyzoites attack with the RH strain in high virulence, compared with the other groups (less than 8 days). Additionally, the cyst quantity is remarkably lower and the rate of reduction could reach 59.34%.

CONCLUSION

All the results indicated effective protection of DNA vaccine encoding GRA41 against T. gondii.

IL-17 and IL-22 elicited by a DNA vaccine encoding ROP13 associated with protection against Toxoplasma gondii in BALB/c mice

Toxoplasma gondii, an intracellular parasitic protozoan, is capable of infecting man and all warm-blooded animals. Cell-mediated immunity is vital in mounting protective responses against T. gondii infection. Recent studies have shown that T-helper (Th) 17 responses may play a key role in parasite control. In this current study, we constructed a DNA vaccine encoding T. gondii ROP13 in a pcDNA vector. Groups of BALB/c mice were immunized intramuscularly with pcROP13 or controls and challenged with the RH strain of T. gondii. The results showed that immunization with pcROP13 could elicit an antibody response against T. gondii. The expression of the canonical Th17 cytokines, interleukin (IL)-17 and IL-22, were significantly increased after immunization with pcROP13 compared with control groups ( p < 0.05). Furthermore, vaccination resulted in a significant decrease in parasite load ( p < 0.05). The induction of Th17 related cytokines, using a ROP13 DNA vaccine, against T. gondii should be considered as a potential vaccine approach for the control of toxoplasmosis.

In vitro therapeutic effect of Hemiscorpius lepturus venom on tachyzoites of Toxoplasma gondii

Pyrimethamine which is a main anti-Toxoplasma gondii drug has a serious side and toxic effects on the host. Accordingly, the development of new treatment options for toxoplasmosis with less toxic effects, low teratogenicity and parasiticidal effect against the various stage of T. gondii are dramatically crucial. Currently, natural molecules from scorpion and snake venoms are widely used as an alternative treatment against human disease, these compounds considered to be safe and to have low toxicity in comparison with synthetic drugs. Therefore, the goal of our study was to investigate the anti-Toxoplasma gondii activities of Hemiscorpius lepturus venom. We measured cytotoxicity of H. lepturus whole venom on Vero cells as well as effectiveness of this compound on viability of T. gondii applying colorimetric assay, according to mitochondrial oxidation of the MTT reagent (Methylthiazol tetrazolium 98%). The results of this study indicated that the H. lepturus whole venom has an anti-Toxoplasma effects with less toxic effect on Vero cells. Also, the T. gondii tachyzoites were treated with H. lepturus venom reached better results in comparison with Pyrimethamine-treated group. This research will serve as a base for future studies on toxoplasmosis and suggest a role for scorpion venom in promoting natural drugs.

Evaluation of Protective Immune Response Induced by a DNA Vaccine Encoding GRA8 against Acute Toxoplasmosis in a Murine Model

Toxoplasma gondii is an apicomplexan zoonotic protozoan parasite that infects most species of warm-blooded animals, including humans. The heavy incidence and severe or lethal damage caused by T. gondii infection clearly indicate a need for the development of an effective vaccine. T. gondii GRA8 is a member of the dense granules protein family and is used as a marker of acute infection. In the present study, we evaluated the protective immunity induced by DNA vaccination based on a recombinant eukaryotic plasmid, pDsRed2-GRA8, against acute toxoplasmosis in mice. BALB/c mice were intramuscularly immunized with the pDsRed2-GRA8 plasmid and then challenged by infection with the highly virulent GFP-RH strain of T. gondii. The specific immune responses and protective efficacy against T. gondii of this vaccine were analyzed by measuring cytokine and serum antibody titers, splenocyte proliferation assays, and the survival times of mice after challenge. Our results showed that mice immunized with pDsRed2-GRA8 demonstrated specific humoral and cellular responses, induced higher IgG antibody titers with predominant IgG2a production; increased levels of IL-10, IL-12 (p70), IFN-γ, TNF-α, and splenocyte proliferation; and prolonged survival times compared to those of control mice. The present study showed that DNA immunization with pDsRed2-GRA8 induced humoral and cellular immune responses, and all immunized mice showed greater Th1-type immune responses and longer survival times than those of control mice. These results indicated that T. gondii GRA8 DNA immunization induces a partial protective effect against acute toxoplasmosis.

Effects of Aloe vera and Eucalyptus methanolic extracts on experimental toxoplasmosis in vitro and in vivo

Toxoplasmosis is a worldwide disease caused by the protozoan parasite Toxoplasma gondii (T. gondii), which is most commonly treated by pyrimethamine and sulfadiazine. However, this treatment presents several adverse side effects; Thus, new drugs with lower toxicities are urgently needed. In this study the anti-T. gondii activity of A. vera and Eucalyptus extracts were evaluated in vitro using a MTT (3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyltetrazolium bromide) assay and in vivo by measuring the survival rates of mice infected with 2 × 10³ tachyzoites of RH strain of T. gondii and then injected intraperitoneally by different concentrations of extracts for 4 days. Biochemical parameters such as Ferric Reducing Antioxidant Potential (FRAP) and malondialdehyde (MDA) assay were also evaluated. As results, in the in vitro assay, the IC₅₀ values were 13.2, 24.7, 2.63 μg/ml, and the selectivity indexes were 3.3, 2.4, 3.03 for the A. vera, Eucalyptus and pyrimethamine, respectively. The mice treated with Eucalyptus showed a better survival rate than others (P < 0.05). The increased weight of liver and spleen, due to infection, was reduced by treatments. In FRAP assay Eucalyptus showed a better antioxidant activity than the other extracts. MDA levels in both liver and spleen were reduced by treatment. The results show that A. Vera and Eucalyptus possess anti-T. gondii activities in vitro and in vivo, in addition, Eucalyptus shows antioxidant activity with a higher survival rate. Therefore, Eucalyptus may be a useful candidate for treating Toxoplasma infection. Moreover, further studies are required to investigate the fractionations of this plant against 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.

Immune responses and protection after DNA vaccination against Toxoplasma gondii calcium-dependent protein kinase 2 (TgCDPK2)

Toxoplasma gondii, an intracellular zoonotic protozoan parasite, is possibly the most widespread parasite of warm-blooded animals and can cause serious public health problems and economic losses worldwide. TgCDPK2, a member of the T. gondii calcium-dependent protein kinase family, was recently identified as an essential regulator for viable cyst development in T. gondii. In the present study, we evaluated the protective immunity induced by DNA vaccination based on a recombinant eukaryotic plasmid, pVAX-TgCDPK2, against acute toxoplasmosis in mice. BALB/c mice were intramuscularly immunized with pVAX-TgCDPK2 plasmid and then challenged by infection with the highly virulent RH strain of T. gondii. The specific immune responses and protective efficacy against T. gondii were analyzed by cytokine and serum antibody measurements, lymphocyte proliferation assays, flow cytometric on lymphocytes and the survival time of mice after challenge. Our results showed that mice immunized with pVAX-TgCDPK2 could elicit special humoral and cellular responses, with higher levels of IgG antibody, and increased levels of Th1-type cytokines IFN-γ, IL-12(p70), and CD3 + CD4 + CD8 − and CD3 + CD8 + CD4 − T cells, and had a prolonged survival time (14.0 ± 2.32 days) compared to control mice. These results demonstrate that pVAX-TgCDPK2 is a potential vaccine candidate against acute toxoplasmosis.