Key Limitations and New Insights Into the Toxoplasma gondii Parasite Stage Switching for Future Vaccine Development in Human, Livestock, and Cats

Investigation of Toxoplasma gondii Infection in Yunnan Semi-fine Wool Sheep (Ovis aries) and wild Rodents in Yunnan, China

BACKGROUND

Toxoplasma gondii, a globally distributed zoonotic obligate intracellular parasite, infects a wide array of mammals, including humans, sheep, and birds. As a unique sheep breed in southwestern China, Yunnan semi-fine wool sheep occupies an important position in animal husbandry in Zhaotong due to its strong adaptability, high reproductive rate, and excellent wool quality. Lambs infected with T. gondii are prone to neurological symptoms and growth retardation, while T. gondii infection in ewes can cause abortions, stillbirths, and deformities, thus affecting sheep reproduction and sheep product quality. Meanwhile, mutton and dairy products contaminated with T. gondii can become potential sources of human infection, potentially threatening public health and safety.

METHOD

To understand the T. gondii infection in semi-fine wool sheep in Zhaotong, Yunnan Province, 586 blood samples were collected and subjected to indirect hemagglutination assay (IHA) for T. gondii antibodies, and the infection-related factors were analyzed through cross-sectional analysis. In the meantime, nested PCR was conducted on a total of 217 samples collected from 31 rodents caught in and around the sheep breeding ground to test the T. gondii B1 gene in rodent tissues.

RESULTS

A total of 94 sera tested positive for T. gondii antibodies, with a total positive rate of 16.04% (94/586) (95% CI: 14.77-20.89). Cross-sectional statistical analysis on factors related to semi-fine wool sheep infection rate, including sampling season, sex, age, and weight, suggested that age (< 6 months: 23.81%; 6-12 months: 11.74%; > 12 months: 15.83%) was a significant factor explaining the infection rate differences (P = 0.003 < 0.05, χ2 = 11.62, df = 2). Thus, age was considered a key risk factor for T. gondii infection in this study (odds ratio, OR = 2.35, 95% CI: 1.42-3.87). Nested PCR analysis on 217 (heart, liver, spleen, lung, kidney, brain, and muscle) tissues from the 31 rodents indicated that 11 tested positive. The total infection rate of rodents in and around the breeding ground was 35.48% (11/31), and 14 samples tested positive, with a positive infection rate of 6.45% (14/217).

CONCLUSION

The T. gondii infection rates of semi-fine wool sheep and rodents from their breeding environment in Zhaotong, Yunnan Province, were high, necessitating enhanced prevention, control, and treatment measures to ensure the healthy breeding of semi-fine wool sheep and veterinary public health and safety.

PruΔcdpk2 Protects Pigs against Acute Toxoplasmosis Depending on T-Lymphocyte Subsets and Natural Killer Cell Responses

Toxoplasma gondii is a widespread protozoan parasite approximately infecting one-third of the world population and can cause serious public health problems. In this study, we investigated the protective effect of the attenuated vaccine Pru:Δcdpk2 against acute toxoplasmosis and explored the underlying immune mechanisms of the protection in pigs. The systemic T-cell and natural killer (NK) cell responses were analyzed, including kinetics, phenotype, and multifunctionality (interferon [IFN]-γ, tumor necrosis factor [TNF]-α), and the IFN-γ levels were analyzed in PBMCs. Our results showed that T. gondii-specific antibodies were induced by Pru:Δcdpk2. After challenging with RH, the antibodies were able to respond quickly in the immunized group, and the expression level was significantly higher than that in the unimmunized group. The expression level of IFN-γ significantly increased after vaccination, and the CD3+ γδ-, NK, and CD3+ γδ+ cell subsets also significantly increased. At the same time, functional analysis indicated that these cells were polarized toward a Th1 phenotype, showing the ability to secrete IFN-γ and TNF-α. The CD4+CD8α-T cell population exhibited a higher frequency of IFN-γ+ producing cells compared with the CD4-CD8α+ and CD4+CD8α+ cell populations during the early days of vaccination. Our results indicated that the attenuated vaccine could induce the expression of NK, γδ, and CD3αβ cells in pigs, and IFN-γ and TNF-α secreted by these cells are important for resistance to T. gondii infection.

Effective factors in the pathogenesis of Toxoplasmagondii

Toxoplasma gondii (T. gondii) is a cosmopolitan protozoan parasite in humans and animals. It infects about 30 % of the human population worldwide and causes potentially fatal diseases in immunocompromised hosts and neonates. For this study, five English-language databases (ScienceDirect, ProQuest, Web of Science, PubMed, and Scopus) and the internet search engine Google Scholar were searched. This review was accomplished to draw a global perspective of what is known about the pathogenesis of T. gondii and various factors affecting it. Virulence and immune responses can influence the mechanisms of parasite pathogenesis and these factors are in turn influenced by other factors. In addition to the host's genetic background, the type of Toxoplasma strain, the routes of transmission of infection, the number of passages, and different phases of parasite life affect virulence. The identification of virulence factors of the parasite could provide promising insights into the pathogenesis of this parasite. The results of this study can be an incentive to conduct more intensive research to design and develop new anti-Toxoplasma agents (drugs and vaccines) to treat or prevent this infection. In addition, further studies are needed to better understand the key agents in the pathogenesis of T. gondii.

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.

Immunization of BALB/c Mice with Killed Tachyzoites of Toxoplasma gondii against Acute Toxoplasmosis

Background

Toxoplasma gondii with widespread distribution infects over one third of human populations in the world and can cause serious life-threatening diseases especially for the immunodeficient patients in acute toxoplasmosis. As the clinical pharmaceutical drugs with severe side effects for treatment and non-ideal extant vaccines for prevention, more work starves to be done for keeping advantages in the athletics.

Methods

Aluminum adjuvant and hybrid formaldehyde-killed tachyzoites of T. gondii RH and GT1 isolates were prepared to intramuscularly immunize BALB/c mice for five times at 0, 3, 7, 14 and 21 days post first injection. The triggered humoral and cellular immune responses at two weeks post the last immunization and the survival times of infected mice were examined for the hybrid immunization scheme judgement.

Results

The anti-RH and anti-GT1 specific antibodies were both increased at one week prior to challenge (P < 0.05), and the survival times of immunized mice (7.33 ± 0.71 d for RH, 7.22 ± 0.97 d for GT1) against acute toxoplasmosis were significantly prolonged by the immunizations performed in the study compared to blank control (6.67 ± 0.50 d for RH, 6.33 ± 0.71 d for GT1; P < 0.05), with the higher IFN-γ, IL-2 and IL-12p70 in sera, the elevated CD3e+CD4+ T and CD3e+CD8a+ T cells, and the enhanced lymphocyte proliferation in spleen (P < 0.05).

Conclusion

The hybrid killed tachyzoites with aluminum adjuvant induced humoral and cellular immune responses of mice, and offered mildly protective efficacy against acute toxoplasmosis.

Novel insights on the therapeutic effect of levamisole on the chronic toxoplasmosis in mice model

Latent toxoplasmosis mostly reactivates which could result in acute encephalitis. Chronic toxoplasmosis treatments are severely constrained by Toxoplasma cyst resistance. Novel therapeutic approaches are therefore becoming more essential. In this study, the effects of levamisole (LEVA) and spiramycin on the early and late stages of experimental toxoplasmosis are investigated.

MATERIALS AND METHODS

Seventy-five Me49 Toxoplasma gondii infected Swiss albino mice were divided into five groups; (GI): noninfected control group; (GII): infected untreated control group; (GIII): infected- LEVA treated group; (GIV): infected and received combination of spiramycin and LEVA and (GV): infected-spiramycin treated group. The impact was assessed through brain cyst count by Quantitative Real-Time Polymerase Chain Reaction (PCR), interferon gamma (IFN-γ) assay, histopathological study, and total blood counts.

RESULTS

The progression of chronic toxoplasmosis could only be partially controlled by using either levamisole or spiramycin as a separate drug. The combined spiramycin and levamisole treatment significantly decreased the burden of Toxoplasma brain cyst, increased IFN-γ level, total blood parameters and improved the histopathological features especially at the late stage of infection.

IN CONCLUSION

Levamisole effectively modulated Toxoplasma-induced immune responses, resulting in chronic toxoplasmosis remission. Further clinical trials will be needed to study the effect of these combination in HIV/AIDS (human immunodeficiency virus) patients with toxoplasmosis.

In silico design of a novel peptide-based vaccine against the ubiquitous apicomplexan Toxoplasma gondii using surface antigens

Human toxoplasmosis is a global public health concern and a commercial vaccine is still lacking. The present in silico study was done to design a novel vaccine candidate using tachyzoite-specific SAG1-realted sequence (SRS) proteins. Overlapping B-cell and strictly-chosen human MHC-I binding epitopes were predicted and connected together using appropriate spacers. Moreover, a TLR4 agonist, human high mobility group box protein 1 (HMGB1), and His-tag were added to the N- and C-terminus of the vaccine sequence. The final vaccine had 442 residues and a molecular weight of 47.71 kDa. Physico-chemical evaluation showed a soluble, highly antigenic and non-allergen protein, with coils and helices as secondary structures. The vaccine 3D model was predicted by ITASSER server, subsequently refined and was shown to possess significant interactions with human TLR4. As well, potent stimulation of cellular and humoral immunity was demonstrated upon chimeric vaccine injection. Finally, the outputs showed that this vaccine model possesses top antigenicity, which could provoke significant cell-mediated immune profile including IFN-γ, and can be utilized towards prophylactic purposes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-023-00140-w.

Cerebral toxoplasmosis in HIV-infected patients: a review

Toxoplasma gondii infection in the central nervous system commonly occurs among immunodeficient patients. Its prevalence is high in countries with a high burden of HIV and low coverage of antiretroviral drugs. The brain is one of the predilections for T. gondii infection due to its low inflammatory reaction, and cerebral toxoplasmosis occurs solely due to the reactivation of a latent infection rather than a new infection. Several immune elements have recently been recognized to have an essential role in the immunopathogenesis of cerebral toxoplasmosis. Although real-time isothermal amplification, next-generation sequencing, and enzyme-linked aptamer assays from blood samples have been the recommended diagnostic tools in some in-vivo studies, a combination of clinical symptoms, serology examination, and neuroimaging are still the daily standard for the presumptive diagnosis of cerebral toxoplasmosis and early anti-toxoplasma administration. Clinical trials are needed to find a new therapy that is less likely to affect folate synthesis, have neuroprotective properties, or cure the latent phase of infection. The development of a vaccine is being extensively tested in animals, but its efficacy and safety for humans are still not proven.

Seroprevalence of Toxoplasma gondii infection in women with a gynecological tumor living in eastern China

The association between Toxoplasma gondii (T. gondii) infection and malignancy has attracted increased attention in recent years, but little is known of T. gondii infection among women diagnosed with a gynecological tumor (GT) in China. We conducted a case-control study involving 460 women diagnosed with a GT and 460 age-matched healthy controls (HCs) to estimate the infection process of T. gondii and understand the risk factors of T. gondii infection in patients with a GT. Levels of anti-T. gondii IgG and IgM were measured by enzyme-linked immunoassays every 12 months. After a median follow-up time of 4.3 years (range 4 to 5 years), 55/460 (11.96%) patients with a GT and 15/460 (3.26%) HCs were seroprevalence for T. gondii antibodies, respectively (P = 0.001). IgG antibodies against T. gondii were found in 54 GT patients (11.74%) and 15 HCs (3.26%), respectively (P = 0.001). The seroprevalence of T. gondii IgM antibodies was similar in patients with a GT and with HCs (2.83% vs 1.3%, P = 0.105). Multivariate stepwise logistic regression analysis revealed contact with cats (OR, 6.67; 95% CI [2.89-10.75]; P = 0.001), exposure to soil (OR, 2.16; 95% CI [1.14-4.10]; P = 0.019), being a farm-worker (OR, 4.17; 95% CI [1.20-11.49]; P = 0.006) and history of chemotherapy (OR, 3.16; 95% CI [1.56-6.45]; P = 0.001) to be independent risk factors for T. gondii infection. Women with an ovarian cancer or endometrial cancer had higher T. gondii seroprevalence than that of HCs. Moreover, T. gondii infection in patients with a GT mostly acquired within two years of diagnosis, but the infection in healthy controls had no obvious time characteristics. Here, we demonstrated that T. gondii infection is significantly higher in patients with a GT (especially in women with an ovarian tumor) compared to HCs. Thus, infection with this parasite should be avoided in patients with a GT, and the causal relationship between T. gondii and GTs should be studied in detail.

Detecting zoonotic and non‐zoonotic pathogens in livestock and their ticks in Corsican wetlands

Background

Corsica is a large French island in the Mediterranean Sea with high human and animal migration rates, especially near wetlands where these migrations are particularly frequent. Among the livestock populations, cattle and sheep are widely present all across the entire Mediterranean region. Trade can be responsible for the circulation of numerous pathogens and their vectors, thereby representing a health and economic threat for the livestock industry.

Objectives

The objective of our study was to investigate the presence of pathogens in cattle and sheep farms in the wetlands of Corsica using a high‐throughput screening technique.

Methods

In our study, blood samples and ticks were collected from cattle and sheep in 20 municipalities near Corsican wetlands to screen for the presence of various types of pathogens. The samples were processed using a high‐throughput screening technique based on real‐time microfluidic PCR: 45 pathogens were screened in 47 samples simultaneously.

Results

A total of 372 cattle and 74 sheep were sampled, and 444 ticks were collected from cattle. Out of the eight tick species detected, the main one was Rhipicephalus bursa (38.7% of the ticks collected). From cattle blood samples, one species and two genera were found: Anaplasma marginale, Trypanosoma sp. and Babesia sp. in respectively 61.5%, 58.3% and 12.2% of the cattle blood samples. From sheep blood samples, 74.3% were positive for Anaplasma sp, 2.7% for Anaplasma ovis and 1.4% for Anaplasma capra. This is the first report of A. ovis DNA in blood samples from sheep in Corsica. Out of 444 the tick samples, 114 were positive: 77.2% for Rickettsia aeschlimannii, 20.2% for Rickettsia sp., 3.5% for Babesia sp. and 1.8% for Anaplasma sp. Among them, 2.7% were co‐infected with R. aeschlimannii and Babesia sp.

Conclusions

Our results confirm the extent of possible circulation of different pathogens near Corsican wetlands, not only in ticks collected from livestock but also directly in cattle and sheep, with two (Trypanosoma sp. and Babesia sp.) being detected for the first time in cattle, one for the first time in sheep (A. ovis) and one for the first time in Corsica (A. capra)

Deletion of Toxoplasma Rhoptry Protein 38 (PruΔrop38) as a Vaccine Candidate for Toxoplasmosis in a Murine Model

Toxoplasmosis is a serious zoonotic disease that threatens human and animal health. Here, we evaluated the vaccine potential of the deletion of Toxoplasma rhoptry protein 38 (PruΔrop38) through its pathogenicity and immunoprotective efficacy in mice. Mice inoculated intraperitoneally with 1 × 10³, 2 × 10³, or 4 × 10³ PruΔrop38 showed no visible signs, whereas mice inoculated with 1 × 10³ parental Pru strain showed obvious wasting and bow-back, suggesting a significantly lower pathogenicity of PruΔrop38 in mice. Vaccination with 1 × 10² PruΔrop38 triggered a mixed Th1/Th2 response (Th1 response predominant), with higher IgG, IgG2a, and IgG1 levels in serum from week 3 to week 12, and a significant increase in IFN-γ, IL-12, and IL-10 in suspensions of splenocytes at 30 or 60 days post-immunization. All vaccinated mice survived when infected intraperitoneally with tachyzoites (RH, Pru, VEG, or TgcatBJ1) or when infected orally with cysts (Pru or ME49). The brain parasite burden during Pru tachyzoite, Pru cyst and ME49 cyst challenges were significantly reduced in vaccinated mice. The duration of immunization showed that vaccination with PruΔrop38 could protect mice from challenge with different varied genotypes of Toxoplasma strains against different routes of infection. Collectively, these findings indicate that PruΔrop38 is an attenuated strain that provides long-term protective efficacy against acute or chronic toxoplasmosis in mice.

Mining the Proteome of Toxoplasma Parasites Seeking Vaccine and Diagnostic Candidates

Simple Summary

The One Health concept to toxoplasmosis highlights that the health of humans is closely related to the health of animals and our common environment. Toxoplasmosis outcomes might be severe and fatal in patients with immunodeficiency, diabetes, and pregnant women and infants. Consequently, the development of effective vaccine and diagnostic strategies is urgent for the elimination of this disease. Proteomics analysis has allowed the identification of key proteins that can be utilized in the development of novel disease diagnostics and vaccines. This work presents relevant proteins found in the proteome of the life cycle-specific stages of Toxoplasma parasites. In fact, it brings together the main functionality key proteins from Toxoplasma parasites coming from proteomic approaches that are most likely to be useful in improving the disease management, and critically proposes innovative directions to finally develop promising vaccines and diagnostics tools.

Abstract

Toxoplasma gondii is a pathogenic protozoan parasite that infects the nucleated cells of warm-blooded hosts leading to an infectious zoonotic disease known as toxoplasmosis. The infection outcomes might be severe and fatal in patients with immunodeficiency, diabetes, and pregnant women and infants. The One Health approach to toxoplasmosis highlights that the health of humans is closely related to the health of animals and our common environment. The presence of drug resistance and side effects, the further improvement of sensitivity and specificity of serodiagnostic tools and the potentiality of vaccine candidates to induce the host immune response are considered as justifiable reasons for the identification of novel targets for the better management of toxoplasmosis. Thus, the identification of new critical proteins in the proteome of Toxoplasma parasites can also be helpful in designing and test more effective drugs, vaccines, and diagnostic tools. Accordingly, in this study we present important proteins found in the proteome of the life cycle-specific stages of Toxoplasma parasites that are potential diagnostic or vaccine candidates. The current study might help to understand the complexity of these parasites and provide a possible source of strategies and biomolecules that can be further evaluated in the pathobiology of Toxoplasma parasites and for diagnostics and vaccine trials against this disease.

TNFα rs1799964 TT genotype may be a susceptibility factor for vertical transmission of Toxoplasma gondii and clinical signs in newborns from pregnant women with acute toxoplasmosis

BACKGROUND

One of the main impacts of Toxoplasma gondii infection occurs during pregnancy and is related to the vertical transmission of the parasite (congenital toxoplasmosis), which can cause severe clinical outcomes and fetal death. During acute infection, in order to control the rapid replication of tachyzoites, different host immune response genes are activated, and these include cytokine-encoding genes. Considering that polymorphisms in cytokine genes may increase susceptibility to vertical transmission of T. gondii by determining the immune status of the pregnant woman, this study evaluated the influence of polymorphisms of tumor necrosis factor alpha (TNFα) rs1799964 (- 1031) and interleukin 1 beta (IL1β) rs16944 (- 511) genes on gestational toxoplasmosis and on the vertical transmission of the parasite and verified the allele and genotype frequency of these polymorphisms in pregnant patients whose respective newborn did or did not present clinical abnormalities suggestive of congenital toxoplasmosis.

METHODS AND RESULTS

A total of 204 pregnant patients with (n = 114) or without (n = 90) infection by T. gondii were enrolled. No associations were found involving the polymorphisms rs1799964 (- 1031) of the TNFα gene and rs16944 (- 511) of the IL1β gene with the increased chance of T. gondii infection during pregnancy. However, it was observed that the maternal TT genotype referring to the polymorphism of the TNFα gene seems to influence the vertical transmission of the parasite (P = 0.01; χ² = 6.05) and the presence of clinical manifestation in newborns from pregnancies with acute toxoplasmosis (P = 0.007; χ² = 9.68).

CONCLUSION

The TNFα rs1799964 TT genotype may act as a susceptibility factor for the vertical transmission of parasite and for the presence of clinical signs in newborns from pregnant women with acute toxoplasmosis.

Enhancing Immune Responses to a DNA Vaccine Encoding Toxoplasma gondii GRA7 Using Calcium Phosphate Nanoparticles as an Adjuvant

Toxoplasma gondii infects almost all warm-blooded animals, including humans. DNA vaccines are an effective strategy against T. gondii infection, but these vaccines have often been poorly immunogenic due to the poor distribution of plasmids or degradation by lysosomes. It is necessary to evaluate the antigen delivery system for optimal vaccination strategy. Nanoparticles (NPs) have been shown to modulate and enhance the cellular humoral immune response. Here, we studied the immunological properties of calcium phosphate nanoparticles (CaPNs) as nanoadjuvants to enhance the protective effect of T. gondii dense granule protein (GRA7). BALB/c mice were injected three times and then challenged with T. gondii RH strain tachyzoites. Mice vaccinated with GRA7-pEGFP-C2+nano-adjuvant (CaPNs) showed a strong cellular immune response, as monitored by elevated levels of anti-T. gondii-specific immunoglobulin G (IgG), a higher IgG2a-to-IgG1 ratio, elevated interleukin (IL)-12 and interferon (IFN)-γ production, and low IL-4 levels. We found that a significantly higher level of splenocyte proliferation was induced by GRA7-pEGFP-C2+nano-adjuvant (CaPNs) immunization, and a significantly prolonged survival time and decreased parasite burden were observed in vaccine-immunized mice. These data indicated that CaPN-based immunization with T. gondii GRA7 is a promising approach to improve vaccination.

Co-delivery of PLGA nanoparticles loaded with rSAG1 antigen and TLR ligands: An efficient vaccine against chronic toxoplasmosis

Although vaccination is a promising approach for the control of toxoplasmosis, there is currently no commercially available human vaccine. Adjuvants such as delivery vehicles and immunomodulators are critical components of vaccine formulations. In this study, Poly (D, l-lactide-co-glycolide) (PLGA) nanoparticles were applied to serve as delivery system for both surface antigen-1 (SAG1), a candidate vaccine against toxoplasmosis and two TLR ligands, monophosphoryl lipid A (MPL) and imiquimod (IMQ), respectively. Compared to rSAG1 alone, CBA/J mice immunized with rSAG1-PLGA produced higher anti-SAG1 IgG antibodies titers. This response was increased by the co-administration of IMQ-PLGA (p < 0.01). Compared to IMQ-PLGA co-administration, MPL-PLGA co-administration further increased the humoral response (p < 0.01) and potentiated the Th1 humoral response. Compared to rSAG1 alone, rSAG1-PLGA, or rSAG1-PLGA mixed with IMQ-PLGA or MPL-PLGA similarly enhanced the cellular response characterized by the production of IFN-γ, IL-2, TNF-α and low levels of IL-5, indicating a Th1-biased immunity. The induced immune responses, led to significant brain cyst reductions (p < 0.01) after oral challenge with T. gondii cysts in mice immunized with either rSAG1-PLGA, rSAG1-PLGA + IMQ-PLGA, rSAG1-PLGA + MPL-PLGA formulations. Taken together the results indicated that PLGA nanoparticles could serve as a platform for dual-delivery of antigens and immunomodulators to provide efficacious vaccines against toxoplasmosis.

Toxoplasma gondii Tyrosine-Rich Oocyst Wall Protein: A Closer Look through an In Silico Prism

Toxoplasmosis is a global threat with significant zoonotic concern. The present in silico study was aimed at determination of bioinformatics features and immunogenic epitopes of a tyrosine-rich oocyst wall protein (TrOWP) of Toxoplasma gondii. After retrieving the amino acid sequence from UniProt database, several parameters were predicted including antigenicity, allergenicity, solubility and physico-chemical features, signal peptide, transmembrane domain, and posttranslational modifications. Following secondary and tertiary structure prediction, the 3D model was refined, and immunogenic epitopes were forecasted. It was a 25.57 kDa hydrophilic molecule with 236 residues, a signal peptide, and significant antigenicity scores. Moreover, several linear and conformational B-cell epitopes were present. Also, potential mouse and human cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte (HTL) epitopes were predicted in the sequence. The findings of the present in silico study are promising as they render beneficial characteristics of TrOWP to be included in future vaccination experiments.

Comprehensive Overview of Toxoplasma gondii-Induced and Associated Diseases

Toxoplasma gondii (T. gondii) is a prevalent protozoan parasite of medical and veterinary significance. It is the etiologic agent of toxoplasmosis, a neglected disease in which incidence and symptoms differ between patients and regions. In immunocompetent patients, toxoplasmosis manifests as acute and chronic forms. Acute toxoplasmosis presents as mild or asymptomatic disease that evolves, under the host immune response, into a persistent chronic disease in healthy individuals. Chronic toxoplasmosis establishes as latent tissue cysts in the brain and skeletal muscles. In immunocompromised patients, chronic toxoplasmosis may reactivate, leading to a potentially life-threatening condition. Recently, the association between toxoplasmosis and various diseases has been shown. These span primary neuropathies, behavioral and psychiatric disorders, and different types of cancer. Currently, a direct pre-clinical or clinical molecular connotation between toxoplasmosis and most of its associated diseases remains poorly understood. In this review, we provide a comprehensive overview on Toxoplasma-induced and associated diseases with a focus on available knowledge of the molecular players dictating these associations. We will also abridge the existing therapeutic options of toxoplasmosis and highlight the current gaps to explore the implications of toxoplasmosis on its associated diseases to advance treatment modalities.

Insights into the biochemical features and immunogenic epitopes of common bradyzoite markers of the ubiquitous Toxoplasma gondii

The widespread distribution of Toxoplasma gondii (T. gondii) infection and its harsh outcomes in pregnant women and immunocompromised patients lead researchers towards vaccination strategies. The present in silico investigation was done to reveal biophysical properties and immunogenic epitopes of six bradyzoite markers for rational vaccine design in future. For this purpose, different web servers were used to predict antigenicity, allergenicity, solubility, physicochemical properties, post-translational modification sites (PTMs), the presence of signal peptide and transmembrane domains. Moreover, the secondary and tertiary structures of the proteins were revealed followed by refinement and validation. Finally, NetCTL server was used to predict cytotoxic T-lymphocyte (CTL) epitopes, with subsequent immunogenicity analysis. Also, IEDB server was utilized to predict helper T-lymphocyte (HTL) epitopes, followed by IFN-γ and IL-4 induction, antigenicity and population coverage analysis. As well, several linear antigenic B-cell epitopes were found, with good water solubility and without allergenicity. Totally, these proteins showed appropriate antigenicity, abundant PTMs as well as many CTL, HTL and B-cell epitopes, which could be directed for future vaccination studies in the context of multi-epitope vaccine design.

The role of IL-12 in stimulating NK cells against Toxoplasma gondii infection: a mini-review

Toxoplasma gondii is an intracellular protozoan parasite that can remarkably infect, survive, and replicate in almost all mammalian cells and can cause severe neurological and ocular damage in immunocompromised individuals. It is known that Natural Killer cells (NK cells), as a type of cytotoxic lymphocyte, have critical protective roles in innate immunity during the T. gondii infection through releasing interferon gamma (IFN-γ). Interleukin 12 (IL-12) is a pivotal critical cytokine for the generation of IFN-γ-producing NK cells. Several studies have shown cytokines' impact on NK cell activation; and IL-2 has an important role with a potent stimulatory factor for NK cells. In this review, we summarized the mechanism of interleukin-12 production stimulation by T. gondii tachyzoites and discussed several factors affecting this mechanism.

PCR-based detection of Toxoplasma gondii from cattle in southern Iran

OBJECTIVE

Toxoplasma gondii is a protozoan parasite that is widely prevalent in most warm-blooded vertebrates. Humans mainly become infected by eating raw or undercooked meat. This study was designed to investigate the infection of cattle with T. gondii in Jahrom, southern Iran.

METHODS

Tissue samples consisting of heart, diaphragm, and tongue were collected from 125 slaughtered cattle. DNA samples were extracted from the homogenized tissues. T. gondii was detected and genotyped using nested-polymerase chain reaction (Nested-PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) based on GRA6 and SAG2 (3', 5' terminal regions) genes, respectively.

RESULTS

The prevalence of T. gondii DNA was 56% in cattle. The most infected tissue was the diaphragm (54.4%) followed by the heart (48.8%) and tongue (43.2%). Type II was the most prevalent genotype (70%) among T. gondii isolates.

CONCLUSION

In this study, the high prevalence of T. gondii infection in cattle meat indicates the important role of cattle in the transmission of infection to humans. Therefore, incorporating the correct method of consuming meat in health education programs is crucial to prevent human infection.

Multi-epitope vaccine expressed in Leishmania tarentolae confers protective immunity to Toxoplasma gondii in BALB/c mice

Current study deals with a novel multi-epitope vaccine designed in silico and its confirmation experiments for potential efficacy in BALB/c mice. Major histocompatibility complex (MHC)-binding and B-cell binding epitopes of five Toxoplasma antigens (SAG1, ROP16, GRA12, MIC4 and M2AP) were predicted. Selected epitopes were fused together using SAPGTP linker, and antigenicity, allergenicity, physico-chemical features, secondary and tertiary structures and validations were all performed via bioinformatics servers. Then, vaccine construct was cloned into pLEXSY-neo 2.1 vector. After Leishmania tarentolae transfection, live recombinant and wild parasites were subcutaneously injected into 6-8 week female BALB/c mice and immune responses were measured. Results showed that the peptide possessed 282 amino acid residues with average molecular weight of 28.06 kDa. About 90% of the peptide residues were incorporated in favored and allowed regions of the Ramachandran plot. Vaccinated mice showed remarkably elevated levels of specific antibodies (P < 0.05) with predominance of IgG2a production. Also, a Th₁ immune response with production of IFN-γ and relatively increased survival rate against intraperitoneal challenge with RH strain was demonstrated in immunized mice than control groups (P < 0.05). Also, very low levels of IL-4 were demonstrated, which showed statistically significant association with controls (P < 0.05). The findings clarified that multi-epitope vaccine expressed in Leishmania tarentolae induced significant immune responses against acute toxoplasmosis.

Development of a chimeric vaccine candidate based on Toxoplasma gondii major surface antigen 1 and apicoplast proteins using comprehensive immunoinformatics approaches

This study was aimed at designing and evaluation of a multimeric vaccine construct against Toxoplasma gondii via utilization of SAG1 along with apicoplast ribosomal proteins (S2, S5 and L11). Top-ranked MHC-I and MHC-II binding as well as shared, immunodominant linear B-cell epitopes were predicted and joined together via appropriate linkers. Also, TLR-4 agonist (RS-09 synthetic protein) and His-tag were added to the N- and C-terminal of the vaccine sequence. The finally-engineered chimeric vaccine had a length of 291 amino acids with a molecular weight of 31.46 kDa. Physico-chemical features showed a soluble, highly-antigenic and non-allergenic candidate. Secondary and tertiary structures were predicted, and subsequent analyses confirmed the construct stability that was capable to properly interact with human TLR-4. Immunoinformatics-based simulation displayed potent stimulation of T- and B-cell mediated immune responses upon vaccination with the proposed multi-epitope candidate. In conclusion, obtained information demonstrated a highly antigenic vaccine candidate, which could develop high levels of IFN-γ and other components of cellular immune profile, and can be directed for toxoplasmosis prophylactic purposes.