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

Global prevalence of Toxoplasma gondii in birds: A systematic review and meta-analysis

Among the potential animal reservoirs of the zoonotic parasite T. gondii, birds have received relatively little attention. This systematic review and meta-analysis aimed to assess the global status and to provide an overview of the epidemiology of T. gondii infection in birds. The standard protocol of preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines were followed. Scopus, PubMed, Web of Science, Science Direct, ProQuest, and Google Scholar were searched for relevant publications from January 1990, to March 2024. All peer-reviewed original research articles describing the prevalence of T. gondii in birds were included. Inclusion and exclusion criteria were applied, and both direct and indirect detection were considered. The point estimates and 95% confidence intervals were calculated using the meta-package in R (version 3.6.1). The variance between studies (heterogeneity) was quantified by the I2 index. Finally, 258 articles (including 380 datasets) were eligible for inclusion in the systematic review and meta-analysis. The global pooled prevalence was 24% (21 - 26%). The highest prevalence of T. gondii was observed in buzzards (52%, 34 - 70%), turkeys (31%, 17 - 46%), and chickens (30%, 26 - 34%). The present study provides a comprehensive view of the global prevalence of T. gondii in birds.

Toxoplasma gondii seroprevalence in the Iranian blood donors: A systematic review and meta-analysis

Background

The present systematic review and meta-analysis was done to assess the rate of Toxoplasma gondii (T. gondii) exposure among Iranian healthy blood donors.

Methods

We searched four English (PubMed, Scopus, Web of Science, and Science Direct) and two Persian databases (Magiran and SID) as well as Google Scholar as a specialized article search engine using specific keywords for relevant papers from the inception up to November 30, 2023.

Results

In total, 19 studies enrolling 8226 apparently healthy blood donors were examined regarding T. gondii-specific IgG and/or IgM antibodies, among which 2666 [32.9% (95% CI: 25.3%-41.6%)], 168 [1.4% (95% CI: 0.9%-2.1%)], and 83 [1.7% (95% CI: 1.3%-2.1%)] subjects were seropositive regarding IgG, IgM, and both IgG/IgM antibodies, respectively. Five risk factors were significantly associated with T. gondii seroprevalence, including gender (OR = 1.98; 95% CI: 1.52-2.58; P < 0.001), contact with cat (OR = 2.41; 95% CI: 1.70-3.41; P < 0.001), contact with soil (OR = 2.83; 95% CI: 1.07-7.45; P = 0.035), consuming raw/undercooked meat (OR = 1.95; 95% CI: 1.03-3.70; P = 0.039), and raw/unwashed vegetables (OR = 1.70; 95% CI: 1.25-2.31; P = 0.001).

Conclusion

A moderate rate of T. gondii exposure was found in the Iranian blood donors, with the association of several risk factors, including gender, contact with cat, contact with soil, consumption of unwashed vegetables and/or undercooked meat. Still, more studies are recommended regarding T. gondii exposure among blood donors in Iran.

Protective efficacy induced by Eimeria maxima rhomboid-like protein 1 against homologous infection

Introduction

Avian coccidiosis, caused by apicomplexan protozoa belonging to the Eimeria genus, is considered one of the most important diseases in the intensive poultry industry worldwide. Due to the shortcomings of live anticoccidial vaccines and drugs, the development of novel anticoccidial vaccines is increasingly urgent.

Methods

Eimeria maxima rhomboid-like protein 1 (EmROM1), an invasion-related molecule, was selected as a candidate antigen to evaluate its protective efficacy against E. maxima in chickens. Firstly, the prokaryotic recombinant plasmid pET-32a-EmROM1 was constructed to prepare EmROM1 recombinant protein (rEmROM1), which was used as a subunit vaccine. The eukaryotic recombinant plasmid pVAX1.0-EmROM1 (pEmROM1) was constructed as a DNA vaccine. Subsequently, 2-week-old chicks were separately vaccinated with the rEmROM1 and pEmROM1 twice every 7 days. One week post the booster vaccination, induced cellular immune responses were determined by evaluating the mRNA level of cytokines including IL-2, IFN-γ, IL-4, IL-10, TGF-β, IL-17, and TNFSF15, as well as the percentages of CD4⁺ and CD8⁺ T cells from spleens of vaccinated chickens. Specific serum antibody level in the vaccinated chickens was determined to assess induced humoral immune responses. Finally, the protective efficacy of EmROM1 was evaluated by a vaccination-challenge trial.

Results

EmROM1 vaccination significantly upregulated the cytokine transcription levels and CD4⁺/CD8⁺ T cell percentages in vaccinated chickens compared with control groups, and also significantly increased the levels of serum-specific antibodies in vaccinated chickens. The animal trial showed that EmROM1 vaccination significantly reduced oocyst shedding, enteric lesions, and weight loss of infected birds compared with the controls. The anticoccidial index (ACI) from the rEmROM-vaccination group and pEmROM1-vaccination group were 174.11 and 163.37, respectively, showing moderate protection against E. maxima infection.

Discussion

EmROM1 is an effective candidate antigen for developing DNA or subunit vaccines against avian coccidiosis.

Nano vaccines for T. gondii Ribosomal P2 Protein With Nanomaterials as a Promising DNA Vaccine Against Toxoplasmosis

Caused by Toxoplasma gondii, toxoplasmosis has aroused great threats to public health around the world. So far, no effective vaccine or drug is commercially available, and the demands for a safe and effective therapeutic strategy have become more and more urgent. In the current study, we constructed a DNA vaccine encoding T. gondii ribosomal P2 protein (TgP2) and denoted as TgP2-pVAX1 plasmid. To improve the immunoprotection, nanomaterial poly-lactic-co-glycolic acid (PLGA) and chitosan were used as the delivery vehicle to construct TgP2-pVAX1/PLGA and TgP2-pVAX1/CS nanospheres. Before vaccinations in BALB/c mice, TgP2-pVAX1 plasmids were transiently transfected into Human Embryonic Kidney (HEK) 293-T cells, and the expression of the eukaryotic plasmids was detected by laser confocal microscopy and Western blotting. Then the immunoprotection of naked DNA plasmids and their two nano-encapsulations were evaluated in the laboratory animal model. According to the investigations of antibody, cytokine, dendritic cell (DC) maturation, molecule expression, splenocyte proliferation, and T lymphocyte proportion, TgP2-pVAX1 plasmid delivered by two types of nanospheres could elicit a mixed Th1/Th2 immune response and Th1 immunity as the dominant. In addition, TgP2-pVAX1/PLGA and TgP2-pVAX1/CS nanospheres have great advantages in enhancing immunity against a lethal dose of T. gondii RH strain challenge. All these results suggested that TgP2-pVAX1 plasmids delivered by PLGA or chitosan nanomaterial could be promising vaccines in resisting toxoplasmosis and deserve further investigations and applications.

Discovery of New Microneme Proteins in Cryptosporidium parvum and Implication of the Roles of a Rhomboid Membrane Protein (CpROM1) in Host-Parasite Interaction

Apicomplexan parasites possess several unique secretory organelles, including rhoptries, micronemes, and dense granules, which play critical roles in the invasion of host cells. The molecular content of these organelles and their biological roles have been well-studied in Toxoplasma and Plasmodium, but are underappreciated in Cryptosporidium, which contains many parasites of medical and veterinary importance. Only four proteins have previously been identified or proposed to be located in micronemes, one of which, GP900, was confirmed using immunogold electron microscopy (IEM) to be present in the micronemes of intracellular merozoites. Here, we report on the discovery of four new microneme proteins (MICs) in the sporozoites of the zoonotic species C. parvum, identified using immunofluorescence assay (IFA). These proteins are encoded by cgd3_980, cgd1_3550, cgd1_3680, and cgd2_1590. The presence of the protein encoded by cgd3_980 in sporozoite micronemes was further confirmed using IEM. Cgd3_980 encodes one of the three C. parvum rhomboid peptidases (ROMs) and is, thus, designated CpROM1. IEM also confirmed the presence of CpROM1 in the micronemes of intracellular merozoites, parasitophorous vacuole membranes (PVM), and feeder organelles (FO). CpROM1 was enriched in the pellicles and concentrated at the host cell–parasite interface during the invasion of sporozoites and its subsequent transformation into trophozoites. CpROM1 transcript levels were also higher in oocysts and excysted sporozoites than in the intracellular parasite stages. These observations indicate that CpROM1, an intramembrane peptidase with membrane proteolytic activity, is involved in host–parasite interactions, including invasion and proteostasis of PVM and FO.

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.

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.

Immunoinformatic Analysis of Calcium-Dependent Protein Kinase 7 (CDPK7) Showed Potential Targets for Toxoplasma gondii Vaccine

Apicomplexan parasites, including Toxoplasma gondii (T. gondii), express different types of calcium-dependent protein kinases (CDPKs), which perform a variety of functions, including attacking and exiting the host cells. In the current bioinformatics study, we have used several web servers to predict the basic features and specifications of the CDPK7 protein. The findings showed that CDPK7 protein has 2133 amino acid residues with an average molecular weight (MW) of 219085.79 D. The aliphatic index with 68.78 and grand average of hydropathicity (GRAVY) with -0.331 score were estimated. The outcomes of current research showed that the CDPK7 protein included 502 alpha-helix, 1311 random coils, and 320 extended strands with GOR4 method. Considering the Ramachandran plot, the favored region contains more than 92% of the amino acid residues. In addition, evaluation of antigenicity and allergenicity showed that CDPK7 protein has immunogenic and nonallergenic nature. The present research provides key data for more animal-model study on the CDPK7 protein to design an efficient vaccine against toxoplasmosis in the future.

Rhomboid protein 2 of Eimeria maxima provided partial protection against infection by homologous species

Rhomboid-like proteases (ROMs) are considered as new candidate antigens for developing new-generation vaccines due to their important role involved in the invasion of apicomplexan protozoa. In prior works, we obtained a ROM2 sequence of Eimeria maxima (EmROM2). This study was conducted to evaluate the immunogenicity and protective efficacy of EmROM2 recombinant protein (rEmROM2) and EmROM2 DNA (pVAX1-EmROM2) against infection by Eimeria maxima (E. maxima). Firstly, Western blot assay was conducted to analyze the immunogenicity of rEmROM2. The result showed that rEmROM2 was recognized by chicken anti-E. maxima serum. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assay revealed apparent transcription and expression of EmROM2 at the injection site. qRT-PCR (quantitative real-time PCR), flow cytometry and indirect ELISA indicated that vaccination with rEmROM2 or EmROM2 DNA significantly upregulated the transcription level of cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-17, TGF-β and TNF SF15), the proportion of CD8⁺ and CD4⁺ T lymphocytes and serum IgG antibody response. Ultimately, a vaccination-challenge trial was performed to evaluate the protective efficacy of rEmROM2 and pVAX1-EmROM2 against E. maxima. The result revealed that vaccination with rEmROM2 or pVAX1-EmROM2 significantly alleviated enteric lesions, weight loss, and reduced oocyst output caused by challenge infection of E. maxima, and provided anticoccidial index (ACI) of more than 160, indicating partial protection against E. maxima. In summary, vaccination with rEmROM2 or pVAX1-EmROM2 activated notable humoral and cell-mediated immunity and provided partial protection against E. maxima. These results demonstrated that EmROM2 protein and DNA are promising vaccine candidates against E. maxima infection.

Seroprevalence and associated risk factors of Toxoplasma gondii infection in patients undergoing hemodialysis and healthy group

Objectives

In this study, the seroprevalence of anti-Toxoplasma gondii (T. gondii) specific antibodies in patients undergoing hemodialysis compared to the control group were evaluated. In this case–control study, 200 hemodialysis patients (HDP) and 100 healthy controls were participated. The specific antibodies (IgG/IgM) in both groups were tested using enzyme-linked immunosorbent assay (ELISA) method. A structured questionnaire containing some demographic information was completed for each person in case and control groups.

Results

The overall seroprevalence of T. gondii infection was 49.5% (99/200) and 23.0% (23/100) in the case and control groups, respectively. There was a significant association between seroprevalence of T. gondii infection and contact with cats (P < 0.001), consumption of raw/undercooked meat (P = 0.01), and source of drinking water (P = 0.001) in the hemodialysis patients. Also, in the control subjects, there were a significant association between consumption of raw/undercooked meat (P = 0.04) and source of drinking water (P = 0.001) with T. gondii infection. The findings showed a high seroprevalence of T. gondii infection in HDP compared with healthy controls; thus, we recommend the regular screening programs for T. gondii infection in this susceptible group.

In-depth computational analysis of calcium-dependent protein kinase 3 of Toxoplasma gondii provides promising targets for vaccination

Purpose

The Toxoplasma gondii calcium-dependent protein kinase-3 (CDPK3) is a key enzyme for parasite egress, control of calcium-dependent permeabilization in parasitophorous vacuole membrane and tissue cyst formation. In this study, we comprehensively explored the bioinformatics features of this protein to improve vaccine design against T. gondii.

Materials and Methods

Various web servers were employed for the analysis of physico-chemical properties, post-translational modifications, localization in the subcellular milieu, secondary and tertiary structures, as well as B-cell, major histocompatibility complex (MHC)-binding and cytotoxic T-lymphocyte (CTL) epitopes.

Results

This protein was a 537 amino acid antigenic and non-allergenic molecule with a molecular weight of 60.42 kDa, a grand average of hydropathicity score of −0.508, and aliphatic index of 79.50. There exists 46.74% alpha helix, 12.48% extended strand, and 40.78% random coil in the secondary structure. Ramachandran plot of the refined model demonstrated 99.3%, 0.7%, and 0.0% of residues in the favored, allowed and outlier areas, respectively. Besides, various potential B-cell (continuous and conformational), MHC-binding and CTL epitopes were predicted for Toxoplasma CDPK3 protein.

Conclusion

This article provides a foundation for further investigations, and laid a theoretical basis for the development of an appropriate vaccine against T. gondii infection.

Effect of Imiquimod on Tachyzoites of Toxoplasma gondii and Infected Macrophages in vitro and in BALB/c Mice

Treatment for toxoplasmosis is not completely successful because of their unwanted side effects, and new treatments are needed. Imiquimod has ability to moderate immune response and used to treat a wide variety of infections and tumors. The aim of the present study was to evaluate the effect of imiquimod on the tachyzoites of T. gondii and infected macrophages in vitro and in BALB/c mice. The viability of T. gondii was assessed in the presence of various concentrations of imiquimod by direct counting after 6 and 24 h. The MTT assay was used to identify the viability of uninfected macrophages. The apoptotic effects were determined with flow cytometry on the tachyzoites and infected macrophages. For evaluation of parasite load in pre-treatment or post-treatment of macrophages Quantitative real time PCR (qPCR) was performed. For in vivo experiments, BALB/c mice received imiquimod before and after challenge with parasites. The mortality rate of mice, parasite numbers in spleen, and the INF-γ and IL-4 cytokine levels in spleen lymphocytes were evaluated. Imiquimod demonstrated anti-Toxoplasma effects by reducing the number of tachyzoites. The results of flow cytometry for drug-treated tachyzoites showed that apoptosis did not rise significantly relative to the control group (p < 0.05). Moreover, apoptosis was enhanced in infected macrophages as the concentration of imiquimod was reduced. The parasitic burden in imiquimod pretreated macrophages was significantly lower than those treated after infection (p < 0.01). A marked reduction was observed in survival rate, parasite load and INF-γ level in BALB/c mice that received imiquimod before parasitic challenge relative to those received drug after parasitic challenge (p < 0.01). Overall, imiquimod in the pretreated group had greater anti-Toxoplasma effects than imiquimod in posttreated group in vitro and in vivo. imiquimod may be considered as a candidate for use against Toxoplasmosis both therapeutically and prophylactically.

Toxoplasma gondii: Preventive and therapeutic effects of morphine and evaluation of treatment parameters of tachyzoites and infected macrophages in vitro and in a murine model

Common medicines for the treatment of toxoplasmosis have limited efficacy and unwanted side effects. Opiates can effect both innate and cell-mediated immunity and stimulate the immune responses in different parasitic infections. In this work, preventive and therapeutic effects of morphine were evaluated on the tachyzoites of Toxoplasma gondii and infected macrophages in vitro and in a murine model. Different concentrations of morphine (0.1 and 0.01 μg/ml) were evaluated on mortality rate of T. gondii by direct counting after 3 and 24 hours. The cytotoxic and apoptotic effects of these drugs were measured by the MTT assays and flow cytometry analysis, respectively. The same procedures were assessed in T. gondii-infected macrophages. The parasite loads were determined using quantitative polymerase chain reaction (qPCR). For in vivo assessment, BALB/c mice treated with morphine before or after infection with tachyzoites. The survival rate of animals, parasite load in the spleen, and the IFN-γ and IL-4 cytokines levels were measured. Morphine was effective on tachyzoites of T. gondii and had a reverse relationship with its concentration. The results of flow cytometry showed that the toxic effects of morphine on tachyzoites after 3 hours was not statistically significant (p<0.05). Also, apoptosis in infected MQs rose with a decreasing concentration of morphine. The parasitic load in MQs treated with morphine before infection was lower than that in cells treated after infection and the differences were statistically significant (p<0.01). In mice that received morphine before infection, survival rate, parasite load and the IFN-γ level were significantly lower than in mice treated after infection (p<0.01). The results of this study have shown that morphine in the pre-treatment group had higher anti-Toxoplasma activity than morphine in post-treatment in vitro and in murine model.