Toxoplasma gondii protease inhibitor-1 (TgPI-1) is a novel vaccine candidate against toxoplasmosis

Study on Circulating Antigens in Serum of Mice With Experimental Acute Toxoplasmosis

Toxoplasma gondii is a ubiquitous apicomplexan protozoan parasite that can infect all warm-blooded animals, causing toxoplasmosis. Thus, efficient diagnosis methods for acute T. gondii infection are essential for its management. Circulating antigens (CAgs) are reliable diagnostic indicators of acute infection. In this study, we established a mouse model of acute T. gondii infection and explored new potential diagnostic factors. CAgs levels peaked 60 h after T. gondii inoculation and 31 CAgs were identified by immunoprecipitation-liquid chromatography-tandem mass spectrometry, among which RuvB-like helicase (TgRuvBL1), ribonuclease (TgRNaseH1), and ribosomal protein RPS2 (TgRPS2) were selected for prokaryotic expression. Polyclonal antibodies against these three proteins were prepared. Results from indirect enzyme-linked immunosorbent assay indicated that anti-rTgRuvBL1, anti-rTgRNase H1, and anti-rTgRPS2 mouse sera were recognized by natural excretory-secretory antigens from T. gondii tachyzoites. Moreover, immunofluorescence assays revealed that TgRuvBL1 was localized in the nucleus, while TgRNase H1 and TgRPS2 were in the apical end. Western blotting data confirmed the presence of the three proteins in the sera of the infected mice. Moreover, mice immunized with rTgRuvBL1 (10.0 ± 0.30 days), TgRNaseH1 (9.67 ± 0.14 days), or rTgRPS2 (11.5 ± 0.34 days) had slightly longer lifespan when challenged with a virulent T. gondii RH strain. Altogether, these findings indicate that these three proteins can potentially be diagnostic candidates for acute toxoplasmosis. However, they hold poor protective potential against highly virulent T. gondii infection.

Protective immunity induced by CpG ODN-adjuvanted virus-like particles containing Toxoplasma gondii proteins

AIMS

To date, a Toxoplasma gondii vaccine for clinical use remains unavailable, though multiple vaccine candidates have been suggested. In our previous studies, unadjuvanted virus-like particles (VLPs) vaccines expressing multiple T. gondii antigens were confirmed to be protective against T. gondii challenge infection. Yet, the protective efficacy of adjuvanted T. gondii VLP in comparison with the unadjuvanted counterpart requires elucidation.

METHODS AND RESULTS

In the present study, mice were immunized with the multi-antigenic VLP vaccines (TG146 VLP) with or without CpG adjuvants and their protective efficacies were compared. CpG-adjuvanted TG146 VLP vaccine elicited enhanced T gondii-specific IgG and IgA antibody responses in the sera, mucosal tissue and the brain compared to unadjuvanted VLPs vaccine. Inclusion of CpG adjuvant in vaccines also induced greater CD4⁺ and CD8⁺ T-cell responses, as well as B cell and germinal centre B cell responses from splenocytes and mesenteric lymph nodes. Pro-inflammatory cytokine response and cyst counts in the brain were drastically diminished in mice immunized with CpG-adjuvanted VLP vaccines.

CONCLUSION

Our results demonstrated that CpG-adjuvanted T. gondii VLPs can significantly enhance the protective efficacy of vaccines against T. gondii infection.

Evaluation of CpG-ODN-Adjuvanted Toxoplasma Gondii Virus-Like Particle Vaccine upon One, Two, and Three Immunizations

Successful vaccines against specific pathogens often require multiple immunizations and adjuvant usage. Yet, assessing the protective efficacy of different immunization regimens with adjuvanted Toxoplasma gondii vaccines remains elusive. In this study, we investigated the vaccine efficacy induced by CpG-ODN-adjuvanted T. gondii virus-like particles (VLPs) after challenge infection with T. gondii (ME49) in mice (BALB/c) upon one, two, and three immunizations. Immunization with adjuvanted T. gondii VLPs induced higher levels of T. gondii-specific IgG and/or IgA antibody responses, germinal center (GC) B cells, total B cells, and CD4⁺ and CD8⁺ T cells compared with unadjuvanted VLPs. Increasing the number of immunizations was strongly correlated with enhanced protective immunity against T. gondii in mice, with the highest protection being demonstrated in mice thrice-immunized with either adjuvanted T. gondii VLPs or VLPs alone. Notably, lesser bodyweight reductions and cerebral cyst counts were observed in mice receiving multiple immunizations with the adjuvanted VLPs, thereby confirming the effectiveness of adjuvanted boost immunizations. These results demonstrated that multiple immunizations with T. gondii VLPs is an effective approach, and the CpG-ODN can be developed as an effective adjuvant for T. gondii VLP vaccines.

Cloning and expression of Toxoplasma gondii GRA-4 recombinant protein as a toxoplasmosis diagnostic kit candidate

Aim:

The objective of this study was to produce recombinant protein GRA-4 (rGRA-4) of a local Toxoplasma gondii isolate as a candidate for a toxoplasmosis diagnosis kit in Escherichia coli BL21 (DE3) competent cells using pET SUMO plasmid.

Materials and Methods:

Samples used were stock T. gondii tachyzoites DNA from the Parasitology Laboratory, Faculty of Veterinary Medicine, Gadjah Mada University, Yogyakarta. Amplified GRA-4 polymerase chain reaction product of T. gondii tachyzoite DNA was cloned in the pET-SUMO TA^R cloning vector. The GRA-4 gene from T. gondii local isolate was sequenced, followed by plasmid transformation, recombinant plasmid DNA isolation, and recombinant protein expression in DE3 competent cells.

Results:

The amplification product of GRA-4T. gondii gene was 1036 bp, with 48 kDa molecular weight after expression in DE3 competent cells. An alignment of the amino acid sequence of GRA-4 from the local isolate which was cloned with GRA-4 was obtained from NCBI database and showed 99.61% homology to the predicted GRA-4 from the T. gondii Izatnagar isolate. Amino acid sequence of the predicted GRA-4 protein from local isolate was different at positions 19 and 304.

Conclusion:

This research cloned rGRA-4 in pET SUMO plasmid.

Plant Hsp90 is a novel adjuvant that elicits a strong humoral and cellular immune response against B- and T-cell epitopes of a Toxoplasma gondii SAG1 peptide

BACKGROUND

The 90-kDa heat-shock protein (Hsp90) from Nicotiana benthamiana (NbHsp90.3) is a promising adjuvant, especially for those vaccines that require a T cell-mediated immune response. Toxoplasma gondii SAG1 is considered one of the most important antigens for the development of effective subunit vaccines. Some epitopes located in the SAG1 C-terminus region have showed a strong humoral and cellular immune response. In the present study, we aimed to assess the efficacy of NbHsp90.3 as carrier/adjuvant of SAG1-derived peptide (SAG1HC) in a T. gondii infection murine model.

METHODS

In the present study, C57BL/6 mice were intraperitoneal immunized with the NbHsp90.3-SAG1HC fusion protein (NbHsp90.3-SAG1HC group), mature SAG1 (SAG1m group), NbHsp90.3 (NbHsp90.3 group) or PBS buffer 1× (PBS group). The levels of IgG antibodies and the cytokine profile were determined by ELISA. Two weeks after the last immunization, all mice were orally challenged with 20 cysts of T. gondii Me49 strain and the number of brain cysts was determined. In addition, both humoral and cellular immune responses were also evaluated during the acute and chronic phase of T. gondii infection by ELISA.

RESULTS

The characterization of the immune response generated after vaccination with NbHsp90.3 as an adjuvant showed that NbHsp90.3-SAG1HC-immunized mice produced antibodies that were able to recognize not only rSAG1m but also the native SAG1 present in the total lysate antigen extract (SAG1TLA) from T. gondii tachyzoites, while control groups did not. Furthermore, anti-rSAG1m IgG2a/2b antibodies were significantly induced. In addition, only the spleen cell cultures from NbHsp90.3-SAG1HC-immunized mice showed a significantly increased production of IFN-γ. During the chronic phase of T. gondii infection, the antibodies generated by the infection were unable to detect the recombinant protein, but they did react with TLA extract. In addition, splenocytes from all groups showed a high production of IFN-γ when stimulated with rGRA4, but only those from NbHsp90.3-SAG1HC group stimulated with rSAG1m showed high production of IFN-γ. Finally, NbHsp90.3-SAG1HC-immunized mice exhibited a significant reduction in the cyst load (56%) against T. gondii infection.

CONCLUSIONS

We demonstrated that NbHsp90.3 enhances the humoral and cell-mediated immune response through a Th1 type cytokine production. Mice vaccinated with NbHsp90.3-SAG1HC exhibited a partial protection against T. gondii infection and it was correlated with the induction of memory immune response. We developed and validated a vaccine formulation which, to our knowledge, for the first time includes the NbHsp90.3 protein covalently fused to a peptide from T. gondii SAG1 protein that contains T- and B-cell epitopes.

Schistosoma mansoni SmKI-1 or Its C-Terminal Fragment Induces Partial Protection Against S. mansoni Infection in Mice

Current schistosomiasis control strategies are mainly based on chemotherapy, but the development of a vaccine against this parasitic disease would contribute to a long-lasting decrease in disease spectrum and transmission. When it comes to vaccine candidates, several genes encoding Schistosoma mansoni proteins expressed at the mammalian host-parasite interface have been tested. Among the most promising molecules are the proteins present on the tegument and digestive tract of the parasite. In this study, we evaluate the potential of SmKI-1, the first Kunitz-type protease inhibitor functionally characterized in S. mansoni, as a vaccine candidate. Bioinformatic analysis points to the C-terminal fragment as the main region of the molecule responsible for the development of a potential protective immune response induced by SmKI-1. Therefore, for the vaccine formulations, we produced the recombinant (r) SmKI-1 and two different fragments, its Kunitz (KI) domain and its C-terminal tail. First, we demonstrate that mice immunized with recombinant SmKI-1 (rSmKI-1) or its fragments, formulated with Freund's adjuvant, induced the production of IgG-specific antibodies. Further, all vaccine formulations tested here also induced a Th1-type of immune response, as suggested by the production of IFN-γ and TNF-α by protein-stimulated cultured splenocytes. However, the protective effect conferred by vaccination was only observed in groups which received rSmKI-1 or C-terminal domain vaccines. Mice administered with rSmKI-1 demonstrated reduction of 47% in worm burden, 36% in egg number in mouse livers, and 33% in area of liver granulomas. Additionally, mice injected with C-terminal domain showed reduction of 28% in worm burden, 38% in egg number in liver, and 25% in area of liver granulomas. In contrast, KI domain immunization was unable to reduce worm burden and ameliorate liver pathology after challenge infection. Taken together, our data demonstrated that SmKI-1 is a potential candidate for use in a vaccine to control schistosomiasis, and its C-terminal tail seems to be the main region of the molecule responsible for protection conferred by this antigen.

Toxoplasma gondii serine-protease inhibitor-1: A new adjuvant candidate for asthma therapy

Serine-proteases are important players in the pathogenesis of asthma, promoting inflammation and tissue remodeling. It’s also known that many serine protease inhibitors display immunomodulatory properties. TgPI-1 is a Toxoplasma gondii protein that exhibits broad spectrum inhibitory activity against serine proteases. In view of the increased prevalence of atopic disorders and the need to develop new treatment strategies we sought to investigate the potential of TgPI-1 for treating respiratory allergies. For this purpose, we developed a therapeutic experimental model. BALB/c mice were rendered allergic by intraperitoneal ovalbumin-alum sensitization and airway-challenged. Once the asthmatic phenotype was achieved, mice were intranasally treated with rTgPI-1 alone or with a mixture of rTgPI-1 and ovalbumin (OVA). A week later mice were given a secondary aerosol challenge. Treatment with rTgPI-1 alone or co-administered with OVA diminished bronchoalveolar eosinophilia, mucus production and peribronchial lung infiltration. This effect was accompanied by a lung resistance reduction of 26.3% and 50.3% respectively. Both treatments resulted in the production of lower levels of IL-4, IL-5, IFN-γ and regulatory IL-10 by thoracic lymph node cells stimulated with OVA. Interestingly, significant decreases in OVA specific IgE and T cell proliferation, and increases in FoxP3⁺ T cells at local and systemic levels were only detected when the inhibitor was administered along with OVA. These results show that both rTgPI-1 treatments reduced asthma hallmarks. However, co-administration of the inhibitor with the allergen was more effective. Hence, rTgPI-1 emerges as a novel adjuvant candidate for asthma treatment.

Vaccination with Toxoplasma gondii calcium-dependent protein kinase 6 and rhoptry protein 18 encapsulated in poly(lactide-co-glycolide) microspheres induces long-term protective immunity in mice

Background

Toxoplasmosis is a worldwide zoonosis caused by the intracellular parasite Toxoplasma gondii. However, no effective vaccine is yet available. Poly(lactide-co-glycolide) polymers can reduce protein degradation and sustain the release of antigens over a long period, which could generate a long-lasting immune response in vivo. Using a mouse model of toxoplasmosis, we evaluated the protective efficacy of vaccination with two recombinant proteins, which are formulated in biodegradable polymers.

Methods

Two recombinant proteins, rCDPK6 and rROP18, were encapsulated in poly(d,l-lactide-co-glycolide) (PLG), and then injected subcutaneously into Kunming mice. The mice immune responses were evaluated in terms of lympho-proliferation, cytokine expression, and antibodies. The survival of infected mice and brain cyst formation were also evaluated at 6 weeks after challenge with T. gondii RH strain (genotype I) or PRU strain (genotype II).

Results

Both protein vaccines induced Th1-biased immune responses, with increased specific antibodies and T cells, high levels of interferon-γ and interleukin 2, and strong lymphocyte proliferative responses. The mice immunized with the various protein vaccines survived slightly longer time than the control groups (P > 0.05) after injection with T. gondii RH strain. There were fewer brain cysts in the mice in all the immunized groups than that in the control groups, and the brain cysts were significantly reduced in mice immunized with proteins + 206, rCDPK6 + PLG and rCDPK6 + rROP18 + PLG (P < 0.05) compared controls. Further comparison of the immune responses to the proteins adjuvanted with PLG or Montanide™ ISA 206 VG 6 weeks after the last immunization revealed that antigens encapsulated in PLG conferred greater protective immunity against challenge.

Conclusions

These findings suggest that the two recombinant T. gondii proteins encapsulated in PLG conferred immunity to T. gondii for an extended period, providing the foundation for the further development of a commercial vaccine against toxoplasmosis.

Homologous prime-boost strategy with TgPI-1 improves the immune response and protects highly susceptible mice against chronic Toxoplasma gondii infection

Subunit-based vaccines are safer than live or attenuated pathogen vaccines, although they are generally weak immunogens. Thus, proper combination of immunization strategies and adjuvants are needed to increase their efficacy. We have previously protected C3H/HeN mice from Toxoplasma gondii infection by immunization with the serine protease inhibitor-1 (TgPI-1) in combination with alum. In this work, we explore an original vaccination protocol that combines administration of recombinant TgPI-1 by intradermal and intranasal routes in order to enhance protection in the highly susceptible C57BL/6 strain. Mice primed intradermally with rTgPI-1 plus alum and boosted intranasally with rTgPI-1 plus CpG-ODN elicited a strong specific Th1/Th2 humoral response, along with a mucosal immune response characterized by specific-IgA in intestinal lavages. A positive cellular response of mesentheric lymph node cells and Th1/Th2 cytokine secretion in the ileon were also detected. When immunized mice were challenged with the cystogenic Me49 T. gondii strain, they displayed up to 62% reduction in brain parasite burden. Moreover, adoptive transfer of mesenteric lymph node cells from vaccinated to naïve mice induced significant protection against infection. These results demonstrate that this strategy that combines the administration of TgPI-1 by two different routes, intradermal priming and intranasal boost, improves protective immunity against T. gondii chronic infection in highly susceptible mice.

Comparing the effect of IL-12 genetic adjuvant and alum non-genetic adjuvant on the efficiency of the cocktail DNA vaccine containing plasmids encoding SAG-1 and ROP-2 of Toxoplasma gondii

Various methods are available for enhancing the potency of DNA vaccines, including employment of different forms of adjuvant. The current study was carried out to evaluate and compare the effects of genetic and non-genetic adjuvants on the immune response stimulated by DNA vaccine. Thus, two adjuvants, IL-12 (genetic adjuvant) and aluminum hydroxide (alum, non-genetic adjuvant), were used with cocktail DNA vaccine containing plasmids encoding complete rhoptry antigen 2 (ROP-2) and surface major antigen 1 (SAG-1) of Toxoplasma gondii. The efficacy of pcROP2+pcSAG1 in stimulation of the immune response against toxoplasmosis with and without adjuvant was evaluated in female BALB/c mice by measuring the level of total IgG antibody and cytokines. The results obtained indicated that after challenging the mice with the fatal RH strain of T. gondii, the survival rates of mice immunized with pcROP2+pcSAG1 (DNA cocktail), pcSAG1+pcROP2+alum, and pcSAG1+pcROP2+IL-12 were significantly greater than that of the control groups (p<0.05). Moreover, measurement of total IgG antibody indicated the significant difference between the control and experimental groups (p<0.05). Finally, the results obtained by measurement of cytokines (IFN-γ and IL-4) showed high levels of IFN-γ and low levels of IL-4 in groups vaccinated with pcROP2+pcSAG1 (DNA cocktail), pcSAG1+pcROP2+alum, and pcSAG1+pcROP2+IL-12 as the experiment groups, in comparison with the controls groups (PBS, pc-DNA3, alum+PBS, and pCAGGS-IL-12+pcDNA3). The results of the study showed that use of adjuvants (IL-12 and alum) coincident with DNA cocktail leads to significant change in the survival rates of the experiment groups in comparison with control groups. Also, there is no significant difference between adjuvants to induce immune responses.

Immunological responses induced by a DNA vaccine expressing RON4 and by immunogenic recombinant protein RON4 failed to protect mice against chronic toxoplasmosis

The development of an effective vaccine against Toxoplasma gondii infection is an important issue due to the seriousness of the related public health problems, and the economic importance of this parasitic disease worldwide. Rhoptry neck proteins (RONs) are components of the moving junction macromolecular complex formed during invasion. The aim of this study was to evaluate the vaccine potential of RON4 using two vaccination strategies: DNA vaccination by the intramuscular route, and recombinant protein vaccination by the nasal route. We produced recombinant RON4 protein (RON4S2) using the Schneider insect cells expression system, and validated its antigenicity and immunogenicity. We also constructed optimized plasmids encoding full length RON4 (pRON4), or only the N-terminal (pNRON4), or the C-terminal part (pCRON4) of RON4. CBA/J mice immunized with pRON4, pNRON4 or pCRON4 plus a plasmid encoding the granulocyte-macrophage-colony-stimulating factor showed high IgG titers against rRON4S2. Mice immunized by the nasal route with rRON4S2 plus cholera toxin exhibited low levels of anti-RON4S2 IgG antibodies, and no intestinal IgA antibodies specific to RON4 were detected. Both DNA and protein vaccination generated a mixed Th1/Th2 response polarized towards the IgG1 antibody isotype. Both DNA and protein vaccination primed CD4+ T cells in vivo. In addition to the production of IFN-γ, and IL-2, Il-10 and IL-5 were also produced by the spleen cells of the immunized mice stimulated with RON4S2, suggesting that a mixed Th1/Th2 type immune response occurred in all the immunized groups. No cytokine was detectable in stimulated mesenteric lymph nodes from mice immunized by the nasal route. Immune responses were induced by both DNA and protein vaccination, but failed to protect the mice against a subsequent oral challenge with T. gondii cysts. In conclusion, strategies designed to enhance the immunogenicity and to redirect the cellular response towards a Th1 type response against RON4 could lead to more encouraging results.

Combination of CpG-oligodeoxynucleotides with recombinant ROP2 or GRA4 proteins induces protective immunity against Toxoplasma gondii infection

Synthetic oligodeoxynucleotides containing unmethylated CpG motifs (CpG-ODN) have been characterized as Th1-promoting immunopotentiators, an adjuvant activity desirable for vaccination against intracellular parasites like Toxoplasma gondii. In an attempt to find new antigen-adjuvant combinations that enhance the immunogenicity of antigen candidates for toxoplasma vaccines, we analyzed the extent of protection in mice immunized with ROP2 and GRA4 recombinant proteins when co-administered with CpG-ODN. Both GRA4+CpG-ODN and ROP2+CpG-ODN formulations were shown to induce a strong humoral Th1-biased response characterized by a high IgG(2a) to IgG(1) antibody ratio. Both vaccination regimens led to increased secretion of IFN-γ and IL-10, and negligible amounts of IL-4, upon specific re-stimulation of spleen cells from these groups of mice. After a non-lethal challenge with tissue cysts of a moderately virulent strain, only the brains from mice vaccinated with ROP2 or GRA4 in combination with CpG-ODN showed a significant reduction (63% and 62%, respectively) in their parasite load compared to the controls. The rate of protection obtained with GRA4+ROP2+CpG-ODN resulted equivalent (66%) to those achieved with the single antigens plus CpG-ODN. Taken together, these results indicate that CpG-ODN is an important candidate adjuvant for use in potential multicomponent anti-T. gondii vaccines for animals and humans.

The Differential Effect of Toxoplasma Gondii Infection on the Stability of BCL2-Family Members Involves Multiple Activities

The regulation of mitochondrial permeability, a key event in the initiation of apoptosis is governed by the opposing actions of the pro- and anti-apoptotic members of the BCL2-family of proteins. The BCL2-family can be classified further based on the number of BCL-homology (BH) domains they encode. Pathogen mediated modulation of BCL2-family members play a significant role in their ability to affect the apoptotic pathways in the infected host cell. The protozoan parasite Toxoplasma gondii establishes a profound blockade of apoptosis noted by a requirement for host NFκB activity and correlating with the selective degradation of pro-apoptotic BCL2-family members. In this study, we explore the potential activities associated with the inherent stability of the anti-apoptotic BCL2 as well as the selective degradation of the pro-apoptotic proteins BAX, BAD, and BID. We find that multiple activities govern the relative stability of BCL2-family members suggesting a complex and balanced network of stability-enhancing and–destabilizing activities are perturbed by parasite infection. The data leave open the possibility for both parasite induced host activities as well as the direct consequence of parasite effectors in governing the relative levels of BCL2-proteins in the course of infection.

Vaccines against Toxoplasma gondii: challenges and opportunities

Development of vaccines against Toxoplasma gondii infection in humans is of high priority, given the high burden of disease in some areas of the world like South America, and the lack of effective drugs with few adverse effects. Rodent models have been used in research on vaccines against T. gondii over the past decades. However, regardless of the vaccine construct, the vaccines have not been able to induce protective immunity when the organism is challenged with T. gondii, either directly or via a vector. Only a few live, attenuated T. gondii strains used for immunization have been able to confer protective immunity, which is measured by a lack of tissue cysts after challenge. Furthermore, challenge with low virulence strains, especially strains with genotype II, will probably be insufficient to provide protection against the more virulent T. gondii strains, such as those with genotypes I or II, or those genotypes from South America not belonging to genotype I, II or III. Future studies should use animal models besides rodents, and challenges should be performed with at least one genotype II T. gondii and one of the more virulent genotypes. Endpoints like maternal-foetal transmission and prevention of eye disease are important in addition to the traditional endpoint of survival or reduction in numbers of brain cysts after challenge.

Protection against intestinal amebiasis by a recombinant vaccine is transferable by T cells and mediated by gamma interferon

We have previously shown that vaccination with purified Entamoeba histolytica Gal/GalNAc lectin or recombinant subunits can protect mice from intestinal amebiasis upon intracecal challenge. In this study, we demonstrated with adoptive-transfer experiments that this lectin vaccine protection is mediated by T cells but not serum. The cell-mediated immune (CMI) response was characterized by significant gamma interferon (IFN-gamma), interleukin 12 (IL-12), IL-2, IL-10, and IL-17 production. To move toward a human vaccine, we switched to a recombinant protein and tested a range of adjuvants and routes appropriate for humans. We found that subcutaneous delivery of LecA with IDRI's adjuvant system EM014 elicited a potent Th1-type CMI profile and provided significant protection, as measured by culture negativity (79% efficacy); intranasal immunization with cholera toxin provided 56% efficacy; and alum induced a Th2-type response that protected 62 to 68% of mice. Several antibody and CMI cytokine responses were examined for correlates of protection, and prechallenge IFN-gamma(+) or IFN-gamma-, IL-2-, and tumor necrosis factor alpha-triple-positive CD4 cells in blood were statistically associated with protection. To test the role of IFN-gamma in LecA-mediated protection, we neutralized IFN-gamma in LecA-immunized mice and found that it abrogated the protection conferred by vaccination. These data demonstrate that CMI is sufficient for vaccine protection from intestinal amebiasis and reveal an important role for IFN-gamma, even in the setting of alum.

Vaccination concepts against Toxoplasma gondii

Toxoplasma gondii is a parasite that infects animals and humans worldwide. Despite the current knowledge of immunology, pathology and genetics related to the parasite, a safe vaccine for prevention of the infection in both humans and animals does not exist. Here, we review some aspects concerning vaccination against T. gondii.

Toxoplasma gondii: proteomic analysis of antigenicity of soluble tachyzoite antigen

The obligate intracellular parasite Toxoplasma gondii is an important pathogen of humans and animals. The tachyzoite of T. gondii is the main life-cycle stage that is responsible for toxoplasmosis. Study of the antigenicity of soluble tachyzoite antigen (STAg) is important for discovery of protective antigens which will aid in the detection and prevention of toxoplasmosis. At present, no complete proteome map of T. gondii STAg is established, although a large-scale whole proteomic analysis of tachyzoites is underway. In this study, 1227 protein spots of T. gondii soluble tachyzoite antigen (STAg) were fractionated by 2-dimensional electrophoresis (2-DE) at pH range 3-10. By mass spectrometry (MS) analysis, among the separated 1227 protein spots, 426 were identified by searching the Swissport and NCBI nr databases. Two hundred and thirty of these identified spots (230/426, 54%) were demonstrated to be T. gondii protein by MS. Of the 21 Toxoplasma protein spots identified by Western blot with rabbit anti-T. gondii serum, 16 had immunoregulatory functions and five had immune defense functions. Due to multiple spots for a single protein, these 16 spots represented 11 proteins: a putative protein disulfide isomerase (PDI), heat shock protein 60 (Hsp60), a pyruvate kinase (PK), a putative glutamate dehydrogenase (GDH), a coronin, a heat shock protein 70 (Hsp70), a protein kinase C receptor 1 (RACK1), a malate dehydrogenase (MDH), a major surface antigen 1 (SAG1), an uridine phosphorylase (UPase) and a peroxiredoxin (Prx). Among the identified 11 proteins, except that the antigenicity and immunogenicity of the SAG1 has been reported and antigenicity of Hsp70 has been disputed, the remaining antigenic proteins were first identified in this study. In conclusion, we obtained nine novel types of immunogenic proteins that might be potential candidates of vaccine development for toxoplasmosis, which we will confirm in later studies.