200 Gy sterilised Toxoplasma gondii tachyzoites maintain metabolic functions and mammalian cell invasion, eliciting cellular immunity and cytokine response similar to natural infection in mice

A novel enemy of cancer: recent investigations into protozoan anti-tumor properties

Cancer remains a significant global health issue, despite advances in screening and treatment. While existing tumor treatment protocols such as surgery, chemotherapy, radiotherapy, targeted therapy, and immunotherapy have proven effective in enhancing the prognosis for some patients, these treatments do not benefit all patients. Consequently, certain types of cancer continue to exhibit a relatively low 5-year survival rate. Therefore, the pursuit of novel tumor intervention strategies may help improve the current effectiveness of tumor treatment. Over the past few decades, numerous species of protozoa and their components have exhibited anti-tumor potential via immune and non-immune mechanisms. This discovery introduces a new research direction for the development of new and effective cancer treatments. Through in vitro experiments and studies involving tumor-bearing mice, the anti-tumor ability of Toxoplasma gondii, Plasmodium, Trypanosoma cruzi, and other protozoa have unveiled diverse mechanisms by which protozoa combat cancer, demonstrating encouraging prospects for their application. In this review, we summarize the anti-tumor ability and anti-tumor mechanisms of various protozoa and explore the potential for their clinical development and application.

Apicomplexan parasites are attenuated by low-energy electron irradiation in an automated microfluidic system and protect against infection with Toxoplasma gondii

Radiation-attenuated intracellular parasites are promising immunization strategies. The irradiated parasites are able to invade host cells but fail to fully replicate, which allows for the generation of an efficient immune response. Available radiation technologies such as gamma rays require complex shielding constructions and are difficult to be integrated into pharmaceutical production processes. In this study, we evaluated for the first time low-energy electron irradiation (LEEI) as a method to generate replication-deficient Toxoplasma gondii and Cryptosporidium parvum. Similar to other radiation technologies, LEEI mainly damages nucleic acids; however, it is applicable in standard laboratories. By using a novel, continuous, and microfluidic-based LEEI process, tachyzoites of T. gondii and oocysts of C. parvum were irradiated and subsequently analyzed in vitro. The LEEI-treated parasites invaded host cells but were arrested in intracellular replication. Antibody-based analysis of surface proteins revealed no significant structural damage due to LEEI. Similarly, excystation rates of sporozoites from irradiated C. parvum oocysts were similar to those from untreated controls. Upon immunization of mice, LEEI-attenuated T. gondii tachyzoites induced high levels of antibodies and protected the animals from acute infection. These results suggest that LEEI is a useful technology for the generation of attenuated Apicomplexan parasites and has potential for the development of anti-parasitic vaccines.

Scavenger receptors mediate increased uptake of irradiated T.gondii extracts by J774 macrophages

PURPOSE

Protein extracts developed increased immunogenicity without the aid of adjuvants after gamma irradiation. Gamma irradiation of snake venom increased antivenin production by detoxification and enhanced immunity, probably due preferential uptake of irradiated venoms by macrophage scavenger receptors. We studied this uptake of irradiated soluble Toxoplasma gondii extract (STag) by the J774 macrophage cell line similar to antigen presenting cells.

MATERIAL AND METHODS

We labeled STag by biosynthesis in living tachyzoites with radioactive amino acids before purification and irradiation or by adding labels as biotin or fluorescein in stored STag, for quantitative studies or subcellular distribution visualization.

RESULTS

There was enhanced binding and uptake of irradiated STag into the cells compared to non-irradiated STag. Using fluorescein labeled antigens and morphological assays, we confirmed that cells avidly ingested both native and irradiated proteins but native STag were digested after ingestion while irradiated proteins remained in the cell, suggesting diverse intracytoplasmic pathways. Native or irradiated STag present the same in vitro sensitivity to three types of peptidases. Inhibitors of scavenger receptors (SRs) such as Dextran sulfate (SR-A1 blocker) or Probucol (SR-B blocker) affect the specific uptake of irradiated antigens, suggesting its association with enhanced immunity.

CONCLUSIONS

Our data suggests that cell SRs recognize irradiated proteins, mainly SRs for oxidized proteins, leading to antigen uptake by an intracytoplasmic pathway with fewer peptidases that prolongs presentation to nascent major histocompatibility complex I or II and enhances immunity by better antigen presentation.

Vaccination with recombinant Toxoplasma gondii bradyzoite-formation deficient 1 (rTgBFD1) antigen provides partial protective immunity against chronic T. gondii infection

As an apicomplexan pathogen, Toxoplasma gondii still remains a major threat to public health and requires special attention. In fact, positive attempts to identify more effective antigens to provide protection are important to control toxoplasmosis. Latest scientific advances in T. gondii study hint at the probability of the T. gondii bradyzoite-formation deficient 1 (TgBFD1) as an ideal vaccine candidate, since this molecule plays a critical role in regulating the chronic infection of T. gondii. Thus, BALB/c mouse models of acute and chronic T. gondii infections were used to evaluate the TgBFD1 protection efficacy in this study. Before conducting animal trials, antigen analysis of TgBFD1 was performed using DNAstar software and Western blots. The preliminary results suggested that TgBFD1 should be a potent immunogen. Then, this conclusion is confirmed by ELISA assays. After immunization with rTgBFD1, high levels of specific IgG, IgG1, IgG2a, and cytokines (Interferon γ and interleukin 10) were observed, indicating that TgBFD1 could induce strong protective antibody responses. While TgBFD1-specific IgG antibodies were measurable in vaccinated mice, no protection was observed in the acute T. gondii infection (RH strain) assay. However, a noticeable decrease in brain cysts counts of immunized mice compared with negative controls in the latent T. gondii infection (PRU strain) assay was observed. Taken together, these results indicated that rTgBFD1 had the remarkable ability to elicit both humoral and cellular immune responses and could provide partial protective immunity against chronic T. gondii infection.

A recombinant protein vaccine encoding Toxoplasma gondii Cyst wall 2 (dense granule protein 47) provides partial protection against acute and chronic T. gondii infection in BALB/c mice

Toxoplasma gondii poses a major threat to economies and public health, and there are still no available vaccines for human against T. gondii infection. T. gondii cyst wall 2 (TgCST2, also known as dense granule protein-47) is a critical molecule in the establishment of chronic infection, making it a potential vaccine candidate. In this research, the recombinant TgCST2 (rTgCST2) was employed to evaluate the protective efficacy of TgCST2 antigen using BALB/c mice model against T. gondii infections via active immunization trials. First, the strong immunogenicity of TgCST2 was indicated by immunoblotting and immunofluorescence, which mean that TgCST2 might elicit robust immune responses in the organism. Then, after triply subcutaneous immunization with rTgCST2/ISA 201 emulsion, high levels of Toxoplasma-specific IgG, IgG1, IgG2a and cytokines (Interferon γ and interleukin 10) further suggested that TgCST2 was a promising immunogenic antigen. More importantly, this antigen could prolong survival in RH strain infected mice and resulted in the lower brain cysts size and number of PRU strain infected mice. These preliminary results demonstrated the immunoprophylactic effects of TgCST2 antigen and will inform new studies in developing subunit recombinant vaccines against T. gondii.

Ionizing Radiation Technologies for Vaccine Development - A Mini Review

Given the current pandemic the world is struggling with, there is an urgent need to continually improve vaccine technologies. Ionizing radiation technology has a long history in the development of vaccines, dating back to the mid-20th century. Ionizing radiation technology is a highly versatile technology that has a variety of commercial applications around the world. This brief review summarizes the core technology, the overall effects of ionizing radiation on bacterial cells and reviews vaccine development efforts using ionizing technologies, namely gamma radiation, electron beam, and X-rays.

Assessment of microbiological correlates and immunostimulatory potential of electron beam inactivated metabolically active yet non culturable (MAyNC) Salmonella Typhimurium

This study investigates the microbiological and immunological basis underlying the efficacy of electron beam-inactivated immune modulators. The underlying hypothesis is that exposure to eBeam-based ionization reactions inactivate microorganisms without modifying their antigenic properties and thereby creating immune modulators. The immunological correlates of protection induced by such eBeam based Salmonella Typhimurium (EBST) immune modulators in dendritic cell (DC) (in vitro) and mice (in vivo) models were assessed. The EBST stimulated innate pro inflammatory response (TNFα) and maturation (MHC-II, CD40, CD80 and CD86) of DC. Immuno-stimulatory potential of EBST was on par with both a commercial Salmonella vaccine, and live Salmonella cells. The EBST cells did not multiply under permissive in vitro and in vivo conditions. However, EBST cells remained metabolically active. EBST immunized mice developed Salmonella-specific CD4+ T-cells that produced the Th1 cytokine IFNγ at a level similar to that induced by the live attenuated vaccine (AroA^- ST) formulation. The EBST retained stable immunogenic properties for several months at room temperature, 4°C, and -20°C as well as after lyophilization. Therefore, such eBeam-based immune modulators have potential as vaccine candidates since they offer the safety of a “killed” vaccine, while retaining the immunogenicity of an “attenuated” vaccine. The ability to store eBeam based immune modulators at room temperature without loss of potency is also noteworthy.

Gamma Radiation-Attenuated Toxoplasma gondii Provokes Apoptosis in Ehrlich Ascites Carcinoma-Bearing Mice Generating Long-Lasting Immunity

Purpose:

Pathological angiogenesis and apoptosis evasions are common hallmarks of cancer. A different approach to the antitumor effect of parasitic diseases caused by certain protozoans and helminthes had been adopted in recent years as they can affect many cancer characteristics. The present work is an attempt to assess the effect of gamma radiation-attenuated Toxoplasma gondii ME49 as an antiapoptotic and angiogenic regulator modifier on tumor growth aimed at improving cancer protective protocols.

Methods:

Attenuated Toxoplasma gondii ME49 was administered orally to mice 2 weeks before inoculation with Ehrlich ascites carcinoma to allow stimulation of the immune response. Hepatic histopathology and immune responses were determined for each group.

Results:

Marked suppression of the tumor proliferation with induction of long-lasting immunity by stimulating interferon γ and downregulating transforming growth factor β. The level of tumor promoting inflammatory markers (STAT-3 and tumor necrosis factor α), the angiogenic factors (vascular endothelial growth factor A, integrin, and matrix metallopeptidase 2 and matrix metallopeptidase 9), as well as nitric oxide concentration were significantly decreased. This was collimated with an improvement in apoptotic regulators (cytochrome-c, Bax, Bak, and caspase 3) in liver tissues of vaccinated mice group compared to Ehrlich ascites carcinoma-bearing one. Moreover, the histopathological investigations confirmed this improvement.

Conclusion:

Hence, there is an evidence of potency of radiation attenuated Toxoplasma vaccine in immune activation and targeting tumor cell that can be used as a prophylactic or an adjuvant in combination with chemotherapeutic drugs.

Vaccination with gamma radiation-attenuated Toxoplasma gondii protects against ovarian infiltration in mice-bearing Ehrlich ascites carcinoma

Purpose: Cancer is one of the most common causes of mortality and morbidity worldwide. Vaccines have been emerged as an attractive approach for their capacity of eliciting long-term immune response targeting cancer cells. Attenuated avirulent Toxoplasma gondii stimulate immunity and activate antitumor cells thereby eliciting rejection of some established cancer. The purpose of this study was to evaluate the antitumor-protective capacity of vaccination with gamma radiation-attenuated T. gondii against ovarian penetration in Ehrlich ascites carcinoma (EAC)-bearing mice.Materials and methods: Forty-five mice were randomly divided into three groups as follows: nontumor-bearing (normal control); EAC-bearing group (EAC); and mice vaccinated orally with gamma radiation-attenuated T. gondii then inoculated 2 weeks later with EAC (TG + EAC). Survival rate, serum interleukin-12 (IL-12), and levels of IFN-γ mRNA, CD4, and CD8 in ovarian tissues homogenate were assessed. Also, ovarian histopathology and immunohistochemical expressions of metalloproteinase-2, CD34, and vimentin were determined.Results: The group vaccinated with attenuated T. gondii showed significantly increased survival rates, serum IL-12, and levels of IFN-γ, CD4, and CD8 in ovarian tissue homogenates as well as an enhancement of histopathological and immunohistochemical changes compared to EAC-bearing group.Conclusion: Vaccination with gamma radiation-attenuated T. gondii has the capacity to supply immunoprotective impact against ovarian invasion in EAC-bearing mice.

Radiation effects on Toxoplasma antigens: different immune responses of irradiated intact tachyzoites or soluble antigens in experimental mice models

Purpose: Purpose: Protein irradiation causes aggregation, chain breakage, and oxidation, enhancing its uptake by antigen-presenting cells. To evaluate if irradiated proteins participate on the protection, we studied the immune response induced in mice immunized with irradiated soluble extracts of T. gondii tachyzoites (STag) or irradiated intact T. gondii RH tachyzoites (RH^0.25 kGy).Material and Methods: Soluble extracts of Toxoplasma gondii tachyzoites (STag) were irradiated at different dose by Cobalt-60 source. By polyacrylamide gel electrophoresis (SDS-Page) we evaluated the effects on primary structures of protein STags induced by irradiation. By Enzyme-linked Immunosorbent Assay (ELISA) we evaluated the difference between humoral immune response induced by irradiated STag or RH tachyzoites in immunized mice from the detection of specific immunoglobulin G (IgG) antibodies in the serum of immunized mice. From challenge with viable RH strain of T. gondii we evaluated the protection induced in the immunized animals. By cytometry we performed the phenotyping of T and B lymphocytes in the peripheral blood of the immunized animals.Results: Irradiation dose of 1.5 kGy induced minimal changes in most proteins, without affecting their antigenicity or immunogenicity. Immunization showed saturation at the dose of 10 µg/mice, with worst response at higher doses. STag irradiated at 1.5  kGy (STag^1.5 kGy) induced higher survival and protection similar to T. gondii RH strain irradiated at 0.25 kGy (RH^0.25 kGy), with higher serum levels of high affinity IgG compared to STag native. Blood immune memory cells of mice immunized with STag^1.5 kGy had higher proportions of CD19⁺ (cluster of differentiation 19) and CD4⁺ (cluster of differentiation 14) cells, whereas mice RH^0.25 kGy had high proportion of memory CD8⁺ (cluster of differentiation 8) cells.Conclusions: Our data suggest that major histocompatibility complex type I (MHCI) pathway, appears seem to be used by RH^0.25 kGy to generate cytotoxic cells while STag1.5 kGy uses a major histocompatibility complex type II (MHCII) pathway for B-cell memory, but both induce sufficient immune response for protection in mice without any adjuvant. Irradiation of soluble protein extracts enhances their immune response, allowing similar protection against T. gondii in mice as compared to irradiated intact parasites.

The course of infection with Toxoplasma gondii RH strain in mice pre-vaccinated with gamma irradiated tachyzoites

Toxoplasma gondii is a ubiquitous protozoan of major medical and veterinary importance. Its treatment is difficult since the available drugs have severe side effects and reactivation may occur anytime. Vaccination with irradiated parasites exhibits ideal characteristics for vaccine development. In our experimental mice model, the protection against challenge with the virulent RH strain was assessed, using 255Gy irradiated tachyzoites. Eighty mice were allocated into 3 groups: naive control group, challenged with virulent RH tachyzoites group and a third group which is challenged with 1 × 10⁶ irradiated tachyzoites, administered as two biweekly doses intraperitoneally. Protection was tested by challenging vaccinated mice with the virulent type RH tachyzoites 30 days after the 2nd vaccination dose. The assessment was built on qualitative clinical, quantitative parasitological, histopathological parameters and measurement of serum Nitric Oxide (NO). The results showed prolonged survival rate, absence of tachyzoites in the peritoneal aspirate by counting, absence of tachyzoites in all examined organs by impression smears, amelioration of histopathological changes in the liver, spleen, brain and lung specimens and increase of the serum NO level in the vaccinated group. Therefore, we propose that irradiated Toxoplasma tachyzoites confer protection for challenged mice and could be an alternative immunization schedule for vaccine development especially for who are at risk of severe immunosuppression.

Gamma irradiation of Toxoplasma gondii protein extract improve immune response and protection in mice models

Gamma radiation induces protein changes that enhance immunogenicity for venoms, used in antivenin production. Coccidian parasites exposed to gamma radiation elicit immune response with protection in mice and man, but without studies on the effect of gamma radiation in soluble acellular extracts or isolated proteins. Toxoplasmosis is a highly prevalent coccidian disease with only one vaccine for veterinary use but with remaining tissue cysts. Total parasite extracts or recombinant proteins used as immunogen induce usually low protection. Here, we study gamma radiation effect on T. gondii extracts proteins (STAG) and its induced immunity in experimental mice models. By SDS-PAGE, protein degradation is seen at high radiation doses, but at ideal dose (1500 Gy), there are preservation of the antigenicity and immunogenicity, detected by specific antibody recognition or production after mice immunization. Immunization with STAG irradiated at 1500 Gy induced significant protection in mice immunized and challenged with distinct T. gondii strains. In their blood, higher levels of specific CD19⁺, CD3⁺CD4⁺ and CD3⁺CD8⁺ activated cells were found when compared to mice immunized with STAG. Irradiated T. gondii tachyzoites extracts induce immune response and protection in mice in addition, could be a feasible alternative for Toxoplasma vaccine.

Continuous Effector CD8(+) T Cell Production in a Controlled Persistent Infection Is Sustained by a Proliferative Intermediate Population

Highly functional CD8(+) effector T (Teff) cells can persist in large numbers during controlled persistent infections, as exemplified by rare HIV-infected individuals who control the virus. Here we examined the cellular mechanisms that maintain ongoing T effector responses using a mouse model for persistent Toxoplasma gondii infection. In mice expressing the protective MHC-I molecule, H-2L(d), a dominant T effector response against a single parasite antigen was maintained without a contraction phase, correlating with ongoing presentation of the dominant antigen. Large numbers of short-lived Teff cells were continuously produced via a proliferative, antigen-dependent intermediate (Tint) population with a memory-effector hybrid phenotype. During an acute, resolved infection, decreasing antigen load correlated with a sharp drop in the Tint cell population and subsequent loss of the ongoing effector response. Vaccination approaches aimed at the development of Tint populations might prove effective against pathogens that lead to chronic infection.

X-ray Irradiated Vaccine Confers protection against Pneumonia caused by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a gram-negative bacterium and one of the leading causes of nosocomial infection worldwide, however, no effective vaccine is currently available in the market. Here, we demonstrate that inactivation of the bacteria by X-ray irradiation inhibits its replication capability but retained antigenic expression functionally thus allowing its use as a potential vaccine. Mice immunized by this vaccine were challenged by the parental strain, the O-antigen-homologous strain PAO-1 (O2/O5) and heterologous strain PAO-6 (O6) in an acute pneumonia model. We further measured the protective effect of the vaccine, as well as host innate and cellular immunity responses. We found immunized mice could protect against both strains. Notably, the antiserum only had significant protective role against similar bacteria, while adoptive transfer of lymphocytes significantly controlled the spread of the virulent heterologous serogroup PAO-6 infection, and the protective role could be reversed by CD4 rather than CD8 antibody. We further revealed that vaccinated mice could rapidly recruit neutrophils to the airways early after intranasal challenge by PAO-6, and the irradiated vaccine was proved to be protective by the generated CD4(+) IL-17(+) Th17 cells. In conclusion, the generation of inactivated but metabolically active microbes is a promising strategy for safely vaccinating against Pseudomonas aeruginosa.

Immunity in the spleen and blood of mice immunized with irradiated Toxoplasma gondii tachyzoites

Toxoplasma gondii infection induces a strong and long-lasting immune response that is able to prevent most reinfections but allows tissue cysts. Irradiated, sterilized T. gondii tachyzoites are an interesting vaccine, and they induce immunity that is similar to infection, but without cysts. In this study, we evaluated the cellular immune response in the blood and spleen of mice immunized with this preparation by mouth (v.o.) or intraperitoneally (i.p.) and analyzed the protection after challenge with viable parasites. BALB/c mice were immunized with three i.p. or v.o. doses of irradiated T. gondii tachyzoites. Oral challenge with ten cysts of the ME-49 or VEG strain at 90 days after the last dose resulted in high levels of protection with low parasite burden in the immunized animals. There were higher levels of specific IgG, IgA and IgM antibodies in the serum, and the i.p. immunized mice had higher levels of the high-affinity IgG and IgM antibodies than the orally immunized mice, which had more high-affinity IgA antibodies. B cells (CD19(+)), plasma cells (CD138(+)) and the CD4(+) and CD8(+) T cell populations were increased in both the blood and spleen. Cells from the spleen of the i.p. immunized mice also showed antigen-induced production of interleukin-10 (IL-10), interferon gamma (IFN-γ) and interleukin 4 (IL-4). The CD4(+) T cells, B cells and likely CD8(+) T cells from the spleens of the i.p. immunized mice proliferated with a specific antigen. The protection was correlated with the spleen and blood CD8(+) T cell, high-affinity IgG and IgM and antigen-induced IL-10 and IL-4 production. Immunization with irradiated T. gondii tachyzoites induces an immune response that is mediated by B cells and CD4(+) and CD8(+) T cells, with increased humoral and cellular immune responses that are necessary for host protection after infection. The vaccine is similar to natural infection, but free of tissue cysts; this immunity restrains infection at challenge and can be an attractive and efficient model for vaccine development in toxoplasmosis.

Research advances in microneme protein 3 of Toxoplasma gondii

Toxoplasma gondii (T. gondii) is an obligate intracellular protozoan parasite. It has extensive host populations and is prevalent globally; T. gondii infection can cause a zoonotic parasitic disease. Microneme protein 3 (MIC3) is a secreted protein that is expressed in all stages of the T. gondii life cycle. It has strong immunoreactivity and plays an important role in the recognition, adhesion and invasion of host cells by T. gondii. This article reviews the molecular structure of MIC3, its role in the invasion of host cells by parasites, its relationship with parasite virulence, and its induction of immune protection to lay a solid foundation for an in-depth study of potential diagnostic agents and vaccines for preventing toxoplasmosis.

Studying host-pathogen interaction events in living mice visualized in real time using biophotonic imaging

Despite progress in mouse models of bacterial pathogens, studies are often limited by evaluating infections in an individual organ or tissue or at a given time. Here we present a technique to engineer the pathogen, e.g., Brucella melitensis, with a bioluminescent marker permitting analysis of living bacteria in real time during the infectious process from acute to chronic infection. Using this bioluminescent approach, tissue preference, differences between virulent and mutant bacteria, as well as the response of the bacteria to host metabolites can provide extraordinary data enhancing our understanding of host-pathogen interactions.

Therapy with radio-attenuated vaccine in experimental murine visceral leishmaniasis showed enhanced T cell and inducible nitric oxide synthase levels, suppressed tumor growth factor-beta production with higher expression of some signaling molecules

Background

Visceral leishmaniasis (VL) or Kala-Azar (KA) is one of the most deadly forms of disease among all neglected tropical diseases. There are no satisfactory drugs or vaccine candidates available for this dreaded disease. Our previous studies showed promising therapeutic and prophylactic efficacy of the live, radio-attenuated parasites through intramuscular (I.M.) and intraperitoneal (I.P.) route in BALB/c mice model.

Methods

The T-cell proliferation level, the mRNA expression level of inducible nitric oxide synthase (iNOS) and tumor growth factor-beta (TGF-β) genes and finally the phosphorylation levels of phosphoinositide dependent kinase 1 (PDK1), phosphoinositide 3 kinase (PI3K) and p38 mitogen activated protein kinase (p38MAPK) molecules were checked in BALB/c mice model immunized with radio-attenuated Leishmania donovani parasites through I.M. route.

Results

Higher T-cell proliferation, increased iNOS level, and suppressed TGF-β level were found in treated infected animal groups (100 and 150 Gy) in relation to untreated infected animals. Likewise, phosphorylation levels of PDK1, PI3K and p38MAPK of these two groups were increased when compared to untreated infected controls.

Conclusion

The clearance of the parasites from treated infected groups of animals may be mediated by the restoration of T-cell due to therapy with radio-attenuated L. donovani parasites. The killing of parasites was mediated by increase in nitric oxide release through PDK1, PI3K and p38MAPK signaling pathways. A lower TGF-β expression has augmented the restored Th1 ambience in the 100 and 150 Gy treated animal groups proving further the efficacy of the candidate vaccine.

Research progress on surface antigen 1 (SAG1) of Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasitic protozoan that has a wide host range and causes a zoonotic parasitosis called toxoplasmosis. This infection causes significant morbidity, costs for care and loss of productivity and suffering. The most effective measures to minimize this parasite’s harm to patients are prompt diagnosis and treatment and preventing infection. A parasite surface antigen, SAG1, is considered an important antigen for the development of effective diagnostic tests or subunit vaccines. This review covers several aspects of this antigen, including its gene structure, contribution to host invasion, mechanisms of the immune responses and its applications for diagnosis and vaccine development. This significant progress on this antigen provides foundations for further development of more effective and precise approaches to diagnose toxoplasmosis in the clinic, and also have important implications for exploring novel measures to control toxoplasmosis in the near future.

DNA prime and peptide boost immunization protocol encoding the Toxoplasma gondii GRA4 induces strong protective immunity in BALB/c mice

Background

Toxoplasma gondii is a widespread intracellular parasite, which infects most vertebrate animal hosts and causes zoonotic infection in humans. Vaccine strategy remains a promising method for the prevention and control of toxoplasmosis. T. gondii GRA4 protein has been identified as a potential candidate for vaccine development. In our study, we evaluated the immune response induced by four different immunization vaccination strategies encoding TgGRA4.

Methods

BALB/c mice were intramuscularly (i.m.) immunized four times according to specific immunization schedules. Generally, mice in experimental groups were immunized with polypeptide, pGRA4, peptide/DNA, or DNA/peptide, and mice in the control groups were injected with PBS or pEGFP. After immunization, the levels of IgG antibodies and cytokine productions were determined by enzyme-linked immunosorbent assays (ELISA). The survival time of mice was also evaluated after challenge infection with the highly virulent T. gondii RH strain.

Results

The results showed that mice vaccinated with different immunization regimens (polypeptide, pGRA4, peptide/DNA, or DNA/peptide) elicited specific humoral and cellular responses, with high levels of total IgG, IgG2a isotype and gamma interferon (IFN-γ), which suggested a specific Th1 immunity was activated. After lethal challenge, an increased survival time was observed in immunized mice (11.8 ± 4.8 days) compared to the control groups injected with PBS or pEGFP (P < 0.05). Mice injected with PBS or pEGFP died within 8 days, and there was no significant difference in the protection level in two groups (P > 0.05).

Conclusions

These results demonstrated that this DNA prime and peptide boost immunization protocol encoding the TgGRA4 can elicit the highest level of humoral and cellular immune responses compared to other immunized groups, which is a promising approach to increase the efficacy of DNA immunization.

A new alternative in vitro method for quantification of Toxoplasma gondii infectivity

An in vitro method to determine the infectious potency of an unknown suspension of the protozoan parasite Toxoplasma gondii based on kinetics of host cells lysis was developed. Mic1-3KO a mutant strain of T. gondii RH tachyzoites was inoculated in 25-cm² flasks containing a 90% confluent monolayer of human foreskin fibroblasts. Lysis kinetics was monitored for infection ratios ranging from 1∶10⁶ to 1∶10; we defined 10⁶ tachyzoites/ml⁻¹ as the threshold value for parasite egress. Results allowed us to build a calibration curve relating the initial infection ratios to the time needed to reach 10⁶ tachyzoites/ml⁻¹. Finally, we validated the method using a known mixture of dead and live parasites. This method was found to estimate with accuracy the initial ratio of infection of the unknown parasite suspension. This easy-to-use method is reproducible and can be applied to any T. gondii tachyzoite RH strain, genetically modified or not. This method is also suitable for testing promising candidates for an effective live vaccine.

Return of inactivated whole-virus vaccine for superior efficacy

The swine, influenza, H1N1 outbreak in 2009 highlighted the inadequacy of the currently used antibody-based vaccine strategies as a preventive measure for combating influenza pandemics. The ultimate goal for successful control of newly arising influenza outbreaks is to design a single-shot vaccine that will provide long-lasting immunity against all strains of influenza A virus. A large amount of data from animal studies has indicated that the cross-reactive cytotoxic T (Tc) cell response against conserved influenza virus epitopes may be the key immune response needed for a universal influenza vaccine. However, decades of research have shown that the development of safe T-cell-based vaccines for influenza is not an easy task. Here, I discuss the overlooked but potentially highly advantageous inactivation method, namely, γ-ray irradiation, as a mean to reach the Holy Grail of influenza vaccinology.

Humoral responses and immune protection in mice immunized with irradiated T. gondii tachyzoites and challenged with three genetically distinct strains of T. gondii

Toxoplasma gondii is an obligate intracellular parasite that infects a variety of mammals and birds. T. gondii also causes human toxoplasmosis; although toxoplasmosis is generally a benign disease, ocular, congenital or reactivated disease is associated with high numbers of disabled people. Infection occurs orally through the ingestion of meat containing cysts or by the intake of food or water contaminated with oocysts. Although the immune system responds to acute infection and mediates the clearance of tachyzoites, parasite cysts persist for the lifetime of the host in tissues such as the eye, muscle, and CNS. However, T. gondii RH strain tachyzoites irradiated with 255Gy do not cause residual infection and induce the same immunity as a natural infection. To assess the humoral response in BALB/c and C57BL/6J mice immunized with irradiated tachyzoites either by oral gavage (p.o.) or intraperitoneal (i.p.) injection, we analyzed total and high-affinity IgG and IgA antibodies in the serum. High levels of antigen-specific IgG were detected in the serum of parenterally immunized mice, with lower levels in mice immunized via the oral route. However, most serum antibodies exhibited low affinity for antigen in both mice strain. We also found antigen specific IgA antibodies in the stools of the mice, especially in orally immunized BALB/c mice. Examination of bone marrow and spleen cells demonstrated that both groups of immunized mice clearly produced specific IgG, at levels comparable to chronic infection, suggesting the generation of IgG specific memory. Next, we challenged i.p. or p.o. immunized mice with cysts from ME49, VEG or P strains of T. gondii. Oral immunization resulted in partial protection as compared to challenged naive mice; these findings were more evident in highly pathogenic ME49 strain challenge. Additionally, we found that while mucosal IgA was important for protection against infection, antigen-specific IgG antibodies were involved with protection against disease and disease pathogenesis. Most antigen responsive cells in culture produced specific high-affinity IgG after immunization, diverse of the findings in serum IgG or from cells after infection, which produced low proportion of high-avidity IgG.

Nondividing but metabolically active gamma-irradiated Brucella melitensis is protective against virulent B. melitensis challenge in mice

Brucella spp. are gram-negative bacteria that cause the most frequent zoonotic disease worldwide, with more than 500,000 human infections yearly; however, no human vaccine is currently available. As with other intracellular organisms, cytotoxic mechanisms against infected cells are thought to have an important role in controlling infection and mediating long-term immunity. Live attenuated strains developed for use in animals elicit protection but retain unacceptable levels of virulence. Thus, the optimal design for a brucellosis vaccine requires a nonliving vaccine that confers effective immunity. Historically, inactivation methods such as chemical or heat treatment successfully impair Brucella reproductive capacity; nevertheless, metabolically inactive vaccines (subunit or killed) present very limited efficacy. Hence, we hypothesized that bacterial metabolism plays a major role in creating the proper antigenic and adjuvant properties required for efficient triggering of protective responses. Here, we demonstrate that inactivation of Brucella melitensis by gamma-irradiation inhibited its replication capability and yet retained live-Brucella protective features. Irradiated Brucella possessed metabolic and transcriptional activity, persisted in macrophages, generated antigen-specific cytotoxic T cells, and protected mice against virulent bacterial challenge, without signs of residual virulence. In conclusion, pathogen metabolic activity has a positive role in shaping protective responses, and the generation of inactivated and yet metabolically active microbes is a promising strategy for safely vaccinating against intracellular organisms such as B. melitensis.

AJ, Hiramoto RM, Terentowicz HCK, Andrade Júnior HFD. Quantitative toxoplasma gondii oocyst detection by a modified Kato Katz test using Kinyoun staining (KKK) in ME49 strain experimentally infected cats

We detected Toxoplasma gondii oocysts in feces of experimentally infected cats, using a Kato Katz approach with subsequent Kinyoun staining. Animals serologically negative to T. gondii were infected orally with 5x10² mice brain cysts of ME49 strain. Feces were collected daily from the 3rd to the 30th day after challenge. Oocysts were detected by qualitative sugar flotation and the quantitative modified Kato Katz stained by Kinyoun (KKK). In the experimentally infected cats, oocysts were detected from the 7th to 15th day through sugar flotation technique, but oocysts were found in KKK from the 6th to 16th day, being sensitive for a larger period, with permanent documentation. The peak of oocysts excretion occurred between the 8th to 11th days after challenge, before any serological positive result. KKK could be used in the screening and quantification of oocysts excretion in feces of suspected animals, with reduced handling of infective material, decreasing the possibility of environmental and operator contamination.

Toxoplasma gondii: Differential protection rates by two strains against cyst formation in a rat model

A previous infection with the ME-49 strain of Toxoplasma gondii (of low pathogenicity for mice), protected 17 of 20 rats against formation of brain cysts, following challenge with 10(3) oocysts of the high pathogenicity M3 strain, as determined by bioassay of rat brains in mice. The low pathogenic KSU strain did not afford comparable protection. Protection was further tested in rats that were orally or subcutaneously immunized with cysts or oocysts of the ME-49 strain, and later challenged with 2 x 10(2) cysts or 10(2) oocysts of the highly pathogenic strains M3, M-7741 and C. Protection ranged from 43 to 100%, compared to non immunized control rats and was independent of the stage of ME-49 strain and of the routes used to immunize the rats. The results obtained encourage further investigation into prevention of toxoplasmosis in humans and food animals.

Vaccination with replication-deficient recombinant adenoviruses encoding the main surface antigens of toxoplasma gondii induces immune response and protection against infection in mice

We have generated recombinant adenoviruses encoding three genetically modified surface antigens (SAGs) of the parasite Toxoplasma gondii, that is, AdSAG1, AdSAG2, and AdSAG3. Modifications included the removal of their glycosylphosphatidylinositol (GPI) anchoring motifs and, in some cases, the exchange of the native signal peptide for influenza virus hemagglutinin signal sequence. Adenovirus immunization of BALB/c mice elicited potent antibody responses against each protein, displaying a significant bias toward a helper T cell type 1 (Th1) profile in animals vaccinated with AdSAG1. Furthermore, the presence of parasite-specific IFN-gamma-producing T cells was analyzed by proliferation assays and enzyme-linked immunospot assays in the same animals. Splenocytes from immunized mice secreted IFN-gamma after in vitro stimulation with tachyzoite lysate antigen or with a fraction enriched for membrane-purified GPI-anchored proteins (F3) from the T. gondii tachyzoite surface. Epitopes recognized by CD8+ T cells were identified in SAG1 and SAG3, but not SAG2, sequences, although this protein also induced a specific response. We also tested the capacity of the immune responses detected to protect mice against a challenge with live T. gondii parasites. Although no protection was observed against tachyzoites of the highly virulent RH strain, a significant reduction in cyst loads in the brain was observed in animals challenged with the P-Br strain. Thus, up to 80% of the cysts were eliminated from animals vaccinated with a mixture of the three recombinant viruses. Because adenoviruses seemed capable of inducing Th1-biased protective immune responses against T. gondii antigens, other parasite antigens should be tested alone or in combination with those described here to further develop a protective vaccine against toxoplasmosis.

Vaccination with gamma-irradiated Neospora caninum tachyzoites protects mice against acute challenge with N. caninum

Neospora caninum, an apicomplexan parasite, is a leading cause of bovine abortions worldwide. The efficacy of gamma-irradiated N. caninum strain NC-1 tachyzoites as a vaccine for neosporosis was assessed in C57BL6 mice. A dose of 528 Gy of gamma irradiation was sufficient to arrest replication but not host cell penetration by tachyzoites. Female C57BL6 mice were vaccinated with two intraperitoneal inoculations of 1 x 10(6) irradiated tachyzoites at 4-wk intervals. When stimulated with N. caninum tachyzoite lysates, splenocytes of vaccinated mice, cultured 5 and 10 wk after vaccination, secreted significant (P<0.05) levels of interferon gamma, interleukin (IL)-10, and small amounts of IL-4. Antibody isotype-specific ELISA of sera from vaccinated mice exhibited both IgG1 and IgG2a isotypes of antibodies. Vaccinated mice were challenged intraperitoneally with 2 x 10(7)N. caninum tachyzoites. All vaccinated mice remained healthy and showed no obvious signs of neosporosis up to the 25th day post-challenge when the study was terminated. All unvaccinated control mice died within 1 wk of infection. Gamma-irradiated N. caninum tachyzoites can serve as an effective, attenuated vaccine for N. caninum.

Induction of antigen-specific Th1-type immune responses by gamma-irradiated recombinant Brucella abortus RB51

Brucella abortus strain RB51 is an attenuated rough mutant used as the live vaccine against bovine brucellosis in the United States and other countries. We previously reported the development of strain RB51 as a bacterial vaccine vector for inducing Th1-type immune responses against heterologous proteins. Because safety concerns may preclude the use of strain RB51-based recombinant live vaccines, we explored the ability of a gamma-irradiated recombinant RB51 strain to induce heterologous antigen-specific immune responses in BALB/c mice. Exposure of strain RB51G/LacZ expressing Escherichia coli beta-galactosidase to a minimum of 300 kilorads of gamma radiation resulted in complete loss of replicative ability. These bacteria, however, remained metabolically active and continued to synthesize beta-galactosidase. A single intraperitoneal inoculation of mice with 10(9) CFU equivalents of gamma-irradiated, but not heat-killed, RB51G/LacZ induced a beta-galactosidase-specific Th1-type immune response. Though no obvious differences were detected in immune responses to B. abortus-specific antigens, mice vaccinated with gamma-irradiated, but not heat-killed, RB51G/LacZ developed significant protection against challenge with virulent B. abortus. In vitro experiments indicated that gamma-irradiated and heat-killed RB51G/LacZ induced maturation of dendritic cells; however, stimulation with gamma-irradiated bacteria resulted in more interleukin-12 secretion. These results suggest that recombinant RB51 strains exposed to an appropriate minimum dose of gamma radiation are unable to replicate but retain their ability to stimulate Th1 immune responses against the heterologous antigens and confer protection against B. abortus challenge in mice.

Paracoccidioides brasiliensis: attenuation of yeast cells by gamma irradiation

Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis, the most prevalent mycosis in Latin America, and currently there is no effective vaccine. The aim of this study was to attenuate the yeast form of P. brasiliensis by gamma irradiation for further studies on vaccine research. Paracoccidioides brasiliensis (strain Pb 18) cultures were irradiated at doses between 0.5 and 8.0 kGy. After each dose the viability, reproductive ability and protein metabolism were evaluated. The comparison between the antigenic profile of irradiated and control yeast was made by Western blot and the virulence evaluated by the inoculation in C(57)Bl/J6 mice. At 6.5 kGy the yeast lost its reproductive capacity. The viability and the incorporation of [L-(35)S]-methionine were the same in control and up to 6.5 kGy irradiated cells, but 6.5 kGy-irradiated yeast secreted 40% less proteins. The Western blot profile was clearly similar in control and 6.5 kGy-irradiated yeast. No colony-forming unit (CFU) could be recovered from the tissues of the mice infected with the radioattenuated yeast. We concluded that for P. brasiliensis yeast it is possible to find a dose in which the pathogen loses its reproductive ability and virulence, while retaining its viability, metabolic activity and the antigenic profile.

Characterization of the B-cell immune response elicited in BALB/c mice challenged with Neospora caninum tachyzoites

Activation of B cells occurring in hosts infected with protozoan parasites has been implicated either in protective or parasite-evasion immune-mediated mechanisms. Intraperitoneal inoculation of Neospora caninum tachyzoites into BALB/c mice induces an acute response characterized by a rapid increase in the numbers of CD69-expressing peritoneal and splenic B cells. This early B-cell stimulatory effect preceded an increase in the numbers of total and immunoglobulin-secreting splenic B cells and a rise in serum levels of N. caninum-specific immunoglobulins, predominantly of the immunoglobulin G2a (IgG2a) and IgM isotypes. Increased numbers of B cells expressing the costimulatory molecules CD80 and CD86 were also observed in the N. caninum-infected mice. The B-cell stimulatory effect observed in mice challenged with N. caninum tachyzoites was reduced in mice challenged with gamma-irradiated parasites. Contrasting with the peripheral B-cell expansion, a depletion of B-lineage cells was observed in the bone-marrow of the N. caninum-infected mice. Intradermal immunization of BALB/c mice with diverse N. caninum antigenic preparations although inducing the production of parasite-specific antibodies nevertheless impaired interferon-gamma (IFN-gamma) mRNA expression and caused lethal susceptibility to infection in mice inoculated with a non-lethal parasitic inoculum. This increased susceptibility to N. caninum was not observed in naïve mice passively transferred with anti-N. caninum antibodies. Taken together, these results show that N. caninum induces in BALB/c mice a parasite-specific, non-polyclonal, B-cell response, reinforce previous observations made by others showing that immunization with N. caninum whole structural antigens increases susceptibility to murine neosporosis and further stress the role of IFN-gamma in the host protective immune mechanisms against this parasite.

Suppressed Cytokine and Immunoglobulin Secretions by Murine Splenic Lymphocytes Infected In Vitro with Toxoplasma gondii Tachyzoites

Mechanisms of host immunosuppression after infection with Toxoplasma gondii are unclear. This study was performed to observe cytokine and immunoglobulin secretions by murine splenic lymphocytes infected in vitro with live, nonreplicating (irradiated) RH tachyzoites on stimulation with concanavalin A (Con A) or lipopolysaccharide (LPS). For lymphocyte cultivation, 3 groups were prepared: coculture with live nonirradiated tachyzoites separated by a transwell (group T), live irradiated tachyzoites without a transwell (group R), and no tachyzoites (group C). Compared with group T, groups R and C, on stimulation with Con A, revealed significantly (P < 0.05) lower levels of interleukin-2 (IL-2) and IFN-gamma, but not IL-10. The levels of IgG1, IgG2a, IgG2b, IgG3, IgA, and IgM were also significantly (P < 0.05) lower in groups R and C than in group T after stimulation with LPS. The results suggest that intracellular infection of murine splenic lymphocytes with T. gondii tachyzoites could impair their capacity to produce cytokine and immunoglobulin secretions.