Toxoplasma gondii: cloning, expression and immunoreactivity of recombinant ROP5 and ROP18 antigens

Evaluation of a DNA vector plasmid encoding a partial rop18 gene from toxoplasma gondii in domestic cats as a vaccine candidate

The present study aimed to evaluate a DNA vector plasmid encoding a partial rop18 gene from Toxoplasma gondii in domestic cats as a potential vaccine candidate. Four domestic cats (Felis catus) were used, of which two animals received 25 μg of pcDNA 3.1 + rop18, and two received 25 μg of pcDNA 3.1. All animals received intramuscular immunizations with four doses every three weeks along with 1.5 % levamisole. Thirty days after the last immunization, the animals were infected with 300 tissue cysts from ToxoDB #182 strain, a non-archetypal genotype isolated from a wild cat. Fecal examinations were performed for oocyst shedding. Enzyme-linked immunosorbent assay and western blotting analyses with recombinant ROP18 were performed to assess the humoral immune response. Animals that received plasmid containing the partial T. gondii rop18 gene produced specific IgG antibodies and shed 53.3 % fewer oocysts than controls. The two groups of animals showed no statistically significant differences (p > 0.05) in oocyst shedding; however, they showed significant differences in the detection of anti-Toxoplasma antibodies (p < 0.05). In conclusion, the T. gondii rop18 gene is a potential vaccine candidate against oocyst shedding in cats.

Serotyping of Toxoplasma gondii Infection Using Peptide Membrane Arrays

The intracellular parasite Toxoplasma gondii can cause chronic infections in most warm-blooded animals, including humans. In the USA, strains belonging to four different Toxoplasma clonal lineages (types 1, 2, 3, and 12) are commonly isolated, whereas strains not belonging to these lineages are predominant in other continents such as South America. Strain type plays a pivotal role in determining the severity of Toxoplasma infection. Therefore, it is epidemiologically relevant to develop a non-invasive and inexpensive method for determining the strain type in Toxoplasma infections and to correlate the genotype with disease outcome. Serological typing is based on the fact that many host antibodies are raised against immunodominant parasite proteins that are highly polymorphic between strains. However, current serological assays can only reliably distinguish type 2 from non-type 2 infections. To improve these assays, mouse, rabbit, and human infection serum were reacted against 950 peptides from 62 different polymorphic Toxoplasma proteins by using cellulose membrane peptide arrays. This allowed us to identify the most antigenic peptides and to pinpoint the most relevant polymorphisms that determine strain specificity. Our results confirm the utility of previously described peptides and identify novel peptides that improve and increase the specificity of the assay. In addition, a large number of novel proteins showed potential to be used for Toxoplasma diagnosis. Among these, peptides derived from several rhoptry, dense granule, and surface proteins represented promising candidates that may be used in future experiments to improve Toxoplasma serotyping. Moreover, a redesigned version of the published GRA7 typing peptide performed better and specifically distinguished type 3 from non-type 3 infections in sera from mice, rabbits, and humans.

An evaluation of a recombinant multiepitope based antigen for detection of Toxoplasma gondii specific antibodies

BACKGROUND

The inefficiency of the current tachyzoite antigen-based serological assays for the serodiagnosis of Toxoplasma gondii infection mandates the need for acquirement of reliable and standard diagnostic reagents. Recently, epitope-based antigens have emerged as an alternative diagnostic marker for the achievement of highly sensitive and specific capture antigens. In this study, the diagnostic utility of a recombinant multiepitope antigen (USM.TOXO1) for the serodiagnosis of human toxoplasmosis was evaluated.

METHODS

An indirect enzyme-linked immunosorbent assay (ELISA) was developed to evaluate the usefulness of USM.TOXO1 antigen for the detection of IgG antibodies against Toxoplasma gondii in human sera. Whereas the reactivity of the developed antigen against IgM antibody was evaluated by western blot and Dot enzyme immunoassay (dot-EIA) analysis.

RESULTS

The diagnostic performance of the new antigens in IgG ELISA was achieved at the maximum values of 85.43% and 81.25% for diagnostic sensitivity and specificity respectively. The USM.TOXO1 was also proven to be reactive with anti- T. gondii IgM antibody.

CONCLUSIONS

This finding makes the USM.TOXO1 antigen an attractive candidate for improving the toxoplasmosis serodiagnosis and demonstrates that multiepitope antigens could be a potential and promising diagnostic marker for the development of high sensitive and accurate assays.

Induction of specific humoral immune response in mice immunized with ROP18 nanospheres from Toxoplasma gondii

Toxoplasmosis is one of the most common zoonotic protozoal diseases. Recent advances in biotechnology have produced recombinant protein, which are immunogenic, and progress in nano-pharmaceutics has generated encapsulated protein in nanospheres, which are suitable for vaccine delivery. DNA was extracted from Toxoplasma gondii oocysts and was confirmed through nested PCR and sequencing. The 1665 bp of ROP18 was cloned into the easy vector system: pGEM-T by the T-A cloning method. DH5α bacteria were transfected with pGEM-ROP18. ROP18 was subcloned from pGEM-ROP18 into pET28-ROP18. BL21 bacteria were transfected with pET28-ROP18. Thus, rROP18 protein was expressed in BL21 bacteria by induction at different concentrations of isopropyl β-D-1-thiogalactopyranoside. Protein expression was confirmed through SDS-PAGE and Western blotting. The immunoblot of rROP18 was recognized by anti-HIS antibodies and sera from infected mice at 67 kDa. Recombinant ROP18 protein was encapsulated in nanoparticles with PLGA and was characterized through scanning electron microscopy. Intraperitoneal immunizations with rROP18 protein and intranasal immunization of nanospheres were carried out in mice, and the immune response was detected by ELISA. Results showed that rROP18 in nanospheres administered intra-nasally elicited elevated responses of specific IgA and IgG2a as compared to groups inoculated intra-nasally with rROP18 alone, or injected subcutaneously with rROP18 in montanide adjuvant. It was concluded that nanospheres of ROP18 would be a non-invasive approach to develop vaccination against T. gondii. Further experiments are needed to determine the cellular response to these nanospheres in a mouse model for chronic toxoplasmosis.

Evaluation of immune responses induced by rhoptry protein 5 and rhoptry protein 7 DNA vaccines against Toxoplasma gondii

Infection with the protozoan parasite Toxoplasma gondii is widespread, and the organism can cause congenital infections in humans. The horizontal transmission of Toxoplasma is even more common than congenital. An effective vaccine strategy brings the prospect of improving Toxoplasma disease control. Rhoptry protein 5 (ROP5) and ROP7 are potential stimulators of humoral and cellular immune responses. In this study, we constructed a multi-antigenic DNA vaccine expressing ROP5 and ROP7 of T. gondii and compared the protective efficacy to single-gene vaccines and control groups. BALB/c mice were immunized intramuscularly three times. The levels of IgG antibodies and cytokines in mice immunized with the multi-antigenic DNA vaccine (pROP5/ROP7) were significantly higher than those in the control mice. Mice vaccinated with pROP5/ROP7 showed a longer survival time (16 days) than single-gene-immunized mice (11 and 12 days, respectively) or control mice (8 days) after a challenge with 1 × 10(4) tachyzoites of RH strain of T. gondii. Furthermore, after intragastric infection with 20 cysts of PRU strain of T. gondii, the number of brain cysts in mice immunized with pROP5/ROP7 was only 25% of the number in control mice. Our results showed that a DNA vaccine encoding ROP5 and ROP7 significantly enhanced protection against T. gondii challenge.

Recent advances in developing vaccines against Toxoplasma gondii: an update

Toxoplasma gondii, a significant public health risk, is able to infect almost all warm-blooded animals including humans, and it results in economic losses in production animals. In the last three years, a large number of vaccination experiments have been performed to control T. gondii infection, with the target of limiting the acute infection and reducing or eliminating tissue cysts in the intermediate hosts. In this paper, we summarize the latest results of the veterinary vaccines against T. gondii infection since 2013. Immunization with live-attenuated whole organisms of non-reverting mutants has been shown to induce remarkably potent immune responses associated with control of acute and chronic toxoplasmosis. The non-cyst-forming mutants are promising new tools for the development of veterinary vaccines against T. gondii infection.

Towards vaccine against toxoplasmosis: evaluation of the immunogenic and protective activity of recombinant ROP5 and ROP18 Toxoplasma gondii proteins

Toxoplasmosis is one of the most common parasitic infections worldwide. An effective vaccine against human and animal toxoplasmosis is still needed to control this parasitosis. The polymorphic rhoptry proteins, ROP5 and ROP18, secreted by Toxoplasma gondii during the invasion of the host cell have been recently considered as promising vaccine antigens, as they appear to be the major determinants of T. gondii virulence in mice. The goal of this study was to evaluate their immunogenic and immunoprotective activity after their administration (separately or both recombinant proteins together) with the poly I:C as an adjuvant. Immunization of BALB/c and C3H/HeOuJ mice generated both cellular and humoral specific immune responses with some predominance of IgG1 antibodies. The spleen cells derived from vaccinated animals reacted to the parasite's native antigens. Furthermore, the immunization led to a partial protection against acute and chronic toxoplasmosis. These findings confirm the previous assumptions about ROP5 and ROP18 antigens as valuable components of a subunit vaccine against toxoplasmosis.

Human toxoplasmosis: a comparative evaluation of the diagnostic potential of recombinant Toxoplasma gondii ROP5 and ROP18 antigens

Toxoplasmosis is one of the most common parasitic diseases worldwide and it poses a serious challenge regarding prevention, diagnosis and therapy. The commonly used diagnostic methods are mostly based on the detection of specific antibodies in sera. Since they are not always accurate enough and do not allow precise definition of the phase of the Toxoplasma gondii infection, there is an urgent need to find specific molecular markers of acute or chronic infection stages. This study provides a comparative assessment of recombinant ROP5 and ROP18 T. gondii proteins in the serodiagnosis of human toxoplasmosis. We found that both ROP5 and ROP18 proteins allowed the detection of specific IgM and IgG antibodies with a relatively low sensitivity; however, ROP18 IgM ELISA proved to be more sensitive than the SAG1 assay. This study also points to a relatively weak potential of the corresponding native ROP5 and ROP18 kinases in the generation of a strong antibody response in humans.