Toxoplasmosis in humans and other animals is caused by the protozoan parasite Toxoplasma gondii. During the process of host cell invasion and parasitophorous vacuole formation by the tachyzoites, the parasite secretes Rhoptry protein 8 (ROP8), an apical secretory organelle. Thus, ROP8 is an important protein for the pathogenesis of T. gondii. The ROP8 DNA was constructed into a pVAX-1 vaccine vector and used for immunizing BALB/c mice. Immunized mice developed immune response characterized by significant antibody responses, antigen-specific proliferation of spleen cells, and production of high levels of IFN-γ (816 ± 26.3 pg/mL). Challenge experiments showed significant levels of increase in the survival period (29 days compared with 9 days in control) in ROP8 DNA vaccinated mice after a lethal challenge with T. gondii. Results presented in this study suggest that ROP8 DNA is a promising and potential vaccine candidate against toxoplasmosis.
Matched MeSH terms: Toxoplasmosis, Animal/prevention & control
The full length surface antigen 2 (SAG2) gene of the protozoan parasite Toxoplasma gondii was cloned and intracellularly expressed in the Pichia pastoris expression system. The molecular weight of the expressed recombinant SAG2 (36 kDa) was much larger than the native SAG2 (22 kDa). This discrepancy in size was due to hyperglycosylation, as deglycosylation assay reduced the size of the recombinant SAG2 to 22 kDa. Despite being hyperglycosylated, the recombinant SAG2 reacted strongly with pooled anti-Toxoplasma human serum, pooled anti-Toxoplasma mouse serum and a SAG2-specific monoclonal antibody. The glycosylated recombinant SAG2 was further evaluated in Western blot and in-house enzyme-linked immunosorbent assay (ELISA) using 80 human serum samples, including confirmed early acute (IgM positive, IgG negative; n=20), acute (IgM positive, IgG positive; n=20) and chronic (IgM negative, IgG positive; n=20) toxoplasmosis patients, and toxoplasmosis negative control patients (n=20). Results of the Western blot showed that the recombinant SAG2 reacted with all 60 samples of the toxoplasmosis cases but not with the Toxoplasma-negative samples. The sensitivity of in-house ELISA was 80%, 95% and 100% for early acute, acute and chronic patients' serum samples, respectively. Vaccination study showed that serum from mice immunised with the glycosylated recombinant SAG2 reacted specifically with the native SAG2 of T. gondii. The mice were significantly protected against lethal challenge with live T. gondii RH strain tachyzoites (P<0.01) and their survival time was increased compared to controls. Therefore, the present study shows that the P. pastoris-derived recombinant SAG2 was specific and suitable for use as antigen for detecting anti-Toxoplasma IgG and IgM antibodies. The vaccination study showed that recombinant SAG2 protein was immunoprotective in mice against lethal challenge.
Matched MeSH terms: Toxoplasmosis, Animal/prevention & control
AbstractToxoplasma gondii infects a broad range of warm-blooded hosts, including humans. Important clinical manifestations include encephalitis in immunocompromised patients as well as miscarriage and fetal damage during early pregnancy. Toxoplasma gondii dense granule antigen 2 and 5 (GRA2 and GRA5) are essential for parasitophorous vacuole development of the parasite. To evaluate the potential of GRA2 and GRA5 as recombinant DNA vaccine candidates, these antigens were cloned into eukaryotic expression vector (pcDNA 3.1C) and evaluated in vaccination experiments. Recombinant DNA vaccines constructed with genes encoding GRAs were validated in Chinese hamster ovary cells before evaluation using lethal challenge of the virulent T. gondii RH strain in BALB/c mice. The DNA vaccines of pcGRA2 and pcGRA5 elicited cellular-mediated immune response with significantly higher levels of interferon-gamma, interleukin-2 (IL-2), IL-4, and IL-10 (P < 0.05) compared with controls. A mixed T-helper cell 1 (Th1)/Th2 response was associated with slightly prolonged survival. These findings provide evidence that DNA vaccination with GRA2 and GRA5 is associated with Th1-like cell-mediated immune responses. It will be worthwhile to construct recombinant multiantigen combining full-length GRA2 or/and GRA5 with various antigenic proteins such as the surface antigens and rhoptry antigens to improve vaccination efficacy.