Abstract
BackgroundToxoplasma 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.MethodsBALB/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.ResultsThe 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).ConclusionsThese 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.
Highlights
Toxoplasma gondii is a widespread intracellular parasite, which infects most vertebrate animal hosts and causes zoonotic infection in humans
Expression of plasmid pGRA4 in HEK293T cell Forty-eight hours after HEK cells were transfected with pGRA4 or empty plasmid pEGFP, specific green fluorescence was observed under a fluorescence microscope, whereas there was no signal in the untransfected cells (Figure 1A, B & C)
These results indicated that the recombinant plasmid was successfully constructed and expressed in vitro and recombinant TgGRA4 protein possessed immunological activity
Summary
Toxoplasma gondii is a widespread intracellular parasite, which infects most vertebrate animal hosts and causes zoonotic infection in humans. Toxoplasma gondii is a widespread intracellular parasite belonging to the phylum Apicomplexa, which infects most vertebrate animal hosts and causes zoonotic infection in humans [1]. The development of an effective and safe vaccine against T. gondii acute and chronic infection is an important and urgent goal. DNA vaccines against T. gondii have been proved that they can induce antibody, specific T-cell responses and protective immunity against acute and chronic challenge in mice [13,14]. Several studies have demonstrated the power of synthetic polypeptides vaccines in eliciting protective immunity to intracellular parasites such as Plasmodium falciparum [18], Schistosoma mansoni [19], T. gondii [17], and Paracoccidioides brasiliensis [20]
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