Abstract
Toxoplasma gondii, an obligate intracellular protozoan parasite, can cause infect almost all warm-blooded animals and humans. To evaluate the immunogenicity and protective efficacy of T. gondii GRA39 (TgGRA39) in mice by using DNA immunization, we constructed a recombinant eukaryotic plasmid pVAX-TgGRA39. The specific immune responses in immunized mice were analyzed by serum antibody and cytokine measurements, lymphocyte proliferation assays and flow cytometry of T lymphocyte subclasses. Also, protective efficacy against acute and chronic T. gondii infection was assessed by observing the survival time after challenge with the highly virulent T. gondii RH strain (Genotype I) and counting the number of cyst-forming in brain at 4 weeks post-infection with the cyst-forming PRU strain of T. gondii (Genotype II), respectively. Our results showed that DNA immunization with pVAX-GRA39 via intramuscular injection three times, at 2-week intervals could elicit humoral and cellular immune response, indicated by enhanced levels of IgG and IgG2a antibodies (a slightly elevated IgG2a to IgG1 ratio), and increased levels of cytokines IFN-γ, IL-2, IL-12, IL-17A, IL-17F, IL-22 and IL-23 and percentages of CD3+ CD4+ CD8- and CD3+ CD8+ CD4– T cells, in contrast to non-immunized mice. The significant increase in the expression levels of IL-6, TGF-β1, IL-1β, and the transcription factor factors RORγt, RORα, and STAT3 involved in the activation and pathway of Th17 and Tc17 cells, were also observed. However, no significant difference was detected in level of IL-4 and IL-10 (p > 0.05). These effective immune responses had mounted protective immunity against T. gondii infection, with a prolonged survival time (16.80 ± 3.50 days) and reduced cyst numbers (44.5%) in comparison to the control mice. Our data indicated that pVAX-TgGRA39 could induce effective humoral, and Th1-type, Th17, and Tc17 cellular immune responses, and may represent a promising vaccine candidate against both acute and chronic T. gondii infection.
Highlights
MATERIALS AND METHODSToxoplasma gondii is an obligate intracellular protozoan parasite that infects a broad range of warm-blooded vertebrates, including humans and birds (Gangneux and Dardé, 2012; Hakimi et al, 2017; Kochanowsky and Koshy, 2018)
Specific green fluorescence was observed in the Marc-145 cells transfected with pVAXGRA39, while no fluorescence was observed in cells transfected with the empty pVAX I (Figure 2A)
The western blotting results revealed a single band of about 100 kDa, which was consistent with the expected molecular size, indicating that pVAX-granule protein 39 (GRA39) was expressed in Marc-145 cells (Figure 2B)
Summary
Toxoplasma gondii is an obligate intracellular protozoan parasite that infects a broad range of warm-blooded vertebrates, including humans and birds (Gangneux and Dardé, 2012; Hakimi et al, 2017; Kochanowsky and Koshy, 2018). Specific-pathogen-free (SPF) female Kunming mice of six to eight weeks old were purchased from Zhejiang Laboratory Animal Center, Hangzhou, China, which have been used as a proper model for T. gondii vaccine evaluation and challenge in previous studies (Chen et al, 2016; Zhang et al, 2018a; Zhu et al, 2020). As described in our previous studies (Chen et al, 2016; Zhang et al, 2018a; Zhu et al, 2020), 2 weeks after the last immunization, 10 mice in all groups were challenged with 103 tachyzoites of the highly virulent T. gondii RH strain intraperitoneally and the survival periods were recorded daily until all mice were dead. The level of significant difference in comparisons between groups was considered significantly different if p < 0.05
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
