Abstract
BackgroundToxoplasma gondii can infect almost all warm-blood animals including human beings. The plant-like calcium-dependent protein kinases (CDPKs) harbored by T. gondii are involved in gliding motility, cell invasion, egress and some other developmental processes, and so have been implicated as important virulence factors.MethodsIn the present study, we constructed a DNA vaccine expressing T. gondii CDPK3 (TgCDPK3) and evaluated its protective efficacy against T. gondii infection in Kunming mice. The gene sequence encoding TgCDPK3 was inserted into the eukaryotic expression vector pVAX I, and mice were immunized with pVAX-CDPK3 intramuscularly.ResultsThe results showed that mice immunized with pVAX-CDPK3 developed a high level of specific antibodies and a strong lymphoproliferative response. The significantly increased levels of IFN-γ, IL-2, IL-12 (p70) and IL-23 and high ratio of IgG2a to IgG1 antibody titers indicated that a Th1 type response was elicited after immunization with pVAX-CDPK3. Furthermore, the percentage of CD4+ T cells in mice vaccinated with pVAX-CDPK3 was significantly increased. After lethal challenge with the tachyzoites of the virulent T. gondii RH strain, the mice immunized with pVAX-CDPK3 prolonged the survival time from 10 days to 24 days (13.5 ± 4.89) compared to untreated mice or those received PBS or pVAX I which died within 7 days (P < 0.05). In chronic infection model (10 cysts of the T. gondii PRU strain), the numbers of brain cysts of the mice immunized with pVAX-CDPK3 reduced significantly when compared with those in control groups (P < 0.05), and the rate of reduction could reach to about 50%.ConclusionsTgCDPK3 can generate protective immunity against acute and chronic T. gondii infection in Kunming mice and is a promising vaccine candidate for further development of an effective vaccine against T. gondii.
Highlights
Toxoplasma gondii can infect almost all warm-blood animals including human beings
A family of calcium-dependent protein kinases (CDPK) is known as key effectors in regulating calcium related signaling pathways in apicomplexan, which control a diverse array of functions in the life cycle including gliding motility, cell invasion, egress and some other developmental processes that occur at distinct stages in their complex life [14]
Specific green fluorescence was observed in HEK293 cells transfected with the eukaryotic recombinant plasmid pVAX-CDPK3, but not in the negative controls that transfected with the same amount of empty pVAX I. These results revealed that the T. gondii CDPK3 (TgCDPK3) protein was expressed successfully in HEK293 cells
Summary
Toxoplasma gondii can infect almost all warm-blood animals including human beings. The plant-like calcium-dependent protein kinases (CDPKs) harbored by T. gondii are involved in gliding motility, cell invasion, egress and some other developmental processes, and so have been implicated as important virulence factors. The only licensed vaccine based on the attenuated-live T. gondii S48 strain (Toxovax®) can be used to prevent the incidence of abortion in sheep [11], it is limited to be further explored in food-producing animals or humans in view of the safety concerns on its reverting to a virulence wild type. A family of calcium-dependent protein kinases (CDPK) is known as key effectors in regulating calcium related signaling pathways in apicomplexan, which control a diverse array of functions in the life cycle including gliding motility, cell invasion, egress and some other developmental processes that occur at distinct stages in their complex life [14]. No studies have evaluated the immunogenicity of TgCDPK3 and its potential as a vaccine candidate against T. gondii infection
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