title: Protective immunity against Toxoplasma gondii induced by DNA immunization with the gene encoding a novel vaccine candidate: calcium-dependent protein kinase 3.
abstract: BACKGROUND
  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.
  
  
  METHODS
  In 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.
  
  
  RESULTS
  The 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%.
  
  
  CONCLUSIONS
  TgCDPK3 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.
authors.forename: Nian-Zhang
authors.initials: NZ
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Veterinary Etiological Biology, Key Laboratory of Veterinary Parasitology of Gansu Province, Lanzhou Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Lanzhou, Gansu Province 730046, PR China. huangsiyang@caas.cn.
authors.forename: Si-Yang
authors.initials: SY
authors.lastname: Huang
authors.forename: Dong-Hui
authors.initials: DH
authors.lastname: Zhou
authors.forename: Jia
authors.initials: J
authors.lastname: Chen
authors.forename: Ying
authors.initials: Y
authors.lastname: Xu
authors.forename: Wei-Peng
authors.initials: WP
authors.lastname: Tian
authors.forename: Jing
authors.initials: J
authors.lastname: Lu
authors.forename: Xing-Quan
authors.initials: XQ
authors.lastname: Zhu
mesh_terms: D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000276:immunology*; D016207:Cytokines / Q000097:blood; D005260:Female; D051379:Mice; D011494:Protein Kinases / Q000235:genetics / Q000276:immunology*; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology*; D016052:Protozoan Vaccines / Q000235:genetics / Q000276:immunology / Q000494:pharmacology*; D011897:Random Allocation; D014122:Toxoplasma / Q000235:genetics / Q000276:immunology*; D014124:Toxoplasmosis, Animal / Q000276:immunology / Q000517:prevention & control*; D019444:Vaccines, DNA / Q000235:genetics / Q000276:immunology / Q000494:pharmacology*
chemical_list: D000913:Antibodies, Protozoan; D002135:Calcium-Binding Proteins; D016207:Cytokines; D015800:Protozoan Proteins; D016052:Protozoan Vaccines; D019444:Vaccines, DNA; D011494:Protein Kinases