title: DNA prime and peptide boost immunization protocol encoding the Toxoplasma gondii GRA4 induces strong protective immunity in BALB/c mice.
abstract: BACKGROUND
  Toxoplasma 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.
  
  
  METHODS
  BALB/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.
  
  
  RESULTS
  The 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).
  
  
  CONCLUSIONS
  These 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.
authors.forename: Min
authors.initials: M
authors.lastname: Meng
authors.affiliation: Department of Parasitology, Shandong University School of Medicine, Jinan, Shandong Province, 250012, Peoples Republic of China. zhouah@sdu.edu.cn.
authors.forename: Aihua
authors.initials: A
authors.lastname: Zhou
authors.forename: Gang
authors.initials: G
authors.lastname: Lu
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.forename: Guanghui
authors.initials: G
authors.lastname: Zhao
authors.forename: Yali
authors.initials: Y
authors.lastname: Han
authors.forename: Huaiyu
authors.initials: H
authors.lastname: Zhou
authors.forename: Hua
authors.initials: H
authors.lastname: Cong
authors.forename: Qunli
authors.initials: Q
authors.lastname: Zhao
authors.forename: Xing-Quan
authors.initials: XQ
authors.lastname: Zhu
authors.forename: Shenyi
authors.initials: S
authors.lastname: He
mesh_terms: D000818:Animals; D016054:DNA, Protozoan / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D007273:Injections, Intramuscular; D007371:Interferon-gamma / Q000097:blood; D051379:Mice; D008807:Mice, Inbred BALB C; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology*; D016052:Protozoan Vaccines / Q000235:genetics / Q000276:immunology / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000276:immunology; 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: D016054:DNA, Protozoan; C079248:GRA4 protein, Toxoplasma gondii; D007074:Immunoglobulin G; D015800:Protozoan Proteins; D016052:Protozoan Vaccines; D011994:Recombinant Proteins; D019444:Vaccines, DNA; D007371:Interferon-gamma