Abstract
BackgroundInfection with the protozoan Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide. Protection from acute toxoplasmosis is known to be mediated by CD8+ T cells, but the T. gondii antigens and host genes required for eliciting protective immunity have been poorly defined. The T. gondii dense granule protein 6 (GRA6), recently proved to be highly immunogenic and produces fully immune protection in T. gondii infected BALB/c mice with an H-2Ld gene. The CD8+ T cell response of H-2Ld mice infected by the T. gondii strain seemed to target entirely to a single GRA6 peptide HF10-H-2Ld complex.ResultsTo determine whether a GRA6-based DNA vaccine can elicit protective immune responses to T. gondii in BALB/c mice, we constructed a eukaryotic expression vector pcDNA3.1-HisGRA6 and tested its immunogenicity in a mouse model. BALB/c mice were vaccinated intramuscularly with three doses of GRA6 DNA and then challenged with a lethal dose of T. gondii RH strain tachyzoites. All immunized mice developed high levels of serum anti-GRA6 IgG antibodies, and in vitro splenocyte proliferation was strongly enhanced in mice adjuvanted with levamisole (LMS). Immunization with pcDNA3.1-HisGRA6 with LMS resulted in 53.3% survival of challenged BALB/c mice as compared to 40% survival of BALB/c without LMS. Additionally, immunized Kunming mice without an allele of H-2Ld failed to survive.ConclusionsOur result supports the concept that the acquired immune response is MHC restricted. This study has a major implication for vaccine designs using a single antigen in a population with diverse MHC class I alleles.
Highlights
Infection with the protozoan Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide
The resulting vector consisted of 698 bases of the entire sequence of the open reading frame (ORF) of the granule protein 6 (GRA6) gene, encoding 230 amino acids, followed by a stop codon
The IgG antibody titer was greater in the sera of mice co-inoculated with LMS than in the sera of mice immunized with pcDNA3.1-HisGRA6 alone, but there was no statistically significant difference between the two groups (P > 0.05)
Summary
Infection with the protozoan Toxoplasma gondii causes serious public health problems and is of great economic importance worldwide. The T. gondii dense granule protein 6 (GRA6), recently proved to be highly immunogenic and produces fully immune protection in T. gondii infected BALB/c mice with an H-2Ld gene. Infection with the intracellular parasite Toxoplasma gondii is responsible for toxoplasmosis in humans and other warm-blooded animals. A live attenuated vaccine has been developed for the prevention of chronic infection in sheep [4] It cannot be used in humans because of the risk of reversion to a pathogenic form [5]. Immunization of C3H mice with a plasmid expressing granule protein 1 (GRA1) showed 75-100% protection to challenge with T. gondii cysts [10]. DNA vaccination with protein GRA1, GRA7, and rhoptry protein ROP2 induced protection against infection with different virulent T. gondii strains in C3H mice but not in BALB/c and C57BL/6 mice [11]. Intramuscular injection of sheep with a DNA liposome formulated plasmid coding for GRA1, GRA4, GRA6 and GRA7 is an effective system that induces a significant immune response against T. gondii [13]
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