DNA vaccination with a gene encoding Toxoplasma gondii GRA6 induces partial protection against toxoplasmosis in BALB/c mice

<p>Abstract</p> <p>Background</p> <p>Infection with the protozoan <it>Toxoplasma gondii </it>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 <it>T. gondii </it>antigens and host genes required for eliciting protective immunity have been poorly defined. The <it>T. gondii </it>dense granule protein 6 (GRA6), recently proved to be highly immunogenic and produces fully immune protection in <it>T. gondii </it>infected BALB/c mice with an H-2L^dgene. The CD8+ T cell response of H-2L^dmice infected by the <it>T. gondii </it>strain seemed to target entirely to a single GRA6 peptide HF10-H-2L^dcomplex.</p> <p>Results</p> <p>To determine whether a GRA6-based DNA vaccine can elicit protective immune responses to <it>T. gondii </it>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 <it>T. gondii </it>RH strain tachyzoites. All immunized mice developed high levels of serum anti-GRA6 IgG antibodies, and <it>in vitro </it>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-2L^dfailed to survive.</p> <p>Conclusions</p> <p>Our 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.</p