No abstract

Protective immunity against Toxoplasma gondii is known to be mediated mainly by T lymphocytes and gamma interferon (IFN-␥). The contribution of CD4؉ and CD8 ؉ T-lymphocyte subsets to protective immune responses against T. gondii infection, triggered by a GRA1 (p24) DNA vaccine, was assessed in this study. In vitro T-cell depletion experiments indicated that both CD4؉ and CD8 ؉ T-cell subsets produced IFN-␥ upon restimulation with a T. gondii lysate. In addition, the GRA1 DNA vaccine elicited CD8 ؉ T cells that were shown to have cytolytic activity against parasite-infected target cells and a GRA1-transfected cell line. C3H mice immunized with the GRA1 DNA vaccine showed 75 to 100% protection, while 0 to 25% of the mice immunized with the empty control vector survived challenge with T. gondii cysts. In vivo T-cell depletion experiments indicated that CD8 ؉ T cells were essential for the survival of GRA1-vaccinated C3H mice during the acute phase of T. gondii infection, while depletion of CD4 ؉ T cells led to an increase in brain cyst burden during the chronic phase of infection.