Induction of Protective Immunity by hsp70 Derived from Intracellular Parasites

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(1) We have cloned a full-length cDNA of Toxoplasma hsp7O and produced its recombinant protein as well as monoclonal antibodies against it. Using these reagents, we identified two hsp7O-like protein expressed in T.gondii. Mice orally infected with T.gondii showed significant antibody responses against T.gondii hsp7O during acute phase but not during chronic phase of infection. Immunization of mice with purified T.gondii hsp7O conferred protective immunity against challenge infection with T.goiidii. The protective effect was more significant in mice immunized with hsp7O purified from T.gondii than those immunized with recombinant hsp7O, suggesting that hsp7O-associated molecule may play a role in inducing the protective immunity.(2) The effect of CD8 cytotoxic T lymphocyte (CTL)-mediated lysis of host cells on the viability of intracellular T.gondii was investigated. Quantitative competitive PCR of the gene encoding T.gondii major surface antigen (SAG-1) was combined with treatment of the parasites with DNase, which removed the DNA template of non-viable parasites. The induction by CD8 CTL of apoptosis in cells infected with T.gondii did not result in the reduction of live parasites, indicating that intracellular T.gondii remains alive after lysis of host cells by CTL.