HUMORALIMMUNE RESPONSES AGAINST MEMBERS OF THE HSP70 FAMILY IN TOXOPLASMA GONDII

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The cDNA for a member of stress induced 70-kDa protein family (hsp70) from Toxoplasma gondii was cloned. The deduced amino acid sequence revealed a 667 amino acid protein70-80% homologous to other parasite and mammalian hsp70s. Southern blot analysis suggested that it is encoded by an intronless gene. A protein of-77-kDa was identified in a lysate of T. gondii tachyzoites by mAbs generated against the recombinant hsp70 protein. Anti-human hsp70 mAb also cross-reacted with a T gondii protein of the identical molecular weight. However, immunoprecipitation and Western blot analysis of these proteins indicated that it was distinct from the cloned hsp70 product, suggesting that T gondii expresses another hsp 70-like protein. Among 22 mice infected with a low virulence Fukaya strain of T. gondii, 6 mice exhibited significant humoral anti-hsp70 Ab responses. This Ab responses peaked at 1-2 weeks of infection, plateaued for 2-3 weeks and gradually declined to nearly undetectable levels at 6 weeks of infection. In contrast, the levels of serum Ab specific for soluble tachyzoite Ags continued to increase during the infection in all mice examined. These features suggest that pathogen-derived hsp70 may play a unique role in the induction and maintenance of the host immune responses.