ROLE OF A 65-KDA HEAT SHOCK PROTEIN IN PROTECTIVE IMMUNITY AGAINST TOXOPLASMA INFECTION

A 65-kDa heat shock protein (HSP65) is present in mouse peritoneal macrophages that have been infected with a low-virulence Beverley strain of Toxoplasma gondii or immunized with Toxoplasma homogenate, as determined by electroblot assay using a monoclonal antibody specific for microbial HSP65. This HSP65 is, however, not expressed in the infection with the high-virulence RH strain of T. gondii. Furthermore, mice previously vaccinated with a sublethal dose of live Beverley strain bradyzoites of T. gondii, acquired resistance against infection with the virulent RH strain and they likewise expressed HSP65. Rats are genetically resistant against the infection even with high dose of RH strain, and HSP65 is also expressed in their peritoneal macrophages. These results suggest the important role played by HSP65 in developing effective defense reactions that include effective immune response against infection with T. gondii in vivo. We clarified that gamma delta T cells as well as CD4(+) T cells play a crucial role in the expression of HSP65 in macrophages of animals which have acquired resistance against Toxoplasma infection. The expression mechanism(s) and the function of HSP65 are still unknown.