GAMMA-DELTA-T-CELLS PLAY A CRUCIAL ROLE IN THE EXPRESSION OF 65000-MWHEAT-SHOCK PROTEIN IN MICE IMMUNIZED WITH TOXOPLASMA ANTIGEN

Toxoplasma gondii is an obligate intracellular protozoan parasite and cellular immunity plays a crucial role in protection against infection with this pathogen. When mice are immunized with Toxoplasma homogenat e, they readily acquire resistance against infection with a lethal dos e of a low virulence Beverley strain of T. gondii. We have reported pr eviously that expression of 65 000 MW heat-shock protein (hsp 65) in h ost macrophages closely correlates with protective potentials of hosts , while this protein is not expressed in Toxoplasma themselves. In thi s study, we examined the mechanism of expression of hsp65 in mice immu nized with Toxoplasma homogenate. Heat-shock protein was detected in p eritoneal macrophages of BALB/c mice immunized 7 days previously by el ectroblot assay with a specific monoclonal antibody (mAb) for microbia l hsp 65. Furthermore, an immunogold ultracytochemistry assay demonstr ated that this protein was expressed on the cell surface of peritoneal macrophages in immune mice. This expression was not induced in those of immune athymic nude mice and SCID mice. Treatment of BALB/c mice wi th anti-Thy-1.2 mAb 1 day before immunization led to an almost complet e loss of the expression of hsp 65. To determine the subsets of T cell s responsible for induction of this protein, mice were depleted of gam ma delta T cells, alpha beta T cells, CD4(+) T cells or CD8(+) T cells by treating with corresponding antibodies before immunization. From t hese experiments, gamma delta T cells were shown to be essential for t he expression of hsp 65, although CD4(+) alpha beta T cells also contr ibuted to some extent. Thus, gamma delta T cells appear to play an imp ortant role in protective immunity against infection with T. gondii th rough mediating the expression of hsp 65 in host macrophages.