Antigen-specific CD8+ T cell clone protects against acute Toxoplasma gondii infection in mice.

Encephalitis caused by the obligate intracellular protozoan, Toxoplasma gondii, is a major cause of morbidity and mortality in those afflicted with AIDS. The cell-mediated response is critical for host immunity against this parasite. A panel of T cell clones that proliferate in response to a major parasite protein, p30 (SAG-1) were isolated from mice. One of these clones (C3) bearing the CD8+ phenotype was able to induce nearly 100% protection against acute infection when adoptively transferred into naive mice. In contrast, an Ag-specific CD4+ T cell clone (C2) failed to show significant protection in spite of its ability to produce similar quantities of IFN-gamma. Depletion of host CD4+ T cells with mAb had no effect on CD8(+)-mediated adoptive protection, whereas treatment with anti-IFN-gamma completely abrogated this protection. These results indicate that Ag-specific CD8+ T cells in combination with IFN-gamma are able to induce significant protection against acute toxoplasmosis in the experimental murine model.