IL-15 AUGMENTS CD8(-MEDIATED-IMMUNITY AGAINST TOXOPLASMA-GONDII INFECTION IN MICE() T CELL)

Cytokines of the Th1 profile are important mediators of protective hos t immunity against Toxoplasma gondii infection in mice, In this study we describe the effect of the recently identified cytokine, IL-15, on prevention of murine infection with T. gondii. Administration of exoge nous rIL-15 with soluble Toxoplasma lysate Ag (TLA) provides complete protection against a lethal parasite challenge, whereas treatment with either rIL-15 or TLA alone is not protective. Following immunization with TLA/rIL-15, there is a significant proliferation of splenocytes e xpressing the CD8(+) phenotype in response to TLA. A significant rise in the level of serum IFN gamma was observed in vaccinated mice. Adopt ive transfer of CD8(+) T cells, but not CD4(+) T cells, from TLA/rIL-1 5-vaccinated mice protects naive mice from a lethal parasite challenge . These CD8(+) T cells exhibit enhanced CTL activity against target ma crophages infected with T. gondii. Mice that have been immunized are p rotected against lethal parasite challenge for at least 1 mo postvacci nation. These observations demonstrate that TLA when administered with exogenous rIL-15 generates toxoplasmacidal Ag-specific CD8(+) T cells . These T cells proliferate upon exposure to parasite Ag, exhibit long term memory CTL against infected target cells, and may be involved in host immune memory to this parasite.