TOXOPLASMA-GONDII - EFFECT OF SUBLETHAL IRRADIATION ON HOST-RESISTANCE IN MICE

The effect of sublethal whole-body irradiation (500 rad) on the resist ance of C57BL/6 mice to infection with Toxoplasma gondii was studied. Mice irradiated I day before or 4 days after infection via the intrape ritoneal or peroral route with cysts of the mildly virulent ME49 strai n of T. gondii died sooner than did unirradiated controls. The time to death of irradiated mice was suggestive of impaired acquired immunity . Irradiated mice infected intraperitoneally with T. gondii cysts exhi bited reduced levels of Thy-1(+)CD4(-)CD8(-) cells, less natural kille r cell activity against YAC-1 targets, and lower levels of IFN-gamma t han controls. Numbers of CD4(+) and CD8(+) cells were also lower in in fected, irradiated mice. Irradiated mice immunized with a vaccine stra in of T. gondii, and later challenged with a highly virulent strain, w ere less well protected than unirradiated controls. Irradiation appear s to impair early, CD4(+)- and CD8(+)-independent resistance to T. gon dii, as well its acquisition of immunity. (C) 1995 Academic Press, Inc .