The protective effects of IFNγ are mediated through host tissue. Balb/c donors were mobilized with G-CSF and splenocytes were transplanted into irradiated (1000 rad) wt (n = 15) or IFNγR^−/− (n = 20) B6 recipients. TCD splenocytes were transplanted into wt (n = 6) or IFNγR^−/− recipients (n = 6) as non-GVHD controls. Data pooled from 2 identical experiments. (A) Survival determined by Kaplan-Meier analysis. #P < .001, IFNγR^−/− versus wt recipients. (B) GVHD clinical scores were determined as a measure of GVHD severity in surviving animals. **P < .01, IFNγR^−/− versus wt recipients. Data expressed as means ± SE.