Absence of either recipient or donor-derived IL-6 is insufficient to protect mice from lethal GVHD. (A-B) Lethally irradiated (1000 cGy) B6 (n = 13) or IL-6^−/− (n = 13) animals received a transplant of 10 × 10⁶ BM and 15 × 10⁶ spleen cells from Balb/c mice. Overall survival (A) and the percentage of original body weight over time (B) are depicted. Data are cumulative results from 4 independent experiments. (C-D) Lethally irradiated (900 cGy) Balb/c mice received a transplant of 10 × 10⁶ BM and 0.5 to 0.7 × 10⁶ spleen cells from either B6 (n = 16) or IL-6^−/− (n = 16) animals. Overall survival (C) and the percentage of original body weight over time (D) are depicted. Data are cumulative results from 4 independent experiments. (Statistics: **P < .01.)