Requirement of T-cell polarization and STAT6 but not STAT4 signaling in donor cells for IL-18–mediated GVHD protection.

(A) B6 mice were irradiated and received transplants of control-treated 5 × 10⁶ TCD BM and with 2 × 10⁶ purified CD4⁺ cells from either control-treated (▴, n = 10) or IL-18–treated (●, n = 10) allogeneic BALB/c donors. Syngeneic controls (▪, n = 5) received similar number of T and BM cells from B6 donors. BMT recipients of IL-18–treated CD4⁺ cells showed significantly improved survival (▴ vs ●; **P < .01). (B) B6 mice underwent transplantation as in Figure 1 with either syngeneic B6 (H2^b) donors (▪, n = 6) or allogeneic STAT6-deficient (H2^d) donor mice injected with control diluent (▴, n = 15) or IL-18 (●, n = 15) for 10 days. Data combined from 2 similar experiments are shown (▴ vs ●; P = NS). (C) B6 mice underwent transplantation as in Figure 1 with either syngeneic B6 (H2^b) donors (▪, n = 6) or allogeneic STAT4-deficient (H2^d) donor mice injected with control diluent (▴, n = 15) or IL-18 (●, n = 15) for 10 days (▴ vs ●; *P < .02). Data combined from 2 similar experiments are shown.