Th17 cells play a role in the early stage of CD4-mediated GVHD. (A) Lethally irradiated (850 cGy) BALB/c mice were reconstituted with 5 × 10⁶ WT B6 TCD-BM alone, or with TCD-BM and 10⁶ nylon wool–passed (NWP) WT B6 T cells or IL-17^−/− T cells. Data represent 3 combined experiments: mice either received TCD-BM only (n = 15; dotted line, black square), IL-17^−/− T cells + TCD-BM (n = 30; gray line, gray triangles) or WT T cells ⁺ TCD-BM (n = 30; solid line, black squares). (B) Lethally irradiated BALB/c mice received 5 × 10⁶ WT B6 TCD-BM and 0.5 × 10⁶ CD4⁺ WT B6 T cells or IL-17^−/− T cells. Data represent 4 combined experiments: mice received either TCD-BM only (n = 30) (dotted line, black square), IL-17^−/− CD4⁺ T cells + TCD-BM (n = 35) or WT B6 CD4⁺ T cells + TCD-BM (n = 45), P < .04. (C) Lethally irradiated (1300 cGy) C3FeB6F1 mice were reconstituted with 5 × 10⁶ WT B6 TCD-BM and 2 × 10⁶ NWP T cells WT B6 T cells or IL-17^−/− T cells. Data represent 2 combined experiments: mice received TCD-BM only (n = 10; dotted line, black square), IL-17^−/− T cells ⁺ TCD-BM (n = 20; gray line, gray triangles) or WT T cells + TCD-BM (n = 20; solid line, black squares). (D) Lethally irradiated BALB/c mice were reconstituted with 5 × 10⁶ WT B6 TCD-BM (n = 20; dotted line, black square), or 5 × 10⁶ WT B6 TCD-BM + 0.5 × 10⁶ A20 cells (n = 20; gray line, gray circles), and 0.5 × 10⁶ NWP WT B6 T cells + 0.5 × 10⁶ A20 cells (n = 40; solid line, black squares) or IL-17^−/− T cells + 0.5 × 10⁶ A20 cells (n = 40; gray line, gray triangles). Data represent 4 combined experiments. Survival curves are shown.