IL-17^−/− donor cells induced exacerbated acute GVHD. (A) Sublethally irradiated BALB/c recipients were transplanted with graded numbers (1.25∼2.5 × 10⁶) spleen cells and 2.5 × 10⁶ TCD-BM cells from wild-type (WT) or IL-17^−/− C57BL/6 donors. The recipients were checked for clinical signs of GVHD and body weight every 5 days and monitored for survival daily. Body weight change and survival curves are shown. There were 12 mice in each group, and 3 replicated experiments were combined, except the group given TCD-BM alone had 4 recipients. (B,C) Histopathology of liver, gut, and lung of recipients given TCD-BM alone or TCD-BM and spleen cells (2.5 × 10⁶) from WT or IL-17^−/− donor 13 days after HCT. One representative histopathology and mean (± SE) of histologic score of 6 examined recipients in each group are shown. (D,E) Sublethally irradiated BALB/c recipients were transplanted with sorted T cells (0.5 × 10⁶) from WT or IL-17^−/− donors. Clinical score and survival curves are shown. There were 8 recipients in each group; 2 replicated experiments were combined. (F) Liver mononuclear cells of the recipients were stained for H-2^b (donor marker), CD4, CD8, and intracellular IL-17 on day 10 after HCT. Gated H-2b⁺ cells are shown in IL-17 versus CD4 or CD8. The percentage of IL-17 CD4⁺ or CD8⁺ T cells is shown beside the gating boxes. Mean (± SE) of the IL-17⁺ CD4⁺ or CD8⁺ T cells in the liver of recipients given WT donor T cells are 0.69 (± 0.02) or 0.77 (± 0.08). IL-17⁺ T cells in the spleen of the recipients given IL-17^−/− donor T cells were not detectable (< 0.05%).