Recipients of IL-17^−/− CD4⁺ T cells have a decrease in splenic Th1 cells and produce decreased levels of proinflammatory cytokines. Lethally irradiated BALB/c mice were reconstituted with 5 × 10⁶ WT TCD-BM and 0.5 × 10⁶ WT or IL-17^−/− CD4⁺ T cells. Spleens from recipient mice were harvested on days 7, 14, and 21 after BMT. (A) The absolute number of splenoctyes in recipients of CD4⁺ WT (gray) versus CD4⁺IL-17^−/− (black). The mean of each group is shown; data represent 3 combined experiments on days 7 (n = 48) and 14 (n = 28) and one experiment on day 21 (n = 9). (B) The percentage of donor-derived CD4⁺CD25⁺Foxp3⁺ cells (black) and donor-derived CD4⁺Tbet⁺ cells (gray) in the spleen was determined using flow cytometry. The mean of each group is shown; data represent one of 3 experiments (days 7 and 14), day 7 (n = 6), day 14 (n = 9), or day 21 (n = 9; 1 experiment on day 21). (C) The number of IFN-γ⁺ cells on day 7 was determined by intracellular cytokine staining in recipients of CD4⁺ WT (gray) and CD4⁺ IL-17^−/− (black) T cells. Two combined experiments (n = 12). (D) Splenocytes from recipients of WT B6 CD4⁺ T cells (gray) and IL-17^−/− CD4⁺ T cells (black) on day 7 after BMT were stimulated in vitro for 4 hours, the supernatant was collected, and a CBA or an ELISA was performed to determine cytokine levels. Graphs represent the amount of cytokine secreted per 10⁴ cells stimulated. The mean of each group is shown (n = 8); data represent one experiment of 2. *P ≤ .05, **P ≤ .01, ***P ≤ .001.