Recipients of IL-17^−/− CD4⁺ T cells have decreased frequency of CD4⁺ Tbet⁺ cells in the MLN and decreased IFN-γ levels in the serum on day 7 after BMT. Lethally irradiated BALB/c mice were reconstituted with 5 × 10⁶ WT TCD-BM and 0.5 × 10⁶ WT or IL-17^−/− CD4⁺ T cells. MLN from recipient mice were harvested on days 7, 14, and 21 after BMT. (A) The absolute number of MLN from recipients of CD4⁺ WT (gray) and CD4⁺IL-17^−/− (black) T cells. The mean of each group is shown; data represent 3 combined experiments on days 7 (n = 48) and 14 (n = 28), and 1 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 MLN was determined using flow cytometry. The mean of each group is shown, and data represent one of 3 experiments (days 7 and 14), day 7 (n = 6), day 14 (n = 9) or a single experiment (day 21, n = 9). (C) MLN 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), and data represent one experiment of 2. (D) Cytokine levels in the serum on day 7 after BMT were measured by CBA and ELISA. Shown is the mean for each group (n = 7), one representative experiment of 3. **P ≤ .01.