A specific inhibitor of NOS restores T-cell proliferation and Stat5 phosphorylation. (A) Effect of L-NAME on thymidine incorporation. Top panel, splenocytes (1 × 10⁵) were activated with Con A in the presence or absence of 2.5 × 10³ irradiated MSCs and in the presence or absence of 1 mM L-NAME. The incorporation of [³H]-thymidine is shown relative to that in the absence of MSCs. The values are the means ± SD from 3 independent experiments. *P < .05. Bottom panel, dose-dependent restoration of T-cell proliferation by L-NAME. Splenocytes (1 × 10⁵) were activated with Con A in the presence of the indicated number of irradiated MSCs for 48 hours. The concentrations of L-NAME are shown. Shown is a typical result of 3 independent experiments. (B) L-NAME restores Stat5 phosphorylation. Splenocytes (2 × 10⁶) were activated with anti-CD3/CD28 beads in the presence or absence of 0.5 × 10⁵ to 1 × 10⁵ MSCs for 48 hours and in the presence or absence of 1 mM L-NAME. Western blotting for phosphorylated and total Stat5 was performed as described in Figure 2. Shown is a representative result from 5 independent experiments.