Relationship between NO production and T-cell suppression. (A) Production of NO. Splenocytes (1 × 10⁶) were incubated with or without Con A in the presence or absence of MSCs for 48 hours. “Transwell” indicates experiments performed in 12-well dishes in which the T cells were separated from MSCs by a 1-μm-pore membrane. The values are the means ± SD from 3 independent experiments. *P < .05. (B) T-cell proliferation in the presence or absence of the transwell system. Splenocytes (1 × 10⁶) were activated with Con A in the presence or absence of 1 × 10⁵ MSCs or RAW264.7 cells for 48 hours with or without the transwell. 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. (C) T cells but not B cells induce NO production. Purified CD4 or CD8 T cells (1 × 10⁵; ∼80% purity) induce NO in the presence of MSCs (1 × 10⁴), whereas purified CD19 B cells (1 × 10⁵; ∼95% purity) do not induce significant NO production. The mitogen for T cells was Con A, and for B cells, it was lipopolysaccharide (1 μg/mL). The values are the means ± SD from 3 independent experiments. *P < .05.