MSCs inhibit the production of IL-12 and the capability of stimulating T-cell response in MLR of monocyte-derived cells. (A) Il-12p70 production was measured in culture SN after 48-hour stimulation with LPS of monocyte-derived cells cultured for 5 days with GM-CSF and IL-4 under different culture conditions. Standard (ctr), with the addition of MSCs or of MSCs and the PGE₂ inhibitor NS-398 or of PGE₂ (1 μM) added at day 0, with MSCs added at day 5. Results are expressed as pg/mL. (B) In MLR experiments, monocyte-derived cells were irradiated and used in graded doses to stimulate allogeneic T cells (10⁵ responder cells/well). After culture for 5 days, T-cell proliferation was evaluated by incubating cells with ³H-thymidine for additional 16 hours. Cells were then harvested and ³H-thymidine uptake was measured. Because of the variable degree of proliferation of different T-cell populations used as responder cells, data are not expressed as cpm values but as percentages. We considered 100% the maximal proliferation of T cells stimulated with DCs (5 × 10² cells/well) obtained under standard conditions, and relative percentage the proliferation of T cells stimulated by cells obtained under the other culture conditions. Bars represent mean ± SD from 5 independent experiments. *P < .05; **P < .01.