MAPCs inhibit T-cell alloresponses through the secretion of PGE₂. B6 > BALB/c MLR cultures were arranged as before. MAPCs, either untreated, treated overnight with 5 μM indomethacin to inhibit production of PGE₂, or treated with vehicle, were titrated in at 1:10 ratios. Proliferation was assessed as above (panel A).