Stimulation of allogeneic PBMCs by TAMs and monocytes exposed to GM-CSF or medium alone. CD14⁺ monocytes isolated from 4 different donors were cultured for 3 days in medium alone or in the presence of either 100 nM Trx80 (TAMs) or GM-CSF + IL-4. These cells were subsequently harvested, irradiated, and tested as stimulators of freshly separated allogeneic PBMCs (responders). Each such stimulator cell preparation was tested with 3 or 4 different responder preparations, to give a total number of 14. For this purpose, the PBMCs (10⁶/mL) were cultured in triplicate on 96-well plates in the presence of 1/10 to 1/10 000 as many stimulator cells. Following 5 days of such culture, 1 μCi (0.037 MBq) [³H]thymidine was added to each well 8 hours prior to termination of the incubation. The SI was calculated as the ratio of the radioactivity incorporated (cpm) by the responder cells in the presence of stimulator cells to the corresponding value for the responder cells cultured alone. The data presented are the median values obtained with the 14 different cell preparations of the responders which incorporated between 180 and 665 cpm tritiated thymidine when cultured alone. • indicates responders cells in the presence of stimulator cells exposed to GM-CSF + IL-4; ▵, responder cells cultured with TAMs; ♦, responder cells cultured together with stimulator cells exposed only to medium. The stimulatory index for stimulator cells cultured in the presence of GM-CSF + IL-4 was significantly higher than that for TAMs or monocytes cultured in medium alone (P < .05), as determined by the Wilcoxon matched-pairs test.