Effect of maturing myeloid precursors on stromal production of IL-6 and G-CSF. From 10,000 to 50,000 CD15⁺/CD14⁻ myeloid precursors/well were seeded in contact (stroma contact, SC) or separated by a transwell insert (stroma noncontact, SNC) from irradiated stromal layers in 24-well plates. SNs were obtained 2 and 7 days after seeding, and cytokine levels were determined by ELISA. Numbers within the figure indicate number of experiments. Comparison between stroma only and stroma plus precursors (cells either in contact with or separated from stroma): ¥P < .005, ¥¥P < .001.