FACS analysis of F4/80^high and Mac-1^high cells in culture medium of irradiated wild-type or IL-6^-/- stroma seeded with Lin^- wild-type or IL-6^-/- BM cells. LTBMCs were established, irradiated, and seeded as in Figure 4. F4/80^high (A) and Mac-1^high (B) cells were analyzed weekly in culture medium. Results are expressed as the mean ± SD of 6 experiments. ^*P < .01, for wild-type stroma versus IL-6^-/- stroma.