FACS analysis of wild-type and IL-6^-/- stromata. Wild-type and IL-6^-/- BM cells were cultured for 2 weeks in Dulbecco modified Eagle medium plus 10% FCS at 37°C, with weekly medium exchange. Cells were harvested by brief trypsinization and FACS analyzed as described (“Materials and methods”). Results are expressed as the mean ± SD of 4 experiments. ^*P < .01, for wild-type versus IL-6^-/- stromal cells.