Effect of phenotypically defined groups of 2-day C OBs on HPC function. (A) Two-day C OBs were stained as described in “Methods.” Gated CD45⁻CD31⁻Ter119⁻ cells were separated into Sca1⁻ALCAM⁺ and Sca1⁻ALCAM⁻ cells, which were used in assays shown in panel B. (B) Increase in cell number from the original LSK cells and production of clonogenic progenitors in the presence of phenotypically defined groups of OBs. +P < .01 compared with fold increase in cell number in calvarial OB cultures. *P < .01 compared with fold increase in CFU in calvarial OB cultures.