CD150 divides the SP into 2 distinct fractions. (A) From mice at 10 weeks of age, bone marrow SP cells that are c-Kit+, Sca-1+, Lin− (SPKLS) were examined for expression of SLAM family members CD41, CD48, and CD150. (B) At 10 weeks of age, all SPKLS cells express little or no CD41 and CD48, and only one-third of SPKLS cells express CD150. Percentages shown correspond to the gated proportion of the plot.