Effect of IFNα on cell cycle and apoptosis of LSK and SLAM cells from KI and WT mice. (A) Percentages of LSK (top) or SLAM (below) in G0 (Ki67^Low/H33342²ⁿ, quiescent), G1 (Ki67^High/H33342²ⁿ, activated), and S/G2/M (Ki67^High/H33342⁴ⁿ, cycling) phases after 3 days of in vivo treatment by vehicle or IFNα. Results show that KI SLAM are more proliferative than WT SLAM but that IFNα induced proliferation of WT LSK and SLAM cells, reducing the differences in cycle between WT and KI SLAM cells. (B) Percentage of apoptotic cells (annexin V) in BM (top) and spleen (bottom) of Lin-, LK, LSK, and SLAM cells after 3 days of in vivo treatment by vehicle or IFNα. Results showed that BM and spleen LSK and SLAM cells are less apoptotic in KI mice than in WT mice and that IFNα slightly increased apoptosis, especially of spleen KI cells. *P ≤ .05 with the 2-tailed unpaired Student t test. Both cycle and apoptosis results are mean values ± SEM, n = 6, of 2 independent experiments each including 3 IFNα-treated and 3 VEH-treated WT and KI mice around 3 months of age.