Effects of delayed addition of growth factors on survival of CFU-GEMM, CFU-GM, and BFU-E. Results shown are a combined analysis for 6 mice each for CCR2 (−/−) and (+/+) mice using unseparated BM cells and purified c-kit⁺lin⁻ cells as described in Materials and Methods, in which hemin was either in all plates before addition of growth factors or in which hemin was left out of the plates, but present in the cocktail of growth factors added at time 0 or during addition at later time points. Survival of MPC is based on time 0 control colony counts. Each point represents the mean of the combined data ±1 SEM. P values were less than .01 for each graph at each time point, except for the 24-hour point in the BFU-E graph, in which the P value is .04.