Schematic representation of the different steps to determine the proliferative and (anti-)apoptotic fractions in the different differentiation stages of maturating erythroid cells. (A) Either the Ki-67⁺ or Bcl-2⁺ fraction was first gated. (B) The maturation pathway was then drawn (based on CD117 and HLA-DR expression in the case of erythroid differentiation) and automatically divided into 20 equal maturation stages by the Infinicyt (version 2.0) software package. (C) The Ki-67⁺ or Bcl-2⁺ fraction was then calculated per maturation stage and plotted against the different maturation stages. The proliferative fraction of erythroid cells, as determined by the Ki-67⁺ fraction, was significantly lower for MDS patients in all stages of maturation compared with the proliferative fraction in healthy BM.³²  SSC, side scatter.