Recombinant human IL-3 (HZ-1074) stimulates dose-dependent proliferation of the TF-1 human erythroleukemic indicator cell line. Cell number was quantitatively assessed by PrestoBlue® Cell Viability Reagent. TF-1 cells were treated with increasing concentrations of recombinant IL-3 for 72 hours. The EC50 was determined using a 4-parameter non-linear regression model. The EC50 range is 0.4-2.0 ng/mL