The inhibitory effect of hTpo on erythroid and the positive effect of hTpo on CFU-MIX and CFU-Meg are blocked by adding neutralizing anti-hTpo antibody in the cultures.

E8.5 yolk sac cells were plated at 2500 cells/250 μL in 24-well plates in the primitive erythroid colony assay containing various concentrations of neutralizing anti-hTpo antibody or control antibody (A). E9.5 yolk sac cells were plated at 10 000 cells/mL in the progenitor assay or megakaryocyte assay containing 0.5 μg/mL neutralizing anti-hTpo antibody or control antibody (B). *The statistical significance when various conditions are compared with the condition of no Tpo, P < .05. **The statistical significance when hTpo + anti-hTpo group is compared with that of hTpo and hTpo + control antibody, P < .05. Data represent the mean values of triplicate samples from 4 experiments; error bars represent SEM.