Effect of the Jak2 inhibitor AG 490 on the growth and differentiation of 32D transfectants. Cells were cultured in IMDM/10% FCS containing 2 ng/mL IL-3 (32D/neo cells) or 2 U/mL Epo (32D/EpoR WT and 32D/EpoR FE cells). The indicated concentration of the Jak2 inhibitor AG 490 was added at 0 hours and again at 24 and 48 hours. The cells were studied at 72 hours. AG 490 concentrations were 0, 0.1, 1, 2, 5, and 10 μmol/L. 32D/neo (□), 32D/EpoR WT (○), 32D/EpoR FE (•). (A) The viable cells were counted and expressed as a function of increasing AG 490. The initial cell number (10,000 cells) is indicated by the dotted line. Each point was done in triplicate. Standard error at each point was 10% or less of indicated value and has been omitted for clarity. (B) Cytospins were stained for Mpo. Mpo positive cells were counted and expressed as a function of increasing AG 490. Each point was done in triplicate with standard error bars shown. (C) Representative fields of Mpo-stained cytospins of 32D/EpoR WT cells at the indicated AG 490 concentrations.