Sensitivities to EPO and TPO of Ba/F3-EPOR and Ba/F3-MPL cells. (A) Ba/F3-EPOR cells expressing each of the JAK2 forms were cultured for 48 hours either in the absence of cytokine (black arrow, x-axis) or in the presence of increasing doses of EPO (0.01, 0.02, 0.03, 0.05, 0.1, 0.3, and 1 U/mL). Viable cells were quantified by WST-1 proliferation assay. Dose-response curves are means expressed in percentages of maximum growth value ± standard error of the mean (SEM; n = 4 in triplicate). (B) Proliferation was assayed 48 hours after culturing Ba/F3-MPL cells expressing each of the JAK2 forms in the absence of cytokine (black arrow, x-axis) or in the presence of increasing doses of TPO (0.005, 0.015, 0.05, 0.15, 0.5, 1.5, and 5 ng/mL). The asterisk indicates 0.05 ng/mL TPO. Data are means ± SEM (n = 4 independent experiments performed in triplicate). Two-tailed Student t test: **P < .01; ****P < .0001. (C) Ba/F3-MPL cell lines were plated at 30 000 cells and cultured over a period of 72 hours in the absence or presence of either 0.05 ng/mL or 5 ng/mL TPO and numbered. Curves show cumulative cell number ± standard deviation of a typical experiment out of 3 performed in triplicate. Insert represents data at 5 ng/mL TPO with an adapted y-axis scale.