MPN monocytes persistently produce high levels of TNF-α. (A) MPN (n = 7 PV, 5 ET, and 4 MF) and normal (n = 13) monocytes were stimulated with 10 ng/mL LPS for 4, 9,18, and 24 hours before harvesting supernatant for ELISA. The amount of TNF-α produced at 4 hours was normalized to 1. (B) MPN (n = 5 PV, 4 ET, and 2 MF) and normal (n = 6) monocytes were stimulated with 10 ng/mL LPS for 4, 8, 13, and 22 hours before harvesting for flow cytometry analysis. All samples were treated with brefeldin A for 4 hours before harvesting. The percentage of monocytes expressing TNF-α at 4 hours was normalized to 1. *P < .05.