MPN monocytes produce adequate IL-10 but are less responsive to IL-10. (A) MPN (n = 4 PV, 4 ET, and 3 MF) and normal (n = 7) monocytes were stimulated with 10 ng/mL of LPS for 4, 9, 18, and 24 hours before harvesting supernatant for quantification of IL-10 via ELISA. (B) MPN (n = 2 PV and 3 ET) and normal (n = 6) monocytes were stimulated with 10 ng/mL LPS and various concentration of IL-10 simultaneously for 4 hours between harvesting of the supernatant for ELISA. The percentage change in TNF-α is measured by the difference in TNF-α production between adding IL-10 and without IL-10. (C) MPN (n = 2 PV and 3 ET) and normal (n = 5) monocytes were stimulated with 10 ng/mL LPS and various concentrations of IL-10 for 4 hours with brefeldin A before performing intracellular staining for TNF-α. The changes in TNF-α–positive monocytes are measured by the difference in monocytes expressing TNF-α between adding IL-10 and without IL-10. (D) The mean fluorescence intensity (MFI) of IL-10 receptor α is measured by gating on MPN (n = 4 PV, 3 ET, and 2 MF) and normal (n = 5) CD33^high CD14⁺ monocytes from mononuclear cells, using flow cytometry analysis. *P < .05. ns, not significant.