IL21 and acquired polycythemia vera: In this study, we interrogated serum samples from 116 PV patients and 29 healthy controls by multiplexed bead array assays across a comprehensive set of cytokines and chemokines covering several functional categories, including IL-1α, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IL-9, IL-10, IL-12, IL-13, IL-15, IL-17, IL-21, IL-22, IL-23, TNFα, IFNγ, MCP-1, and Eotaxin.