To explore the role of IL-29 in the pathogenesis of PV, the authors assayed the effects of IL-29 on cytokines mRNA expression (including IL-6, TNF-α, IL-17, IL-4, IFN-γ, and IL-10) in PBMCs from 10 PV patients by real-time quantitative PCR. This evidence concerns the gene IL4 and acquired polycythemia vera.