To study the role of IL-29 in the pathogenesis of PV, the authors investigate the effects of IL-29 on mRNA expression of cytokines (including IL-6, TNF-α, IL-17, IL-8, IL-4, IFN-γ, and IL10) in PBMCs from PV patients and keratinocyte cell line HaCaT in this study. The gene discussed is IL4; the disease is acquired polycythemia vera.