IL21 and acquired polycythemia vera: Overall, Th1 predominant and Th2 suppressant responses have been demonstrated in PV.4 Recent studies have shown that the activation of Th17 pathway may be involved in the pathogenesis of PV.8 In our study, we found a significant increase in the plasma concentrations of IL‐6, IL‐8, IL‐7, IL‐1β, IL17A, IL‐5 and IL‐21 in patients with PV, which is consistent with the results of previous studies.