These authors showed that only 2 cytokines (IL-6 and TNF-α) out of 13 (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-11, IL-12, IFN-γ, TNF-α, and TGF-β) were increased in PV patients. Here, IL4 is linked to acquired polycythemia vera.