TNF and acquired polycythemia vera: Researches have demonstrated that serum levels of tumor necrosis factor-α (TNF-α) and several type I and II cytokines, such as IL-1β, IL-4, IL-6, IL-8, IL-10, IL-12, and IL-15, are increased in patients with PV, while levels of IFN-γ are decreased (18–20).