Finally, another plausible mechanism for the ability of hydroxychloroquine to induce PV may involve drug-mediated changes in the expression of cytokines such as IL-1, IL-6, TNF-α, and IFN- γ in mononuclear cells (53) and TNF-α, IFN-α, IL-6, and CCL-4 by plasmacytoid dendritic cells (54, 55) together with the subsequent alterations of immunologic signaling pathways regulated by those cytokines. Here, CCL4 is linked to acquired polycythemia vera.