IL9 and acquired polycythemia vera: Of note, we found IL-2, IL-5, IL-22, and IL-9 to be significantly higher in PV patients compared to both HLA-matched controls and HLA-unmatched controls (Figure 3), reflecting changes unlinked to HLA type and suggesting cytokine activation is not strictly HLA driven, implicating the existence of additional genetic (and/or environmental) factors operative in patients.