However, it is unclear if the involvement of Th17 is contributory to PV pathogenesis or merely a consequence of PV, as levels of IL-17A were not found to correlate with PV disease severity.19 While increased oxidative stress was identified in this review, it is again unclear if this is contributory or a consequence of PV (Supplemental Table 7). This evidence concerns the gene IL17A and acquired polycythemia vera.