A significant increase in IL-17 expression has been detected in lesional skin of PP, despite the absence of any significant increase in IL-12/IL-23 levels [44]; this is strikingly different from PV, where increased IL-17 levels are typically mirrored by analogous changes in IL-12/IL-23 expression [7, 37, 43]. Here, IL23A is linked to acquired polycythemia vera.