IL13 and acquired polycythemia vera: We found the only significant differences between morphological groups to be for Th9 cytokine IL-9 and the Th2 cytokine IL-13, which were significantly elevated in those who had active mucocutaneous PV compared to those who had active mucosal only PV (p-value: 0.035 and 0.022, respectively) (Figure 4A and Table 5).