IL17A and granulomatosis with polyangiitis: Interestingly, a significant positive correlation was observed between IL-21+IL-17- Th-cells and IL-21-IL-17+ Th-cells in both GPA patients and HCs (r = 0.58, P < 0.0001 and r = 0.37, P = 0.04, respectively) (Figure 2A and 2B).