IL17A and granulomatosis with polyangiitis: CXCR5+PD-1+ cTfh cells (80) and CD4+IL-21+ IL-17A+ T cells were increased significantly in GPA patients, and ANCA-positive GPA patients had more CD4+IL-21+ and CD4+BCL6+ T cells in peripheral blood than HC and ANCA-negative GPA patients (81).