Increased frequencies of CD4+CCR4+ and CD4+CCR6+ T cells in patients with granulomatosis with polyangiitis (GPA). Percentages of CCR4+ (a) and CCR6+ (b) cells within the total CD4+ T cell population in patients with GPA and healthy controls (HCs). Percentages of positive cells were assessed by flow cytometry. Values are presented as mean ± standard error of the mean. ***P < 0.001, Mann-Whitney U test. CCR, CC chemokine receptor.