CCR4 and granulomatosis with polyangiitis: Apart from the CCR4+CCR6- and CCR4-CCR6+ 'single positive' subsets, a smaller fraction of CCR4+CCR6+ 'double positive' cells was detected within the CD4+ T cell population in patients with GPA and healthy controls (17.5% ± 4.8% versus 10.3% ± 0.6%, mean ± standard error of the mean, no significant difference, Mann-Whitney U test).