CCL22 and acquired polycythemia vera: Moreover, the expression of FoxP3 and CTLA-4 in CD4+ CD25 bright Treg cells was significantly down-regulated in patients with PV compared to that in healthy people, along with dysregulation of CCR4 and CCL22 expression (46, 47), thus suggesting the possibility of defective trafficking of Treg cells in skin lesions of patients with PV.