Impaired migratory ability of Tregs was because of lower CXCR4 (but not for CXCR7 expression) in AA. (A) PB Tregs from both NSAA (n = 8, P = .001) and SAA patients (n = 8, P < .001) had less migratory capacity toward SDF-1α compared with those in controls (n = 8). PB Tregs from SAA had less migratory ability than that from NSAA (P < .001). CXCR4 blockade resulted in significant reduced migratory capacity of Tregs in controls, NSAA, and SAA, which were comparable among the 3 groups. (B) Healthy Tregs migrated equally toward BM fluid obtained from NSAA (n = 5), SAA patients (n = 5), and controls (n = 5). (C-D) The levels of SDF-1α both in serum (NSAA, n = 18; SAA, n = 17; controls, n = 22) and BM fluid (NSAA, n = 10; SAA, n = 7; controls, n = 9) detected by ELISA were comparable among the 3 groups. (E-F) The results of quantitative analysis of CXCR4 and CXCR7 mRNA expression showed that a significantly lower expression of CXCR4 on PB Tregs from both NSAA (n = 15, P = .026) and SAA patients (n = 15, P < .001) compared with that of controls (n = 17). Similarly, CXCR4 expression was significantly lower on BM Tregs from AA patients (n = 5) compared with that of controls (n = 7, P = .015). In contrast, there were no significant differences in CXCR7 mRNA expression on PB and BM Tregs among the 3 groups. (G) Representative CXCR4 expressions on the CD4⁺CD25⁺ Tregs from a (i) healthy control and a (ii) AA patient. AA patients (n = 6) had significantly lower frequencies of CXCR4-positive cells (P < .001) and lower relative fluorescence intensity (RFI; P = .003), compared with healthy controls (n = 6). *P < .05; **P < .001.