ATP enhances NK-cell chemotactic response to CXCL12. (A) Migratory response of NK cells to CXCL12 gradients in the presence (●) or absence (○) of 100μM ATP. *P < .05 versus cells stimulated with same CXCL12 dose in the presence of UTP. (B) Expression of CXCR4 on NK cells surface after 1-hour exposure to 100μM ATP. (C) Migratory response of NK cells to 100 ng/mL CXCL12 after 16-hour incubation with or without 1000 U/mL IL-2 in the presence or absence of 100μM ATP. (D) Expression of CXCR4 after 16-hour incubation with or without 1000 U/mL IL-2 in the presence or absence of 100μM ATP. (D) Data are the mean fluorescence intensity and percentages of CXCR4⁺ cells. (A,C) Data are the mean ± SD of 3 experiments. (B,D) Data are representative from 1 of 3 experiments. *P < .05. All P values were calculated by Student t test for paired samples.