Regulation of the expression of chemokine receptors CXCR1, CXCR3, and CXCR4 on purified CD56⁺CD16⁺ NK and CD56⁺CD3⁺ NK T cells. (A) (i) CD56⁺ cells were purified from peripheral blood lymphocytes. (ii) Three major subpopulations of CD56⁺ NK cells were found: CD56⁺CD3⁺CD16^– NK T cells (35%), CD56⁺CD16⁺CD3^– NK cells (60%), and CD56⁺CD16^–CD3^– NK cells (5%). (B) CD56⁺CD16⁺ NK cells, but not NK T cells, express CXCR1 (ii); after 48 hours' incubation with IL-2 (1000 IU/mL), the cell-surface expression of CXCR1 is down-regulated (iii). (C) CD56⁺CD3⁺ NK T cells, but not NK cells, express high levels of CXCR4 (ii); after 48 hours' incubation with IL-2, the cell-surface expression of CXCR4 is down-regulated on both types of cells (iii). (D) NK and NK T cells express low levels of CXCR3 (ii); after 48 hours' incubation with IL-2, the cell-surface expression of CXCR3 is up-regulated on both NK and NK T cells (iii). IgG2APE and IgG1PE were used as control antibodies (panels Bi, Ci, and Di).