Acquisition of CCR7 surface expression by CD56^dull NK cells. (A-D) Freshly isolated NK cells were purified and cultured for 18 hours either in medium alone or in the presence of the indicated HLA-class I–negative cell lines and then analyzed by 2-color immunofluorescence for the expression of C-C chemokine receptor type 7 (CCR7) in combination with CD56 (A). (B) Freshly isolated natural killer (NK) cells were cultured with the 221 cell line or in the presence of exogenous IL-18 for different time points and analyzed for CCR7 expression in combination with CD56. In both panels A and B, the values reported in the top right corners indicate the percentage of CD56⁺ CCR7⁺ NK cells. (C) Polyclonal IL-2–activated NK cells were cultured for 1 hour in the presence of the HLA-class I–negative 221 cell line and then analyzed by 2-color immunofluorescence for the expression of CCR7 in combination with CD56. Both CD56⁺ CCR7⁻ and CD56⁺ CCR7⁺ NK cells were also analyzed for CD107a expression. Data are representative of 3 independent experiments performed using different donors. (D) CD56^dull NK cells that had acquired the CCR7⁺ phenotype after 18 hours of coculture with the 221 cell line or exogenous IL-18 were analyzed for KIR expression using a mixture of anti-KIR mAbs. The values reported in the top left and in the top right corners indicate the percentage of CD56⁺ KIR⁻ and of CD56⁺ KIR⁺ NK cells, respectively. These experiments are representative of 12 independent experiments performed using different donors.