CD56⁺CD16⁺ NK cell lines, as well as LAK cells, do not express the chemokine receptor CXCR4. (A) CD56⁺CD16⁺ cells grown in the presence of IL-2 (50-100 IU/mL) for 4 weeks (NK cell lines) do not express the chemokine receptors CXCR1 (i) and CXCR4 (ii), but do express the chemokine receptor CXCR3 (iii). (B) After activation with a supraphysiologic concentration of IL-2 (1000 IU/mL), the major effector population of LAK cells, CD56⁺CD16⁺ large granular lymphocytes (LGLs) as well as T cells, down-regulate CXCR4 expression (ii). Staining of control resting lymphoid cells with antibodies against CXCR4 and CD16 is shown in panel i.