Purified NK cell populations are responsive to LFA-1–induced cytolytic activity. (A) CTLs (CD3⁺CD8⁺CD56^–) or NK cells (CD3^–CD8⁺CD56⁺), sorted by FACS, were cultured in IL-2 (200 ng/mL) for 12 hours and treated with either control IgG, ICAM-1, ICAM-2, or ICAM-3 (10 μg/mL) 30 minutes prior to mixing with target CMFDA-labeled HL60 at various effector-target (E/T) cell ratio (as indicated) for 4 hours. Specific cell lysis was quantitated by flow cytometry and displayed as percent specific lysis. Results are representative of 4 independent donors. Numbers indicate population frequencies. (B) CD56⁺CD8⁺CD16^– and CD56⁺CD8⁺CD16⁺ cells, sorted by FACS, were cultured in IL-2 (200 ng/mL) for 12 hours and treated with either control IgG, ICAM-1, ICAM-2, or ICAM-3 (10 μg/mL) 30 minutes prior to mixing with target CMFDA-labeled HL60 at a particular E/T cell ratio (as indicated) for 4 hours. Specific cell lysis was quantitated by flow cytometry and displayed as percent specific lysis. (C) Cytotoxic T-cell lymphocytes (CTL: CD3⁺CD8⁺CD56^–), natural killer T cells (NKT: CD3⁺CD8⁺CD56⁺), natural killer CD56⁺ cells (NK56⁺: CD3^–CD8⁺CD56⁺), and natural killer CD56^– cells (NK56^–: CD3^–CD8⁺CD56^–) were sorted by FACS, cultured in IL-2 (200 ng/mL) for 12 hours, and treated with either control IgG or ICAM-2 (10 μg/mL) 30 minutes prior to mixing with target CMFDA-labeled HL60 at a 1:6.25 E/T cell ratio for 4 hours. Specific cell lysis was quantitated by flow cytometry and computed. Error bars are the standard deviation of 3 experiments.