FIGURE 2.

Blocking homotypic 2B4/CD48 or CD2/CD58 interactions caused reduction of NK cytotoxicity against CD48 negative K562 targets. A, expression of 2B4, CD48, CD2, and CD58 on K562 target cells was assessed by flow cytometry. B, a standard 4-h ⁵¹Cr release assay was performed with NK cells, cultured with 300 units/ml of IL-2 in the presence of 5 μg/ml of mIgG as an isotype control (♦), anti-2B4 mAb (■), anti-CD48 mAb (▴), anti-CD2 mAb (●), or anti-CD58 mAb (×) for 14 days, as effectors and with ⁵¹Cr-labeled K562 cells as target cells (Ab long-term blocking). C, a redirected antibody-dependent cell cytotoxicity assay against ⁵¹Cr-labeled P815 cells pre-coated with anti-NKG2D mAb was performed with NK cells cultured as in B. Specific lysis observed at an E:T ratio of 10:1 was shown. D, a standard 4-h ⁵¹Cr release assay was performed using NK cells cultured with IL-2 without blocking mAbs. Mouse IgG as isotype control (♦), anti-2B4 mAb (■), anti-CD48 mAb (▴), anti-CD2 mAb (●), or anti-CD58 mAb (×) at 5 μg/ml were added only during the 4-h cytotoxicity assay (Ab short-term blocking). All the results are representatives of a minimum of 5 independent experiments. Error bars represent S.D.