Effect of 5E6 F(ab′)2 fragments on 5E6+ NK cells.
The 5E6 F(ab′)2 fragments bind 5E6+ NK cells and increase cytotoxicity mediated by the 5E6+ NK cell subset. (A) IL-2–activated NK cells (5 × 106) were incubated with F(ab′)2 fragments of 5E6 (solid histogram) at 1 × 106/mL or with normal mouse IgG (dashed histogram) at 25 μg/mL for 2 hours at 37°C and stained with FITC goat antimouse IgG specific for F(ab′)2 fragments (left panel). As controls, NK cells were incubated alone and stained with biotinylated 5E6 and secondary antibody, FITC-streptavidin (right panel, solid histogram) or the secondary antibody only (dashed histogram). (B) The NK1.1+5E6+ subset was sorted from B6 SCID splenocytes by flow cytometry, activated with rhIL-2, and used at day 5 as effectors against C1498 or EL4 targets in standard 4-hour cytotoxicity assay as described previously.21 Various numbers of NK1.1+5E6+ effectors were pretreated with media (▪) or 5E6 F(ab′)2 (●), and the effectors were then cocultured with the targets for 4 hours, after which51Cr activity was measured in a liquid scintillation counter. A representative of 3 independent experiments is shown.
