The functional interactions between BW/CEACAM1ζ and CMV-infected HFFs elicit IL-2 secretion. (a) Spontaneous IL-2 secretion by BW and various BW transfectants after 48 hours of incubation. The average of 20 independent experiments is shown. (b) IL-2 secretion by BW/CEACAM1ζ cells coincubated for 24 hours with irradiated .221 or with .221/CEACAM1 cells. The average of six independent experiments is shown. (c) IL-2 secretion after coincubation of BW or BW/CEACAM1ζ cells with uninfected or CMV-infected HFF cells for 48 hours. No IL-2 secretion above background levels was observed when PFA was included in the assay (only day 6 is shown). Experiments were performed concomitantly with the flow cytometry binding assays of CEACAM1-Ig shown in Figure 5. The average of two independent experiments is shown.