Figure 2. IL-15 growth factor activity depends on TCR-signals, but is IL-2-dependent only in CD4⁺ T cells.

(A) CD8⁺ or (B) CD4⁺ T cells were stimulated with anti-CD3 mAb and irradiated TdACs in the absence or presence of 3 ng/ml rhIL-15, or 10 µg/ml anti-IL-2 mAb (JES6-5H4) or isotype control, as indicated. On day 4, ³H-thymidine incorporation was measured. Results are from one of five experiments. (C) IL-2^+/+ or IL-2^−/− CD4⁺ cells were stimulated with anti-CD3 mAb and irradiated IL-2^+/+ and IL-2^−/− splenocytes, respectively, in the absence (white circles) or presence of 1 ng/ml IL-2 (crosses) or 3 ng/ml IL-15 (black circles). (D) CD4⁺ cells were stimulated for 5 days with 0.1 µg/ml anti-CD3 and irradiated TdACs. On day 0, 1, 2, or 3, IL-15 alone or IL-15 plus anti-IL-2 mAb was added. On day 4, proliferation was measured by ³H-thymidine incorporation and represented as bar graphs (with left Y-axis) as ratio of cpm_IL-15/cpm_none (black bars) or cpm_{IL-15 plus anti-IL-2}/cpm_none (white bars). The line represents the percentage of reduction of the IL-15 effect by IL-2 depletion as calculated using the following formula: [(cpm_IL-15– cpm_{IL-15 plus anti-IL-2})/cpm_IL-15]×100. Results are from one representative out of three experiments.