Fig. 4.

Proliferation to IL-15 immobilized by IL-15Rα cannot be blocked by soluble IL-15Rα-Fc. (A) CFSE-labeled T cells were injected i.v. into Thy1-congenic B6 or IL-15Rα^−/− hosts. One day later, mice were injected i.p. with PBS or 500 ng of LPS. As indicated, mice were also treated i.p. with 10 μg of sIL-15Rα-Fc daily beginning the day of LPS injection. Three days after LPS injection, spleens were harvested, and CFSE dilution of MP CD8⁺ T cells was assessed. (B) Ninety-six-well plates were precoated overnight with 10 μg/ml of sIL-15Rα-Fc. Plates were then washed and incubated with 1 μg/ml IL-15 for 1 h at 37°C. Thereafter, plates were washed, and 5 × 10⁴ MP CD8⁺ T cells were added together with (i) 10 μg/ml sIL-15Rα-Fc, (ii) 10 μg/ml of polyclonal anti-IL-15 antibody, or (iii) control media; as an additional control, free IL-15 (32 ng/ml) was added to some wells. The data show mean levels of [³H]thymidine incorporation (SD) for triplicate cultures on day 3.