Effect of IL-15 in the activation of PBTLs. (A) Dose-dependent effect of IL-15 on the expression of CD25 (▪) and CD69 (•) by PBTLs. PBLs were incubated with IL-15 (5, 20, 45, 70, 100, or 150 ng/mL) by 18 hours in the absence (closed symbols) or presence (open symbols) of a blocking anti–IL-15 MoAb (5 μg/mL). Then, the expression of CD25 and CD69 was analyzed in CD3⁺ cells by two-color flow cytometry. The results of three independent experiments are shown as arithmetic mean ± 1 SD. (B) Contribution of endothelial IL-15 to the induction of CD69 in T cells. PBLs were cocultured with nonfixed (left) or fixed (right) TNF-–activated endothelium for 18 hours in the presence or absence of a blocking anti–IL-15 MoAb (5 μg/mL) and/or a blocking anti-CD18 MoAb. Then, the expression of CD69 was analyzed in CD3⁺ cells by two-color flow cytometry. The results of three independent experiments are shown as arithmetic mean ± 1 SD. *, P < .05 compared with untreated (Mann-Whitney U test).