RELEASE OF SIL-2R-ALPHA FROM AND ACTIVATION OF NATIVE HUMAN PERIPHERAL-BLOOD MONONUCLEAR-CELLS BY RECOMBINANT IL-15

The cytokine interleukin (IL)-15 shares several activities with IL-2. Both cytokines induced expression of cell-surface IL-2R alpha (CD25) o n freshly isolated human peripheral blood mononuclear cells (PBMC) in the absence of other exogenous stimuli. They also stimulated the relea se of soluble IL-2R alpha and induced proliferation of these cells in 1-week cultures in a time-and dose-dependent manner. Recombinant IL-7 could also induce the expression of CD25, although sIL-2R alpha was re leased at only low levels. In monocyte-depleted PBMC the sIL-2R alpha release was minimal. When isolated T cells or non-T cells were stimula ted by rIL-15 or rIL-2, cell surface CD25 was expressed, but released sIL-2R alpha was undetectable. On stimulation with rIL-15, more than 8 0% of all natural killer cells expressed CD25 and more CD8(br+) lympho cytes were positive for CD25 compared to stimulation by rIL-2. These r esults may be clinically relevant because several diseases are associa ted with high serum levels of sIL-2R alpha which may be not only due t o IL-2 but also due to IL-15 stimulation. (C) 1996 Academic Press, Inc .