Interleukin-15 is a recently discovered cytokine which is functionally similar to IL-2. In order to learn more about possible targets for modulation of the expression of IL-15 we investigated the expression of IL-15 mRNA and protein in the A549 (human lung carcinoma) cell line. Constitutive expression of IL-15 mRNA was detected in A549 cells. Treatment with TNF-alpha or IL-1 beta (10 ng/ml each) induced an about 2-fold increase of IL-15 mRNA; IFN-gamma induced significant effects only at 100 ng/ml. Stimulation with a combination of TNF-alpha and IFN-gamma was not superior to stimulation with TNF-alpha alone. EGF, KGF and the combination thereof were without effects. IL-15 protein was detected in cellular lysates of unstimulated cells and was increased by stimulation with TNF-alpha or IL-1 beta. No significant amounts of IL-15 protein were detected in cellular supernatants.