Interleukin 2 (IL2) has well recognized pleiotropic effects on the activation, differentiation and proliferation of lymphoreticular cells, mediated via its specific membrane-bound receptors, but its effect on human solid tumour cells is poorly characterised. This study has used the A549 tumour cell line, derived from a human lung carcinoma, to demonstrate the presence of the interleukin 2 receptors (p70/75 beta and/or p55 alpha components) and to document functional activity. Immunohistochemical techniques demonstrated large amounts of the p70/75 beta chain of the interleukin 2 receptor, which is necessary for IL2 internalization, receptor signal transduction and mediation of the biological effects of IL2. In contrast, the p55 alpha chain was detected minimally and sparsely. In addition we documented the presence of IL2 in the nucleus of the A549 cells. The addition of exogenous rIL2 (10-500 IU/ml), to the culture medium of A549 cells over 48 hours resulted in a significant stimulation of DNA synthesis, as assessed by tritiated thymidine uptake. The results were; 9335+/-365, 12669+/-271, 12889+/-255, 19448+/-1427, 20189+/-1004 and 22586+/-1334 CPM, at 0 IU/ml, 10 IU/ml, 50 IU/ml, 100 IU/ml, 250 IU/ml and 500 IU/ml, respectively (means+/-SEM), and were significantly increased when compared with control cultures, p<0.001). These results may have important implications in our understanding of tumour-host interactions and in future strategies involving immunotherapy.

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