Elevated Concentration of Soluble Interleukin-2 Receptors in Serum of Smokers and Patients with Lung Cancer: Correlation with Clinical Activity

Soluble interleukin-2 receptor (sIL-2R) levels in cigarette smokers and in patients with lung cancer were measured using an enzyme immunoassay. The rationale for our study was based on the fact that activation of T-cells is dependent upon the T-cell growth factor, interleukin-2, which may be regulated by its receptor, IL-2R. Measurements of circulating sIL-2R might be useful in the immune assessment of certain conditions. This study assessed elevated concentrations of circulating sIL-2R in smokers and in patients with lung cancer. The data show that healthy smokers, as a group, have an elevated level of sIL-2R compared with that in nonsmokers. Significantly higher than normal levels were found among light, moderate, and heavy smokers. Patients with lung cancer (squamous cell carcinoma [SSC] or adenocarcinoma [AC]) also have abnormally high sIL-2R levels. In the SCC group, the highest level of sIL-2R was among asymptomatic patients with well-differentiated tumors. Similarly, patients with SCC whose tumors were less than 3 cm in diameter had a significantly higher mean level of sIL-2R than did patients whose tumors exceeded 3 cm. The sIL-2R level in the SCC group also correlated with the tumor stage, with the highest level found among Stage I patients. In patients with SCC, but not in those with AC, the sIL-2R level was indicative of the extent of malignancy. These data support the concept that sIL-2R may be important in the pathogenesis of immune alterations associated with smoking and lung cancer.