Serum soluble interleukin-2 receptor: A useful indicator of the clinical course in pulmonary tuberculosis

SETTING: In tuberculosis both host protection and most pathogenic mechanisms depend on T lymphocytes. After activation by mycobacterial antigens, T cells both secrete interleukin-2 (IL-2) and express a high affinity receptor for this molecule (IL-2R) on their own surface. A soluble fraction of IL-2 receptor (sIL-2R), released from cell membrane, is detectable in serum and its concentration is known to be elevated in tuberculosis. OBJECTIVE: To ascertain the role of sIL-2R as an indicator of clinical evolution and response to antituberculosis treatment. DESIGN: A prospective study, in which we have measured serum sIL-2R in 52 patients (42 with active and 10 with inactive pulmonary tuberculosis) and in 36 healthy controls. In 20 patients, serum sIL-2R levels were measured serially throughout the treatment. Levels of sIL-2R were correlated to clinical and radiological parameters. RESULTS: Serum sIL-2R was significantly increased in patients with tuberculosis as compared to healthy subjects. Both the radiological findings and the clinical state of patients showed a good correlation with sIL-2R. All patients with normal values of sIL-2R 6 months after starting therapy had a favourable clinical evolution. CONCLUSION: Serum sIL-2R is a useful marker of the clinical state and evolution of patients with pulmonary tuberculosis. The detection of permanently high values beyond 3-6 months of treatment suggests that additional drugs or prolonged administration would be advisable in order to ensure full recovery.