Soluble interleukin-2 receptor in blood from patients with sarcoidosis and idiopathic pulmonary fibrosis.

Soluble interleukin-2 receptor (sIL-2R) concentration is considered to reflect disease activity in patients with sarcoidosis. However, it remains to be evaluated whether or not the sIL-2R concentration reflects the total burden of granulomatous lesions, or if it can be a useful marker for other interstitial lung diseases such as IPF, the lesions of which are restricted to the lungs. In this study, we demonstrated that sIL-2R concentrations in 16 patients with active sarcoidosis increased (2031 +/- 1222 U/ml), compared to those in 29 patients with inactive disease (796 +/- 313), 24 with IPF (859 +/- 694) and 33 healthy controls (467 +/- 174). sIL-2R concentrations in patients with IPF also increased, more than those in healthy subjects. sIL-2R concentrations in 10 patients with extrathoracic lesions (ETL) were not different from those in 6 patients without ETL. Correlation between serum sIL-2R concentrations and serum ACE activity, BAL macrophage %, and BAL lymphocyte % was shown in patients with sarcoidosis. In patients with IPF, a correlation between sIL-2R concentrations and BAL macrophage % was found but there was no correlation between sIL-2R concentrations and BAL lymphocyte %. In conclusion, serum sIL-2R concentrations seem to reflect total inflammatory lesions. In addition, they reflect total inflammatory lesions of the lungs in sarcoidosis and IPF. For clinical purposes, its measurement may be more useful than that of BAL fluid concentrations in patients with sarcoidosis and IPF.