Soluble interleukin-2 receptors in plasma cell dyscrasias.

Levels of the soluble form of the interleukin-2 receptor (sIL-2R) were evaluated in the peripheral blood of 69 patients with plasma cell dyscrasias. A close relationship was seen between serum sIL-2R levels and clinical features. Among patients with normal BUN and creatinine levels, the mean (+/- 1SD) level of sIL-2R in 44 patients with multiple myeloma (MM) was higher than that of normal controls (457 +/- 227 U/ml vs 288 +/- 124 U/ml, P = 0.01). The mean level of sIL-2R in eight patients with primary macroglobulinemia was 722 +/- 251 U/ml. In MM, those with active or refractory disease showed a significantly higher mean level of sIL-2R than those in the remission phase (577 +/- 240 U/ml vs 335 +/- 103 U/ml, P = 0.01). There was a negative correlation between sIL-2R and hemoglobin levels in MM patients (r = -0.45, P = 0.01). Five patients with complications of renal insufficiency had elevated levels of sIL-2R. In a longitudinal study of a patient with plasmacytoma and an extremely high sIL2-R level, the sIL-2R level showed a strong relationship with tumor burden. Patients with high sIL-2R levels generally had a poor prognosis than those with normal levels. Thus a high sIL-2R level may be an indicator of a poor prognosis in MM.