SERUM LEVELS OF SOLUBLE IL-6 RECEPTOR IN MULTIPLE MYELOMA AS INDICATOR OF DISEASE-ACTIVITY

Serum soluble interleukin-6 receptor (sIL-6R) concentrations were meas ured in 50 patients with plasma cell dyscrasias using a commercially a vailable immunoenzymatic assay kit. There were 40 patients with multip le myeloma (MM), 5 patients with monoclonal gammopathy of undetermined significance (MGUS), 3 patients with solitary plasmacytoma(SPC), 1 pa tient with chronic myelogenous leukaemia and multiple myeloma (CML + M M), and 1 patient with plasma cell leukaemia (PCL). We found that seru m sIL-6R concentrations were higher in MM patients (62.53 +/- 38.85 ng /ml) than in 20 normal volunteers studied (36.75 +/- 13.79 ng/ml) (p < 0.01). The cut-off value of 65 n/ml seen in 2 of our controls was arb itrarily taken as the upper limit of the control range for serum sIL-6 R; according to this criterion, 14 patients with MM (35%), 1 patient w ith SPC, the unique patient with CML + MM, and the unique patient with PCL had elevated concentrations of the receptor. Patients with MGUS h ad normal sIL-6R values. In MM patients, serum sIL-6R levels correlate d with the clinical phase of the disease: they were elevated in patien ts with early or late active disease and ranged within normal limits i n patients with plateau-phase disease (p < 0.001). Thirteen of 27 pati ents with active MM had elevated serum sIL-6R values, i.e. 48.1%, but only 1 out of 13 patients with disease in the plateau phase, i.e. 7.7% (p < 0.05). Furthermore, in the entire group of MM patients, serum sI L-6R levels correlated with the concentrations of serum Pz-microglobul in (p < 0.02), CRP (p < 0.01), ferritin (p < 0.01) and LDH (p < 0.01), while they did not correlate with disease stage, haemoglobin levels, proportion of marrow myeloma cells, the values of serum IL-6, the leve ls of serum albumin, or the grade of bone lesions. We conclude that el evated serum sIL-6R levels should be related to the growth of myeloma cells and suggest that serum sIL-6R concentrations may be used as an i ndicator of disease activity.