High serum interleukin-2 levels in patients with monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma.

Interleukin-1 (IL-1), Interleukin-2 (IL-2) and soluble receptors for IL-2 (sIL-2R) play a crucial role in the immune response. IL-2 in particular is implicated not only in T-cell proliferation but also in normal B-cell proliferation and differentiation and in the development of B and T cell malignancies. We have assayed the serum levels of IL-1, IL-2 and sIL-2R in 12 patients with monoclonal gammopathy of undetermined significance (MGUS) and 44 patients with multiple myeloma (MM). Sera collected from 40 healthy blood donors were used for normal values, and sera from 33 medical volunteers over 48 years of age (median age 52 years) for normal IL-2 values in the elderly. Mean IL-2 serum values were 6.50 U/ml in MGUS and 4.97 U/ml in MM patients. There was a statistical significant elevation of IL-2 levels is both MM and MGUS patients when compared to both normal controls (p less than 0.001, Wilcoxon two tailed test). A significant difference in IL-2 levels (p less than 0.025) was also observed between MGUS and MM patients. The levels of serum IL-1 and sIL-2R were normal both in MGUS and MM patients. In 24 MM patients where the dosage of serum beta-2-microglobulin was available, a significant difference (p less than 0.01) in serum IL-2 levels was found between patients with beta-2-microglobulin greater than 6 micrograms/ml and less than 6 micrograms/ml. Pathogenic mechanisms as well as their possible clinical significance are discussed.