The Use of a Commercially Available Immunoassay to Determine the Level of Interleukin-6 in the Serum of Patients with Myeloma

Interleukin-6 (IL-6) is the B cell growth factor which stimulates the final differentiation of B cells to plasma cells and has been suggested to be an autocrine growth factor in patients with multiple myeloma. We have compared the concentration of IL-6 in the serum of patients with myeloma at diagnosis (n = 11), in plateau phase (n = 10) and with progressive disease (n = 13) using Intertest-6, a commercially available enzyme-linked immunoassay (ELISA). Longitudinal studies were performed with 6 patients. IL-6 levels were normal in all myeloma sera studied and did not change with disease progression. Serum IL-6 levels did not correlate with disease activity as determined by serum thymidine kinase (r = 0.07) nor did serum IL-6 provide any useful prognostic data. These results contradict previous studies using bioassays which reported that IL-6 levels increase significantly during progressive disease. Until this problem is resolved and these assays are validated, studies which attempt to quantitate IL-6 and other growth factors in serum should be treated with some caution.