BSF-2/IL-6 does not augment Ig secretion but stimulates proliferation in myeloma cells

Human myeloma cells were highly purified from bone marrow aspirates of 21 patients with advanced immunoglobulin G (IgG)-type multiple myeloma. B-cell stimulatory factor 2 (BSF-2)/interleukin-6 (IL-6) was originally characterized as a cytokine that can enhance immunoglobulin secretion from activated normal B cells and increase the expression of secretory-type Ig mRNA in these B cells, but that does not augment proliferation of activated B cells. However, recombinant IL-6 (rIL-6) could not enhance M-protein (IgG) secretion in freshly isolated myeloma cells in vitro but could augment proliferation of myeloma cells, although myeloma cells constitutively expressed IL-6 receptors. Furthermore, expression of secretory-type IgG (gamma-chain) mRNA in myeloma cells was not changed in the presence of IL-6. These results show that IL-6 is not an enhancing factor in Ig secretion from myeloma cells, and thus signal transduction through IL-6 in myeloma cells may be altered as opposed to activated B cells.