In vitro Ig-synthesis and proliferative activity in multiple myeloma are stimulated by different growth factors.

Plasma cells isolated from bone marrow (BM) aspirates of 15 patients with active multiple myeloma (MM) were cultured and analysed for in vitro proliferative response and Ig-synthesis upon stimulation with interleukin-3 (IL-3), interleukin-4 (IL-4) and interleukin-6 (IL-6). The proliferative response, determined as Ki-67 positivity in concentrated plasma cells, was increased by IL-6 (Stimulation Index, SI = 1.77 +/- 0.21 (M +/- SEM] but not by IL-3 or IL-4. This proliferation could be blocked by anti-IL-6. In vitro Ig-synthesis was stimulated by IL-4 (SI = 1.62 +/- 0.12 (M +/- SEM) P less than 0.05) but not by IL-6 or IL-3. This effect was not antagonized by anti-IL-6. An inverse correlation was found in this group of patients between the IL-6 induced stimulation of plasma cell proliferative activity and the IL-4 induced increase of Ig-synthesis (P = 0.027). These data indicate in MM that Ig-synthesis and the in vitro proliferative activity may be stimulated by different haematopoietic growth factors, which may reflect the involvement of different responding cells.