Cytokines as autocrine growth factors in malignancies.

Interleukin 6 (IL-6) was originally characterized as a B-cell differentiation factor, responsible for the terminal maturation of activated B cells to immunoglobulin producing cells. Recent works reveal that IL-6 has a wide variety of biological functions on various cells. In particular, IL-6 has been shown to augment the growth of freshly isolated human myeloma cells, and the myeloma cells constitutively produce IL-6 and express IL-6 receptors. Moreover, it has been shown that anti-IL-6 antibody can inhibit the in vitro growth of the myeloma cells. This is direct evidence that an autocrine loop is operating in freshly isolated myeloma cells, and that a constitutive production of IL-6 and activation of the IL-6 gene could be involved in the oncogenesis of human myeloma.