The evidence for interleukin-6 as an autocrine growth factor in malignancy.

Interleukin-6, IL-6, is a pleiotropic cytokine which plays a central role in defense mechanisms, including the immune response, acute phase reaction and hematopoiesis. Abnormal expression of the IL-6 gene has been suggested to be involved in the pathogenesis of a variety of diseases, especially rheumatoid arthritis, Castleman's disease, mesangial proliferative glomerulonephritis, multiple myeloma and Kaposi's sarcoma. In the case of multiple myeloma and Kaposi's sarcoma, the existence of an IL-6-IL-6 receptor autocrine loop has been implicated in the oncogenesis process. On the other hand, IL-6 has a potent anti-tumor activity against certain types of tumors. This anti-tumor effect is mediated by in vivo induction of tumor specific cytotoxic T cells and in part by a growth inhibitory activity of IL-6.