Interleukin-4 and breast cancer.

IL-4 is a pleiotropic cytokine produced by T lymphocytes which acts on various cells of such as T and B lymphocytes, monocytes, fibroblast, endothelial cells, macrophages and some others. IL-4 was originally described as a B cell growth factor, and now known to provide potent anti-tumor activity against various tumors, including breast cancer. IL-4 can induce apoptosis in cultured breast cancer cells. In addition, it has been clarified that IL-4 plays an important role in the regulation of estrogen synthesis enzymes including 17beta-HSD and 3beta-HSD. These findings imply that IL-4 is a key enzyme not only for Th2 type immune reactions but also for tumor cell growth itself in human breast cancer.