Growth of normal cells is regulated by polypeptides that act via specific cellular receptors. Otherwise known as cytokines, these substances include the growth factors that modulate the proliferation of nonimmune cells. Lymphokines or cytokines, on the other hand, are involved in the regulation of immune cells. Advances in the last 15 yr have shown that alterations in cytokines and their receptors may play a central role in the uncontrolled proliferation of tumor cells in vitro, and such cytokine aberrations are possibly responsible for regulation of tumor growth in vivo.
