Interleukin 6 (IL-6) is a pleiotropic cytokine that is produced by many different cell types and plays a role in a wide range of responses, such as immune responses, acute-phase reactions, and hematopoiesis (Sehgal et al., 1989; Heinrich et al., 1990; Hirano and Kishlmoto. 1990; VanSnick. 1990; Hirano, 1992, 1998).