Interleukin 6 (IL-6) is a multifunctional cytokine that plays important roles in host defense, acute phase reactions, immune responses, nerve cell functions and hematopoiesis (1-5).

IL-6 is a prototypic member of the IL-6 superfamily of cytokines that share gp130 as a component required for signal transduction (4). The rat, mouse and human IL-6 cDNAs have been cloned (6-9). Rat IL-6 cDNA encodes a 211 amino acid (aa) residue precursor polypeptide with a hydrophobic signal peptide that is cleaved to generate the 187 aa residue mature protein. At the protein sequence level, there is approximately 39% identity between rat and human, and 87% identity between mouse and rat IL-6 (6).

IL-6 is expressed by a variety of normal and transformed lymphoid and non-lymphoid cells. The production of IL-6 is up-regulated by numerous signals such as mitogenic or antigenic stimulation, lipopolysaccharides, calcium ionophores, cytokines and viruses. IL-4, IL-10 and IL-13 inhibit IL-6 expression in monocytes. Elevated serum IL-6 levels have been observed in a number of pathological conditions, including bacterial and viral infections,trauma, autoimmune diseases, inflammations and malignancies (1-5).