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). It is expressed by a variety of normal and transformed lymphoid and nonlymphoid cells.
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 mouse (6), rat (7) and human (8, 9) IL-6 cDNAs have been cloned. The mouse IL-6 cDNA encodes a 211 amino acid (aa) residue precursor polypeptide with a hydrophobic signal sequence that is cleaved to generate the 187 aa residue mature protein. Mouse to rat and human, there is approximately 87% and 39% aa identity, respectively. Although human and mouse IL-6 are equally active on mouse cells, mouse IL-6 is not active on human cells (10).
The high-affinity IL-6 receptor complex, which mediates IL-6 bioactivity, consists of two membrane glycoproteins. The production of IL-6 is upregulated 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 (3, 5).
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