Interleukin-6 (IL-6) is a multi-functional cytokine that regulates immune responses, acute phase reactions and hematopoiesis and may play a central role in host defense mechanisms. IL-6 is usually not produced constitutively by normal cells, but its expression is readily induced by a variety of cytokines, lipopolysaccharide (LPS) or viral infections. IL-6 is a pleiotropic cytokine produced by a variety of cells. It acts on a wide range of tissues, exerting growth-induction, growth-inhibition, and differentiation respectively, depending on the nature of the target cells.

IL-6 is involved in:

- the induction of B-cell differentiation
- the induction of acute phase proteins in liver cells
- growth promotion of myeloma/plasmacytoma/hybridoma cells
- induction of IL-2 and IL-2 receptor expression
- proliferation and differentiation of T cells
- enhancement of IL-3-induced multipotential colony cell formation in hematopoietic stem cells and induction of maturation of megakaryocytes as a thrombopoietic factor
- induction of mesangial cell growth
- induction of neural differentiation of PC 12 cells
- induction of keratinocyte growth

The abnormal production of IL-6 was first suggested to be related to polyclonal B-cell activation with autoantibody production in patients with cardiac myxoma. Since then, IL-6 has been suggested to be involved in the pathogenesis of a variety of diseases. Measurement of IL-6 levels in serum and other body fluids thus provides more detailed insights into various pathological situations.

Synonyms: Interferon-beta 2, B-cell stimulatory factor 2, HGF