TSG-6: a multifunctional protein associated with inflammation.

TSG-6 expression is upregulated in many cell types in response to a variety of proinflammatory mediators and growth factors. This protein is detected in several inflammatory disease states (e.g. rheumatoid arthritis) and in the context of inflammation-like processes, such as ovulation, and is often associated with extracellular matrix remodelling. TSG-6 has anti-inflammatory and chondroprotective effects in various models of inflammation and arthritis, which suggest that it is a component of a negative feedback loop capable of downregulating the inflammatory response. Growing evidence also indicates that TSG-6 acts as a crucial factor in ovulation by influencing the expansion of the hyaluronan-rich cumulus extracellular matrix in the preovulatory follicle. TSG-6 is a member of the Link module superfamily and binds to hyaluronan (a vital component of extracellular matrix), as well as other glycosaminoglycans, via its Link module. In addition, TSG-6 forms both covalent and non-covalent complexes with inter-alpha-inhibitor (a serine protease inhibitor present at high levels in serum) and potentiates its anti-plasmin activity.