On day 5, the medium was supplemented with/without NGF (50 ng/ml), IL-6 (50 ng/ml), INF (50 ng/ml), or LPS (100 ng/ml), and cells were cultured for 48 h. (26), and serum during bacterial sepsis (27). There is a growing body of evidence to show that the primary function of TSG-6 is to protect tissues from the damaging and unwanted effects of inflammation and that many of the tissue-protective and anti-inflammatory activities of mesenchymal stromal cells are mediated by TSG-6 (28). For example, TSG-6 is a potent inhibitor of neutrophil migration (29) and can also suppress inflammatory signaling in tissue-resident immune cells (30). Some of the effects of TSG-6 on immune cell responses are CD44-dependent (30, 31) where this may be mediated through the direct cross-linking of HA by TSG-6, which is known to enhance HA/CD44 interactions on leukocytes (14, 31,C34). The interaction of TSG-6 with HA, which has been extensively characterized at a biophysical and structural level, promotes TSG-6 oligomerization, allowing multiple polysaccharide chains to link together and the rigidification/condensation of HA-rich matrices (14, 32). As well as its direct interaction with HA, TSG-6 also plays a well defined role in catalyzing the covalent transfer of heavy chains (HCs) from the serum-derived proteoglycan inter–inhibitor (II; a serine protease inhibitor) and the related pre–inhibitor (PI) onto HA chains (35, 36). This HA modification occurs whenever HA, II/PI, and TSG-6 meet, and recently divalent cations (Ca2+, Mg2+, and Mn2+) have been shown to have a key structural and functional role in the TSG-6-mediated transfer of HC from II onto HA (35, 37). For example, HA and TSG-6 levels are generally increased in tissues during inflammation (22, 27, 38), and II/PI can leak into the tissues from the circulation due to increased vascular permeability. The formation of HC-HA complexes is believed to provide ECM stabilization through cross-linking mechanisms (35, 39) and to regulate the interaction/migration of leukocytes (40). In some contexts, HA-HC-containing matrices have been implicated as having anti-inflammatory and tissue-protective properties, in the amniotic membrane (41, 42) and when produced by mesenchymal stem cells (43). However, 2,4,6-Tribromophenyl caproate in other instances, their formation may contribute to pathology, in lung disease (44). HA is 2,4,6-Tribromophenyl caproate present in the extracellular compartment of most tissues, including the CNS, where it is up-regulated after injury in the scar tissue (15). The synthesis of HA is also often up-regulated in response to inflammation, tissue damage, or invasion by tumor cells or pathogens (45,C48). Hyaluronidases, endoglycosidases expressed by mammalian cells, may break high molecular weight HA into low molecular weight HA; however, the transfer of HCs from II to HA, which cross-links HA chains, may protect HA from digestion. TSG-6 also interacts with other ligands in addition to HA, including sulfated glycosaminoglycans (chondroitin sulfate (CS) and heparan sulfate) (49) and core proteins from CS proteoglycans (aggrecan and versican) (50, 51). Furthermore, TSG-6 binds to extracellular signaling molecules, such as bone morphogenetic proteins (52) and chemokines (29, 53). In the case of CXCL8, TSG-6 inhibits the interaction of this proinflammatory chemokine with cell surface heparan sulfate, providing a mechanism by which TSG-6 impairs neutrophil migration into tissues (29). This anti-inflammatory activity of TSG-6 has been suggested, for example, to contribute to the beneficial effects of recombinant TSG-6 administration after tissue damage and recovery of memory in a mouse model of traumatic brain injury (54). Thus, TSG-6 has 2,4,6-Tribromophenyl caproate a wide range of biological activities that are potentially relevant to inflammation and tissue injury/regeneration in the brain and spinal cord. However, to date there has been little analysis of TSG-6 expression in neuronal tissues. The only study we are aware of (non-peer reviewed) analyzed TSG-6 expression in a murine model of transient focal cerebral ischemia; COL5A2 TSG-6 mRNA was significantly increased postreperfusion, and the elevated TSG-6 protein was associated with astrocytes surrounding the infarcted tissue (55). We hereby show that TSG-6 is expressed constitutively in the adult CNS by GFAP+/CD44+ astrocytes. Our findings provide evidence that TSG-6 is not expressed during development of the CNS but does, however, play a role in astrocyte maturation and during pathogenesis. TSG-6 expression is greatly up-regulated following CNS injury and is present within the glial scar most likely bound to HA (or CS) chains. Thus, TSG-6 2,4,6-Tribromophenyl caproate may coordinate assembly and stabilization of the HA-rich matrices that contribute to glial scar formation. Results TSG-6 Is Present in.