Inhibitory effects of TSG-6 link module on leukocyte-endothelial cell interactions in vitro and in vivo

Objective: The authors investigated whether the anti-inflammatory protein tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) and its Link module (Link_TSG6) could affect the complex multistep process of leukocyte/endothelial cell (EC) interaction. Methods: Mouse mesenteries were inflamed with interleukin (IL)-1beta and the extent of leukocyte rolling, adhesion, and emigration was determined after 2 h. Link_TSG6 and a single-point mutant (termed K13E) were given intraperitoneally together with the cytokine. Human neutrophil chemotaxis and transmigration were determined in vitro in response to IL-8 and/or TNF-alpha. TSG-6, Link_TSG6 and K13E were added to the leukocytes or the EC monolayers. Results: Co-injection of Link_TSG6 with IL-1beta selectively inhibited cell flux, adhesion, and emigration as analyzed in mesenteric postcapillary venules. The fewer cells that rolled in the animals treated with Link_TSG6 displayed a velocity similar to that measured in vehicle-treated mice. In vitro, Link_TSG6 did not affect neutrophil chemotaxis or EC activation but did inhibit neutrophil transmigration across EC monolayers. The latter effect was shared by full-length TSC-6 and observed equally in response to IL-8 or TNF-alpha. Conclusions: These data restrict the site of action for at least some of the anti-inflammatory effects ascribed to TSG-6/Link_TSG6 to the microenvironment of the extravasating leukocyte.