Thrombin‐mediated IL‐10 up‐regulation involves protease‐activated receptor (PAR)‐1 expression in human mononuclear leukocytes

Thrombin, the key enzyme of the coag- ulation cascade, exerts cellular effects through ac- tivation of the protease-activated receptors (PARs). Interleukin (IL)-10, besides its anti-inflam- matory properties, is considered a major denomi- nator of the immunosuppressive effect during hu- man endotoxemia. We have recently shown that thrombin inhibits IL-12 production in human mononuclear cells and that such inhibition is ac- companied by IL-10 up-regulation. To our knowl- edge, there are no data available to show that thrombin mediates IL-10 production by its inter- actions with PAR-1. We here report that human -thrombin enhances IL-10 expression in human peripheral blood mononuclear cells and in estab- lished monocytic cell lines and that this up-regula- tion requires PAR-1 expression. The use of pro- teolytically inactive thrombin reveals that such en- hancement requires thrombin proteolytic activity. Addition of PAR-1 agonist peptides, such as SFLLRN, results in a significant increase of IL-10 production. PAR-1 expression is required for thrombin-induced IL-10 production, as shown by experiments performed with antisense or sense PAR-1 oligonucleotides. Treatment with thrombin or SFLLRN of monocytic cell lines, such as U937 and Mono Mac-6, results in an increased IL-10 production. This suggests that the observed IL-10 up-regulation may be the result of a direct interac- tion with monocytes. The observation that throm- bin-mediated up-regulation of IL-10 may require the expression of the PAR-1 receptor identifies a new, functional link between inflammation and co- agulation. Our results may also contribute to better design therapeutic strategies to treat several disor- ders, characterized by the presence of inflamma- tory as well as coagulant responses. J. Leukoc. Biol. 78: 000-000; 2005.