Thrombomodulin Modulates Dendritic Cells via Both Antagonism of High Mobility Group Protein B1 and an Independent Mechanism

ABSTRACTBackgroundThrombomodulin treatment modulates the properties of dendritic cells (DCs) converting them from immunogenic to tolerogenic and inducing its own expression on DCs. Thrombomodulin binds to the inflammatory mediator, high mobility group protein B1 (HMGB1), antagonizing signalling through its receptor, receptor for advanced glycation end products (RAGE).MethodsTo test if soluble thrombomodulin could antagonize HMGB1 signaling via RAGE on DCs. DCs were prepared from mouse bone marrow cells or human monocytes. In some experiments dendritic cells were sorted into thrombomodulin+and thrombomodulin− populations. Expression of surface maturation markers was determined by flow cytometry following treatment with thrombomodulin in the presence or absence of HMGB1.ResultsThrombomodulin+dendritic cells secrete less HMGB1 into the medium. HMGB1 reduces the effects of thrombomodulin on expression of DC maturation markers. Treatment with thrombomodulin reduces the expression of maturation markers such as CD80 and CD86 and increases the expression of thrombomodulin on the DC surface. Treatment of DCs with neutralizing anti-HMGB1 antibody acted synergistically with thrombomodulin in increasing thrombomodulin expression on DCs. Treatment with thrombomodulin can still reduce the expression of surface markers on DCs derived from mice that are deficient in RAGE showing that thrombomodulin can affect DCs by an alternative mechanism.ConclusionsThe results of this study show that thrombomodulin modulates DCs both by antagonizing the interaction of HMGB1 with RAGE and by an independent mechanism