Erythrocyte-Derived Microvesicles Amplify Systemic Inflammation by Thrombin-Dependent Activation of Complement
Objective—Transfusion of aged blood has been associated with increased morbidity and mortality in critically ill patients. During storage, erythrocytes release increasing numbers of microvesicles (red blood cell–derived microvesicles [RBC-MVs]). We hypothesized that RBC-MVs mediate some of the deleterious effects of aged blood transfusions.
Approach and Results—We established a murine transfusion model using RBC-MVs purified from aged mouse erythrocytes. Injection of RBC-MVs into healthy mice had no effect. However, they aggravated pulmonary leukocyte sequestration and peripheral blood leukopenia induced by lipopolysaccharides. Lipopolysaccharide-induced proinflammatory cytokines were significantly increased in plasma after RBC-MV injection. These effects were not seen in C5aR-deficient mice. In vitro, RBC-MVs bound C3 fragments after incubation with plasma but failed to bind immunoglobulins, C1q, or MBL. Preventing thrombin generation inhibited complement activation in vitro and in vivo and reversed the proinflammatory effects of RBC-MVs in lipopolysaccharide-primed mice. Finally, the RBC-MV–induced phenotype was recapitulated using phosphatidylserine-expressing liposomes, suggesting that surface expression of phosphatidylserine by RBC-MVs was mechanistically involved.
Conclusions—These results point toward a thrombin-dependent mechanism of complement activation by RBC-MVs independent of the classical, lectin, or alternative pathway. Besides identifying RBC-MVs as potential mediators of transfusion-related morbidity, our findings may be relevant for other inflammatory disorders involving intravascular microvesicle release, for example, sickle cell disease or thrombotic microangiopathy.
- blood coagulation
- blood component transfusion
- cell-derived microparticles
- complement system proteins
- Received August 14, 2013.
- Accepted November 20, 2013.
- © 2013 American Heart Association, Inc.