The Complement System Is Activated in a Biphasic Pattern After Coronary Artery Bypass Grafting

Background. The complement system is a key component in the inflammatory response after coronary artery bypass grafting (CABG). The routes of complement activation and deactivation after cardiac surgery are not clear. The aim of this study was to analyze routes of complement activation after uncomplicated CABG. Methods. Complement components and activation products were measured in 20 nondiabetic adult patients undergoing elective CABG at several times postoperatively starting at admission to the intensive care unit. Results. Complement activation after uncomplicated CABG showed a biphasic pattern. In the first 8 hours after admission to the intensive care unit, complement activation was initiated by the classical lectin pathway and augmented by the alternative pathway. Ultimately, this resulted in terminal pathway activation and formation of terminal complement complex. In the second phase, starting at 8 hours after the operation, complement was still activated by the classical lectin pathway, but there was no augmentation by the alternative pathway and no terminal complement complex formation. This implies that during this second stage, inhibitory mechanisms beyond C3b are engaged. Conclusions. Complement activation after cardiac surgery is regulated in a complex biphasic way, with additional inhibitory mechanisms engaged from 8 hours postoperatively onward.