Complement activation on the surface of cell-derived microparticles during cardiac surgery with cardiopulmonary bypass - is retransfusion of pericardial blood harmful?

Objectives To investigate whether cell-derived microparticles play a role in complement activation in pericardial blood of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB) and whether microparticles in pericardial blood contribute to systemic complement activation upon retransfusion. Methods Pericardial blood of 13 patients was retransfused in 9 and discarded in 4 cases. Microparticles were isolated from systemic blood collected before anesthesia (T1) and at the end of CPB (T2), and from pericardial blood. The microparticles were analyzed by flow cytometry for bound complement components C1q, C4 and C3, and bound complement activator molecules C-reactive protein (CRP), serum amyloid P-component (SAP), immunoglobulin (Ig) M and IgG. Fluid-phase complement activation products (C4b/c, C3b/c) and activator molecules were determined by ELISA. Results Compared with systemic T1 blood, pericardial blood contained increased C4b/c and C3b/c, and increased levels of microparticles with bound complement components. In systemic T1 samples, microparticle-bound CRP, whereas in pericardial blood, microparticle-bound SAP and IgM were associated with complement activation. At the end of CPB, increased C3b/c (but not C4b/c) was present in systemic T2 blood compared with T1, while concentrations of microparticles binding complement components and of those binding complement activator molecules were similar. Concentrations of fluid-phase complement activation products and microparticles were similar in patients whether or not retransfused with pericardial blood. Conclusions In pericardial blood of patients undergoing cardiac surgery with CPB, microparticles contribute to activation of the complement system via bound SAP and IgM. Retransfusion of pericardial blood, however, does not contribute to systemic complement activation.