C3- AND C5- CONVERTASE INHIBITION PREVENTS MONOCYTE AND PMN ACTIVATION DURING IN VITRO CARDIOPULMONARY BYPASS

Abstract

Introduction: Complement activation contributes to the inflammatory response to cardiopulmonary bypass, but understanding of the role of specific complement components is evolving. We have previously used simulated extracorporeal circulation (SECC) to show that C5a and C5b-9 inhibition blocks PMN but not monocyte activation. This investigation used a complement inhibiting protein (CAB-2.1) which blocks C3a as well as C5a and C5b-9 formation [2] and examined its effects on leukocyte activation during SECC. Methods: SECC circuits were assembled and run as previously described [1]. After HIC approval, 500 ml blood was drawn from healthy volunteers, heparinized (5u/mL), and added to SECC. CAB-2.1 or vehicle was added to the blood immediately before addition to the circuit. Four runs were performed with CAB-2.1 at 30 [micro sign]g/ml, 4 runs at 300 [micro sign]g/ml, and 4 control runs with vehicle alone. Plasma was assayed for C3a, sC5b-9, and PMN elastase. Leukocyte CD11b, an index of activation, was measured by flow cytometry [1]. Significance was accepted at p <or=to 0.05 for repeated measures ANOVA. Results: Control SECC activated complement with C3a and sC5b-9 levels rising 4-fold, and also activated monocytes and PMN, with CD11b levels peaking at 3 times baseline for both and PMN elastase at 10 times baseline (p<0.01 for all). CAB-2.1 at 300[micro sign]g/ml inhibited both C3a and C5b-9 formation by 85%. Both monocyte and PMN CD11b upregulation and PMN elastase release were inhibited by CAB-2.1 at 300 [micro sign]g/ml (Figure 1). Although 30ug/ml CAB-2.1 inhibited C3a and sC5b-9 formation by 55% and 65%, respectively (p<0.01 for both), this dose did not block monocyte or PMN activation.Figure 1Discussion: We have previously shown that inhibition of C5a and C5b-9 generation during SECC inhibits PMN but not monocyte CD11b upregulation. This study confirms the ability of complement inhibition to block PMN activation during SECC. Furthermore, it demonstrates that blockade of C3a generation inhibits monocyte CD11b upregulation as well. This suggests that inhibition early in the complement pathway is required to inhibit both monocyte and PMN activation during CPB.