Inhibition of complement neutrophil, and platelet activation by an anti-factor D monoclonal antibody in simulated cardiopulmonary bypass circuits

Objectives: Patients undergoing cardiopulmonary bypass frequently manifest generalized systemic inflammation and occasionally manifest serious multior gan failure. Inflammatory responses of bypass are triggered by contact of b lood with artificial surfaces of the bypass circuits, surgical trauma, and ischemia-reperfusion injury. We studied the effects of specific inhibition of the alternative complement cascade by using an anti-factor D monoclonal antibody (166-32) in extracorporeal circulation of human whole blood used a s a simulated model of cardiopulmonary bypass. Methods: Five healthy blood donors were used in the study. Monoclonal antib ody 166-32 was added to freshly collected, heparinized human blood recircul ated in a pediatric cardiopulmonary bypass circuit at a final concentration of 18 mug/mL. An irrelevant monoclonal antibody was used as a negative con trol with the same donor blood in a parallel bypass circuit on the same day . Blood samples were collected at different time points during recirculatio n for measurement of activation of complement, neutrophils, and platelets b y immunofluorocytometric methods and enzyme-linked immunosorbent assays. Results: Monoclonal antibody 166-32 inhibited the alternative complement ac tivation and the production of Bb, C3a, sC5b-9, and C5a. Upregulation of CD 11b on neutrophils and CD62P on platelets was also significantly inhibited by monoclonal antibody 166-32. This is consistent with the inhibition of th e release of neutrophil-specific myeloperoxidase and elastase and platelet thrombospondin. The production of proinflammatory cytokine interleukin 8 wa s also suppressed by the antibody. Conclusions: The alternative complement cascade is predominantly activated during extracorporeal circulation. Anti-factor D monoclonal antibody 166-32 is effective in inhibiting the activation of complement, neutrophils, and platelets. Inhibition of the alternative complement pathway by targeting fa ctor D could be useful in reducing systemic inflammation in patients underg oing cardiopulmonary bypass.