title: Selective blockade of membrane attack complex formation during simulated extracorporeal circulation inhibits platelet but not leukocyte activation.
abstract: OBJECTIVE
  Complement activation is induced by cardiopulmonary bypass, and previous work found that late complement components (C5a, C5b-9) contribute to neutrophil and platelet activation during bypass. In the present study, we blocked C5b-9 formation during extracorporeal recirculation of whole blood to assess whether the membrane attack complex was responsible for both platelet and leukocyte activation.
  
  
  METHODS
  In a simulated extracorporeal model that activates complement (C3a and sC5b-9), platelets (CD62P expression, leukocyte-platelet conjugate formation), and leukocytes (increased CD11b expression and neutrophil elastase), we examined an anti-human C8 monoclonal antibody that inhibits C5b-9 generation for its effects on cellular activation.
  
  
  RESULTS
  Anti-C8 significantly inhibited sC5b-9 formation but did not block C3a generation. Anti-C8 also significantly inhibited the increase in platelet CD62P and monocyte-platelet conjugate formation seen with control circulation. Moreover, compared with control circulation, in which the number of circulating platelets fell by 45%, addition of anti-C8 completely preserved platelet counts. In contrast to blockade of both C5a and sC5b-9 during simulated extracorporeal circulation, neutrophil activation was not inhibited by anti-C8. However, circulating neutrophil and monocyte counts were preserved by addition of anti-C8 to the extracorporeal circuit.
  
  
  CONCLUSIONS
  The membrane attack complex, C5b-9, is the major complement determinant of platelet activation during extracorporeal circulation, whereas C5b-9 blockade has little effect on neutrophil activation. These data also suggest a role for platelet activation or C5b-9 (or both) in the loss of monocytes and neutrophils to the extracorporeal circuit.
authors.affiliation: Department of Laboratory Medicine, Yale University School of Medicine, New Haven, Conn. 06510-8051, USA. christine.rinder@yale.edu
authors.forename: C S
authors.initials: CS
authors.lastname: Rinder
authors.forename: H M
authors.initials: HM
authors.lastname: Rinder
authors.forename: M J
authors.initials: MJ
authors.lastname: Smith
authors.forename: J B
authors.initials: JB
authors.lastname: Tracey
authors.forename: J
authors.initials: J
authors.lastname: Fitch
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: S A
authors.initials: SA
authors.lastname: Rollins
authors.forename: B R
authors.initials: BR
authors.lastname: Smith
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D003167:Complement Activation; D015926:Complement C3a / Q000187:drug effects; D003185:Complement C8 / Q000276:immunology; D015938:Complement Membrane Attack Complex / Q000037:antagonists & inhibitors / Q000502:physiology*; D004797:Enzyme-Linked Immunosorbent Assay; D005112:Extracorporeal Circulation; D005434:Flow Cytometry; D006801:Humans; D007958:Leukocyte Count; D019272:Leukocyte Elastase / Q000378:metabolism; D016177:Macrophage-1 Antigen / Q000378:metabolism; D018375:Neutrophil Activation; D009504:Neutrophils / Q000201:enzymology; D019007:P-Selectin / Q000378:metabolism; D015539:Platelet Activation; D010976:Platelet Count; D012016:Reference Values
chemical_list: D000911:Antibodies, Monoclonal; D003185:Complement C8; D015938:Complement Membrane Attack Complex; D016177:Macrophage-1 Antigen; D019007:P-Selectin; D015926:Complement C3a; D019272:Leukocyte Elastase