Selective blockade of membrane attack complex formation during simulated extracorporeal circulation inhibits platelet but not leukocyte activation.
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.
Rinder
C S
CS
Department of Laboratory Medicine, Yale University School of Medicine, New Haven, Conn. 06510-8051, USA. christine.rinder@yale.edu
Rinder
H M
HM
Smith
M J
MJ
Tracey
J B
JB
Fitch
J
J
Li
L
L
Rollins
S A
SA
Smith
B R
BR
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
D000911:Antibodies, Monoclonal; D003185:Complement C8; D015938:Complement Membrane Attack Complex; D016177:Macrophage-1 Antigen; D019007:P-Selectin; D015926:Complement C3a; D019272:Leukocyte Elastase