BOTH PLASMA-ASSOCIATED AND LEUKOCYTE-ASSOCIATED C5A ARE ESSENTIAL FORASSESSMENT OF C5A GENERATION IN-VIVO

Background. Measurement of C5a in plasma is hampered by the rapid clea rance of C5a as a result of cell binding. Therefore, an assessment of whether cell-bound C5a might better reflect C5a generation in vivo is essential. Methods. We quantified plasma and leukocyte-bound C5a in sa mples from patients undergoing cardiopulmonary bypass, which is known to be associated with complement activation. C3 activation products an d the terminal complement complex were measured as well. Results. Plas ma levels of C3 activation products and the terminal complement comple x increased rapidly and significantly after the onset of cardiopulmona ry bypass until they reached a plateau after 30 minutes. The concentra tion of plasma C5a increased steadily to twice baseline at the end of bypass. The concentration of leukocyte-associated C5a increased threef old after 10 minutes of cardiopulmonary bypass, when a plateau was rea ched. A positive correlation was found between levels of plasma C3 act ivation products or terminal complement complex and plasma C5a plus ce ll-associated C5a but not between C3 activation products or terminal c omplement complex and either one of the C5a variables. Conclusions. We conclude that both plasma C5a and leukocyte-associated C5a are needed for monitoring in vivo C5a generation. (C) 1997 by The Society of Tho racic Surgeons.