Interleukin-8 mRNA expression in circulating leucocytes during cardiopulmonary bypass

Interleukin-8 (IL-8) is found in patients following cardiopulmonary bypass (CPB). It may contribute to microvascular injury by activating neutrophils. We examined IL-8 mRNA expression in leucocytes in bypass. IL-8 mRNA levels were measured by Northern analysis and densitometry of isolated mononuclear leucocytes and neutrophils from blood samples taken before, during, and 2 and 48 h after CPB. Plasma IL-8 was measured at each time-point by immunoassay. A strong signal for IL-8 mRNA was detected in neutrophils in five of five and, more weakly, in mononuclear leucocytes of three of five patients studied. The signal peaked consistently during, and fell following bypass, usually to undetectable levels by 48 h. There was always a detectable signal in neutrophils preoperatively. Plasma IL-8 increased from undetectable prebypass levels and peaked later (2 h postbypass) in four of five patients. In the other patient, the cytokine remained detectable throughout. These data demonstrate that IL-8 transcription occurs in leucocytes before and during CPB, but suggest that much of the IL-8 detectable in plasma following bypass may derive, not from these leucocytes, but from other cell types. The release of some IL-8 by neutrophils could lead to local positive feedback in neutrophil recruitment and associated endothelial injury.