Induction of interleukin-1 production in patients undergoing cardiopulmonary bypass

Systemic reactions resembling inflammation occur in patients undergoing cardiopulmonary bypass. We now report that interleukin-1, an endogenous pyrogen and a key mediator of inflammation, is transiently and consistently generated in vivo by circulating monocytes within hours after cardiopulmonary bypass. Interleukin-1 production was assessed by measuring interleukin-1 functional activity and interleukin-1 beta antigen concentration in cell lysates from monocytes of patients during and after bypass. There was no increase in intracellular interleukin-1 activity during bypass and within the first hours after bypass, possibly because of a suppressive effect of hypothermia on interleukin-1 production, as documented in vitro. Maximal generation of interleukin-1 was observed 24 hours after extracorporeal circulation, concomitantly with the occurrence of a peak in body temperature. The amount of interleukin-1 generated at that time was linearly correlated with the increase in patients' body temperature. The peak in interleukin-1 production followed by 20 hours the peak in complement activation as assessed by determining C3a desArg and C5a desArg concentrations in patients' plasma. These results indicate that interleukin-1 may be involved in the pathogenesis of adverse systemic reactions associated with cardiopulmonary bypass.