Interaction between neutrophils and endothelium.

The endothelial permeability associated with cardiopulmonary bypass in children is due, at least in part, to an inflammatory response. Neutrophils and their relationship with endothelium are fundamental to the production of capillary leak. This review discusses current concepts of the mechanisms involved in adhesion between neutrophils and the endothelium and its control. Evidence for modulation of these changes during bypass in children is reviewed. We have shown that cardiopulmonary bypass in children is associated with down-regulation (or shedding) of L-selectin and up-regulation of expression of CD11b/CD18. There may be a role for the cytokine interleukin-8 in the modulation of this process. We have demonstrated in vitro that certain of the procedures associated with bypass are associated with up-regulation of circulating neutrophil adhesion molecules and with the release of interleukin-8. These factors include changes in temperature and circulation. More research is required to tease out the most important components of the mechanisms of adhesion, and clinical correlations must be defined.

Humoral and cellular activation in a simulated extracorporeal circuit.

Endothelial injury consequent upon widespread humoral and cellular activation is probably a major contributor to the phenomenon of cardiopulmonary bypass-induced organ dysfunction. This article reviews some of the mechanisms by which complement and neutrophil activation and interleukin-8 may be involved in this inflammatory response. In a model consisting of a simulated extracorporeal circulation we were able to demonstrate complement activation, profound and specific changes in neutrophil adhesion molecule expression, and interleukin-8 generation. The importance of these changes and their potential interactions are discussed.