Granulocyte- and monocyte-platelet adhesion index in coronary and peripheral blood after extracorporeal circulation and reperfusion

Background: Neutrophil-granulocyte and mononuclear-cell functional changes occur during cardiopulmonary bypass and cardiovascular surgery. Leukocyte-platelet interaction, leading to generation of heterotypic co-aggregates, represents an amplification mechanism of local inflammatory response and tissue damage. Methods: Samples of 20 patients were drawn from coronary sinus before cardioplegia and after reperfusion, as well as from peripheral blood at 5 and 24 hours postoperatively. Granulocyte and monocyte expression of CD162, CD15s, CD18 and CD11b were quantified by flow cytometry at the different times. Parallel variations of leukocyte-platelet conjugates (percentages) and a derived (cell number-normalized) leukocyte-platelet adhesion index were measured using antibodies against CD45, CD14 and CD41a. The evaluation of platelet functional state was carried out using antibodies against CD62P (P-selectin) and PAC-1. Results: Monocyte and granulocyte cell number increased in coronary blood at reperfusion and in peripheral blood post-operatively. A different course characterized the changes of the leukocyte-platelet adhesion index with respect to the variations of circulating leukocyte-platelet co-aggregates . Leukocyte molecules expression showed no significant variations for CD15s on both leukocyte subsets, while a significant up-modulation for CD162 was observed on monocytes at 24 hours after extracorporeal circulation (P=0.0002), and for CD11b on granulocytes at 5 hours post-operatively (P=0.033). A loss of CD162 expression was observed at reperfusion (P=0.0038) on granulocytes, associated to a down-modulation of CD18 (P=0.0033) and CD11b (P=0.0184) in peripheral blood at 24 hours. No significant up-regulation of platelet activatory molecules was found at reperfusion, as well as post-operatively, when compared with the before-cardioplegia derived data. Conclusions: The variations of a normalized leukocyte-platelet adhesion index seem to reflect the leukocyte-platelet functional interaction more accurately than the measurements of cellular conjugates. The absence of platelet activation suggests that the leukocyte membrane modifications play a main role in controlling the formation and stability of heterotypic leukocyte-platelet co-aggregates after cardiac surgery with extracorporeal circulation.