Response of the cellular immune system to cardiopulmonary bypass in vivo.

Cardiopulmonary bypass (CPB) is known to induce an inflammatory response. Previous studies reported an impairment of the cellular immune response with activation of neutrophils and changes in lymphocyte subpopulations. The objective of the present study was to investigate the effect of CPB on leukocyte activation in vivo. In 27 patients undergoing coronary artery bypass grafting, the quantitative and the qualitative response of leukocyte populations to CPB was analysed pre-, intra-, and postoperatively using flow cytometry. A significant increase in leukocyte counts was detected during CPB, resulting in a marked leukocytosis postoperatively. The total number of lymphocytes peaked in the early phase of CPB, followed by a significant decrease, mainly due to a loss in B and cytotoxic T lymphocytes. In contrast, the lymphocytopenia observed 8 h after protamin administration was mainly caused by a drop in the population of helper T lymphocytes. Activation of distinct cell populations could be detected during and following CPB. The results indicate an influence of CPB on the cellular immune system, however an immuno-suppression was detectable only transiently.