Effect of cardiopulmonary bypass on circulating lymphocyte function.

Extracorporeal cardiopulmonary bypass (CPB) has been associated with a wide variety of immunological derangements, including a transient postoperative impairment of lymphocyte function. We examined changes in phenotypic and nonspecific cytotoxicity of peripheral blood mononuclear cells after extracorporeal CPB. The peripheral blood samples obtained from 10 patients were subjected to natural killer and cytotoxic T lymphocyte activity assay before and at intervals after CPB. Phenotypic analysis of peripheral blood lymphocytes was performed in 5 patients before and immediately after CPB. We observed a significant increase in peripheral blood CD8+ cells (cytotoxic/suppressor T lymphocytes) (16.1% +/- 2.5% versus 22.5% +/- 2.1%; p less than .005) and a decrease in CD4+ cells (helper/inducer T lymphocytes) (46.1% +/- 3.5% versus 36.1% +/- 3.5%; p less than 0.02) immediately after extracorporeal circulation. The CD8/CD4 ratio in peripheral blood was significantly increased immediately after bypass (0.53 versus 0.80; p less than 0.001). No significant changes in percentages of other leukocyte subsets in peripheral blood were noted. The activity of cytotoxic T lymphocytes and natural killer cells in peripheral blood was impaired on postoperative days 1 and 3 but was restored to preoperative values by removal of mononuclear phagocytes from these cells. The decrease in natural killer cell and cytotoxic T lymphocyte activity in peripheral blood may signify a temporary impairment of the effector arm of the cell-mediated immunity in the post-operative period. The observed changes in peripheral blood phenotype and function may be involved in early organ injury and infectious complications after CPB.