Detection of leukocyte filtration and potential selective migration during use of cardiopulmonary bypass in cardiac surgery by flow cytometry

Cardiac surgery with cardiopulmonary bypass (CPB) can induce severe post-operative immune responses. During CPB loss of activated lymphocytes from the peripheral blood (PBL) was observed. We investigated if PBL get lost by binding to the CPB or by migration into the peripheral tissue and if the cells adhere selectively to different filter types. PBL were collected before, during and after surgery of pediatric patients and from the filters of the CPB by washing. Immunophenotype was determined by four color flow cytometry (FCM). In addition, PBL adhesion to CPB was analyzed in vitro. During surgery, B-cell counts decreased by greater than 50% due to the loss of CD69+ cells. The fraction of CD25+ and CD54+ T-lymphocytes decreased by 70%, that of CD69+ natural killer cells by 40%. In vivo in the CPB the proportion of CD69+ cells increased by up to 50%. These findings were supported by in vitro filtration studies. In contrast, the proportion of T-lymphocytes CD25+ or CD54+ were lower in the CPB. CD69+ cells adhere selectively to CPB filters. Loss of activated CD25+ or CD54+ T-lymphocytes could be due to their selective migration into the peripheral tissue. This FCM technique could be applied to test various filter types used in CPB in order to test their biocompatibility.