Activated leukocytes adsorbed on the surface of an extracorporeal circuit.

Biocompatibility of extracorporeal circuits has mostly been investigated by sampling blood in circulation. However, a proportion of activated leukocytes leave circulation by sticking to the circuits, and might affect the circuit biocompatibility. To reveal these characteristics, we eluted the adsorbed leukocytes from circuits used for 6 patients by washing with ethylenediaminetetraacetic acid (EDTA)-HEPES buffer. 1.3 x 109 leukocytes, representing 5 to 10% of the circulating leukocytes, were collected. Most were neutrophils expressing CD11b antigens as high as those in circulation during cardiopulmonary bypass. Adsorbed monocytes expressed tissue factor higher than those in circulation (P < 0.05). An elution procedure by EDTA itself induced only a minimal activation of the leukocytes. These results indicate that extracorporeal circuits adsorb a large number of activated neutrophils and a small number of highly thrombogenic monocytes during their use. Although our data is limited, this elution procedure appears useful to investigate the biocompatibility of extracorporeal circuits.