Endpoint-attached heparin blocks neutrophil sticking and spreading

Neutrophils adhere to polymer surfaces by partly unknown mechanisms. Heparin-coating of such surfaces is employed to improve biocompatibility of extracorporeal circulation. The aim of the study was to investigate mechanisms for interactions between neutrophils and uncoated versus heparin-coated surfaces. Isolated human neutrophils were incubated in tissue culture plates. Uncoated plates induced sticking and spreading of unstimulated neutrophils. Heparin-coating reduced sticking by approximately 75%, and adherent cells were less spread (p<0.001). Experiments in plates coated with modified heparins showed that sticking and spreading were not related to anticoagulatory ability or surface charge. Unstimulated neutrophil sticking was unchanged whether the media contained divalent cations or 1mM ethylenediaminetetraacetic acid (EDTA). Spreading on uncoated plates was greater in the presence of Ca(2+) and/or Mg(2+) than with EDTA. Spreading of unstimulated neutrophils on heparin-coated plates varied little with different media. Pre-incubation with anti-CD11b/CD18 antibodies did not significantly influence adhesion to heparin-coated plates. There were no differences in expression of the antiadhesive receptor CD43 (leukosialin) on adherent neutrophils on uncoated and heparin-coated plates, and pre-incubation with anti-CD43 antibody had little effect on neutrophil sticking. These data indicate an adhesive mechanism independent of selectins, integrins, and leukosialin, and inhibition of sticking and spreading by heparin-coating.