Selectins and β₂-integrins mediate post-ischaemic venular adhesion of polymorphonuclear leukocytes, but not capillary plugging, in isolated hearts

Leukocytes adhering to venular endothelium and emigrating into the tissue contribute to myocardial reperfusion injury. The aim of the present study was to characterize the contribution of two different families of adhesion molecules, selectins and integrins, to post-ischaemic capillary plugging and venular adhesion of leukocytes in an isolated heart model. Guinea-pig hearts were perfused using the Langendorff technique. After 20 min stabilization global ischaemia was induced for 15 min at 37 °C. With the onset of reperfusion 107 isolated polymorphonuclear leukocytes (PMN), prelabelled with rhodamine 6G, were infused within 1 min. Perfusion was continued for 2 min to wash out all cells not firmly adhering to the vascular endothelium. Hearts were then arrested, mounted on a microscope stage and perfused with a cardioplegic solution containing 0.01% fluorescein isothiocyanate (FITC)-dextran (MW 150,000). In situ videofluorescence microscopy was used to quantify PMN plugging and adherent PMN. Four groups were studied: control (no treatment or ischaemia, n = 6); ischaemia (no treatment and 15 min ischaemia, n = 5); fucoidin (pretreatment of hearts and PMN with 0.3 mg/ml selectin inhibitor fucoidin and 15 min ischaemia, n = 5) and CD18 (pretreatment of PMN with 0.1 mg monoclonal antibody against CD18 and 15 min ischaemia, n = 5). Capillary plugging by PMN was 25 ± 5 PMN/mm² epicardial surface area and increased moderately to 55 ± 6 PMN/mm² in reperfused hearts. This increase was not affected by fucoidin or CD18 antibody. In contrast, post-ischaemic adhesion of PMN in small venules increased ninefold from 21 ± 5 to 196 ± 23 PMN/mm² endothelial surface area. The increase in PMN adhesion to venular endothelium was blocked completely by pretreatment with fucoidin (19 ± 5 PMN/mm^-2) or CD18 antibody (7 ± 2 PMN/mm^-2). We conclude that selectin interaction alone is not sufficient to account for post-ischaemic PMN adhesion in the small venules of the coronary vasculature, because blocking the integrin subunit CD18 also inhibited PMN adhesion completely. On the other hand, neither integrins nor selectins seem to be involved in post-ischaemic capillary plugging by PMN in our perfused heart model.