Previous studies have demonstrated that polymorphonuclear leukocytes (PMNs) are locally activated in reperfused myocardium and contribute to the myocardial cell injury associated with reperfusion. It has been suggested that the adhesion of activated PMNs in reperfused myocardium is mediated by the PMN adhesion molecule CD-18. In the present study, we performed experiments to determine if the specific anti-CD-18 monoclonal antibody (MAb) R15.7 can prevent PMN adhesion and PMN-mediated reperfusion injury in the heart.

Studies were performed with isolated, Langendorff-perfused rat hearts (nine per group) in which the hearts were subjected to 20 minutes of global ischemia followed by 45 minutes of reperfusion. Human PMNs (50 million) and rat plasma (HNRP) were infused directly into the coronary circulation of nonischemic and postischemic hearts. When HNRP was administered to nonischemic hearts, no significant alterations in coronary flow, left ventricular developed pressure, or left ventricular end-diastolic pressure were observed. When hearts were reperfused in the presence of HNRP, however, marked impairment of contractile function was observed with more than 90% reduction in coronary flow throughout the reperfusion period (P < .001 versus baseline). In addition, left ventricular developed pressure was significantly depressed (P < .001 versus baseline) throughout the reperfusion period in the HNRP group and recovered to only 13.0 +/- 3.0% at 45 minutes of reperfusion. Moreover, left ventricular end-diastolic pressure was significantly elevated (P < .001) in the HNRP group throughout the reperfusion period. Treatment with the anti-CD-18 monoclonal antibody MAb R15.7 (20 micrograms/mL) at the time of reperfusion resulted in a 92.9 +/- 4.9% recovery of coronary flow (P < .001 versus HNRP) as well as a 71.0 +/- 10.1% recovery of left ventricular developed pressure (P < .001 versus HNRP). Administration of MAb R15.7 also very significantly attenuated the elevation in left ventricular end-diastolic pressure that was observed in the untreated HNRP (30.2 +/- 7.8 versus 110.3 +/- 10.3 mm Hg, P < .001) at 45 minutes of reperfusion. Cardiac myeloperoxidase activity, an index of PMN accumulation, was markedly reduced in the MAb R15.7 group at 45 minutes of reperfusion compared with the HNRP group (0.03 +/- 0.01 versus 0.3 +/- 0.05, P < .001). To determine that the protective effect of MAb R15.7 was based on functional blocking of CD-18, additional experiments were performed with identical concentrations of MAb 3.1, which binds to the alpha-subunit of LFA-1. This PMN-binding but non-CD-18-blocking antibody had little effect on the recovery of postischemic function or coronary flow and did not reduce tissue myeloperoxidase activity.

The administration of a specific anti-CD-18 monoclonal antibody, MAb R15.7, attenuates much of the PMN-mediated contractile dysfunction associated with this in vitro model of myocardial ischemia-reperfusion injury by limiting PMN accumulation. We conclude that CD-18-mediated adhesion may play a critical role in the pathogenesis of PMN-induced myocardial injury.