Factors modifying the protective effect of anti-cd18 antibodies on myocardial reperfusion injury in the anesthetized dog. Perez, Roger G., Masazumi Arai, Chris Richardson, Anthony Dipaula, Cynthia Siu, Naoki Matsumoto, James E. K. Hildreth, M. Michele Mariscalco, C. Wayne Smith, and Lewis C. Becker. Cardiology Division, Department of Medicine, and Department of Pharmacology (JEKH), Johns Hopkins Medical Institutions, Baltimore, MD 21224 and the Speros P. Martel Laboratory, Section of Leukocyte Biology (MMM, CWS), Department of Pediatrics, Baylor College of Medicine, Houston TX 77054.
APStracts 2:0055H, 1995.
Anti-CD18 monoclonal antibodies (MAbs) have been shown to prevent adherence of neutrophils (PMNs) to vascular endothelium following ischemia/reperfusion, thereby limiting the tissue influx of PMNs and PMN-mediated reperfusion injury. However, the amount of protection afforded by anti-CD18 MAbs in the heart has been variable in reported studies. To identify factors that might contribute to this variability, open chest dogs underwent coronary artery occlusion for 90 min, followed by reperfusion for 3.5 hr. Ten min prior to reperfusion the dogs received saline (n=18) or one of three anti-CD18 MAbs: (1) MHM.23, (2mg/kg, n=19), (2) R15.7 (1mg/kg, n=8), or (3) PLM-2 (1 mg/kg, n=4). Collateral flow was measured with radioactive microspheres, area at risk was assessed with monastral blue dye, and infarct size was measured post-mortem by TTC. In-vitro, all 3 MAbs bound to canine PMNs, and both MHM.23 and R15.7 produced >85% inhibition of adherence of canine PMNs to KLH-coated plastic, while PLM-2 had no effect on adherence. In-vivo, both MHM.23 and R15.7, but not PLM-2, significantly reduced infarct size, after adjusting for the effect of collateral flow. The degree of myocardial protection by MHM.23 was dependent on the severity of ischemia: for dogs with moderate ischemia (epicardial collateral flow >0.1 ml/min/g), infarct salvage with MHM.23 averaged 46%, but in the presence of severe ischemia (collateral flow </=0.1 ml/min/g), MHM.23 had no effect. Only R15.7 significantly reduced infarct size in dogs with severe ischemia: infarct/risk was 0.58+/-0.04 with saline, 0.56+/-0.05 with PLM-2, 0.52+/-0.03 with MHM.23 and 0.40+/-0.04 with R15.7 (p<0.05). Tissue myeloperoxidase activity within the infarct was reduced to an equal extent by MHM.23 and R15.7 compared to saline (-60.8% and -63.6%, respectively), suggesting equivalent inhibition of PMN accumulation in vivo. Despite similar effects on PMN adhesion and tissue PMN influx, R15.7 produced a marked inhibition of H2O2 production by PMNs following exposure to platelet activating factor, while MHM.23 had only a minimal effect. These results support an important CD18-dependent role of PMNs in myocardial reperfusion injury. The effectiveness of different anti-CD18 MAbs in preventing reperfusion injury appears to be: (1) highly dependent on the specific anti-CD18 MAb employed, (2) predicted only partially by in vitro binding to PMNs, static in vitro tests of PMN adherence, or the extent of inhibition of PMN accumulation in vivo, (3) probably related more to their ability to inhibit oxidant release from activated PMNs, and (4) influenced by the severity of myocardial ischemia prior to reperfusion. 

Received 16 August 1993; accepted in final form 13 February 1995.
APS Manuscript Number H723-3.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  1 March 1995.