We studied the effects of pretreatment of rabbits with a monoclonal antibody (MoAb) IB4 directed against an epitope on the common beta-chain of leukocyte adhesion glycoprotein CD18 on the development of pulmonary edema following pulmonary artery occlusion and reperfusion. A balloon catheter occluded the right pulmonary artery in rabbits for 24 h, and the balloon was then deflated to allow reperfusion for 2 h. The lungs were removed, attached to a weighing balance, and perfused with Ringer-albumin solution (0.5 g/100 ml). IB4 (0.5 mg/kg) was infused 45 min before the start of reperfusion. In another experiment, we infused OKM-1 (0.5 mg/kg), a control MoAb directed against an irrelevant epitope on the alpha-chain of CD11b/CD18. IB4 prevented rabbit neutrophil adherence to pulmonary artery endothelial cells in vitro in response to a variety of stimuli, whereas OKM-1 was ineffective. Pulmonary artery occlusion and reperfusion increased the lung myeloperoxidase (MPO) content, whereas IB4 prevented the increase in MPO content. The increase in lung weight in the IB4-treated group (400 +/- 40 mg from baseline) was less (P less than 0.001) than in the untreated control group (1,400 +/- 90 mg) and the OKM-1-treated control group (1,320 +/- 125 mg). IB4 pretreatment also prevented the increase in pulmonary capillary filtration coefficient (a measure of capillary permeability to water) occurring in control and OKM-1-treated groups. The results indicate that neutrophil sequestration in the pulmonary microcirculation mediated by CD18 glycoprotein is a major determinant of reperfusion-induced lung vascular injury.