CD18 INTEGRIN-DEPENDENT ENDOTHELIAL INJURY - EFFECTS OF OPSONIZED ZYMOSAN AND PHORBOL ESTER ACTIVATION

We examined the hypothesis that neutrophil (PMN)-mediated injury of the vascular endothelium is dependent on adhesion of PMNs to endothelial cells via the leukocyte adhesion glycoprotein CD11/CD18. We compared the PMN activation responses [i.e. adhesion to cultured endothelial cells, superoxide (O-2(-)) production, degranulation, and cytosolic [Ca2+] (Ca2+]i)] and endothelial injury elicited by opsonized zymosan (OZ, which is phagocytosed by PMNs) or phorbol 12-myristate 13-acetate (PMA, a protein kinase C activator). The basal adherence of nonstimulated PMNs to bovine pulmonary artery endothelial cells (BPAEC) was 9.0 +/- 1.1 PMN/field. PMA and OZ increased PMN adherence to BPAEC (to 31.1 +/- 1.4 and 39.8 +/- 3.8 PMN/field, respectively), which in both cases was inhibited by anti-CD18 monoclonal antibody (mAb) IB4. Stimulation of PMNS with PMA or OZ produced injury to 73 degrees and 53% of BPAEC examined, respectively, which corresponded to 6.8-fold and 3.5-fold increases in transendothelial I-125- albumin permeability from baseline. Pretreatment of PMNs with mAb IB4 prevented endothelial injury in both cases. Both PMA and OZ increased the production of O-2(-) (by 7.6-fold and 3.1-fold over control, respectively) and promoted the release of myeloperoxidase (5.2-fold and 9.1-fold over control, respectively) (P <.01). lB4 did not inhibit the PMA- or OZ-induced increases in O-2(-) IB4: did not inhibit the PMA-induced myeloperoxidase release but reduced by -29% the OZ-induced myeloperoxidase release Stimulation of PMNs layered on BPAEC with OZ (0.5 mg/ml) caused an - 7-fold increase in PMN [Ca2+]i over baseline, which decayed to a steady-state level above baseline at 10 min. IB4 (10 mu g/ml) alone did not alter baseline [Ca2+]i and did not inhibit the OZ-induced increase in [Ca2+]i. In contrast to OZ, stimulation of PMNs with PMA did not increase [Ca2+]i. The results indicate that the protective effects of the anti-CD18 mAb IB4: were associated predominantly with its antiadherence property. Therefore, CD18 integrin-mediated PMN adhesion to the endothelium is a critical determinant of endothelial injury irrespective of the PMN-activating stimulus.