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 (O2-) 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% and 53% of BPAEC examined, respectively, which corresponded to 6.8-fold and 3.5-fold increases in transendothelial 125I-albumin permeability from baseline. Pretreatment of PMNs with mAb IB4 prevented endothelial injury in both cases. Both PMA and OZ increased the production of O2- (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). IB4 did not inhibit the PMA- or OZ-induced increases in O2-. IB4 did not inhibit the PMA-induced myeloperoxidase release but reduced by approximately 29% the OZ-induced myeloperoxidase release. Stimulation of PMNs layered on BPAEC with OZ (0.5 mg/ml) caused an approximately 7-fold increase in PMN [Ca2+]i over baseline, which decayed to a steady-state level above baseline at 10 min. IB4 (10 micrograms/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.