POLYMORPHONUCLEAR LEUKOCYTE (PMN) INHIBITORY FACTOR PREVENTS PMN-DEPENDENT ENDOTHELIAL-CELL INJURY BY AN ANTIADHESIVE MECHANISM

Neutrophil inhibitory factor (NIF), a 41-kD glycoprotein isolated from the canine hookworm, inhibits CD11b/CD18-dependent neutrophil adhesio n by binding to CD11b. We studied the effects of NIF on neutrophil-dep endent endothelial cell injury using bovine pulmonary microvessel endo thelial cells grown on microporous filters. Endothelial injury was det ermined as an increase in the transendothelial I-125-albumin clearance rate (a measure of transendothelial permeability). Layering of neutro phils on the endothelial cell monolayer (ratio of 10 neutrophils: 1 en dothelial cell) followed by activation of neutrophils with 500 nM of p horbol 12-myristate 13-acetate (PMA) increased transendothelial permea bility of albumin by 3- to 4-fold over control monolayers. Pretreatmen t of neutrophils with NIF at concentrations of 100 nM and above preven ted the increased permeability. Pretreatment of neutrophils with the a nti-CD18 monoclonal antibody (mAb) IB4 similarly prevented the increas e of permeability. Pretreatment of neutrophils with OKM-1, a control i sotype-matched mAb directed against an irrelevant epitope on CD11b mAb , did not affect the neutrophil-dependent increase in permeability. NI F reduced the adhesion of neutrophils at concentrations of greater tha n or equal to 100 nM and this effect was abolished by an anti-NIF poly clonal Ab. However, NIF did not prevent the generation of superoxide a nions following PMA-induced activation of neutrophils layered on endot helial cell. These findings indicate that NIF inhibits the neutrophil- dependent endothelial injury by preventing CD11b/CD18-mediated neutrop hil adhesion, but without altering the oxidant generating capacity of neutrophils interacting with the endothelial cell monolayer. (C) 1997 Wiley-Liss, Inc.