Neutrophil inhibitory factor abrogates neutrophil adhesion by blockade of CD11a and CD11b beta(2) integrins

We studied the basis of inhibition of polymorphonuclear leukocyte (PMN) adh esion induced by neutrophil inhibitory factor (NIF), a 41-kDa CD11/CD18 bet a(2) integrin-binding protein isolated from the canine hookworm (Ancylostom a caninum). NIF blocked PMN adhesion in a concentration-dependent manner wi th complete blockade occurring at similar to 10 nM NIF. Because CD11a and C D11b beta(2) integrins are functionally active on stimulated PMNs, and yet NIF is postulated to inhibit only CD11b integrin by binding to its I domain , we evaluated the contributions of CD11a and CD11b beta(2) integrins in th e mechanism of inhibition of PMN adhesion to endothelial cells. We observed an additive inhibitory effect (>90% inhibition) of PMN adhesion to endothe lial cells when NIF was used in combination with anti-CD11b monoclonal anti bodies, which alone at saturating concentrations reduced PMN adhesion by on ly 50%. NIF also prevented aggregation of phorbol ester-stimulated JY lymph oblastoid cells that expressed only the functionally active CD11a, suggesti ng that NIF also can inhibit CD11a-dependent response. We transduced the NI F cDNA into human dermal microvessel endothelial cells in which NIF synthes is and release prevented PMN adhesion to the transduced human dermal microv essel endothelial cells. These data indicated that the potent antiadhesive effect of NIF may be the result of inhibition of CD11a and CD11b beta(2) in tegrins on PMNs. Moreover, the strategy of NIF release from transduced endo thelial cells suggests the feasibility of blocking the CD11a- and CD11b bet a(2) integrin-dependent PMN adhesion and PMN migration responses specifical ly at sites of endothelial cell activation.