INDUCTION OF NEUTROPHIL RESPIRATORY BURST BY TUMOR-NECROSIS-FACTOR-ALPHA - PRIMING EFFECT OF SOLID-PHASE FIBRONECTIN AND INTERVENTION OF CD11B-CD18 INTEGRINS

Human neutrophils, added to fibronectin (FN)-coated polystyrene wells and exposed to tumour necrosis factor-alpha (TNF-alpha), were found to exhibit a prolonged production of superoxide anion (O-2(-)) after a l ag period of approx 30 min. The O-2(-) production, but not the cell ad herence to FN, was completely inhibited by two MoAbs against CD18 and by a MoAb against CD11b, suggesting the involvement of CD11b-CD18 inte grins in the neutrophil oxidative response. When neutrophils were indu ced to adhere to FN by incubation for 30 min on FN-coated surfaces and then washed to remove non-adherent cells, FN-anchored cells exhibited a rapid onset of O-2(-) production in response to TNF-alpha. This sug gests that FN primes neutrophils for the TNF-alpha-mediated respirator y burst. The O-2(-) production by adherent neutrophils could be inhibi ted by anti-CD11b and anti-CD18 MoAbs only when the MoAbs were present both during the induction of adherence and during the subsequent expo sure of FN-bound cells to TNF-alpha. The incapacity of MoAbs, added to neutrophils during the induction of adherence, to modify the characte ristics of the subsequent neutrophil response to TNF-alpha suggests th at the FN-mediated cell priming is independent of the interaction of C D11b-CD18 integrins with the FN substrate. The results are consistent with the intervention of three classes of cell receptors in the TNF-al pha-induced oxidative burst of neutrophils plated on FN: (i) neutrophi l FN-binding sites, distinct from CD11b-CD18 and responsible for the c ell priming; (ii) CD11b-CD18 integrins, absolutely required for permit ting the cell triggering; and (iii) TNF-alpha receptors, responsible f or switching on a rapid cell response in primed cells. The requirement of multiple classes of receptors for the full expression of the cell function can be envisaged as a natural precautionary measure to contro l the neutrophil responsiveness to TNF-alpha and, in turn, the TNF-alp ha-dependent neutrophil-mediated oxidative injury at sites of inflamma tion.