Triggering of respiratory burst by tumor necrosis factor in neutrophils adherent to fibronectin. Evidence for a crucial role of CD18 glycoproteins

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Abstract
Human neutrophils, plated on fibronectin (FN)-coated wells, were found to release large quantities of superoxide anion (O 2 − ) in response to tumor necrosis factor alpha (TNF-α). The O 2 − release was completely inhibited by two monoclonal antibodies (MoAbs, MHM23 and TS1/18) against CD18 glycoproteins. An independently derived anti-CD18 MoAb (60.3) was ineffective. These MoAbs failed to inhibit neutrophil adhesion to FN-coated surfaces. Moreover, neutrophils incubated for 30 min on FN and then washed to remove non-adherent cells, were responsive to TNF-α in the presence of anti-CD18 MoAbs MHM23 and TS1/18. Consequently, the CD18-dependent capacitation of the respiratory burst can occur before TNF-α triggering. Finally, neutrophils plated on FN in the presence of anti-CD18 MoAbs and then washed, i.e. adherent cells blocked in their surface CD18 molecules, released O 2 − after adding TNF-α but only in the absence of additional anti-CD18 MoAbs. This is consistent with a TNF-α ability to induce rapid expression and activation of new oxidative burst-capacitating CD18 molecules. The results suggest that the anchorage of neutrophils to FN surfaces depends on adherence molecules apparently unrelated to CD18, probably the so-called fibronectin receptors (FNRs), whereas the capacitation of the respiratory burst in response to TNF-α requires the intervention of CD18 glycoproteins, available on the membrane of “resting” neutrophils or mobilized to the cell surface by TNF-α.