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(Journal of Leukocyte Biology. 2002;72:718-726.)
© 2002 by Society for Leukocyte Biology

Evidence that TNF-induced respiratory burst of adherent PMN is mediated by integrin _Lß₂

Department of Physiology and Pathology, University of Trieste, Italy

Correspondence: Eva Decleva, Department of Physiology and Pathology, University of Trieste, via A. Fleming, 22, 34127 Trieste, Italy. E-mail: declevae{at}univ.trieste.it

Polymorphonuclear leukocytes (PMN) respond to tumor necrosis factor (TNF) with a respiratory burst (RB) only after adherence to surfaces coated with extracellular matrix proteins such as fibronectin and fibrinogen (permissive substrates) but not with others such as laminin or collagen (nonpermissive substrates). As PMN adherence to both types of surfaces is dependent on ß₂ integrins, we investigated the molecular basis of the different metabolic response to TNF. In particular, we evaluated the relative role of each ß₂ integrin (_Lß₂, _Mß₂, and _Xß₂) in adherence and O₂^- production of PMN residing on fibronectin- and laminin-coated surfaces, which were considered as models of permissive and nonpermissive surfaces, respectively. By using chain-specific monoclonal antibodies (mAb), we show that _Mß₂ and _Xß₂ mediate adherence to fibronectin and laminin; _Lß₂ is not involved in adherence to laminin and has only a minimal contribution in adherence to fibronectin. Furthermore, production of O₂^- in response to TNF was induced by immobilized anti-_Lß₂ but not anti-_Mß₂ or anti-_Xß₂ mAb. A strong correlation was also found between expression of _Lß₂ and TNF-induced RB on fibronectin. Lastly, PMN responded to TNF on laminin with a RB after the inclusion of _L-specific mAb in the laminin coat. Thus, we conclude that TNF-induced RB by PMN residing on fibronectin is mediated by _Lß₂ and that _Mß₂ and _Xß₂ are likely to play an ancillary role to the signaling activity of _Lß₂ by facilitating its recruitment to sites of adherence. The nonpermissiveness of laminin appears to be a consequence of its inability to act as a ligand for _Lß₂.

Key Words: adherence • ß₂ integrins • neutrophils • superoxide anion

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