Triggering of chloride ion efflux from human neutrophils as a novel function of leukocyte beta 2 integrins: relationship with spreading and activation of the respiratory burst.

PMN residing on immobilized fibronectin have been shown to respond to TNF with an intense and long lasting Cl- efflux that leads to a marked decrease of the unusually high basal Cl- content of these phagocytes. The finding that this Cl- efflux depends, at least in part, on beta2 integrin engagement stimulated the present investigation, which addresses the question as to whether beta2 integrins per se, in the absence of PMN agonists, are able to generate signals triggering Cl- efflux. We induced beta2 integrin cross-linking by plating PMN onto surface-bound mAbs directed against either the common beta-chain (CD18) or the individual alpha-chains (CD11a, CD11b, CD11c) of LFA-1, CR3, and gp150/95. Anti-CD18 mAbs triggered a marked release of Cl- ions, which was accompanied by spreading and activation of the respiratory burst. Cross-linking of gp150/95 and LFA-1 generated the most powerful signals for the activation of Cl- efflux. The results of three independent experimental approaches, i.e., kinetic studies, use of Cl- transport inhibitors, and modulation of Cl- efflux with different amounts of anti-beta2 integrin mAbs, indicated that Cl- efflux regulates both spreading and respiratory burst triggered by beta2 integrin cross-linking. Cl- efflux appears to be independent on either alterations of [Ca2+]i or changes in the plasma membrane potential and shows sensitivity to a raise in pHi. This study uncovers a new signaling ability of beta2 integrins and contributes to highlight the role of Cl- efflux in the outside-in signal transduction pathway regulating adherence-dependent PMN responses.

Glycosylation improves the priming effect exerted by recombinant human granulocyte colony-stimulating factor (lenograstim) on human neutrophil superoxide production.

The role of glycosylation in modulating the activity of recombinant human granulocyte colony-stimulating factor (rHuG-CSF) on polymorphonuclear leukocytes (PMNs) was investigated. We addressed this study by comparing the effects of lenograstim (glycosylated rHuG-CSF) and its deglycosylated counterpart on superoxide production by PMNs on fibronectin. When the triggering activity of the cytokine was evaluated, no O2- release was elicited from neutrophils treated with either preparation of rHuG-CSF. Instead, a clear potentiation of both fMLP- and TNF-induced respiratory burst was produced by preincubating the cells with rHuG-CSF. Such effect was found to be significantly increased when glycosylated versus deglycosylated preparation was used, leading to the conclusion that the sugar moiety of the molecule could be of importance in improving the priming activity exerted by rHuG-CSF on PMN metabolic response.