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 w ith 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 th at this Cl- efflux depends, at least in part, an beta(2) integrin engagemen t stimulated the present investigation, which addresses the question as to whether beta(2) integrins per se, in the absence of PMN agonists, are able to generate signals triggering Cl- efflux. We induced beta(2) integrin cros s-linking by plating PMN onto surface-bound mAbs directed against either th e common beta-chain (CD18) or the individual alpha-chains (CD11a, CD11b, CD 11c) 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 resp iratory burst. Cross-linking of gp150/95 and LFA-1 generated the most power ful signals for the activation of Cl- efflux. The results of three independ ent experimental approaches, i.e., kinetic studies, use of Cl- transport in hibitors, and modulation of Cl- efflux with different amounts of anti-beta( 2) integrin mAbs, indicated that Cl- efflux regulates both spreading and re spiratory burst triggered by beta(2) integrin cross-linking. Cl- efflux app ears to be independent on either alterations of [Ca2+C](i) or changes in th e plasma membrane potential and shows sensitivity to a raise in pH. This st udy uncovers a new signaling ability of beta(2) integrins and contributes t o highlight the role of Cl- efflux in the outside-in signal transduction pa thway regulating adherence-dependent PMN responses.