Role of intracellular chloride in the reversible activation of neutrophil beta 2 integrins: a lesson from TNF stimulation

• Published in: The Journal of immunology (1950) Vol. 165; no. 8; pp. 4606 - 4614
• Main Authors: Menegazzi, R, Busetto, S, Cramer, R, Dri, P, Patriarca, P
• Format: Journal Article
• Language: English
• Published: United States 15.10.2000
• Subjects: Antiporters - pharmacology; Buffers; Butylated Hydroxytoluene - analogs & derivatives; Butylated Hydroxytoluene - pharmacology; CD18 Antigens - chemistry; CD18 Antigens - metabolism; Cell Adhesion - physiology; Chlorides - metabolism; Chlorides - physiology; Epitopes - biosynthesis; Humans; Hydrogen-Ion Concentration; Intracellular Fluid - drug effects; Intracellular Fluid - metabolism; Intracellular Fluid - physiology; Neutrophil Activation - drug effects; Neutrophils - drug effects; Neutrophils - metabolism; Neutrophils - physiology; Protein Conformation; Tumor Necrosis Factor-alpha - antagonists & inhibitors; Tumor Necrosis Factor-alpha - physiology
• ISSN: 0022-1767

The process of beta(2) integrin activation, which enhances the interaction of these heterodimers with ligands, plays a crucial role in the adherence-dependent neutrophilic polymorphonuclear leukocytes' (PMN) responses to TNF. Our previous observation, showing that a marked decrease of the high basal Cl(-) content (Cl(-)(i)) is an essential step in the TNF-induced activation of PMN, stimulated this study, which investigates the role of alterations of Cl(-)(i) in the activation of beta(2) integrins triggered by TNF. Here we show that TNF enhances the expression of activation-specific neoepitopes of beta(2) integrins, namely, epitope 24, a unique epitope present on all three leukocyte integrin alpha subunits, and epitope CBRM1/5, localized to the I domain on the alpha-chain of Mac-1 (CD11bCD18). Moreover, we demonstrate that the conformational changes underlying the expression of the neoepitopes are dependent on a drop in Cl(-)(i) because 1) inhibition of Cl(-)(i) decrease is invariably accompanied by inhibition of beta(2) integrin activation, 2) Cl(-)(i) decrease induced by means other than agonist stimulation, i.e., by placing PMN in Cl(-)-free buffers, activates beta(2) integrins, and 3) restoration of the original Cl(-)(i) levels is accompanied by deactivation of beta(2) integrins. We also show that Cl(-)(i) decrease is required for TNF-induced cytoplasmic alkalinization, but such a rise in pH(i) does not seem to be relevant for beta(2) integrin activation. The results of our study emphasize the role of Cl(-) as a new PMN "second messenger."