Chloride Ion Efflux Regulates Adherence, Spreading, and Respiratory Burst of Neutrophils Stimulated by Tumor Necrosis Factor-α (TNF) on Biologic Surfaces

Chloride ion efflux is an early event occurring after exposure of neutrophilic polymorphonuclear leukocytes (PMN) in suspension to several agonists, including cytokines such as tumor necrosis factor-α (TNF) and granulocyte/macrophage-colony stimulating factor. We have studied TNF-induced Cl-movements in PMN residing on fibronectin (FN) (FN-PMN) and their relationships to adherence, spreading, and activation of the respiratory burst. Occupancy of the TNF-R55 and engagement of β2 integrins cosignaled for an early, marked, and prolonged Cl-efflux that was accompanied by a fall in intracellular chloride levels (Cl- i). A possible causal relationship between Cl-efflux, adherence, and respiratory burst was first suggested by kinetic studies, showing that TNF-induced Cl-efflux preceded both the adhesive and metabolic response, and was then confirmed by inhibition of all three responses by pretreating PMN with inhibitors of Cl-efflux, such as ethacrynic acid. Moreover, Cl-efflux induced by means other than TNF treatment, i.e., by using Cl--free media, was followed by increased adherence, spreading, and metabolic activation, thus mimicking TNF effects. These studies provide the first evidence that a drastic decrease of Cl- iin FN-PMN may represent an essential step in the cascade of events leading to activation of proadhesive molecules, reorganization of the cytoskeleton network, and assembly of the O2 --forming NADPH oxidase.