Chloride ion efflux regulates adherence, spreading, and respiratory burst of neutrophils stimulated by tumor necrosis factor-alpha (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- alpha (TNF) and granulocyte/macrophage-colony stimulating factor (Shimizu, Y., R.H. Daniels, M.A. Elmore, M.J. Finnen, M.E. Hill, and J.M. Lackie. 1993. Biochem. Pharmacol. 9:1743-1751). 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 beta 2 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-i in 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.