CHLORIDE-ION EFFLUX REGULATES ADHERENCE, SPREADING, AND RESPIRATORY BURST OF NEUTROPHILS STIMULATED BY TUMOR-NECROSIS-FACTOR-ALPHA (TNF) ONBIOLOGIC SURFACES

Chloride ion efflux is an early event occurring after exposure of neut rophilic polymorphonuclear leukocytes (PMN) in suspension to several a gonists, 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- mo vements in PMN residing on fibronectin (FN) (FN-PMN) and their relatio nships to adherence, spreading, and activation of the respiratory burs t. Occupancy of the TNF-R55 and engagement of beta 2 integrins cosigna led for an early, marked, and prolonged Cl- efflux that was accompanie d by a fall in intracellular chloride levels (Cl-i(-)). A possible cau sal relationship between Cl- efflux, adherence, and respiratory burst was first suggested by kinetic studies, showing that TNF-induced Cl- e fflux 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- effl ux induced by means other than TNF treatment, i.e., by using Cl--free media, was followed by increased adherence, spreading, and metabolic a ctivation, thus mimicking TNF effects. These studies provide the first evidence that a drastic decrease of Cl-i(-) in FN-PMN may represent a n essential step in the cascade of events leading to activation of pro adhesive molecules, reorganization of the cytoskeleton network, and as sembly of the O-2(-)-forming NADPH oxidase.