CROSS-LINKING OF CD18 PRIMES HUMAN NEUTROPHILS FOR ACTIVATION OF THE RESPIRATORY BURST IN RESPONSE TO SPECIFIC STIMULI - IMPLICATIONS FOR ADHESION-DEPENDENT PHYSIOLOGICAL-RESPONSES IN NEUTROPHILS

Adhesion is known to prime neutrophils for physiological activation in response to cytokines and other stimuli. We have employed the techniq ue of receptor cross-linking to study the potential role of CD18, the common beta-subunit of the beta(2)-integrin family of adhesion molecul es, in the regulation of the respiratory burst, as measured by luminol -enhanced chemiluminescence and iodination, in human neutrophils. CD18 cross-linking primed neutrophils to activate the respiratory burst af ter stimulation with tumor necrosis factor alpha (TNF-alpha) (100 unit s/mL), formylmethionyl-leucyl-phenylalanine (fMLP) (1 mu M), and granu locyte-macrophage colony-stimulating factor (GM-CSF) (1 mu g/mL), but not granulocyte colony-stimulating factor (G-CSF) (1 mu g/mL), interfe ron-gamma (IFN-gamma) (100 U/mL), or phorbol myristate acetate (100 nM ). The maximal rate of chemiluminescence induced by fMLP, TNF-alpha, a nd GM-CSF was enhanced 8-, 6-, and 1.5-fold, respectively, following C D18 cross-linking. Priming of the respiratory burst by direct engageme nt of CD18 was confirmed in neutrophil-mediated iodination experiments , where iodination induced by TNF-alpha, fMLP, and GM-CSF was increase d 15-, 20-, and 7-fold, respectively, by CD18 cross-linking. Immunoblo t experiments demonstrated that TNF-alpha-induced tyrosine phosphoryla tion was both accelerated and more intense in neutrophils after cross- linking of CD18. Major tyrosine phosphoprotein products include protei ns with approximate molecular masses of 40, 70, and 110 kDa. Genistein (50 mu M), a selective tyrosine kinase inhibitor, reduced the TNF-alp ha-stimulated respiratory burst by >80% whether or not CD18 was cross- linked. These results affirm the importance of CD18 II adhesion-depend ent priming of neutrophil functions and demonstrate that CD18 engageme nt per se is sufficient to prime neutrophils for cytokine-induced sign al transduction mediated by tyrosine phosphorylation.