title: 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.
abstract: Adhesion is known to prime neutrophils for physiological activation in response to cytokines and other stimuli. We have employed the technique of receptor cross-linking to study the potential role of CD18, the common beta-subunit of the beta 2-integrin family of adhesion molecules, 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 after stimulation with tumor necrosis factor alpha (TNF-alpha) (100 units/mL), formylmethionyl-leucyl-phenylalanine (fMLP) (1 microM), and granulocyte-macrophage colony-stimulating factor (GM-CSF) (1 micrograms/mL), but not granulocyte colony-stimulating factor (G-CSF) (1 micrograms/mL), interferon-gamma (IFN-gamma) (100 U/mL), or phorbol myristate acetate (100 nM). The maximal rate of chemiluminescence induced by fMLP, TNF-alpha, and GM-CSF was enhanced 8-, 6-, and 1.5-fold, respectively, following CD18 cross-linking. Priming of the respiratory burst by direct engagement of CD18 was confirmed in neutrophil-mediated iodination experiments, where iodination induced by TNF-alpha, fMLP, and GM-CSF was increased 15-, 20-, and 7-fold, respectively, by CD18 cross-linking. Immunoblot experiments demonstrated that TNF-alpha-induced tyrosine phosphorylation was both accelerated and more intense in neutrophils after cross-linking of CD18. Major tyrosine phosphoprotein products include proteins with approximate molecular masses of 40, 70, and 110 kDa. Genistein (50 microM), a selective tyrosine kinase inhibitor, reduced the TNF-alpha-stimulated respiratory burst by > 80% whether or not CD18 was cross-linked. These results affirm the importance of CD18 in adhesion-dependent priming of neutrophil functions and demonstrate that CD18 engagement per se is sufficient to prime neutrophils for cytokine-induced signal transduction mediated by tyrosine phosphorylation.
mesh_terms: D018821:CD18 Antigens / Q000502:physiology*; D002448:Cell Adhesion; D019833:Genistein; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D007529:Isoflavones / Q000494:pharmacology; D017493:Leukocyte Common Antigens / Q000502:physiology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D018375:Neutrophil Activation; D009504:Neutrophils / Q000502:physiology*; D010766:Phosphorylation; D016897:Respiratory Burst; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
chemical_list: D018821:CD18 Antigens; D007529:Isoflavones; D014409:Tumor Necrosis Factor-alpha; D014443:Tyrosine; D009240:N-Formylmethionine Leucyl-Phenylalanine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D019833:Genistein; D017493:Leukocyte Common Antigens