title: Cell density regulates neutrophil IL-8 synthesis: role of IL-1 receptor antagonist and soluble TNF receptors.
abstract: Although cytokine synthesis in polymorphonuclear leukocytes (PMN) was shown to be modulated by soluble mediators, the impact of microenvironmental conditions has not been elucidated. In this study, we investigated the effect of cell density on cytokine release from human neutrophils. PMN were cultured at various cell densities (10 x 10(6) PMN/ml; 60 x 10(6) PMN/ml), and LPS-induced release of cytokines was quantified by ELISA technique. Upon an increase in PMN density, secretion of the CXC chemokine IL-8 was progressively reduced. This effect was paralleled by a decrease in IL-8 mRNA. In contrast, TNF-alpha and IL-1beta rose proportionally with increasing cell density. The inhibition of IL-8 secretion was reproduced by conditioned media of PMN at high cell density, but was not affected by blocking beta(2) integrin-dependent adhesion. When analyzing the supernatant of LPS-challenged neutrophils, large amounts of soluble TNFRs p55 and p75 (sTNFRI, sTNFRII), and IL-1R antagonist (IL-1RA), rising constantly with the cell density, were detected. Interestingly, combined blocking of the bioactivities of these mediators completely restored neutrophil IL-8 secretion at high cell densities, with the anti-IL-1RA Ab being the more potent agent. Moreover, combined application of exogenous IL-1RA and sTNFRs to 10 x 10(6) PMN/ml reproduced the suppression of IL-8 generation. We conclude that neutrophil IL-8 synthesis is autoregulated, being suppressed under conditions of high cell density. IL-1RA and sTNFRs, accumulating under these circumstances, seem to be centrally involved in this regulatory mechanism by interfering with the IL-1beta- and TNF-alpha-dependent IL-8 generation. This feedback mechanism may control further neutrophil recruitment and activation in a neutrophil-rich environment, thereby preventing tissue destruction.
authors.affiliation: Department of Internal Medicine, Justus-Liebig University, Giessen, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Hattar
authors.forename: L
authors.initials: L
authors.lastname: Fink
authors.forename: K
authors.initials: K
authors.lastname: Fietzner
authors.forename: B
authors.initials: B
authors.lastname: Himmel
authors.forename: F
authors.initials: F
authors.lastname: Grimminger
authors.forename: W
authors.initials: W
authors.lastname: Seeger
authors.forename: U
authors.initials: U
authors.lastname: Sibelius
mesh_terms: D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D015232:Dinoprostone / Q000037:antagonists & inhibitors / Q000378:metabolism; D015536:Down-Regulation / Q000276:immunology; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1 / Q000378:metabolism; D016209:Interleukin-8 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism; D007958:Leukocyte Count; D008070:Lipopolysaccharides / Q000494:pharmacology; D016859:Lipoxygenase Inhibitors; D009504:Neutrophils / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors; D011726:Pyridinium Compounds / Q000494:pharmacology; D017472:Receptors, Interleukin-1 / Q000037:antagonists & inhibitors*; D018124:Receptors, Tumor Necrosis Factor / Q000502:physiology*; D012795:Sialoglycoproteins / Q000494:pharmacology / Q000502:physiology*; D012995:Solubility; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation / Q000276:immunology; D002722:Chlorobenzenes
chemical_list: D001094:Arachidonate 5-Lipoxygenase; D017077:Culture Media, Conditioned; D016861:Cyclooxygenase Inhibitors; D015232:Dinoprostone; D007166:Immunosuppressive Agents; D007211:Indoles; D007213:Indomethacin; D053590:Interleukin 1 Receptor Antagonist Protein; D007375:Interleukin-1; D016209:Interleukin-8; D008070:Lipopolysaccharides; D016859:Lipoxygenase Inhibitors; D010972:Platelet Activating Factor; D011726:Pyridinium Compounds; D017472:Receptors, Interleukin-1; D018124:Receptors, Tumor Necrosis Factor; D012795:Sialoglycoproteins; D014409:Tumor Necrosis Factor-alpha; C507763:IL1RN protein, human; C060893:MK-886; D002722:Chlorobenzenes; C053321:CV 6209