title: The leukotriene B4 paradox: neutrophils can, but will not, respond to ligand-receptor interactions by forming leukotriene B4 or its omega-metabolites.
abstract: Leukotriene B4 (5S,12R-dihydroxy-6,14-cis,8,10-trans-eicosatetraenoic acid, LTB4) is released from neutrophils exposed to calcium ionophores. To determine whether LTB4 might be produced by ligand-receptor interactions at the plasmalemma, we treated human neutrophils with serum-treated zymosan (STZ), heat-aggregated IgG and fMet-Leu-Phe (fMLP), agonists at the C3b, Fc and fMLP receptors respectively. STZ (10 mg/ml) provoked the formation of barely detectable amounts of LTB4 (0.74 ng/10(7) cells); no omega-oxidized metabolites of LTB4 were found. Adding 10 microM-arachidonate did not significantly increase production of LTB4 or its metabolites. Addition of 50 microM-arachidonate (an amount which activates protein kinase C) before STZ caused a 40-fold increase in the quantity of LTB4 and its omega-oxidation products. Neither phorbol myristate acetate (PMA, 200 ng/ml) nor linoleic acid (50 microM), also activators of protein kinase C, augmented generation of LTB4 by cells stimulated with STZ. Neither fMLP (10(-6) M) nor aggregated IgG (0.3 mg/ml) induced LTB4 formation (less than 0.01 ng/10(7) cells). Moreover, cells exposed to STZ, fMLP, or IgG did not form all-trans-LTB4 or 5-hydroxyeicosatetraenoic acid; their failure to make LTB4 was therefore due to inactivity of neutrophil 5-lipoxygenase. However, adding 50 microM-arachidonate to neutrophil suspensions before fMLP or IgG triggered LTB4 production, the majority of which was metabolized to its omega-oxidized products (fMLP, 20.2 ng/10(7) cells; IgG, 17.1 ng/10(7) cells). The data show that neutrophils exposed to agonists at defined cell-surface receptors produce significant quantities of LTB4 only when treated with non-physiological concentrations of arachidonate.
mesh_terms: D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D006801:Humans; D007074:Immunoglobulin G / Q000494:pharmacology; D007975:Leukotriene B4 / Q000097:blood*; D008024:Ligands; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000494:pharmacology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015054:Zymosan / Q000494:pharmacology
chemical_list: D001095:Arachidonic Acids; D007074:Immunoglobulin G; D008024:Ligands; D008041:Linoleic Acids; D011955:Receptors, Drug; D007975:Leukotriene B4; D016718:Arachidonic Acid; D009240:N-Formylmethionine Leucyl-Phenylalanine; D015054:Zymosan; D019787:Linoleic Acid; D013755:Tetradecanoylphorbol Acetate