Superantigen-mediated human monocyte-T lymphocyte interactions are associated with an MHC class II-, TCR/CD3-, and CD4-dependent mobilization of calcium in monocytes

The present study was designed to examine the potential involvement of calcium ions as second messengers in the mediation of the staphylococcal enterotoxin A (SEA)/MHC class II-induced activation of human monocytes. Treatment of monocytes with a monomeric form of SEA failed to induce detectable changes in the level of intracellular calcium in either monocytes or THP-1 cells. However, cross-linking of SEA with biotin-avidin induced a rapid and transient increase in calcium levels in monocytes and in INF-gamma-treated THP-1 cells. This artificial cross-linking system was reproduced by natural physiologic ligands expressed on the surface of T lymphocytes. Delayed, transient, and concentration (cell as well as toxin)-dependent increases in the cytoplasmic level of free calcium in SEA-treated monocytes were observed upon the addition of autologous resting T cells or purified CD4+ cells, but not of CD8+ cells, B cells, or neutrophils. Antibodies against MHC class II Ag, TCR/CD3, and CD4 molecules inhibited the SEA-dependent interaction between monocytes and T cells as indicated by significant decreases in the rise of calcium levels observed in monocytes. Anti-CD8 and anti-class I antibodies did not affect the interaction between the monocytes and the T cells and failed to alter the calcium response. Taken together, these results suggest that the SEA-induced, T cell-dependent calcium mobilization in monocytes requires physical interactions between SEA-MHC class II, TCR/CD3, and CD4 molecules. The ability to mediate a T cell-dependent calcium increase in monocytes was shared by several enterotoxins including staphylococcal enterotoxin B and toxic shock syndrome toxin-1. The characteristics of the SEA-mediated calcium mobilization in monocytes strongly support the hypothesis that this response is an integral part of the signal transducing machinery linked to MHC class II molecules.

Activation of the human neutrophil 5-lipoxygenase by leukotriene B4

1. In the present study, we demonstrate that leukotriene B4 (LTB4) has the ability to activate the human neutrophil 5-lipoxygenase (5-LO). 2. Stimulation of neutrophils with 30 nM 14,15-dideuterio-LTB4 (D2-LTB4) failed to induce the synthesis of LTB4 from endogenous arachidonic acid (AA), but stimulated the formation of LTB4 from 3.3 microM exogenous AA, as determined by GC-MS analysis. 3. The stimulatory effect of LTB4 on 5-LO activity was further examined with an alternative substrate; LTB4 time- and dose-dependently stimulated the 5-LO-mediated conversion of exogenous 15(S)-hydroperoxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoate (15-HpETE) into 5(S),15(S)-dihydroxy-6,8,11,13,-(E,Z,Z,E)-eicosatetraenoate (5,15-DiHETE), with a threshold effect at 300 pM. 4. The ability of LTB4 to activate the 5-LO showed structural specificity, since LTB4 was found to be 100 times more potent than omega-hydroxy-LTB4, and 300 times more potent than its delta 6-trans-12-epi-isomer. 5. The LTB4-induced 5-LO activation was effectively inhibited by MK-886 (an inhibitor of 5-LO translocation), by pertussis toxin, and by the LTB4 receptor antagonist, LY-223982. 6. These results demonstrate that the binding of LTB4 to its cell-surface receptor results in 5-LO activation in a process mediated by pertussis toxin-sensitive guanine nucleotide-binding proteins. Our data also suggest that the underlying mechanism involves a translocation of the 5-LO to the membrane. These findings raise the possibility that LTB4 produced by phagocytes may positively feedback on its own synthesis.

Evidence for the involvement of tyrosine kinases in the locomotory responses of human neutrophils

Erbstatin, a recently described inhibitor of tyrosine kinases, has been used to examine the potential role of tyrosine phosphorylation in human neutrophil locomotion. Preincubation of human neutrophils with erbstatin inhibited both spontaneous and directed migration induced by chemotactic factors such as formylmethionylleucylphenylalanine (fMet-Leu-Phe) and leukotriene B4. The decreased migratory responses were correlated with an inhibition of adherence of neutrophils to serum-coated surfaces. Erbstatin did not, however, affect the adherence of human neutrophils to uncoated surfaces. These results indicated that the inhibitory effects of erbstatin were specific and not due to a generalized alteration of the surface of human neutrophils. To elucidate the mechanism of the inhibitory effect of erbstatin on adherence properties, the expression of the leukocyte integrin Mo1 was studied. Erbstatin induced a small but significant increase in the expression of Mo1, but decreased the stimulation of the expression of Mo1 elicited by fMet-Leu-Phe. These results suggest that mechanisms in addition to alteration of the number of surface integrins are involved in the inhibition of neutrophil adherence and locomotion by erbstatin.

Calcium mobilization and right-angle light scatter responses to 12-oxo-derivatives of arachidonic acid in neutrophils: evidence for the involvement of the leukotriene B4 receptor

The biological activities of two carbonyl compounds derived from arachidonic acid, (5Z,8Z,10E,14Z)-12-keto-5,8,10,14-eicosatetraeno ic acid (12-OxoETE) and (5Z,8Z,10E)-12-oxo-5,8,10-dodecatrienoic acid (12-OxoDTrE) were investigated. The ability of these compounds to induce a mobilization of calcium and to trigger a right-angle scatter response in isolated peripheral blood human neutrophils was determined. The two compounds induced a rapid and dose-dependent increase in the concentration of cytoplasmic free calcium; these effects were clearly detectable at concentrations greater than or equal to 10(-8) M. Pre-exposure of neutrophils to leukotriene B4 completely abolished the calcium mobilization induced by 12-OxoDTre and 12-OxoETE, while pre-exposure of the cells to the carbonyl compounds only slightly reduced the response to subsequent stimulation of neutrophils by leukotriene B4. The carbonyl compounds also induced a decrease in right-angle light scatter and these effects were abolished by pretreatment of neutrophils with leukotriene B4. These data demonstrate that 12-OxoETE and 12-OxoDTrE show significant agonist activities towards human neutrophils and strongly suggest that their mechanisms of action involve the leukotriene B4 binding sites or a common activation sequence.

Studies on the activation of human neutrophil 5-lipoxygenase induced by natural agonists and Ca2+ ionophore A23187

By using exogenous substrates, activation of human neutrophil 5-lipoxygenase can be investigated independently of the release of endogenous arachidonic acid. We have developed a sensitive assay to measure 5-LO activation which takes advantage of the 5-LO-mediated conversion of 15S-hydroperoxy-5,8,11,13(Z,Z,Z,E)-eicosatetraenoic acid (15-HpETE) into 5S,15S-dihydroxy-6,8,11,13(E,Z,Z,E)-eicosatetraenoic acid (5,15-DiHETE). When resting neutrophils were incubated with low micromolar concentrations of 15-HpETE, a minor dose- and time-dependent formation of 5,15-DiHETE was observed. In contrast, co-addition of 15-HpETE with Ca2+ ionophore A23187 or with the neutrophil agonists platelet-activating factor (PAF), fMetLeuPhe or complement component C5a resulted in a sizeable concentration-dependent synthesis of 5,15-DiHETE, while lyso-PAF and phorbol myristate acetate were without effect on 5,15-DiHETE formation from 15-HpETE. This stimulation of 5,15-DiHETE synthesis by A23187 or by natural agonists was effectively inhibited by MK-886, a compound that has recently been reported to inhibit the A23187-induced translocation of 5-LO to membrane structures. Furthermore, natural-agonist-induced activation of the 5-LO-mediated transformation of 15-HpETE was inhibited by pertussis toxin, indicating the involvement of a GTP-binding protein in the 5-LO activation process.

Pertussis toxin selectively interferes with the responses of the HL-60 human promyelocytic cell line to dimethylsulfoxide

The effects of pertussis toxin (PT) on the growth and dimethylsulfoxide (Me2SO4)-induced differentiation of the HL-60 human promyelocytic leukemia cell line were tested. Cell growth was quantified by direct cell counts. Cell differentiation was estimated by measuring the expression of myeloid-specific cell-surface antigens (Mo-1 and fMet-Leu-Phe [fMLP] receptors), the ability of the cells to produce superoxide anions on stimulation with fMLP, the calcium ionophore A23187 and phorbol 12-myristate 13-acetate (PMA), and by monitoring the level of expression of messenger RNA (mRNA) for tumor necrosis factor alpha (TNF alpha). By itself, PT did not affect the proliferation of HL-60 cells in serum-containing medium. In contrast, PT (but not its B-oligomer) dose-dependently inhibited the Me2SO4-induced expression of Mo-1, fMLP receptors, and the oxidative responses to the chemotactic factor and to A23187, but not to PMA. The addition of Me2SO4 induced a significant increase in the steady-state levels of TNF alpha mRNA, and this effect was strongly inhibited by PT. Finally, the bacterial toxin did not reverse the block of cell division that follows the addition of Me2SO4. These results provide evidence for the involvement of a PT substrate (presumably a guanine nucleotide-binding protein) in the regulation of the maturation of the excitation-response coupling sequence in human myeloid cell precursors and show that the regulation of cell division and maturation of HL-60 cells are under distinct sets of control mechanisms.

Involvement of tyrosine kinases in the activation of human peripheral blood neutrophils by granulocyte-macrophage colony-stimulating factor

The aim of the present study is to evaluate the involvement of human neutrophil tyrosine kinase(s) in the signal transduction mechanism of granulocyte-macrophage colony-stimulating factor (GM-CSF). Stimulation of neutrophils with GM-CSF resulted in a time- and dose-dependent phosphorylation of several proteins having estimated molecular weights of approximately 40, 55, 74, 97, 118, and 155 Kd, detected by immunoblot using a monoclonal antibody directed against phosphotyrosine. GM-CSF-induced tyrosine phosphorylation was inhibited in a dose- and time-dependent manner by the tyrosine kinase inhibitor erbstatin. Using this inhibitor, we were able to correlate tyrosine phosphorylation with several functional effects of GM-CSF on human neutrophils. Pretreatment of neutrophils with erbstatin before incubation with GM-CSF completely inhibited the GM-CSF-induced intracellular alkalinization, downregulation of the leukotriene B4 receptor, enhancement of fMet-Leu-Phe-induced intracellular calcium mobilization, as well as the accumulation of mRNA for the proto-oncogene c-fos. Taken together, these data suggest that tyrosine kinase activation in human neutrophils plays a critical regulatory role in both the stimulation and priming of neutrophil function by GM-CSF.

Crystal-neutrophil interactions lead to interleukin-1 synthesis

Normal human blood neutrophils were studied for their capacity to synthesize and release interleukin-1 (IL-1) species after phagocytosis of triclinic monosodium urate (MSU) and calcium pyrophosphate dihydrate crystals (CPPD). MSU crystals were more potent inducers of IL-1 generation than CPPD or unopsonized zymosan. Microcrystal-stimulated neutrophils characteristically secreted most of the newly synthesized IL-1. Colchicine partly inhibited the secretion of IL-1 by neutrophils during phagocytosis of solid particles. However, colchicine selectively inhibited IL-1 synthesis induced by microcrystals. These results suggest that neutrophil-derived IL-1 may contribute to the pathogenesis of crystal-induced arthritis.

Crystal-induced neutrophil activation. I. Initiation and modulation of calcium mobilization and superoxide production by microcrystals

The effects of monosodium urate and calcium pyrophosphate dihydrate crystals on the levels of cytoplasmic free calcium and on the oxidative burst in normal human blood neutrophils were examined. The pattern of sensitivity to granulocyte-macrophage colony-stimulating factor, colchicine, cytochalasin B, pertussis toxin, diglyceride kinase, and protein kinase C inhibitors differentiated the mechanism(s) of neutrophil activation by the crystals from that involved in the responses to soluble chemotactic factors and indicated that individual crystals can use several activation pathways.

Granulocyte-macrophage colony-stimulating factor increases the synthesis of leukotriene B4 by human neutrophils in response to platelet-activating factor. Enhancement of both arachidonic acid availability and 5-lipoxygenase activation

Granulocyte-macrophage CSF (GM-CSF) primes human neutrophils for increased functional responsiveness to a variety of inflammatory agonists. In the present report, we have investigated the effect of human GM-CSF on the ability of platelet-activating factor (PAF) to induce the synthesis of 5-lipoxygenase products in human neutrophils. Human neutrophils stimulated with PAF in the range of 10(-5) to 10(-7) M for 15 min released small quantities of leukotriene B4 and its omega-oxidation products, 20-OH- and 20-COOH-leukotriene B4 in amounts that were detectable by enzyme immunoassay. Preincubation of normal peripheral blood neutrophils with human rGM-CSF enhanced the synthesis of the 5-lipoxygenase products in a time- and dose-dependent manner. Treatment with GM-CSF enabled their detection in response to lower concentrations of PAF (greater than or equal to 10(-9) M). The PAF receptor antagonist BN52021 inhibited the synthesis of 5-lipoxygenase products by GM-CSF-treated neutrophils in response to PAF. In addition to its effect on PAF-induced leukotriene synthesis, GM-CSF also augmented intracellular calcium mobilization by PAF. This observation prompted us to examine the effect of GM-CSF on two calcium-dependent events that are essential for leukotriene synthesis, arachidonic acid liberation, and 5-lipoxygenase activation. GM-CSF by itself, did not directly activate either of these two processes, however, it consistently and markedly enhanced the ability of PAF to do so. These results indicate that preincubation of peripheral blood neutrophils with GM-CSF enhances the ability of PAF to stimulate leukotriene synthesis by increasing both arachidonic acid availability and 5-lipoxygenase activation in response to PAF. These observations provide additional evidence of an important role for GM-CSF in the modulation of inflammatory responses to endogenous agonists through enhancement of the production of potent cellular inflammatory mediators such as leukotrienes.

Granulocyte-macrophage colony-stimulating factor increases the synthesis of leukotriene B4 by human neutrophils in response to platelet-activating factor. Enhancement of both arachidonic acid availability and 5-lipoxygenase activation

Granulocyte-macrophage CSF (GM-CSF) primes human neutrophils for increased functional responsiveness to a variety of inflammatory agonists. In the present report, we have investigated the effect of human GM-CSF on the ability of platelet-activating factor (PAF) to induce the synthesis of 5-lipoxygenase products in human neutrophils. Human neutrophils stimulated with PAF in the range of 10(-5) to 10(-7) M for 15 min released small quantities of leukotriene B4 and its omega-oxidation products, 20-OH- and 20-COOH-leukotriene B4 in amounts that were detectable by enzyme immunoassay. Preincubation of normal peripheral blood neutrophils with human rGM-CSF enhanced the synthesis of the 5-lipoxygenase products in a time- and dose-dependent manner. Treatment with GM-CSF enabled their detection in response to lower concentrations of PAF (greater than or equal to 10(-9) M). The PAF receptor antagonist BN52021 inhibited the synthesis of 5-lipoxygenase products by GM-CSF-treated neutrophils in response to PAF. In addition to its effect on PAF-induced leukotriene synthesis, GM-CSF also augmented intracellular calcium mobilization by PAF. This observation prompted us to examine the effect of GM-CSF on two calcium-dependent events that are essential for leukotriene synthesis, arachidonic acid liberation, and 5-lipoxygenase activation. GM-CSF by itself, did not directly activate either of these two processes, however, it consistently and markedly enhanced the ability of PAF to do so. These results indicate that preincubation of peripheral blood neutrophils with GM-CSF enhances the ability of PAF to stimulate leukotriene synthesis by increasing both arachidonic acid availability and 5-lipoxygenase activation in response to PAF. These observations provide additional evidence of an important role for GM-CSF in the modulation of inflammatory responses to endogenous agonists through enhancement of the production of potent cellular inflammatory mediators such as leukotrienes.

Priming of calcium mobilization in human neutrophils by granulocyte-macrophage colony-stimulating factor: evidence for an involvement of phospholipase D-derived phosphatidic acid

Human neutrophils pre-incubated with granulocyte-macrophage-colony-stimulating factor (GM-CSF) exhibit an enhanced mobilization of calcium in response to secondary stimuli such as chemotactic factors. The mechanisms underlying this priming effect of GM-CSF were examined. It was first demonstrated that the additional calcium mobilized by chemotactic factors in GM-CSF-treated cells was derived from intracellular stores and was associated neither with an increased permeability to calcium nor with production of inositol 1,4,5-trisphosphate. These results indicated that GM-CSF called upon a novel mechanism in order to enhance the mobilization of calcium in human neutrophils. The growth factor has recently been shown to prime phospholipase D leading to an enhanced activation by chemotactic factors and an augmented production of phosphatidic acid. Furthermore the ability of exogenous phosphatidic acid to mobilize calcium in cell types other than neutrophils has been previously demonstrated. Therefore, we examined the potential involvement of phospholipase D in the priming of the calcium response by GM-CSF in human neutrophils. Inhibition of the production of the fMet-Leu-Phe-stimulated production of phosphatidic acid by ethanol or wortmannin had only marginal effects on the concurrent mobilization of calcium. However, the priming of the mobilization of calcium by GM-CSF was greatly decreased in cells treated with either ethanol or wortmannin. These results provide strong support for the hypothesis that the production of phosphatidic acid, which is enhanced in GM-CSF-treated cells, is linked to an increased mobilization of intracellular calcium. These results may have relevance to the mechanism of action of GM-CSF in mature haematopoeitic cells as well to the mitogenic activity of other growth factors.

Selective inhibition of human neutrophil functional responsiveness by erbstatin, an inhibitor of tyrosine protein kinase

The role of tyrosine kinases in the responses of human neutrophils to chemotactic factors was examined using the recently described inhibitor erbstatin. Pre-incubation with erbstatin decreased the amount of tyrosine phosphorylation induced by the formylated oligopeptide formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) without effecting the binding of [3H]-fMet-Leu-Phe. Erbstatin also dose-dependently inhibited the production of superoxide anion induced by fMet-Leu-Phe and platelet-activating factor, but did not affect the oxidative burst induced by either the calcium ionophore A23187 or the phorbol ester phorbol 12-myristate 13-acetate. Furthermore, erbstatin diminished the cytosolic acidification elicited by fMet-Leu-Phe, platelet-activating factor, and leukotriene B4. In contrast, erbstatin was without effect on the increase in the levels of cytoplasmic free calcium and polymerized actin elicited by fMet-Leu-Phe, C5a, leukotriene B4 and platelet-activating factor, whereas the increase in cytoplasmic free calcium elicited by platelet-derived growth factor was inhibited by erbstatin. In addition, erbstatin affected neither the release of elastase stimulated by these agonists nor the release of beta-glucosaminidase, lysozyme or vitamin B12-binding protein induced by fMet-Leu-Phe. These results indicate that tyrosine protein kinases are involved in the signaling pathways employed by chemotactic factors in the stimulation of selective functional responses (and superoxide production in particular) in human neutrophils.

Priming of the human neutrophil respiratory burst by granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-alpha involves regulation at a post-cell surface receptor level. Enhancement of the effect of agents which directly activate G proteins

Over the last few years, several studies showing that production of superoxide by neutrophils in response to chemotactic factors such as FMLP is enhanced after preincubation of the cells with granulocyte-macrophage (GM)-CSF or TNF-alpha have been published. Subsequent reports have indicated that this effect of the cytokines may be mediated by modulation of the number and/or affinity of surface receptors for FMLP. In the present study we have investigated the effect of preincubation with GM-CSF and TNF-alpha on the oxidative burst induced by sodium fluoride and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)-agents which directly activate guanine-nucleotide binding proteins in neutrophils. Pretreatment of neutrophils with either GM-CSF or TNF-alpha dose-dependently enhanced the production of superoxide induced by NaF, as determined by the superoxide dismutase-inhibitable reduction of ferricytochrome c. Furthermore, preincubation of neutrophils with these cytokines enhanced the production of hydrogen peroxide induced by GTP gamma S in electroporated neutrophils. Because both NaF and GTP gamma S directly activate G proteins independently of external receptor-G protein interaction, these results imply that both GM-CSF and TNF-alpha alter the neutrophil signal transduction pathway in response to subsequent agonists independently of a modulation in the expression of the cell surface receptors for such agonists.

Priming of the human neutrophil respiratory burst by granulocyte-macrophage colony-stimulating factor and tumor necrosis factor-alpha involves regulation at a post-cell surface receptor level. Enhancement of the effect of agents which directly activate G proteins

Over the last few years, several studies showing that production of superoxide by neutrophils in response to chemotactic factors such as FMLP is enhanced after preincubation of the cells with granulocyte-macrophage (GM)-CSF or TNF-alpha have been published. Subsequent reports have indicated that this effect of the cytokines may be mediated by modulation of the number and/or affinity of surface receptors for FMLP. In the present study we have investigated the effect of preincubation with GM-CSF and TNF-alpha on the oxidative burst induced by sodium fluoride and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)-agents which directly activate guanine-nucleotide binding proteins in neutrophils. Pretreatment of neutrophils with either GM-CSF or TNF-alpha dose-dependently enhanced the production of superoxide induced by NaF, as determined by the superoxide dismutase-inhibitable reduction of ferricytochrome c. Furthermore, preincubation of neutrophils with these cytokines enhanced the production of hydrogen peroxide induced by GTP gamma S in electroporated neutrophils. Because both NaF and GTP gamma S directly activate G proteins independently of external receptor-G protein interaction, these results imply that both GM-CSF and TNF-alpha alter the neutrophil signal transduction pathway in response to subsequent agonists independently of a modulation in the expression of the cell surface receptors for such agonists.

Biosynthesis and biological activity of leukotriene B4

The leukotrienes are a family of biologically active molecules derived from arachidonic acid. While prostaglandins and thromboxanes are products of the cyclooxygenase pathway of arachidonic acid metabolism, the leukotrienes are formed by arachidonate 5-lipoxygenase, an enzyme present in phagocytes, mast cells, and basophils. Inflammatory stimuli, such as chemotactic peptides, platelet-activating factor, phagocytic particles, and immunological stimuli, which activate phagocytes and mast cells, stimulate leukotriene synthesis. Leukotriene B4, a dihydroxy derivative of arachidonic acid, has a unique stimulatory activity on important functional responses of phagocytes; leukotriene B4 exerts chemotactic and chemokinetic activity towards phagocytes in vitro and in vivo, and it is a putative mediator of inflammation.

Involvement of a phospholipase D in the mechanism of action of granulocyte-macrophage colony-stimulating factor (GM-CSF): priming of human neutrophils in vitro with GM-CSF is associated with accumulation of phosphatidic acid and diradylglycerol

The generation of diradylglycerol (DRG) and phosphatidic acid (PdtOH) was investigated in neutrophils primed with granulocyte-macrophage colony-stimulating factor (GM-CSF). Mass accumulation of DRG and PdtOH was measured using reversed-phase high performance liquid chromatography and thin layer chromatography, respectively. GM-CSF had no direct effect on the levels of PdtOH and DRG, but it increased PdtOH generation and the late phase of DRG accumulation in human neutrophils stimulated with FMLP. The elevation of the mass of PdtOH peaked approximately 100 s and clearly preceded that of DRG, which peaked at 150 s. The diacylglycerol kinase inhibitor R59022 enhanced the sustained increase in DRG but did not produce a parallel inhibition in PdtOH production. GM-CSF was without effect on the level of inositol 1,4,5-triphosphate [Ins(1,4,5)P3] and did not affect the liberation of Ins(1,4,5)P3 induced by FMLP. These findings exclude the involvement of the PtdIns(4,5)P2-specific phospholipase C/diacylglycerol pathway in the sustained phase of DRG accumulation. The early (30-s) appearance of PdtOH clearly suggests that GM-CSF enhanced FMLP receptor-linked phospholipase D (PLD) generation of PdtOH. PLD was assessed more directly by formation of labeled phosphatidylethanol (PEt) through PLD capacity of catalyzing a trans-phosphatidylation in presence of ethanol. The formation of PEt associated with a concomitant decrease in PdtOH directly demonstrated that the mechanism by which GM-CSF enhances PdtOH production is activation of a PLD active on phosphatidylcholine. This study provides evidence that the mechanism of action of GM-CSF involves upregulation of PLD activity leading to enhanced generation of PdtOH and DRG in FMLP-stimulated neutrophils. These findings may provide the basis for several of the priming effects of GM-CSF.

Inhibitory effects of MK-886 on arachidonic acid metabolism in human phagocytes

1. We have investigated the inhibitory activity of compound MK-886 (formerly L-663,536), an indole derivative, on 5-lipoxygenase product synthesis in various human phagocytes stimulated with either the ionophore A23187, in the presence and absence of exogenous arachidonic acid, or platelet-activating factor (PAF). The lipoxygenase products were analysed by reversed-phase h.p.l.c. 2. MK-886 inhibited the formation of 5-hydroxy-eicosatetraenoic acid (5-HETE), leukotriene B4 (LTB4), its omega-oxidation products and 6-trans-isomers with an IC50 value of 10-14 nM in A23187-stimulated neutrophils. In the same system, nordihydroguaiaretic acid (NDGA), AA-861 and L-655,240 showed IC50 values of 250-510, 110-420 nM and 1.7-3.9 microM, respectively. 3. MK-886 inhibited 5-lipoxygenase product synthesis in A23187-stimulated blood eosinophils and monocytes, and in neutrophils primed with granulocyte-macrophage colony-stimulating factor and stimulated with PAF with IC50 values of 1-13 nM. 4. The inhibitory activity of MK-886 was not reversed by addition of 10 microM arachidonic acid to A23187-stimulated neutrophils. 5. Compound MK-886 had no effect on 15-lipoxygenase product synthesis in blood eosinophils and neutrophils up to a concentration of 1 microM. 6. At 100 nM compound MK-886 had no significant effects on calcium ion mobilization, superoxide anion production and actin polymerization in neutrophils. 7. In conclusion, MK-886 is a very potent and specific inhibitor of both LTB4 and LTC4 synthesis in various types of human phagocytes.

Calcium is necessary but not sufficient for the platelet-activating factor release in human neutrophils stimulated by physiological stimuli. Role of G-proteins

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycerol-3-phosphocholine; PAF) enhances the release of newly synthesized PAF as measured by [3H]acetate incorporation into PAF in human neutrophils. The response was dose-dependent, rapid, transient, and inhibitable by the PAF antagonist BN-52021. The non-metabolizable bioactive PAF analogue (C-PAF) but not lyso-PAF enhances the release of newly synthesized PAF. Newly synthesized PAF was also released after stimulation of these cells with fMet-Leu-Phe. The human granulocyte-macrophage colony-stimulating factor potentiates the stimulated release of PAF. The intracellular calcium chelator BAPTA inhibits the rise of [Ca2+]i and the release of PAF but not the Na+/H+ antiport activity. PAF release, but not the rise in the intracellular concentration of free calcium, was inhibited in pertussis toxin-treated neutrophils stimulated with PAF. The release of PAF in pertussis toxin-treated cells was also inhibited in cells stimulated with fMet-Leu-Phe or opsonized zymosan. These results suggest that functional pertussis toxin-sensitive guanine nucleotide regulatory protein and/or one or more of the changes produced by phospholipase C activation are necessary for PAF release produced by physiological stimuli. It appears that PAF release requires a coordinated action of receptor-coupled G-proteins, calcium, and other parameters.

Guanine nucleotide-induced polymerization of actin in electropermeabilized human neutrophils

The effects of exogenous guanine nucleotides on the polymerization of actin in human neutrophils were tested in an electropermeabilized cell preparation. Close to 40% permeabilization was achieved with a single electric discharge as measured by nucleic acid staining with ethidium bromide or propidium iodide with minimal (less than 2%) release of the cytoplasmic marker lactate dehydrogenase. In addition, electropermeabilized neutrophils retained their capacity to produce superoxide anions and to sustain a polymerization of actin in response to surface-receptor dependent stimuli such as chemotactic factors. Electropermeabilization produced a rapid and transient permeabilization that allowed the entry of guanine nucleotides into the cells. GTP and, to a larger extent, its nonhydrolyzable analog guanosine 5'-O-2-thiotriphosphate (GTP[S]), induced a time- and concentration-dependent polymerization of actin, as determined by increased staining with 7-nitrobenz-2-oxa-1,3-diazolylphallacidin. The effects of the aforementioned guanine nucleotides were antagonized by GDP[S], but were insensitive to pertussis toxin. Cholera toxin potentiated to a small degree the amount of actin polymerization induced by GTP[S]. These results provided direct evidence for the involvement of GTP-binding proteins in the regulation of the organization of the cytoskeleton of neutrophils, an event that is of crucial importance to the performance of the defense-oriented functions of these cells.

Activation of the human neutrophil 5-lipoxygenase by exogenous arachidonic acid: involvement of pertussis toxin-sensitive guanine nucleotide-binding proteins

1. The mechanism by which incubation of human peripheral blood neutrophils with exogenous arachidonic acid leads to 5-lipoxygenase product synthesis was investigated. 2. Incubation of neutrophils with arachidonic acid caused a concentration- and time-dependent synthesis of leukotriene B4, its omega-oxidation products, and 5-hydroxyeicosatetraenoic acid. 3. The threshold concentration of arachidonic acid required for this effect was equal to, or greater than 3.3 microM and the synthesis increased with up to 33 microM arachidonic acid, the highest concentration used. Synthesis induced by arachidonic acid increased with time for up to 15 min and the major products detected were the omega-oxidation products of leukotriene B4. 4. Pre-incubation of neutrophils with pertussis toxin inhibited the synthesis of 5-lipoxygenase products induced by arachidonic acid by 75% or more, but had no effect on either arachidonic acid-induced synthesis of the 15-lipoxygenase product, 15-hydroxyeicosatetraenoic acid, or activation of the 5-lipoxygenase induced by the calcium ionophore A23187. 5. Pre-incubation of neutrophils with granulocyte-macrophage colony-stimulating factor lead to enhanced leukotriene synthesis in response to arachidonic acid. 6. These results imply that exogenous arachidonic acid is not only used as a substrate, but also activates the 5-lipoxygenase. Possible mechanisms of action are discussed.

Arachidonic acid-induced mobilization of calcium in human neutrophils: evidence for a multicomponent mechanism of action

1. The mechanism(s) involved in the mobilization of calcium induced by arachidonic acid in human neutrophils was investigated. 2. The addition of arachidonic acid to a suspension of human neutrophils led to a time- and concentration-dependent mobilization of calcium which was the result of two separate and experimentally differentiable processes. The latter consisted of a rapid and transient phase followed by a slower and more sustained response. 3. The initial phase of calcium mobilization elicited by arachidonic acid was decreased in the presence of EGTA, inhibited by pertussis toxin as well as by nordihydroguaiaretic acid (NDGA), and diminished following a pre-incubation with leukotriene B4, but not platelet-activating factor. 4. The characteristics of the first phase of the mobilization of calcium were consistent with an interaction of the fatty acid with the leukotriene B4 receptors, either directly or indirectly following the synthesis of leukotriene B4, as well as with a release of internal calcium. 5. The second, slower and more sustained phase of calcium mobilization was more apparent at high concentrations (greater than or equal to 8-16 microM) of arachidonic acid, and was relatively insensitive to pertussis toxin, EGTA or NDGA. 6. The characteristics of the 'slow' phase of calcium mobilization by arachidonic acid are consistent with its being associated primarily with a release of calcium from internal storage pools. 7. The data presented indicate that the mechanism of mobilization of calcium by arachidonic acid in human neutrophils is complex and involves specific activation pathways employed, in part at least, by other neutrophil agonists. These findings may have relevance to various inflammatory situations in which the elevated levels of extracellular arachidonic acid known to be present could modulate the functional responsiveness of the neutrophils to other stimuli.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) and opsonization synergistically enhance leukotriene B4 (LTB4) synthesis induced by phagocytosis in human neutrophils

Normal human blood neutrophils were studied for their capacity to synthesize leukotriene B4 (LTB4) and its omega-oxidized metabolites after phagocytosis of zymosan. Phagocytosis of serum-opsonized particles led to a higher release of LTs than did unopsonized zymosan. The most striking effect of phagocytosis was observed when neutrophils were primed with granulocyte-macrophage colony-stimulating factor (GM-CSF): opsonization and GM-CSF synergistically increased LTB4 synthesis by neutrophils.

Chemoattractant-induced cytoplasmic pH changes and cytoskeletal reorganization in human neutrophils. Relationship to the stimulated calcium transients and oxidative burst

The relationships between the chemotactic factor-stimulated mobilization of calcium, activation of the NADPH-oxidase, changes in cytosolic pH, and in the level of polymerized actin in human neutrophils have been examined. The approach taken was to use intracellular calcium chelators, and pharmacologic modulators (both positive and negative) of the NADPH-oxidase to measure the aforementioned responses under conditions where the calcium transients were abrogated and/or the generation of superoxide anions was either inhibited or augmented. The decrease in cytosolic pH induced by chemoattractants was inhibited by the calcium chelator BAPTA and by the diglyceride kinase inhibitor 6-[2-(4-[(4-fluorophenyl)phenylmethylene]-1-piperidinylethyl ]-7-methyl-5H-thiazolo[3,2-alpha]pyriimidin-5-one (R59022) (this latter compound enhanced the oxidative response of the cells). Furthermore, a specific inhibitor of the NADPH-oxidase (diphenyleneiodonium) had no significant effect on the cytosolic acidification induced by FMLP or leukotriene B4. These results indicate that the initiation of the cytosolic acidification induced by chemotactic factors is a calcium-dependent event that is not directly linked to the activation of the NADPH-oxidase. In contrast, the stimulated polymerization of actin was insensitive to BAPTA, R59022, and diphenyleneiodonium. Thus, neither the calcium transients nor the oxidative burst play a signaling role in the initiation of actin polymerization elicited by chemoattractants. These data indicate that additional investigations are needed to uncover the biochemical basis of the signals initiated in human neutrophils by chemotactic factors that lead to the polymerization of actin and to the cytosolic acidification.