Effects of immune complexes, zymosan preparations and ionophore A 23187 on leukotriene formation in human leukocytes

Incubation of human leukocytes with opzonized zymosan or IgG immune complexes led to a time dependent release of leukotrienes (LT) B₄ and C₄. After 3–4 min, the levels of LTB₄ and LTC₄ were 93 and 35 pmol/310⁷ cells, respectively. These amounts were 2–4 times lower than those released by leukocytes stimulated with the calcium ionophore A 23187. The levels of LTC₄ were 8 and 20 times lower than those of LTB₄ after incubation with opsonized zymosan or immune complexes, respectively. Heat-inactivation of the serum prior to zymosan coating decreased the effect of opsonized zymosan. Uncoated zymosan was an even weaker stimulus of leukotriene formation. These results suggest that both complement factors and immunoglobulins play a pivotal role in activating leukotriene synthesis in a mixed suspension of human leukocytes.     

Release of adenosine from human neutrophils stimulated by platelet activating factor, leukotriene B(4) and opsonized zymosan

Isolated human polymorphonuclear leukocytes (PMNL) stimulated by platelet activating factor (PAF), leukotriene B(4) (LTB(4)) or opsonized zymosan (OZ) released adenosine measured by thermospray high performance liquid chromatography mass spectrometry in the cell-free supernatants. Stimulation by PAF or LTB(4) resulted in a bellshaped concentration-effect curve; 5 x 10(-7) M PAF, 10(-8) M LTB(4) and 500 mug ml(-1) OZ induced peak adenosine release, thus cytotoxic concentrations did not elevate adenosine level in the supernatants. Therefore adenosine release was characteristic of viable cells. As calculated from concentration-effect curves, the rank order of potency for adenosine release was PAF > LTB > OZ. These resuits suggest that adenosine, when bound specifically to membrane receptor sites, may initiate signal transduction, and, in co-operation with other inflammatory mediators, may modulate phagocyte function, e.g. production of chemoluminescence (CL).     

Evaluation of inhibitors of eicosanoid synthesis in leukocytes: possible pitfall of using the calcium ionophore A23187 to stimulate 5' lipoxygenase

The effect on arachidonate metabolism of two compounds (BW755C and benoxaprofen) which have been reported to inhibit 5' lipoxygenase in leukocytes has been evaluated in human polymorphonuclear leukocytes (PMN) stimulated with the calcium ionophore A23187 and serum-treated zymosan (STZ). The syntheses of leukotriene B4 (LTB4) and thromboxane B2 (TXB2) from endogenous substrate were determined by specific radioimmunoassays as indicators of 5' lipoxygenase and cyclo-oxygenase activity in the PMN respectively. Benoxaprofen inhibited the synthesis of leukotriene B4 by human PMN stimulated with the calcium ionophore A23187, but it was approximately 5 times less potent than BW755C. However, benoxaprofen (IC50 1.6 X 10(-4)M) was approximately 100 times less potent than BW755C (IC50 1.7 X 10(-6)M) at inhibiting leukotriene B4 synthesis induced by serum-treated zymosan. Both drugs inhibited thromboxane synthesis by leukocytes stimulated with A23187 or serum-treated zymosan at similar concentrations (approximately 5 X 10(-6)M). The data obtained using STZ as stimulus are consistent with previous in vivo studies and indicate that benoxaprofen is a relatively selective inhibitor of cyclo-oxygenase. However, this selectivity was far less apparent when A23187 was used as a stimulus to release the eicosanoids which suggests that this inhibition could be via an indirect mechanism and therefore A23187 should be used with caution as a stimulus of 5' lipoxygenase for evaluating inhibitors of eicosanoid synthesis.     

Opsonized bacteria stimulate leukotriene synthesis in human leukocytes

Incubation of human leukocytes with opsonized bacteria led to leukotriene formation. The main products identified were leukotriene B4, 20-OH leukotriene B4 and 20-COOH leukotriene B4. A lesser amount of leukotriene C4 was formed. In contrast, only minor amounts of leukotrienes were formed by leukocytes challenged with uncoated bacteria. However, both opsonized and unopsonized bacteria stimulated the synthesis of 5S,12S-DHETE and 5S,12S,20-THETE. Opsonized bacteria caused a transient elevation of leukotriene B4 levels, with a maximum after 5 min. After 20 min of incubation the levels of 20-OH leukotriene B4, and 20-COOH leukotriene B4 were 7- and 20-times higher than those of leukotriene B4, showing that the leukocytes effectively degrade leukotriene B4 via omega-oxidation. In the light of the profound biological effects of leukotrienes, the present report indicates that leukotriene formation induced by opsonized bacteria might be important in the host defense against microorganisms.     

Exclusive leukotriene C4 synthesis by purified human eosinophils induced by opsonized zymosan

Purified human eosinophils were challenged with N-formyl-methionyl-leucyl-phenylalanine, leukotriene B4, platelet-activating-factor, valyl-glycyl-seryl-glutamic acid, phorbol myristate acetate, zymosan, opsonized zymosan and the calcium ionophore A23187 to induce leukotriene synthesis. Reversed-phase high performance liquid chromatography analysis demonstrated the almost exclusive synthesis of leukotriene C4 by eosinophils of 11 healthy donors after challenge with opsonized zymosan [(22 +/- 4) X 10(6) molecules LTC4/cell, mean +/- SE] or the calcium ionophore A23187 [(54 +/- 7) X 10(6) molecules LTC4/cell, mean +/- SE]. The other agents were not capable of inducing leukotriene formation. When in addition to opsonized zymosan N-formyl-methionyl-leucyl-phenylalanine or platelet-activating factor were added a significant increase of the leukotriene C4 synthesis by eosinophils was observed. These results suggest that eosinophils might be triggered to produce considerable amounts of the spasmogenic leukotriene C4 in vivo by C3b- and/or IgG-mediated mechanisms e.g. phagocytosis.     

Effect of the 5-lipoxygenase inhibitor piriprost on superoxide production by human neutrophils

The effect of 6,9-deepoxy-6,9-(phenylimino)-delta 6,8-prostaglandin I1 (Piriprost) on the oxidative response was studied in human neutrophils stimulated by N-formyl-methionyl-leucyl-phenylalanine (fMLP), phorbol 12-myristate, 13-acetate (PMA) or opsonized zymosan. Piriprost inhibited the stimulatory effect of fMLP on superoxide anion (O2-) generation, at concentrations higher than those which depress leukotriene B4 (LTB4) formation. This inhibition was overcome by increasing the concentration of fMLP. Neither exogenous LTB4 nor indomethacin were able to reverse the inhibitory effect of piriprost on fMLP action. In contrast, piriprost did not inhibit the stimulation of O2- production induced by PMA or zymosan. Piriprost behaves thus as a specific and apparently competitive antagonist of fMLP: this action does not seem to involve lipoxygenase inhibition and might be exerted at the level of the fMLP receptor or its associated mechanisms of transduction.     

Stimulus-specific induction of phospholipid and arachidonic acid metabolism in human neutrophils

Phospholipid remodeling resulting in arachidonic acid (AA) release and metabolism in human neutrophils stimulated by calcium ionophore A23187 has been extensively studied, while data obtained using physiologically relevant stimuli is limited. Opsonized zymosan and immune complexes induced stimulus-specific alterations in lipid metabolism that were different from those induced by A23187. [3H]AA release correlated with activation of phospholipase A2 (PLA2) but not with cellular activation as indicated by superoxide generation. The latter correlated more with calcium-dependent phospholipase C (PLC) activation and elevation of cellular diacylglycerol (DAG) levels. When cells that had been allowed to incorporate [3H]AA were stimulated with A23187, large amounts of labeled AA was released, most of which was metabolized to 5-HETE and leukotriene B4. Stimulation with immune complexes also resulted in the release of [3H]AA but this released radiolabeled AA was not metabolized. In contrast, stimulation with opsonized zymosan induced no detectable release of [3H]AA. Analysis of [3H]AA-labeled lipids in resting cells indicated that the greatest amount of label was incorporated into the phosphatidylinositol (PI) pool, followed closely by phosphatidylcholine and phosphatidylserine, while little [3H]AA was detected in the phosphatidylethanolamine pool. During stimulation with A23187, a significant decrease in labeled PI occurred and labeled free fatty acid in the pellet increased. With immune complexes, only a small decrease was seen in labeled PI while the free fatty acid in the pellets was unchanged. In contrast, opsonized zymosan decreased labeled PI, and increased labeled DAG. Phospholipase activity in homogenates from human neutrophils was also assayed. A23187 and immune complexes, but not zymosan, significantly enhanced PLA2 activity in the cell homogenates. On the other hand, PLC activity was enhanced by zymosan and immune complexes. Stimulated increases in PLC activity correlated with enhanced superoxide generation induced by the stimulus.     

Intracellular retention of the 5-lipoxygenase pathway product, leukotriene B4, by human neutrophils activated with unopsonized zymosan

The cellular and extracellular distribution of leukotriene B4 (LTB4) generated in human neutrophilic polymorphonuclear leukocytes (PMN) stimulated with unopsonized zymosan has been compared with that generated in PMN activated by the calcium ionophore. The amounts of extracellular and intracellular LTB4 were quantitated by radioimmunoassay. The authenticity of the immunoreactive LTB4 was confirmed by the elution of a single immunoreactive peak after reverse phase-high performance liquid chromatography (RP-HPLC) at the retention time of synthetic LTB4, by the identical elution time of a peak of radiolabeled product derived from [3H]arachidonic acid-labeled PMN with the immunoreactive product, and by the comparable chemotactic activity on a weight basis of immunoreactive LTB4 and synthetic LTB4 standard. Under optimal conditions of stimulation by unopsonized zymosan, more than 78% of the generated immunoreactive LTB4 remained intracellular, whereas with optimal activation by the ionophore, less than 8.6% of immunoreactive LTB4 was retained. Resolution by RP-HPLC of the products from the supernatants and cell extracts of [3H]arachidonic acid-labeled PMN stimulated with unopsonized zymosan and those stimulated with calcium ionophore allowed identification and measurement of 5-hydroxyeicosatetraenoic acid (5-HETE), 6-trans-LTB4, LTB4, and omega oxidation products of LTB4 by radioactivity. With zymosan stimulation of PMN, 5-HETE and the 6-trans-LTB4 diastereoisomers were not released, LTB4 was partially released, and the omega oxidation products of LTB4 were preferentially extracellular in distribution. In contrast, with ionophore stimulation, only 5-HETE had any duration of intracellular residence being equally distributed intra- and extracellularly throughout the 30-min period of observation; 6-trans-LTB4, LTB4, and the omega oxidation products of LTB4 were retained at less than 19%. The respective distributions of 5-HETE after zymosan and ionophore stimulation were not altered by the introduction of albumin to the reaction mixtures to prevent reacylation, or by hydrolysis of the cell extract to uncover any product that had been reacylated. The finding that stimulation of PMN with unopsonized zymosan results in the cellular retention of 5-lipoxygenase products suggests that release of these metabolites may be an event that is regulated separately from their generation.     

Induction of endogenous arachidonic acid metabolism in human neutrophils with snake venom phospholipase A2, immune complexes, and A23187

The stimuli responsible for eicosanoid secretion of phagocytes in chronic inflammatory disorders like rheumatoid arthritis and chronic inflammatory bowel disease are unknown. Phospholipase A2 (PLA2), found in Russelli vipera snake venom, has been proposed to be more than 100 times more potent on a molar basis than A23187 in releasing leukotriene B4 (LTB4) from porcine neutrophils. Therefore, this enzyme was investigated as a challenger of human neutrophils (PMNs) and compared with immune complexes and A23187. 1-14C-Arachidonic acid (AA) was incorporated into purified human PMNs until steady state conditions were obtained. AA release and metabolism were stimulated with either PLA2 isoenzyme of Russelli vipera, immune complexes, or A23187. The radioactive eicosanoids released were extracted and separated by thin layer chromatography, followed by autoradiography and quantitative laser densitometry. Stimulation with PLA2, immune complexes, or A23187 resulted in LTB4 formation of 0%, 1.8%, and 5.3%, respectively, of total released radioactivity. In conclusion, Russelli vipera PLA2 does not stimulate AA-release and metabolism in human PMNs, and immune complexes are weak as compared to the unphysiologic challenger A23187 in this respect.     

Perturbation of beta-glucan receptors on human neutrophils initiates phagocytosis and leukotriene B4 production

Normal human neutrophils were stimulated with the yeast cell wall product, zymosan, and examined for two biologic responses, ingestion of particles and production of leukotriene B4 (LTB4), under conditions that were comparable and optimal for the quantitation of each response. Monolayers of adherent neutrophils ingested unopsonized zymosan particles, at particle-to-cell ratios of 12.5:1 to 125:1, in a dose- and time-related manner. At a ratio of 125:1, the percentages of neutrophils ingesting greater than or equal to 1 and greater than or equal to 3 zymosan particles reached plateau levels of 55 +/- 6 and 32 +/- 9% (mean +/- SD, n = 8), respectively, within 30 min. At this same ratio, neutrophils during gravity sedimentation with zymosan particles synthesized LTB4 in a time-dependent manner for at least 45 min. The maximum amount of immunoreactive LTB4 released into supernatants was 3.8 +/- 1.2 ng per 10(6) neutrophils (mean +/- SD, n = 5) and the corresponding total immunoreactive LTB4 was 6.2 +/- 1.9 ng per 10(6) neutrophils. Treatment of 2 x 10(7) suspended neutrophils with 250 micrograms of trypsin for 20 min before concurrent assessment of neutrophil phagocytosis and LTB4 production reduced both of these responses by about 50%. Pretreatment of neutrophils with 800 micrograms/ml of soluble yeast beta-glucan inhibited their ingestion of zymosan by 84% (mean +/- SD, n = 3), with 50% inhibition occurring with 100 micrograms/ml of soluble beta-glucan; 800 micrograms/ml of soluble yeast alpha-mannan had no inhibitory effect. Pretreatment of neutrophils with 400 micrograms/ml of soluble yeast beta-glucan inhibited neutrophil synthesis of LTB4 by 90%, with 50% occurring with 200 micrograms/ml; 400 micrograms/ml of soluble yeast alpha-mannan had no inhibitory effect. The presence of 1.25 micrograms/ml of cytochalasin B during incubation with zymosan particles reduced neutrophil phagocytosis from 65 to 6%, and neutrophil synthesis of LTB4 from total levels of 6.0 +/- 0.3 ng/10(6) cells to zero (mean +/- SD, n = 3). Pretreatment with either cytochalasin B or vinblastine did not alter neutrophil generation of LTB4 induced by calcium ionophore. Neutrophils pretreated with vinblastine, at 4 x 10(-6) to 4 x 10(-4) M, and then maintained at one-half these concentrations during incubation with unopsonized zymosan particles exhibited no diminution in particle ingestion, but were markedly reduced in zymosan-induced synthesis of LTB4.(ABSTRACT TRUNCATED AT 400 WORDS)     

Heat shock induces alterations of the lipoxygenase pathway in human polymorphonuclear granulocytes

We have investigated the effect of the heat shock response on the leukotriene generation, chemotaxis, and generation of oxygen radicals of human polymorphonuclear granulocytes (PMNs) by preincubating the PMNs at 42 degrees C. Subsequently, the different test systems were performed at 37 degrees C. As we confirmed by the release of lactate dehydrogenase and beta-glucuronidase the elevated temperatures did not result in cytotoxic or degranulating processes. After heat shock treatment the generation of leukotrienes induced by the Ca(++)-ionophore A23187, fMLP or opsonized zymosan was inhibited in a time and temperature dependent manner (preincubation phase) as was measured by HPLC-analysis. In contrast, the conversion of 14C-arachidonic acid revealed the generation of LTB4, 5-HPETE and 5-HETE solely as a result of the preincubation at 42 degrees C without any further stimulation. In addition, the chemiluminescence response induced by opsonized zymosan and the chemotaxis against C5a and LTB4 was clearly inhibited after heat shock treatment. With regard to enzyme activities of the heat treated PMNs the protein kinase C activities were enhanced whereas the LTD4-dipeptidase and the LTB4-omega-hydroxylase were not affected.     

The development of a sensitive and specific radioreceptor assay for leukotriene B4

To establish a simple and sensitive quantitation of leukotriene B4 (LTB4), we developed a radioreceptor assay (RRA) using a highly specific [3H]leukotriene B4[( 3H]LTB4) binding to a guinea pig spleen homogenate. The assay detected LTB4 levels as low as 0.12 pmol per tube. Fifty percent inhibition of bound [3H]LTB4 was obtained by 2.5 nM of unlabeled LTB4. [3H]LTB4 competition studies indicated that 20-hydroxy-LTB4 was 8 times, 6-trans-LTB4 was 640 times and 20-carboxy-LTB4 was 1000 times less effective than LTB4. The peptide leukotrienes C4, D4 and E4 showed no effect on [3H]LTB4 binding. Recovery rates averaged 97% after ethanol extraction and evaporation of known amounts of LTB4. The intra-assay coefficients of variation for three samples were 2.4%, 7.2% and 8.4%, respectively. This assay was validated by measuring LTB4 released from human granulocytes stimulated with calcium ionophore A23187. The LTB4 level was maximal at 10 min (156.8 +/- 36.2 pmol/3 x 10(6) cells) and decreased rapidly after 15 min. This radioreceptor assay for leukotriene B4 is highly sensitive and is comparable to the reported sensitivity by radioimmunoassay. The method is simpler and less expensive than other methods such as high pressure liquid chromatography and is suitable for routine measurement of leukotriene B4.     

Leukotriene B4 production by stimulated whole blood: comparative studies with isolated polymorphonuclear cells

A new method was developed to study leukotriene B4 (LTB4) production by stimulated whole blood. The calcium ionophore A23187 and serum-treated zymosan induced LTB4 production, measured by radioimmunoassay, in a dose- and time-dependent manner. The pattern of LTB4 production by whole blood differed markedly from that observed with isolated, purified polymorphonuclear leukocytes. Higher levels of LTB4 were reached and maintained in whole blood. The system allowed to detect drug effects on LTB4 synthesis in vitro. This new method to study the synthesis of LTB4 takes into account the complex interactions between different cell types which can modulate LTB4 metabolism.     

Differences in arachidonic acid release, metabolism and leukotriene B4 synthesis in human polymorphonuclear leukocytes activated by different stimuli

Products of the 5-lipoxygenase pathway were analyzed after different stimuli in human polymorphonuclear leukocytes prelabeled with 3H-arachidonic acid. Upon stimulation with the Ca2+ ionophore, A23187, polymorphonuclear leukocytes generate 118.2 +/- 18 pg [3H]dihydroxyeicosatetraenoic acids (diHETEs, including 3H-leukotriene B4 and its 6-trans-stereoisomers), after exposure to serum coated zymosan (35.8 +/- 9 pg) and N-fMet-Leu-Phe (39.5 +/- 9 pg). Conversion of 3H-arachidonic acid paralleled its release after A23187 and fMet-Leu-Phe exposure leaving only 13.8 +/- 7% and 13.6 +/- 3% of the released 3H-arachidonic acid unmetabolized, respectively. In contrast, after stimulation with serum-coated zymosan only a small fraction of the released 3H-arachidonate was converted to 5-lipoxygenase products leaving 73.0 +/- 5% of the released 3H-arachidonic acid unmetabolized. In parallel, leukotriene B4 synthesis was studied in unlabeled polymorphonuclear leukocytes, resulting in 40 +/- 15 ng upon A23187 stimulation, 4 +/- 0.9 ng upon stimulation with fMet-Leu-Phe and 1.8 +/- 0.9 ng after serum-coated zymosan, showing a different ratio of leukotriene B4 to 3H-diHETE for A23187 in contrast to serum-coated zymosan and fMet-Leu-Phe. These results indicate that the coupling between the release of the precursor fatty acid and the metabolism via the 5-lipoxygenase pathway differs greatly between different stimuli.     

Studies of the inhibitory activity of MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-indol- 2-yl]-2,2-dimethyl propanoic acid) on arachidonic acid metabolism in human phagocytes.

We have investigated the inhibitory activity of compound MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-i ndol-2- yl]-2,2-dimethyl propanoic acid) on 5-lipoxygenase (5-LO) product synthesis in various human phagocytes stimulated with either the ionophore A23187, opsonized zymosan (OPZ), platelet-activating factor (PAF), or formyl-methionyl-leucyl-phenylalanine (fMLP). The lipoxygenase products were analyzed by reversed-phase HPLC. MK-0591 inhibited the formation of 5-hydroxyeicosatetraenoic acid, leukotriene (LT) B4, its omega-oxidation products, and 6-trans-isomers with IC50 values of 2.8-4.8 nM in A23187-stimulated neutrophils. In these conditions, arachidonic acid at a concentration of 10 microM had no effect on MK-0591 inhibitory activity. In neutrophils stimulated with OPZ, the synthesis of LTB4, its omega-oxidation products, and 6-trans-isomers was inhibited with IC50 values of 9.5-11.0 nM. MK-0591 inhibited 5-LO product synthesis in A23187-stimulated blood monocytes, eosinophils, and alveolar macrophages with IC50 values of 0.3-0.9, 3.7-5.3, and 8.5-17.3 nM, respectively. In neutrophils primed with granulocyte--macrophage colony-stimulating factor and stimulated with PAF, lipoxygenase product synthesis was inhibited with IC50 values of 7.7-8.7 nM. At the concentration of 1 microM, MK-0591 had no inhibitory effect on 15-lipoxygenase activity in human polymorphonuclear leukocytes, nor on human platelet 12-lipoxygenase and cyclooxygenase. In conclusion, MK-0591 is a very potent and specific inhibitor of 5-LO product synthesis in various types of human phagocytes.     

Stereochemical requirements for substrate specificity of LTB4 20-hydroxylase

LTB4 20-hydroxylase (P-450LTB) is the cytochrome P-450 in the microsomes of human polymorphonuclear leukocytes that catalyzes the omega-oxidation of leukotriene B4 (LTB4) to 20-OH LTB4. The activity of P-450LTB for LTB4 compared to isomers and analogs of LTB4 at a concentration of 0.3 microM revealed a preference of P-450LTB for both the triene bond configuration of LTB4 and for the chirality of the 5S and 12R hydroxyl groups. 15S-Hydroxyeicosatetraenoic acid, 8(R/S), 15S-dihydroxy-5-cis-9,11,13-trans-eicosatetraenoic acid, 8R,15S-dihydroxy-5,13-cis-9,11-trans-eicosatetraenoic acid, and 5S,15S-dihydroxy-6,13-trans-8,11-cis-eicosatetraenoic acid were each not subject to omega-oxidation, indicating a negative effect of the presence of a 15-hydroxyl group on substrate recognition. At a concentration of 1.5 microM, 12R- and 12S-hydroxyeicosatetraenoic acid were converted to their respective 20-OH derivatives at rates that were 34.2 +/- 11.6% (mean +/- S.D., n = 3) and 3.5 +/- 4.3% (mean +/- S.D., n = 4), respectively, of that of LTB4 to 20-OH LTB4, further indicating that P-450LTB can distinguish the chirality of the 12-hydroxyl group. The lower Km of LTB4 (2.0 microM), as compared to those of its 6-trans-12-epi isomer (3.8 microM) and 5-epi-LTB4 (6.6 microM) confirmed the preference of P-450LTB for the specific triene bond structure of LTB4 and its preference for the chirality of the hydroxyl groups of LTB4 within this structurally related class of molecules. At equal 1.5-microM concentrations, LTB4 completely inhibited the omega-oxidation of all other substrates and partially suppressed that of leukotriene B5, consistent with the lower Km of LTB4 and indicating that P-450LTB catalyzed the omega-oxidation of all substrates. Thus, P-450LTB is a novel cytochrome P-450 of human polymorphonuclear leukocytes with substrate recognition determined by the triene bond configuration and the chirality of the hydroxyl groups.     

Release of leukotrienes by human monocytes on stimulation of their phagocytic receptor for particulate activators

The respective capacities of adherent human monocytes to metabolize endogenous arachidonic acid into leukotrienes C4 (LTC4) and B4 (LTB4) in response to activation with an ionophore, A23187, or to phagocytosis of unopsonized zymosan particles and IgG-sensitized sheep erythrocytes ( EsIgG ) were compared under optimal conditions for each stimulus. Resolution of the cellfree supernatant, after ionophore activation, by reverse-phase high performance liquid chromatography (RP-HPLC) identified only two products which eluted at the retention times of LTC4 and LTB4. There was correspondence between their quantitation by integrated optical density and radioimmunoassay, and the recoveries from the initial supernatant were 80% by radioimmunoassay. Activation of adherent monocytes from 12 donors by ionophore and by zymosan particles released 68.1 ng and 10.0 ng LTB4 and 29.5 ng and 2.1 ng LTC4, respectively. With trypsin pretreatment, the monocytes responded fully to ionophore activation but were inhibited in their response to zymosan particles as assessed by phagocytosis and leukotriene release, indicating that the zymosan stimulus acted through a trypsin-sensitive membrane receptor. When the response of adherent monocytes from nine donors to zymosan particles and to EsIgG were compared at identical particle concentrations and with similar numbers of ingesting monocytes, zymosan elicited LTB4 release (mean 6.7 ng) from all and LTC4 (mean 1.5 ng) from eight donors, while EsIgG caused low level release of LTB4 (mean 0.7 ng) from six and LTC4 from only one of the donors. Neither zymosan nor ionophore stimulation led to the metabolism of exogenously added [3H]LTB4 or [3H]LTC4 as assessed by RP-HPLC of the cellfree supernatants and by quantitation of the eluted labeled products. Thus, transmembrane activation of adherent monocytes by their receptor for particulate activators, in contrast to stimulation of their IgG-Fc receptor, reproducibly releases substantial quantities of LTB4 and LTC4, and may represent an important mechanism for regulating the microenvironment in the nonimmune host.     

Leukotriene C4 formation by enriched human basophil preparations from normal and asthmatic subjects.

Numbers of circulating basophils are increased in asthmatic subjects, compared to normal subjects. Basophil enriched cell preparations from normal and asthmatic subjects were challenged in vitro with the calcium ionophore A23187, anti-IgE, or opsonized zymosan to study leukotriene C4 formation, histamine release, and prostaglandin D2 formation. No prostaglandin D2 formation by basophils was observed. Furthermore, opsonized zymosan was not capable of inducing any mediator formation or release from basophils. At optimal stimulation conditions no differences were found between basophils from normal and asthmatic subjects concerning A23187 or anti-IgE induced leukotriene C4 formation or histamine release. A23187 and anti-IgE induced leukotriene C4 formation were in the range of 1-20 and 0.6-4.8 pmol/10(6) basophils respectively.     

Transduction by leukotriene B4 receptors of increases in cytosolic calcium in human polymorphonuclear leukocytes

The uptake of Quin-2 by human polymorphonuclear (PMN) leukocytes permitted accurate fluorimetric quantification of the cytosolic concentration of intracellular calcium [( Ca+2]in), without altering the expression of the two subsets of leukotriene B4 (LTB4) receptors, as assessed by the binding of [3H]LTB4. Chemotactic concentrations of LTB4 elicited a rapid increase in [Ca+2]in, which reached a peak within 0.6 to 1 min and then decayed back to baseline levels by 6 to 10 min. The maximal increase and the half-maximal increase in [Ca+2]in were achieved by LTB4 at mean concentrations of 5 X 10(-10) M and 2 X 10(-10) M, respectively, where the binding of LTB4 to high-affinity receptors predominates. A rank order of potency of LTB4 greater than 5(S),12(S)-6-trans-LTB4 greater than 12(S)-LTB4 was established for the elicitation of increases in [Ca+2]in, which reflects the binding of the isomers to low-affinity receptors. PMN leukocytes were preincubated with 10(-8) M LTB4 to induce chemotactic deactivation, which eliminates the expression of high-affinity receptors without altering the expression of the low-affinity receptors for LTB4. LTB4 elicited an increase in [Ca+2]in in the deactivated PMN leukocytes with an EC50 of 3 X 10(-8) M, which is similar to the Kd for LTB4 binding to the low-affinity receptors. Two lines of cultured human leukemic cells, IM-9 and HL-60, did not bind LTB4 specifically and did not show any change in [Ca+2]in upon the addition of 3 X 10(-8) M LTB4. The HL-60 human promyelocytic leukemia cell line was induced to differentiate in 1% dimethyl sulfoxide to leukocytes with more mature myelocytic characteristics. Differentiated HL-60 cells expressed an average of 54,000 low-affinity receptors for LTB4 per cell with an average dissociation constant of 7.3 X 10(-8) M and concurrently developed the capacity to respond to LTB4 with an increase in [Ca+2]in. The binding of LTB4 to either high-affinity or low-affinity receptors appears to be sufficient to initiate an increase in [Ca+2]in in human PMN leukocytes and differentiated HL-60 cells. The specificity of LTB4 receptors in transducing maximum increases in [Ca+2]in is determined by the subset of receptors that predominate as a result of the concentration of LTB4 and the state of the responding cells.     

Specific binding of leukotriene B4 to receptors on human polymorphonuclear leukocytes

Leukotriene B4 (5(S),12(R)-di-hydroxy-eicosa-6,14-cis-8,10-trans-tetraenoic acid [LTB4]) is a product of the 5-lipoxygenation of arachidonic acid, which elicits human PMN leukocyte chemotactic responses in vitro that are 50% of the maximal level at concentrations of 3 X 10(-9) M to 10(-8) M and are maximal at 2 X 10(-8) M to 10(-7) M. The specific binding of highly purified [3H]LTB4 to human PMN leukocytes was assessed both by extracting the unbound and weakly bound [3H]LTB4 with acetone at -78 degrees C and by centrifuging the PMN leukocytes through cushions of phthalate oil to separate the unbound from bound [3H]LTB4. The levels of total binding of [3H]LTB4 and of nonspecific binding of [3H]LTB4, in the presence of a 1500-fold molar excess of nonradioactive LTB4, were approximately two times higher with the phthalate oil method. Scatchard plots of the concentration dependence of the specific binding (total - nonspecific binding) of [3H]LTB4 to PMN leukocytes were linear for the acetone extraction and phthalate oil methods and revealed dissociation constants of 10.8 X 10(-9) M and 13.9 X 10(-9) M, respectively, and mean of 2.6 X 10(4) and 4.0 X 10(4) receptors per PMN leukocyte. The 5(S),12(S)-all-trans-di-HETE analog of LTB4 and 5-HETE competitively inhibited by 50% the binding of [3H]LTB4 to PMN leukocytes at respective concentrations that evoked half-maximal chemotactic responses, whereas neither N-formyl-methionyl-leucyl-phenylalanine nor chemotactic fragments of C5 inhibited the binding. Human erythrocytes exhibited no specific binding sites for [3H]LTB4. Human PMN leukocytes possess a subset of receptors for LTB4 that are distinct from those specific for peptide chemotactic factors.