A transient rise in intracellular free calcium is not a sufficient stimulus for respiratory burst activation in human polymorphonuclear leukocytes

Phenanthrene decreases neutrophil function by disrupting intracellular redox balance

The aim of the present work was to evaluate whether the treatment of human neutrophils with phenanthrene (PHN) can alter the phagocytic and microbicidal capacity of these cells by causing a disruption in redox balance. Peripheral neutrophils from healthy subjects were treated for up to 24 h with increasing concentrations of phenanthrene. Phagocytic/microbicidal activities, antioxidant enzymes, oxidative lesions (thiobarbituric acid-reactive substances and protein thiol and carbonyl groups) and redox signaling compounds (intracellular Ca(2+), superoxide, hydrogen peroxide and nitric oxide) were monitored on neutrophils exposed to 10 microg PHN ml(-1). Cell viability decreased abruptly at PHN concentrations above 10 microg ml(-1) (LC50 = 20.86 +/- 0.51 microg ml(-1) and p-sigmoidal slope = 19.88 +/- 10.11). Phagocytic and microbicidal capacities were decreased by 60 and 82%, respectively. Substantial increases in total-/Mn-SOD, catalase, glutathione peroxidase and glutathione reductase activities (by 61, 15, 87, 245 and 70%, respectively) matched the oxidative injury obtained in TBARS (2.5-fold higher) and protein thiol (54% lower). Diminished productions of superoxide by 18% and hydrogen peroxide by 29% were observed in association to exacerbated calcium (27%) and nitric oxide (63%) levels. The data indicate that phenanthrene might be associated with substantial reduction in human neutrophil functions due to severe intracellular redox imbalances.

The effect of platelet-activating factor on the generation of superoxide anion in human eosinophils and neutrophils

The precise role of platelet-activating factor (PAF) in asthma has yet to be established. Nonetheless, the potential relationship between PAF and asthma appears to include the eosinophil (EOS) as an important link. Thus, to evaluate the effect of PAF on leukocyte-dependent inflammation, purified populations of human blood EOSs and neutrophils were isolated from the same subject. The two granulocyte populations were then incubated with PAF, and superoxide anion (O2-) generation was measured by reduction of cytochrome c in a microassay system. Both granulocyte cell types generated O2- when they were incubated with PAF. However, the generation of O2- was 3.4 times greater with EOSs (9.8 +/- 1.5 nmole of cytochrome c reduced per 5 x 10(5) cells) than neutrophils (2.9 +/- 0.4 nmole of cytochrome c reduced per 5 x 10(5) cells; p less than 0.0001). When the effect of PAF on [Ca++]i was measured with the fluorescent label, Indo-1, PAF caused similar increases in cellular fluorescence in both neutrophils and EOSs, but the increase in [Ca++]i of neutrophils occurred with lower concentrations of PAF. Furthermore, when similar experiments were conducted in the presence of an extracellular calcium chelator, ethylene glycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraacetic acid, there was partial suppression in both the cellular fluorescence and O2- generation to PAF; this suggests that full expression of EOS generation of O2- by PAF requires both intracellular mobilization and a transmembrane influx of Ca++. Our data indicate that PAF can stimulate leukocyte O2- generation, but this response is greater in the EOS than the neutrophil. Therefore, our findings support the observation that the EOS is more responsive to PAF activation than other granulocytes and that this difference may contribute to participation of PAF in asthma.

Inhibitory effects of phenyltin compounds on stimulus-induced changes in cytosolic free calcium and plasma membrane potential of human neutrophils

To clarify the inhibitory mechanisms by triphenyltin chloride (TPTCl) on superoxide anion formation in neutrophils, the effects of phenyltin compounds [TPTCl, diphenyltin dichloride (DPTCl2) and phenyltin trichloride (MPTCl3) on the increase of cytosolic free calcium and the changes in membrane potential in neutrophils stimulated by n-formyl-methionyl-leucyl-phenylalanine (FMLP) were examined. TPTCl and DPTCl2 concentration dependently inhibited the increase of fluorescence intensity of the dye 3,3'-dipropyl-thiodicarbocyanine iodide [diS-C3-(5)] (membrane potential probe) in neutrophils induced by 0.1 microM FMLP in the presence or absence of extracellular calcium (1.26 mM). TPTCl had a greater inhibitory effect on FMLP-mediated membrane potential change than that of DPTCl2. In the presence of extracellular calcium, TPTCl and DPTCl2 increased intracellular free calcium [( Ca2+]i) of unstimulated fura-2-loaded neutrophils at concentrations from 1.0 to 10 microM TPTCl and from 2.5 to 10 microM DPTCl2. TPTCl and DPTCl2 also increased slightly, in the absence of extracellular calcium, [Ca2+]i without stimulation of FMLP in neutrophils. However, TPTCl and DPTCl2 significantly inhibited the rise of [Ca2+]i in neutrophils stimulated by FMLP at concentrations from 2.5 microM to 10 microM TPTCl and at a concentration of 10 microM DPTCl2 in the absence of extracellular calcium. TPTCl and DPTCl2 significantly inhibited the superoxide anion production by FMLP at concentrations over 2.5 microM in the presence of extracellular calcium. In the absence of extracellular calcium, TPTCl and DPTCl2 also inhibited the superoxide anion production by FMLP at concentrations over 1.5 microM TPTCl and over 5.0 microM DPTCl2.(ABSTRACT TRUNCATED AT 250 WORDS)

Roles of Ca2+ in human neutrophil responses to receptor agonists

Previous studies have concluded that cytosolic Ca2+ [( Ca2+]i) transients are essential for neutrophils (PMN) to degranulate and make superoxide anion when challenged with the receptor agonists N-formyl-methionyl-leucyl-phenylalanine, platelet-activating factor and leukotriene B4. This view is based on the profound unresponsiveness of PMN that have their [Ca2+]i fixed at resting levels by removing storage Ca2+ and loading the cells with greater than or equal to 20 microM of a Ca2+ chelator, quin2 AM. We too observed this unresponsive state in PMN loaded with 10-32 microM-quin2 AM, fura-2 AM or 1,2-bis-(2-aminophenoxy) ethane-NNN'N'-tetra-acetic acid (BAPTA). When loaded with less than or equal to 1 microM fura-2 AM, however, Ca(2+)-depleted PMN failed to alter [Ca2+]i appreciably, yet still had substantial degranulation and superoxide-anion-generating responses to the receptor agonists. Function thus did not require [Ca2+]i transients. Moreover, Ca(2+)-depleted PMN had 20-35% decreases in receptor numbers for each of the three agonists, and chelator loading of these cells decreased receptor availability by 30-50%. All receptor losses were reversed by incubating PMN with Ca2+ at 37 degrees C, but not at 4 degrees C, and agonist binding at 4 degrees C was not influenced by the presence or absence of extracellular Ca2+. Ca2+ thus caused PMN to up-regulate their agonist receptors at 37 degrees C, and the effect persisted at 4 degrees C regardless of ambient Ca2+. We conclude that Ca2+ acts in at least three ways to regulate responses to receptor agonists. First, some pool of (probably cellular) Ca2+ maintains receptor expression. Second, [Ca2+]i transients potentiate, but are not required for, function. The [Ca2+]i pool may or may not be the same as that influencing receptors. Finally, another pool(s) of Ca2+ signals or permits responses. This last pool, rather than [Ca2+]i transients, appears essential for the bioactions of standard Ca(2+)-mobilizing stimuli.

The effect of 20-trifluoromethyl leukotriene B4 on neutrophil functional responses

20-trifluoromethyl-leukotriene B4 (20CF3-LTB4) is a stable derivative of leukotriene B4 (LTB4) that is not subjected to omega-oxidation to less active metabolites. 20CF3-LTB4 was as potent as LTB4 as a chemotactic, adhesion-promoting and aggregatory agent for human neutrophils, but had only 11 +/- 3% of the ability to induce an oxidative response. Nonetheless, both compounds were equally efficient in order to confer a rapid and monophasic increment of the concentration of cytosolic calcium. The kinetics of the calcium, aggregatory and chemiluminescent responses to 20CF3-LTB4 were similar to that of LTB4. These findings suggest that the insertion of the trifluoromethyl group into the LTB4 molecule causes a shift of the biological activity profile, suggesting that 20CF3-LTB4 binds mainly to high affinity LTB4 receptors. Moreover, the similarity of the response kinetics of LTB4 and 20CF3-LTB4 suggests that the mechanism for the rapid and transient responses of LTB4 is not due to its omega-oxidation.

Functional, physical, and ultrastructural localization of CD15 antigens to the human polymorphonuclear leukocyte secondary granule

A murine monoclonal IgM antibody, M3, which interferes with both polymorphonuclear leukocyte (PMN) phagocytosis and bactericidal activity, was used to examine the subcellular location of antigens bearing 3-fucosyllactosamine (CD15 antigens) within this cell type. Percoll gradient-separated secondary granule fractions were rich in CD15 antigens, with at least seven antigens recognizable in SDS-PAGE/electroblot studies. Sonication/sedimentation experiments using secondary granule fractions showed that both soluble and sedimentable CD15 antigens were present. Exposure of purified PMN to the secondary granule secretagogue phorbol myristate acetate caused extracellular release of two or three CD15 antigens, which could be purified by immunoprecipitation using antibody M3. Triton X-114 phase-partition experiments showed that secondary granule fraction CD15 antigens could be partitioned into hydrophilic (aqueous phase) and hydrophobic (detergent phase) antigens, suggesting that several of these antigens were integral secondary granule membrane components. Ultrastructurally, PMN intracellular granules showed two patterns of CD15 expression, localization over both granule matrix/granule membrane and localization to only granule membrane. Colocalization studies showed that lactoferrin and CD15 antigens were both present in a subset of intracellular granules, confirming a secondary granule location for these antigens.

Interactions between alkylglycerols and human neutrophil granulocytes

We evaluated whether various alkylglycerols would initiate a functional response of human neutrophils or modify responses induced by a formyl peptide (fMLP) in vitro. We found that platelet activating factor (PAF) was the most potent with regard to the ability to produce an oxidative response (assessed by cytochrome c reduction and/or chemiluminescence), followed by ET-16-OCH3. Lyso-PAF, ET-18-OCH3, batyl- and chimyl alcohols exhibited only a weak activity. PAF was also the most efficient lipid conferring a rise of intracellular calcium concentrations ([Ca2+]i). ET-16-OCH3, ET-18-OCH3 and lysoPAF were less potent, although maximal [Ca2+]i levels were similar to that of 0.1 mumol/l fMLP. The kinetics of the calcium responses were highly specific for each ether lipid. When neutrophils had been treated with PAF or ET-18-OCH3 and were subsequently stimulated by fMLP, enhancement of the oxidative response was noted. Thus, this study shows that there was an association between the ability of an alkylglycerol to initiate oxidative and calcium responses, indicating strict structure-activity relationships for these lipids.

Independence of neutrophil respiratory burst oxidant generation from the early cytosolic calcium response after stimulation with unopsonized Candida albicans hyphae

We previously noted differences between neutrophil responses to unopsonized Candida albicans hyphae and responses to other particulate stimuli such as opsonized hyphae or zymosan; these differences include delayed rises in cytosolic calcium [( Ca2+]i), 1,4,5-inositol trisphosphate, and superoxide release and the total absence of early membrane depolarization. Respiratory burst stimulation is required for killing of C. albicans hyphae. Since an early rise in [Ca2+]i may act as a second messenger for burst activation by most agonists, we chelated (Ca2+)i and extracellular Ca2+ [( Ca2+)e] to compare requirements for superoxide responses to hyphae and other stimuli. Intracellular chelation, which ablated early [Ca2+]i rises, eliminated the fMet-Leu-Phe-induced respiratory burst and profoundly reduced that response to opsonized zymosan (by 96.7%), but chelation of both (Ca2+)i and (Ca2+)e only partially inhibited responses to opsonized and unopsonized hyphae (60.5 and 23.3%, respectively; the latter exceeded absolute responses evoked by opsonized zymosan, a 12-fold-more-potent stimulus for unchelated cells). Simultaneous (Ca2+)i and (Ca2+)e chelation further decreased superoxide responses to opsonized zymosan and hyphae (99.4 and 90.4%, respectively) but not to unopsonized hyphae (26.7% inhibition). Though both ingestible (zymosan) and uningestible (hyphae) opsonized particulate stimuli elicited reduced but significant respiratory bursts without early [Ca2+]i rises, the greater superoxide responses and sensitivity to chelation with opsonized zymosan suggest important differences in initiation and/or regulation of responses to these particulate stimuli. In contrast, the respiratory burst elicited by unopsonized hyphae appeared largely Ca2+ independent. If different events mediate neutrophil activation by opsonized and unopsonized hyphae, candidacidal activity in vivo may vary under divergent conditions with specific localized sites of infection.

Role of CD2 cross-linking in cytoplasmic calcium responses and T cell activation

The relationship between the increase of intracellular free Ca2+ concentration ([Ca2+]i) in resting T cells after stimulation with monoclonal antibody (mAb) to CD2 (E rosette receptor) and the subsequent proliferation response was investigated. Although the combination of 9.6 plus 9-1 mAb to CD2 was both mitogenic and induced an increase in [Ca2+]i, cross-linking of an individual CD2 mAb on the cell surface induced an increase in [Ca2+]i without directly stimulating T cell proliferation. The [Ca2+]i response from cross-linking an individual mAb was not epitope dependent, since 21 of 21 mAb to CD2 were effective when cross-linked with a polyclonal goat anti-mouse Ig second step. The kinetics of calcium mobilization was highly dependent upon the procedure for cross-linking, since the binding of biotin-conjugated 9.6 mAb followed by avidin gave a large and rapid response, whereas cross-linking of 9.6 with an anti-kappa mAb, 187.1, caused a minimal response, and the cross-linking of 9.6 followed by a polyclonal goat anti-mouse Ig gave an intermediate response. In addition, ligation of CD2 by rosetting with sheep red blood cells alone was sufficient to cause increased [Ca2+]i. In functional studies only the procedures associated with minimal CD2 cross-linking induced proliferation of resting T cells in combination with interleukin (IL)2. The proliferation also required IL 1 or accessory cells. Cross-linking 9.6 on the cell surface also enhanced proliferation in the presence of phorbol myristate acetate or a CD28 mAb, 9.3, under conditions that were accessory cell independent. In contrast to the proliferation following stimulation with 9.6 plus 9-1, the combination of 9.6 plus 9-1 F(ab')2 fragments lost mitogenic activity. The 9.6 plus 9-1 F(ab')2 combination was similar to 9.6 cross-linking in that either could induce responsiveness to recombinant IL2 or CD28 mAb 9.3. The combination of 9.6 plus 9-1 F(ab')2 fragments was still able to increase [Ca2+]i in T cells with slow kinetics. Together these results suggest that the binding of mAb to CD2 under conditions that cause a slow rather than a rapid increase in [Ca2+]i is associated with T cell activation. Furthermore, they suggest that in studies of T cell activation, sheep erythrocyte rosette formation should not be used to isolate T cells since rosetting may effect [Ca2+]i.

Clostridium difficile toxin A stimulates intracellular calcium release and chemotactic response in human granulocytes

Clostridium difficile, a common enteric pathogen, mediates tissue damage and intestinal fluid secretion by release of two protein exotoxins: toxin A, an enterotoxin, and toxin B, a cytotoxin. Because toxin A elicits an intense inflammatory reaction in vivo, we studied the effects of highly purified C. difficile toxins on activation of human granulocytes. Toxin A at concentrations of 10(-7) to 10(-6) M, but not toxin B, elicited a significant chemotactic and chemokinetic response by granulocytes that was comparable with that induced by the chemotactic factor N-FMLP (10(-7) M). Neither toxin stimulated release of superoxide anion from granulocytes. Toxin A produced a rapid, transient rise in cytosolic [Ca2+]i, as measured by quin 2 fluorescence. Pertussis toxin and depletion of intra- and extracellular calcium blocked the toxin A effect on cytosolic [Ca2+]i. These findings suggest that the inflammatory effects of C. difficile toxin A in the intestine may be related to its ability to mobilize intracellular Ca2+ and elicit a chemotactic response by granulocytes.

The role of transmembrane cationic gradients in immune complex stimulation of human polymorphonuclear leukocytes

The role of monovalent cationic gradients in human polymorphonuclear leukocyte (PMNL) stimulation was investigated by monitoring immune complex-stimulated transmembrane depolarization and superoxide production, events which accompany--and have been used as indicators of --PMNL activation. Abolishing only the Na+ gradient by substitution of choline for extracellular Na+ did not affect the resting membrane potential but reduced the rate of stimulus-induced transmembrane depolarization to 50% of control. In contrast, collapsing both Na+ and K+ gradients by suspension in K+ buffer (high K-PRK) depolarized the cells and reduced the stimulus-induced rate of depolarization to 11% of control. Pretreatment of cells suspended in Na+ buffers with 5-(N,N-dimethyl)amiloride hydrochloride (DMA) or with valinomycin reduced by one-half the rate of immune complex induced membrane depolarization. Conversely, in the absence of either or of both Na+ or K+ gradients, or in the presence of valinomycin, immune complex elicited an enhanced rate of superoxide production. However, PMNL prepared via NH4Cl (NH4Cl-PMNL) instead of H2O (H2O-PMNL) lysis of residual red blood cells exhibited an absolute requirement for an intact Na+ gradient in cell stimulation. The present results thus demonstrate that: 1) both Na+ and K+ gradients participate equally in the membrane depolarization elicited by immune complex; 2) neither a Na+ or a K+ gradient is required for immune complex activation, or for activity of the respiratory burst; and 3) an artifactual requirement for an intact Na+ gradient occurs in neutrophils prepared by the NH4Cl lysis technique.

The superoxide-forming enzymatic system of phagocytes

The formation of oxygen-derived free radicals by the phagocytes (neutrophils, eosinophils, monocytes and macrophages) is catalysed by a membrane-bound NADPH oxidase which is dormant in resting cells and becomes activated during phagocytosis or following interaction of the cells with suitable soluble stimulants. This enzyme is under investigation in many laboratories but its molecular structure remains to be clarified. Possible components such as flavoproteins, cytochrome b558, and quinones have been proposed on the basis of enzyme purification studies, effects of inhibitors, kinetic properties and analysis of genetic defects of the oxidase. An extensive discussion of the evidence for the participation of these constituents is reported. On the basis of the available information on the structure and the catalytic properties of the NADPH oxidase, a series of possible models of the electron-transport chain from NADPH to O2 is presented. Finally, the triggering mechanism of the respiratory burst is discussed, with particular reference to the stimulus-response coupling and the final modification(s) of the oxidase (phosphorylation, assembly, change of lipid environment, etc.) which are involved in its activation.

Lack of correlation between calcium mobilization and respiratory burst activation induced by chemotactic factors in rabbit polymorphonuclear leukocytes

Low concentrations of FMLP, partially purified rabbit C5a, leukotriene B4 and platelet activating factor induced a rapid rise of intracellular free Ca2+ in rabbit polymorphonuclear leukocytes. However, the four factors differed markedly in their ability to activate the respiratory burst. The peptides FMLP and C5a induced a single, strong chemiluminescence response whereas the lipids leukotriene B4 and platelet activating factor induced a markedly less intense response with a two-peak profile. Respiratory burst activation by the peptides was dependent on extracellular Ca2+ whereas the lipids required both Mg2+ and Ca2+. The results indicate that mobilization of intracellular Ca2+ is insufficient by itself to induce respiratory burst activation and that the intracellular pathways leading to activation differ depending on the nature of the stimulus.