Double tether extraction from human neutrophils and its comparison with CD4+ T-lymphocytes

The initial arrest and subsequent rolling of a leukocyte on the vascular endothelium is believed to be facilitated by the extraction of tethers, which are narrow membranous tubes drawn from the leukocyte. Although single tether extraction from neutrophils has been studied thoroughly, the relationship between the tether force (F) and tether-growth velocity (U(t)) is still unknown for double tethers drawn from neutrophils. In this study, we have determined this relationship with the micropipette-aspiration technique. As a comparison, tether extraction from CD4+ T-lymphocytes was also studied. The threshold force and effective viscosity for single tether extraction from passive CD4+ T-lymphocytes were found to be 46 pN and 1.55 pN x s/microm, respectively. These values were modulated by stimulation with phorbol myristate acetate (PMA), but not interleukin-8 (IL-8). More importantly, for both types of leukocyte, the threshold force and effective viscosity for double tether extraction are about twice as large as those corresponding to single tether extraction. Neither IL-8 nor PMA stimulation had any effect on this correlation. These results indicate that double tethers are highly localized on cellular surfaces and independent of each other during the rolling process.     

Signaling pathways involved in IL-8-dependent activation of adhesion through Mac-1

In human neutrophils, IL-8 induces chemotaxis, the respiratory burst, and granule release, and enhances cellular adhesion, a beta(2) integrin-dependent event. IL-8 stimulates neutrophil adhesion to purified fibrinogen in a Mac-1-dependent manner. Mitogen-activated protein kinase (MAPK) activation was detected in human neutrophil lysates after treatment with IL-8 and PMA, but not the activating mAb CBR LFA 1/2. IL-8-stimulated neutrophil adhesion to fibrinogen was blocked 50% by the MAPK/extracellular signal-related kinase-activating enzyme inhibitor PD098059. Adhesion was blocked approximately 75% by inhibition of the phosphatidylinositol-3 kinase (PI3K) pathway with LY294002, supporting that activation of both MAPK and PI3K may play a role in IL-8-dependent inside-out signals that activate Mac-1. Activation of MAPK was inhibited in IL-8-stimulated cells in the presence of PI3K inhibitors LY294002 or wortmannin, supporting a model in which PI3K is upstream of MAPK. IL-8-stimulated neutrophil adhesion was inhibited 50% by bisindolylmaleimide-I, implicating protein kinase C (PKC) in the intracellular signaling from the IL-8R to Mac-1. A 74-kDa molecular mass species was detected by an activation-specific Ab to PKC when cells were stimulated with PMA or IL-8, but not a beta(2)-activating Ab. Inhibition of either MAPK or PKC resulted in partial inhibition of IL-8-stimulated polymorphonuclear neutrophil adhesion, and treatment with both inhibitors simultaneously completely abolished IL-8-stimulated adhesion to ligand. Inhibition of PI3K blocked MAPK activation, but not PKC activation, suggesting a branch point that precedes PI3K activation. These data suggest that both MAPK and PKC are activated in response to IL-8 stimulation, and that these may represent independent pathways for beta(2) integrin activation in neutrophils.     

Neutrophil dysfunction in guanosine 3',5'-cyclic monophosphate-dependent protein kinase I-deficient mice

The regulation of neutrophil functions by Type I cGMP-dependent protein kinase (cGKI) was investigated in wild-type (WT) and cGKI-deficient (cGKI-/-) mice. We demonstrate that murine neutrophils expressed cGKIalpha. Similar to the regulation of Ca2+ by cGKI in other cells, there was a cGMP-dependent decrease in Ca2+ transients in response to C5a in WT, but not cGKI-/- bone marrow neutrophils. In vitro chemotaxis of bone marrow neutrophils to C5a or IL-8 was significantly greater in cGKI-/- than in WT. Enhanced chemotaxis was also observed with cGKI-/- peritoneal exudate neutrophils (PE-N). In vivo chemotaxis with an arachidonic acid-induced inflammatory ear model revealed an increase in both ear weight and myeloperoxidase (MPO) activity in ear punches of cGKI-/- vs WT mice. These changes were attributable to enhanced vascular permeability and increased neutrophil infiltration. The total extractable content of MPO, but not lysozyme, was significantly greater in cGKI-/- than in WT PE-N. Furthermore, the percentage of MPO released in response to fMLP from cGKI-/- (69%) was greater than that from WT PE-N (36%). PMA failed to induce MPO release from PE-N of either genotype. In contrast, fMLP and PMA released equivalent amounts of lysozyme from PE-N. However, the percentage released was less in cGKI-/- (approximately 60%) than in WT (approximately 90%) PE-N. Superoxide release (maximum velocity) revealed no genotype differences in responses to PMA or fMLP stimulation. In summary, these results show that cGKIalpha down-regulates Ca2+ transients and chemotaxis in murine neutrophils. The regulatory influences of cGKIalpha on the secretagogue responses are complex, depending on the granule subtype.     

Induction of CD69 activation molecule on human neutrophils by GM-CSF,IFN-gamma,and IFN-alpha

The CD69 glycoprotein is an early activation antigen of T and B lymphocytes but it expression is induced in vitro on cells of most hematopoietic lineages, including neutrophils after stimulation with PMA or fMLP. In this study, we investigated whether CD69 expression on human neutrophils could be modulated by inflammatory or anti-inflammatory cytokines (IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12, IL-18, G-CSF, GM-CSF, TNF-alpha, TGF-beta, IFN-alpha, IFN-gamma). Resting neutrophils from healthy subjects did not express CD69 on the cell surface; moreover, a preformed intracellular pool of CD69 was not evident in these cells. CD69 was barely detectable on these cells after overnight incubation in medium while overnight incubation with GM-CSF, IFN-gamma or IFN-alpha significantly induced CD69 expression on neutrophils with GM-CSF appearing to be the most potent inducer. This induction was dependent on a new protein synthesis as it was significantly inhibited by cycloheximide (about 50% inhibition). CD69 cross-linking on GM-CSF-primed neutrophils sinergized with LPS and increased TNF-alpha production and secretion suggesting a role for CD69-positive neutrophils in the pathogenesis and maintenance of different inflammatory diseases.     

Host defense function in neutrophils from the American bison (Bison bison)

Selected host defense functions of neutrophils isolated from American bison (Bison bison) were characterized and compared with those of cattle (Bos taurus). Bison neutrophils had a robust chemotactic response to both IL-8 and LTB(4), with maximal responses occurring at 10(-7) M (IL-8) and 10(-8) M (LTB(4)). The magnitude of the chemotactic response to IL-8 was similar in bison and bovine neutrophils (except at 10(-7) M IL-8, where bison had a stronger response). In response to LTB(4), bison neutrophils had a much stronger chemotaxis at both 10(-8) and 10(-7) M than did bovine cells. Production of reactive oxygen species (ROS) in response to phorbol myristate acetate (PMA) and opsonized zymosan (OpZ) was similar between bison and bovine neutrophils. However, the production of ROS in bison neutrophils stimulated with OpZ was primarily intracellular, while extracellular release of ROS was evident in bovine neutrophils stimulated with OpZ. Like bovine neutrophils, bison neutrophils did not generate a respiratory burst in response to fMLF. Granules prepared from bison neutrophils had potent direct killing action on the Gram-negative bacteria Escherichia coli but failed to kill the Gram-positive bacteria Staphylococcus aureus and, at intermediate doses, actually had a permissive effect for this bacteria. Thus, bison neutrophils have potent host defense capabilities similar in quality to those of bovine neutrophils; however, unique differences are present, which may allow bison neutrophils to respond to the distinct immunological challenges that bison encounter.     

1,2-dioctanoyl-sn-glycerol can stimulate neutrophils by different mechanisms. Evidence for a pathway that does not involve phosphorylation of the 47-kDa protein

Neutrophils treated with 1,2-dioctanoyl-sn-glycerol (DiC8) are known to release large quantities of superoxide (O2-) and to exhibit an intense phosphorylation of two proteins with molecular masses of approximately 47 and 49 kDa. In this paper, we report that O2- release from guinea pig cells stimulated with a near optimal amount of DiC8 (2.0 microM) is markedly inhibited (greater than or equal to 70%) by antagonists of protein kinase C (i.e. 150 nM staurosporine; 200 microM 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7], whereas that from cells stimulated with an optimal amount of DiC8 (7.8 microM) is not (approximately 25% inhibition). However, staurosporine (150 nM) effectively reduced the level of phosphorylation of the 47- and the 49-kDa proteins to that observed in unstimulated cells when either amount of DiC8 (i.e. 2.0 or 7.8 microM) was utilized. Thus, neutrophils stimulated with 7.8 microM DiC8 in the presence of staurosporine release large quantities of O2- without an enhanced phosphorylation of the 47- and the 49-kDa proteins. In contrast, these antagonists of protein kinase C effectively blocked O2- release from neutrophils stimulated with an optimal amount of phorbol 12-myristate 13-acetate (PMA), and the percentage of inhibition was not affected by increasing the concentration of PMA 160-fold. These data show that DiC8 and PMA, both activators of protein kinase C, can have distinct effects on O2- release by neutrophils. Moreover, they suggest that DiC8 (or a metabolite) under certain circumstances may function in a stimulatory pathway for O2- release that is independent of protein kinase C. Differences in the morphology of neutrophils stimulated with PMA and DiC8 are presented. Ancillary data on human neutrophils are also provided.     

Generation of biologically active C-reactive protein peptides by a neutral protease on the membrane of phorbol myristate acetate-stimulated neutrophils

The association of human C-reactive protein (CRP) with nonstimulated and PMA-stimulated human neutrophils and the concomitant degradation of CRP (monitored by TCA-soluble peptides and SDS-PAGE analysis) has been studied. Maximum association of 125I-labeled CRP with neutrophils and 125I-labeled CRP degradation during association with these cells was achieved by stimulating the neutrophils with PMA at 10 ng/ml; a concentration in which azurophil granule release was not significant. For PMA-stimulated neutrophils, the association of 125I-labeled CRP was 1.8 times higher and PMA-stimulated neutrophil-mediated degradation of the ligand was three times faster than that for nonstimulated cells. The neutrophil-associated 125I-labeled CRP in the absence and presence of PMA proved on SDS-PAGE analysis to be approximately 50% degraded. There was a positive correlation between the extent of CRP degradation and the association of 125I-labeled CRP with neutrophils. In addition to generation of neutrophil associated CRP intermediates, small soluble CRP peptides were generated during association of CRP with neutrophils. These peptides inhibited superoxide production from opsonized zymosan-activated neutrophils by approximately 40% at 10 micrograms/ml. 125I-labeled CRP degradation mediated by nonstimulated neutrophils, and neutrophil-conditioned medium (from both non-stimulated and PMA-stimulated cells) was inhibitable by alpha 1-antitrypsin and approximately seven times less at 1 h than that occurring during 125I-labeled CRP-association with PMA-stimulated neutrophils. The degradation of 125I-labeled CRP mediated by PMA-stimulated neutrophils was not fully inhibitable by alpha 1-antitrypsin. The data point to the involvement of a membrane-associated serine protease, which is maximally activated by PMA, in the degradation of 125I-labeled CRP during association with neutrophils. Our results indicate that at an inflammatory site CRP-derived peptides can be produced that inhibit the action of activated neutrophils.     

Characterization of a receptor for human monocyte-derived neutrophil chemotactic factor/interleukin-8

Monocyte-derived neutrophil chemotactic factor/interleukin-8 (MDNCF/IL-8) is an 8,000-dalton protein produced by monocytes which exhibits activity as a chemoattractant for neutrophils with maximal activity achieved at a concentration of 50 ng/ml. This polypeptide has been iodinated by chloramine-T methodology (350 Ci/mM), and specific receptors for MDNCF/IL-8 have been detected on human neutrophils, U937 cells, THP-1 cells, and dimethyl sulfoxide-differentiated HL-60 cells. The binding of MDNCF/IL-8 to human neutrophils is not inhibited by interleukin-1 alpha, tumor necrosis factor-alpha, insulin, or epidermal growth factor. In addition, chemoattractants such as C5a, fMet-Leu-Phe, leukotriene B4, and platelet-activating factor fail to inhibit binding, suggesting that MDNCF/IL-8 utilizes a unique receptor. The receptor for MDNCF/IL-8 is apparently glycosylated since ligand binding is inhibited by the presence of wheat germ agglutinin, a lectin with a binding specificity for N-acetylglucosamine and neuraminic acid. Steady state binding experiments indicate Kd values of 4 and 0.5 nM and receptor numbers of 75,000 and 7,400 for human neutrophils and differentiated HL-60 cells, respectively. 125I-MDNCF/IL-8 bound to human neutrophils is rapidly internalized and subsequently released from cells as trichloroacetic acid-soluble radioactivity. Affinity labeling experiments suggest that the human neutrophil MDNCF/IL-8 receptor exhibits a mass of approximately 58,000 daltons.     

Enhanced Neutrophil Stimulation by Phorbol Ester Encapsulated in pH-Sensitive Liposomes

Abstract

Phorbol 12-myristate 13-acetate (PMA) and arachidonic acid (AA) are both hydrophobic stimulators for superoxide release by guinea pig neutrophils. However AA incorporated into liposomes is no longer an effective stimulator. In contrast, PMA incorporated into liposomes is more effective in neutrophil stimulation than free PMA. the ED₅₀ of superoxide release was 3.1 × 10^?8M, and 4.0 × 10^?10 M for free PMA and liposomes composed of egg phosphatidylethanolamine (PE) /AA/ PMA (molar ratio 7:2:1), respectively. PMA incorporated into PE/AA liposomes could also shorten the lag period of superoxide release in a concentration-dependent fashion. the enhanced stimulation activity of PMA in liposomes was correlated with the enhanced liposome uptake by neutrophils, probably via phagocytosis. Weak bases and a proton ionophore inhibited superoxide release by cells stimulated with either free or liposomal PMA. these results suggested that free PMA attached to cell membranes might be endocytosed and stimulate the superoxide-generating systems via an endocytic compartment(s). Since liposomes effectively deliver the contents into the compartments, liposomal PMA may thus be a potent stimulator for neutrophils. This hypothesis is further supported by the observation that pH-sensitive liposomes, which are active in the acidic endocytic compartments, are more effective carriers for PMA than the conventional pH-insensitive liposomes.     

Characterization of two high affinity human interleukin-8 receptors.

Interleukin 8 (IL-8) and melanocyte growth-stimulatory activity/gro (MGSA) are structurally related proinflammatory cytokines that are chemoattractants and activators of neutrophils. Recently, cDNA clones encoding a high affinity IL-8 receptor (IL-8R-A) and a "low affinity" IL-8 receptor (IL-8R-B) have been isolated from human cDNA libraries. These two receptors have 77% amino acid identity and are members of the G protein-coupled superfamily of receptors with seven transmembrane domains. We have expressed these two receptors in mammalian cells and find that in this system both receptors bind IL-8 with high affinity (Kd approximately 2 nM). The receptor affinities differ for MGSA, however. IL-8R-A binds MGSA with low affinity (Kd approximately 450 nM); IL-8R-B binds MGSA with high affinity (Kd approximately 2 nM). The transfected cells respond to ligand binding with a transient increase in the intracellular Ca2+ concentration. A Ca2+ response is found for IL-8R-A following the binding of IL-8; no response is found for MGSA. A Ca2+ response for IL-8R-B follows the binding of both ligands. Blot hybridization with oligonucleotide probes specific for the two receptors shows that mRNA for both receptors is present in human neutrophils. Analysis of IL-8 and MGSA binding data on neutrophils as well as Ca2+ response and desensitization data shows that the presence of these two IL-8 receptors on the cell surface can account for the profile of these two ligands on neutrophils.     

Phorbol myristate acetate and the calcium ionophore A23187 synergistically induce release of LTB4 by human neutrophils: involvement of protein kinase C activation in regulation of the 5-lipoxygenase pathway

Phorbol myristate acetate (PMA), a tumor-promoting phorbol ester, and the calcium ionophore A23187 synergistically induced the noncytotoxic release of leukotriene B4 (LTB4) and other 5-lipoxygenase products of arachidonic acid metabolism from human neutrophils. Whereas neutrophils incubated with either A23187 (0.4 microM) or PMA (1.6 microM) alone failed to release any 5-lipoxygenase arachidonate products, neutrophils incubated with both stimuli together for 5 min at 37 degrees C released LTB4 as well as 20-COOH-LTB4, 20-OH-LTB4, 5-(S),12-(R)-6-trans-LTB4, 5-(S),12-(S)-6-trans-LTB4, and 5-hydroxyeicosatetraenoic acid, as determined by high pressure liquid chromatography. This synergistic response exhibited concentration dependence on both PMA and A23187. PMA induced 5-lipoxygenase product release at a concentration causing a half-maximal effect of approximately 5 nM in the presence of A23187 (0.4 microM). Competition binding experiments showed that PMA inhibited the specific binding of [3H]phorbol dibutyrate ([3H]PDBu) to intact neutrophils with a 50% inhibitory concentration (IC50) of approximately 8 nM. 1-oleoyl-2-acetyl-glycerol (OAG) also acted synergistically with A23187 to induce the release of 5-lipoxygenase products. 4 alpha-phorbol didecanoate (PDD), an inactive phorbol ester, did not affect the amount of lipoxygenase products released in response to A23187 or compete for specific [3H]PDBu binding. PMA and A23187 acted synergistically to increase arachidonate release from neutrophils prelabeled with [3H]arachidonic acid but did not affect the release of the cyclooxygenase product prostaglandin E2. Both PMA and OAG, but not PDD, induced the redistribution of protein kinase C activity from the cytosol to the membrane fraction of neutrophils, a characteristic of protein kinase C activation. Thus, activation of protein kinase C may play a physiologic role in releasing free arachidonate substrate from membrane phospholipids and/or in modulating 5-lipoxygenase activity in stimulated human neutrophils.     

Distinct cytokine production by lung and blood neutrophils from children with cystic fibrosis

Inflammation plays a critical role in lung disease progression in cystic fibrosis (CF). This inflammatory process is dominated by a neutrophil influx in the airways. To determine whether the accumulation of neutrophils in the airways of CF patients is associated with an altered function, we analyzed the capacity of neutrophils isolated from the lung compartment and the blood to release the major neutrophil pro- and anti-inflammatory cytokines IL-8 and IL-1-receptor antagonist (ra) spontaneously and in the presence of LPS. Comparison of cytokine production by blood neutrophils from CF patients and from control subjects showed significantly increased IL-8 and decreased IL-1ra release by CF neutrophils. Comparison of cytokine production by airway and blood neutrophils from CF patients also documented distinct profiles: the spontaneous release of IL-8 and IL-1ra by airway neutrophils was significantly higher than that from blood neutrophils. Culture in the presence of LPS failed to further enhance cytokine production. Analysis of the effect of dexamethasone confirmed the difference in the responsiveness of lung and blood neutrophils in CF. Used at a concentration effective in reducing IL-8 production by blood neutrophils, dexamethasone (10(-6) M) was unable to repress secretion of IL-8 by airway neutrophils. In addition, comparison of cytokine production by airway neutrophils from children with CF and children with dyskinetic cilia syndrome also documented distinct profiles of secretion. These results are consistent with a dysregulated cytokine production by lung and blood neutrophils in CF. They provide support to the hypothesis that not only the CF genotype but also the local environment may modify the functional properties of the neutrophils.     

Il-8((3-73))K11R is a high affinity agonist of the neutrophil CXCR1 and CXCR2

In studies aimed at developing a high affinity IL-8 antagonist, our first objective was to generate a high-affinity IL-8 analogue. We targeted amino acids within the receptor-binding domain and found that IL-8((3-73))K11R induced significantly more neutrophil beta-glucuronidase release than either IL-8 or the alternate analogues and, in chemotaxis assays, induced 2-3-fold greater neutrophil responses than IL-8. Furthermore, in competitive radio- or biotinylated-ligand binding assays, IL-8((3-73))K11R was more effective than IL-8, IL-8((3-73)), or its T12S, H13F, and K11R/T12S/H13F analogues in blocking IL-8 binding to neutrophils; 1.8 pmol IL-8((3-73))K11R inhibited by 50% the binding of approximately 20 pmol (125)I-IL-8 to neutrophils. Both IL-8 (a CXCR1/CXCR2 ligand) and the CXCR2-specific ligand GROalpha differentially inhibited binding of (125)I-IL-8((3-73))K11R to neutrophils, albeit weakly, suggesting that IL-8((3-73))K11R is a high affinity ligand for both the CXCR1 and CXCR2. Thus IL-8((3-73))K11R is an excellent candidate for further studies aimed at generating a high affinity IL-8 antagonist.     

Phorbol myristate acetate-induced release of granule enzymes from human neutrophils: inhibition by the calcium antagonist, 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride

Phorbol myristate acetate (PMA) stimulated the extracellular release of the granule-associated enzyme lysozyme from human neutrophils. The extrusion of lysozyme was not accompanied by the release of β-glucuronidase or the cytosol enzyme lactate dehydrogenase. A time dependent PMA-induced release of lysozyme occurred in the absence of extracellular calcium and when neutrophils were preincubated with EGTA. 8-(N,N-diethylamino)-octyl 3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an antagonist of intracellular calcium, caused a dose-dependent inhibition of lysozyme release from neutrophils exposed to PMA in a calcium-free medium. This effect of TMB-8 could be reversed by the addition of calcium to the extracellular medium. These studies indicate that TMB-8 represents a valuable pharmacologic tool used to define the dependence of a secretagogue such as PMA on intracellular as opposed to extracellular calcium.     

A comparative study of the neutrophil stimulatory activity in vitro and pro-inflammatory properties in vivo of 72 amino acid and 77 amino acid IL-8.

IL-8, a potent neutrophil-activating protein, can be produced by many cell types including monocytes, lymphocytes, fibroblasts, neutrophils, and endothelial cells. Depending on the cell source, the N-terminal amino acid sequence of IL-8 displays heterogeneity that has been shown to confer differences in its neutrophil stimulatory activity in vitro. Despite these observations the relative potency of different IL-8 molecules in vivo is unknown. To address this question we have investigated the biologic activity of the two predominant forms of IL-8, the 72 and the 77 amino acid proteins, in vitro and in vivo. In vitro, human rIL-8(72) and human rIL-8(77) dose dependently induced adherence of rabbit peritoneal neutrophils and human neutrophils to laminin-coated plates and elevated cytoplasmic levels of Ca2+ ([Ca2+]i) in fura-2 loaded neutrophils. In these in vitro assays human rIL-8(72) was more potent than human rIL-8(77) while inducing comparable responses to human rC5a. With respect to enhancing [Ca2+]i, neutrophils desensitized to human rIL-8(72) failed to respond to human rIL-8(77). However, neutrophils fully desensitized to human rIL-8(77) could exhibit a partial response to human rIL-8(72). Further, human rIL-8(72) was approximately 10-fold more effective than human rIL-8(77) in displacing human [125I]rIL-8(72) from rabbit peritoneal neutrophils in a receptor-binding assay. In vivo, intradermally administered human rIL-8(72) and human rIL-8(77) induced 111In-neutrophil accumulation and edema formation in rabbit skin. In contrast to the in vitro studies, the two forms of IL-8 gave identical responses in vivo although they were less potent than human rC5a. Our results demonstrate that, in vitro, human rIL-8(72) is more potent than human rIL-8(77) in stimulating neutrophils. It may be that IL-8)72) has a greater affinity and/or efficacy for the neutrophil IL-8 cell-surface receptors. One possibility for the observation that both forms of IL-8 are equipotent in inducing inflammatory responses in vivo is that the extended form is proteolytically cleaved to the more biologically active IL-8(72).     

Differentiation-associated expression of two functionally distinct classes of granulocyte-macrophage colony-stimulating factor receptors by human myeloid cells

Granulocyte-macrophage colony-stimulating factor (GM-CSF) activates a broad range of myeloid cells through binding to high affinity surface membrane receptors. The effects of this hematopoietin are dependent upon the differentiation status of the myeloid cell and range from proliferation of early myeloid progenitor cells to activation of neutrophil and monocyte function. In addition, many of the biological effects of GM-CSF are shared with interleukin-3 (IL-3), a distantly related lymphokine. In this study, we have characterized the GM-CSF receptor of myeloid cells at various stages of differentiation by comparing the binding characteristics and surface regulation of this receptor in early versus late myeloid cells. Scatchard analysis revealed a single class of high affinity receptors on normal neutrophils, monocytes, and myeloblasts from patients with acute myeloid leukemia. Neutrophils expressed significantly higher numbers of receptors, with an approximately 2-fold lower affinity, when compared with other myeloid cells. Two different patterns of GM-CSF receptor regulation and binding were observed. In the first pattern, the GM-CSF receptor of neutrophils was rapidly down-regulated by GM-CSF itself, by phorbol myristate acetate (PMA), and by the calcium ionophore A23187, and it was not competed for by IL-3 (class I receptor). In contrast to the neutrophil receptor, the GM-CSF receptor of the myeloblast demonstrated resistance to the down-regulatory effects of GM-CSF itself, PMA, and A23187, and it was completely competed for by IL-3 (class II receptor). In some cases of acute myeloid leukemia and monocytes, a mixed pattern of partial PMA responsiveness and partial competition by unlabeled IL-3 was observed, suggesting the coexpression of both class I and II receptors in these cells. In these cells, after down-regulation of the class I receptor by PMA, the remaining receptors were shown to be completely cross-competed for by IL-3, further supporting the hypothesis that these cells have a mixture of class I and II receptors. Chemical cross-linking of radiolabeled GM-CSF to myeloid cells revealed the labeling of three proteins (156, 126, and 82 kDa) which were identical in cells expressing either class I or II binding sites. These data show that there are differentiation-associated differences in the regulation of the GM-CSF receptor which may have important physiological consequences.     

Comparison of taurine chloramine and taurine bromamine effects on rheumatoid arthritis synoviocytes

Summary. Fibroblast-like synoviocytes (FLS) participate in rheumatoid arthritis (RA) chronic synovitis by producing pro-inflammatory cytokines (IL-6, IL-8), growth factors (VEGF) and other inflammatory mediators (PGE₂, NO). We have previously reported that Tau-Cl, generated by neutrophils, inhibits in vitro some of these pathogenic RA FLS functions. Taurine bromamine (Tau-Br) originates from eosinophils and neutrophils, and its immunoregulatory activities are poorly known. Therefore, we investigated the effects of Tau-Br on RA FLS functions and compared it to Tau-Cl anti-inflammatory action. When applied at noncytotoxic concentrations: (i) Tau-Br inhibited IL-6 and PGE₂ production with potency similar to Tau-Cl (IC₅₀ ≈ 250 μM), (ii) Tau-Br failed to affect VEGF and IL-8 synthesis, while Tau-Cl exerted inhibitory effect (IC₅₀ ≈ 400 μM), (iii) none of these compounds affected NO generation and iNOS expression. Thus, Tau-Cl is more effective than Tau-Br in normalization of pro-inflammatory RA FLS functions.     

Zymosan-activated plasma causes prolonged decreases in PMN superoxide release in sheep

It is well established that activation of neutrophils within the pulmonary circulation produces acute lung injury in which adherence of neutrophils to endothelial cells is an obligatory step in the mechanism of injury. The effects of in vivo activation of neutrophils on the in vitro responses of these cells to stimulation have not been determined, although such information may be important in understanding how different etiological factors may interact to produce infection or acute respiratory failure. By using an assay to sequentially measure superoxide anion (O2-) release from adherent neutrophils stimulated with phorbol myristate acetate (PMA), we measured the in vitro activation response of peripheral blood neutrophils isolated before and 24 h after infusion of zymosan-activated plasma (ZAP; or untreated plasma as a control), air bubbles, or PMA in awake, instrumented sheep. Each of the three inflammatory agents produced an increase in lung microvascular permeability characteristic of acute lung injury; control plasma did not. For the in vivo ZAP experiments, stimulated O2- release in vitro by using PMA was approximately 50% lower (P less than 0.05) for neutrophils isolated 24 h after the in vivo infusion (4.3 +/- 0.8 nmol/500,000 cells) than before (8.1 +/- 0.2 nmol/500,000 cells). For the air emboli or PMA in vivo experiments, there were no changes in neutrophil activation responses in vitro. Similarly, infusion of control plasma did not result in reduced neutrophil O2- release. These results show that alterations in the inflammatory potential of neutrophils may occur in vivo and that such alterations appear to be dependent on the mechanism and agent by which lung injury is produced.