Low molecular weight GTP-binding proteins in human neutrophil granule membranes

Degranulation of neutrophils involves the differential regulation of the exocytosis of at least two populations of granules. Low molecular weight GTP-binding proteins (LMW-GBPs) have been implicated in the regulation of vesicular traffic in the secretory pathways of several types of cells. In the present study we identify distinct subsets of LMW-GBPs associated with the membranes of neutrophil-specific and azurophilic granules. Ninety-four percent of total [35S]guanosine 5'-(3-O-thio)triphosphate (GTP gamma S) binding activity was equally distributed between the plasma membrane and cytosol with the remaining 6% localized in the granules. In contrast, the cytosol contained only 10% of the total GTPase activity while the specific granules accounted for 13%. [alpha-32P]GTP binding to proteins transferred to nitrocellulose revealed LMW-GBPs in all fractions except the azurophilic granules. The specific granules contained three out of four bands which were found in the plasma membrane; these ranged from 20 to 23 kDa and all were resistant to alkaline extraction. Photoaffinity labeling with [alpha-32P]8-azido-GTP in the presence of micromolar Al3+ identified proteins of 25 and 26 kDa unique to azurophilic granules; these could not be labeled with [alpha-32P]8-azido-ATP and could be extracted by acidic but not alkaline pH. Botulinum C3-mediated [32P]ADP-ribosylation identified proteins of 16, 20, and 24 kDa both in plasma membranes and those of specific granules. An anti-ras monoclonal antibody, 142-24E5, recognized a 20-kDa protein localized to the plasma and specific granule membranes which could not be extracted by alkaline pH, was not a substrate for botulinum C3 ADP-ribosyltransferase, and was translocated from specific granules to plasma membrane after exposure of neutrophils to phorbol myristate acetate. We conclude that neutrophil-specific and azurophilic granules contain distinct subsets of LMW-GBPs which are uniquely situated to regulate the differential exocytosis of these two compartments.     

Distinctive cationic proteins of the human eosinophil granule: major basic protein, eosinophil cationic protein, and eosinophil-derived neurotoxin

The human eosinophil granule contains a number of cationic proteins that have been identified and purified to homogeneity, including the major basic protein (MBP), the eosinophil cationic protein (ECP), and the eosinophil-derived neurotoxin (EDN). Because of confusion in the literature regarding the distinctiveness of MBP and ECP, we investigated the immunochemical and physicochemical properties of these purified proteins by electrophoresis on sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE), by specific double antibody radioimmunoassays (RIA) for MBP and ECP, and by fractionation of acid-solubilized eosinophil granules on Sephadex G-50 columns. Analysis of a mixture of the three purified proteins by SDS-PAGE showed that they migrated as three distinct bands with differing m.w. Comparison by specific RIA for MBP and ECP did not demonstrate any appreciable immunochemical cross-reactivities among the three proteins. Sephadex G-50 column fractions of acid-solubilized eosinophil granules were analyzed by RIA and by SDS-PAGE analysis of individual column fractions. MBP, ECP, and EDN eluted at different volumes from Sephadex G-50 columns as determined by RIA and SDS-PAGE. Soluble extracts of eosinophil granules from patients with the hypereosinophilic syndrome contained between six and 64 times more MBP than ECP on a weight basis. These observations demonstrate that MBP, ECP, and EDN are distinctive cationic proteins of the human eosinophil granule and that eosinophil granules from patients with eosinophilia contain considerably greater quantities of MBP than ECP.     

In vitro killing of microfilariae of Brugia pahangi and Brugia malayi by eosinophil granule proteins

Eosinophil infiltration and degranulation around the tissue-invasive stages of several species of helminths have been observed. Release of eosinophil granule contents upon the worms is supported by localization of two of the major granule proteins, major basic protein (MBP) and eosinophil peroxidase (EPO), on and around species of trematodes, nematodes, and cestodes. In the case of filarial worms, MBP is deposited on degenerating microfilariae (mf) of Onchocerca volvulus. Here, we performed in vitro assays of the toxicity of four purified eosinophil granule proteins, namely, MBP, EPO, eosinophil cationic protein (ECP), and eosinophil-derived neurotoxin (EDN), for the mf of Brugia pahangi and Brugia malayi. MBP, ECP, and EDN killed these worms in a dose-related manner although relatively high concentrations of EDN were necessary. EPO, in the presence of a H2O2-generating system and a halide, was the most potent toxin on a molar basis; here, the most potent halide was I- followed by Br- and Cl-. Surprisingly, EPO in the absence of H2O2 killed mf at concentrations comparable to those required for MBP and ECP. The toxicity of EPO + H2O2 + halide was inhibited by heparin, catalase, or 1% BSA, whereas the toxicity of EPO alone was inhibited only by heparin. Heparin also inhibited killing by both MBP and ECP. Despite the homology of ECP with certain RNases, placental RNasin, an RNase inhibitor, was unable to inhibit ECP-mediated toxicity. These results indicate that all of the eosinophil granule proteins are toxic to mf and they support the hypothesis that eosinophil degranulation causes death of mf in vivo.     

Comparative toxicity of purified human eosinophil granule proteins for newborn larvae of Trichinella spiralis

Eosinophils have been implicated in both in vivo and in vitro destruction of helminths. One approach toward elucidating the role of the eosinophil in parasite killing has been to test the toxicity of purified eosinophil granule proteins for parasites in vitro. Previously, major basic protein (MBP) and eosinophil cationic protein (ECP) were shown to be toxic for schistosomules of Schistosoma mansoni, while eosinophil-derived neurotoxin (EDN) was only marginally so. We tested the toxicity of MBP, ECP, and EDN over a range of concentrations (0.006-5 X 10(-4) M) for newborn larvae of Trichinella spiralis. Our observations confirm previous reports of toxicity of mildly reduced and alkylated (R & A) MBP. At concentrations of 5 X 10(-5) M and above, R & A MBP killed 75% or more of the larvae within the first hour of culture. ECP was an effective toxin for these larvae after 3 hr of culture, and by 12 hr, dose-related toxicity was evident. After 24 hr, 100% of the larvae were killed at 5 X 10(-5) M ECP. EDN was much less toxic; after 12 hr, 90% of the larvae survived at concentrations of 1 X 10(4) M, while 5 X 10(-4) M EDN killed all the larvae. At the optimal toxic concentrations of 5 X 10(-5) M ECP and 5 X 10(-4) M EDN, kinetics of killing by these 2 proteins were essentially the same. Thus, on a molecular basis, both MBP and ECP appear to be potent helminthotoxins whereas EDN is much less so.     

Post-translational tyrosine nitration of eosinophil granule toxins mediated by eosinophil peroxidase

Nitration of tyrosine residues has been observed during various acute and chronic inflammatory diseases. However, the mechanism of tyrosine nitration and the nature of the proteins that become tyrosine nitrated during inflammation remain unclear. Here we show that eosinophils but not other cell types including neutrophils contain nitrotyrosine-positive proteins in specific granules. Furthermore, we demonstrate that the human eosinophil toxins, eosinophil peroxidase (EPO), major basic protein, eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP), and the respective murine toxins, are post-translationally modified by nitration at tyrosine residues during cell maturation. High resolution affinity-mass spectrometry identified specific single nitration sites at Tyr349 in EPO and Tyr33 in both ECP and EDN. ECP and EDN crystal structures revealed and EPO structure modeling suggested that the nitrated tyrosine residues in the toxins are surface exposed. Studies in EPO(-/-), gp91phox(-/-), and NOS(-/-) mice revealed that tyrosine nitration of these toxins is mediated by EPO in the presence of hydrogen peroxide and minute amounts of NOx. Tyrosine nitration of eosinophil granule toxins occurs during maturation of eosinophils, independent of inflammation. These results provide evidence that post-translational tyrosine nitration is unique to eosinophils.     

Comparative toxicity of the horse eosinophil peroxidase-H2O2-halide system and granule basic proteins

Stimulated eosinophils release cytotoxic granule constituents, including eosinophil peroxidase (EPO) and a group of granule basic proteins (GBP). EPO reacts with H2O2 formed by the respiratory burst and a halide to form cytotoxic oxidants. The relative potency of the EPO-H2O2-halide system and the GBP is considered here. Horse eosinophils were induced to degranulate, the degranulation products were separated by chromatography on Sephadex G-50 and comparable volumes of the column fractions were tested for toxicity to Escherichia coli and the schistosomula of Schistosoma mansoni in the presence and absence of H2O2 and halides. Both the EPO system and GBP were toxic. However, the peak EPO fraction could be diluted 1000-fold at pH 7.0 and 5000-fold at pH 5.0, and with a 10-fold dilution at pH 7.0 incubation time could be reduced to 5 s, with retention of bactericidal activity in the presence of H2O2 and halides, whereas the peak GBP fractions diluted 10-fold had a small bactericidal effect at 1 h which increased with prolongation of incubation to 24 h. A less than 1 log fall in E. coli viable cell count was produced by the GBP fractions under all conditions as compared to total destruction (greater than 5 log fall) with the EPO system. A 1000-fold dilution of the peak EPO fraction was schistosomulocidal in the presence of H2O2 and halides, with toxicity observed at 2 h with a 10-fold dilution. In contrast, no schistosomulocidal activity was observed at 18 h with a 10-fold dilution of the GBP fractions. However, toxicity was observed with a 5- or 50-fold increase in GBP concentration with maximum toxicity observed with fractions between the two major protein peaks. Thus, under the conditions employed, the EPO-H2O2-halide system contributed to a considerably greater degree to the toxic activity of the granule components than did the GBP.     

Applicability of using acrylic resins in post-embedding ultrastructural immunolabelling of human neutrophil granule proteins

Summary In this study, quantitative assessments were carried out, (1) by light microscopy during tissue preparation for electron microscopy and (2) by electron microscopy after on-grid immunogold staining, to determine the suitability of using LR White and Lowicryl K4M thin sections to identify lactoferrin and elastase in the granules of human neutrophil leucocytes. Quantitative assessment of the effect of fixation, dehydration and embedding on the preservation of antigenicity during tissue preparation for electron microscopy, using light microscopic peroxidase anti-peroxidase immunocytochemistry, enabled the selection of preparation conditions that adequately preserved both antigenicity and ultrastructure. OsO₄ post-fixation, following primary aldehyde fixation, improved the retention of antigenicity during dehydration and embedding and the preservation of fine structure. Partial rather than complete dehydration retained more of the antigenicity. The efficiency, sensitivity and resolution of immunolabelling and the ultrastructure and quality of sections achieved after embedding in LR White were superior to those obtained after embedding in Lowicryl K4M. Consequently room temperature embedding in LR White following double fixation and partial dehydration is a better and more reliable preparation technique than low-temperature embedding in Lowicryl K4M following single fixation and partial dehydration for localizing lactoferrin and elastase to the specific and primary granules respectively in human neutrophilic granulocytes by the on-grid immunogold staining method.     

Morphometry of feline neutrophil granule genesis

During neutrophil granule genesis, the formation of primary granules is generally thought to be limited to the promyelocyte stage; whereas synthesis of secondary granules is thought to occur only at the myelocyte stage. This hypothesis was tested morphometrically in feline neutrophils that are known to contain both granule types. Marrow specimens obtained from six cats were stained with peroxidase for identification of neutrophil primary granules and counterstained with periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) for identification of secondary granules. By regression analysis using arithmetic models, numbers of cytoplasmic granules in 311 cells were correlated with the degree of nuclear chromatin condensation, which was shown to be an adequate parameter for cell maturation. Promyelocytes and myelocytes had similar mean numbers of peroxidase-positive granules per unit area. A significant increase (p less than or equal to 0.0001) in the numbers of peroxidase-positive granules was noted between the metamyelocyte and the mature neutrophil stage, despite the lack of peroxidase activity in endoplasmic reticulum and Golgi lamellae. By contrast, a significant increase of peroxidase-negative granules between the metamyelocyte and the mature neutrophil stage was not clearly established with these methods. The increase in peroxidase-positive granules may indicate continued production of peroxidase-containing granules and/or redistribution of peroxidase among lysosomal organelles in late feline neutrophils.     

The actin cytoskeleton regulates exocytosis of all neutrophil granule subsets

A comprehensive analysis of the role of the actin cytoskeleton in exocytosis of the four different neutrophil granule subsets had not been performed previously. Immunoblot analysis showed that, compared with plasma membrane, there was less actin associated with secretory vesicles (SV, 75%), gelatinase granules (GG, 40%), specific granules (SG, 10%), and azurophil granules (AG, 5%). Exocytosis of SV, SG, and AG was measured as increased plasma membrane expression of CD35, CD66b, and CD63, respectively, with flow cytometry, and GG exocytosis was measured as gelatinase release with an ELISA. N-formylmethionyl-leucyl-phenylalanine (FMLP) stimulated exocytosis of SV, GG, and SG with an ED₅₀ of 15, 31, and 28 nM, respectively, with maximal response at 10^–7 M FMLP by 5 min, while no exocytosis of AG was detected. Disruption of the actin cytoskeleton by latrunculin A and cytochalasin D induced a decrease in FMLP-stimulated CD35 expression after an initial increase. Both drugs enhanced the rate and extent of FMLP-stimulated GG, SG, and AG exocytosis, while the EC₅₀ for FMLP was not altered. We conclude that the actin cytoskeleton controls access of neutrophil granules to the plasma membrane, thereby limiting the rate and extent of exocytosis of all granule subsets. Differential association of actin with the four granule subsets was not associated with graded exocytosis. human; cell activation     

Eosinophil activation in acute and chronic chagasic myocardial lesions and deposition of toxic eosinophil granule proteins on heart myofibers

Cardiac lesions in patients with Chagas' disease are infiltrated with various types of inflammatory cells, including eosinophils (EOS). We determined the proportions of resting and activated EOS in 2 types of chagasic myocardial lesions to establish whether their presence correlated with lesion severity. One lesion type was defined by interstitial infiltration associated with degeneration and necrosis of myocardial fibers; the other type presented mild myocarditis but myofibers were preserved. In all cases (1 patient with acute and 5 patients with chronic Chagas' disease), a marked degree of EOS infiltration was seen in the necrotic areas after staining either with Giemsa or immunohistochemically, using antibodies specific for the EOS cationic protein or the major basic protein of the granule. In contrast, a very small number of EOS was present in areas of the very same tissue sections displaying mild myocarditis and preserved myofibers. Of the EOS present in the necrotic areas, 42-78% were in the activated secretory stage as evidenced immunohistochemically after incubation with a monoclonal antibody specific for an epitope of the secretory but not the storage form of the EOS cationic protein. In areas with mild myocarditis this proportion was much smaller, ranging from 9 to 28%. In all cases, both the total level of resting and activated EOS in the necrotic areas correlated well with the overall degree of severity of myocarditis evaluated histopathologically. Deposits of the major basic cationic proteins of the EOS granules were found on myofibers in the necrotic areas from the acute and chronic cases, indicating EOS degranulation.     

The inhibition of neutrophil granule enzyme secretion and chemotaxis by pertussis toxin

Pertussis toxin treatment of rabbit peritoneal neutrophils causes a concentration-dependent inhibition of granule enzyme secretion induced by formylmethionyl-leucyl-phenylalanine, C5a, and leukotriene B4. It also inhibits chemotaxis induced by formylmethionyl-leucyl-phenylalanine. The same toxin treatment, however, has no effect on granule enzyme secretion induced by the calcium ionophore A23187 or phorbol 12-myristate 13-acetate. Moreover, pertussis toxin treatment does not affect either the number or affinity of the formylpeptide receptors on the neutrophil nor does it have any effect on the unstimulated levels of cyclic AMP (cAMP) or the transient rise in cAMP induced by chemotactic factor stimulation in these cells. We hypothesize that pertussis toxin, as in other cells, interacts with a GTP binding regulatory protein identical with or analogous to either Ni or transducin which mediates the receptor-induced inhibition or activation of a target protein or proteins required in neutrophil activation. The nature of the target protein is unknown, but it is not the catalytic unit of adenylate cyclase. The target protein acts after binding of chemotactic factor to its receptor in the sequence that leads to the receptor-induced rise in intracellular Ca2+. It does not affect the responses elicited by the direct introduction of calcium into the cells or the activity of protein kinase C.     

Divergent effect of mometasone on human eosinophil and neutrophil apoptosis

Mometasone is a potent synthetic glucocorticoid, which is under development as an inhaled preparation for the treatment of asthma. Previous studies have suggested that glucocorticoids have direct effects on human eosinophil and neutrophil apoptosis. The present study was designed to characterize the effects of mometasone on constitutive apoptosis and cytokine-afforded survival in isolated human eosinophils and neutrophils. The isolated eosinophils or neutrophils were cultured in vitro, and apoptosis was assessed by flow cytometric analysis of relative DNA content, by annexin-V binding and morphological analysis. Mometasone enhanced constitutive human eosinophil apoptosis in a concentration-dependent manner. The maximal enhancement of eosinophil apoptosis was 2.1-fold with an EC(50) value of 5.63 +/- 2.33 nM. This enhancing effect was reversed by the glucocorticoid receptor antagonist, mifepristone. In the presence of added cytokines, mometasone reversed tumor necrosis factor -alpha-induced eosinophil survival but not that afforded by interleukin -5. In contrast, mometasone inhibited human neutrophil apoptosis in a concentration-dependent manner. The maximal inhibition of neutrophil apoptosis was 50% with an EC(50) value of 0.17 +/- 0.03 nM. The inhibitory effect was partly reversed by mifepristone. In the presence of added cytokines, mometasone further enhanced neutrophil survival induced by the granulocyte-macrophage colony-stimulating factor and leukotriene B(4). The present data suggests that mometasone has opposite effects on apoptosis of human eosinophils and neutrophils at clinically relevant drug concentrations via an effect on glucocorticoid receptor.     

Phosphatidylinositol-linked FcRIII mediates exocytosis of neutrophil granule proteins, but does not mediate initiation of the respiratory burst

In this report, we present data on the activation of different neutrophil effector functions by two distinct Fc-gamma receptors, FcRII and FcRIII. We and others have shown previously that IgG-dependent activation of phagocytosis and superoxide generation is mediated via FcRII. IgG-dependent exocytosis of granule proteins was assessed with Staphylococcus aureus Oxford opsonized with human IgG or with IgG-coated latex. Both anti-FcRII mAb and anti-FcRIII-F(ab')2 mAb inhibited this release, whereas the combination of these mAb inhibited this process more strongly than either mAb alone. This indicates that both FcRII and FcRIII are involved in IgG-dependent release of granule proteins. Cross-linking of the receptors by anti-FcR mAb and F(ab')2 fragments of goat-anti-mouse-Ig showed again that both FcRII and FcRIII mediate lysozyme release, whereas cross-linking of a control antigen (CD67) did not. By measuring the release of elastase and lactoferrin, we found that cross-linking of either FcRII or FcRIII induced release of both azurophilic and specific granules. Under these conditions, we did not measure any activation of the respiratory burst. When FcRIII was removed by treatment of neutrophils with glycosylphosphatidylinositol-specific phospholipase C, the lysozyme release induced by cross-linking of FcRIII was lower than the release from control neutrophils, whereas the release induced by cross-linking of FcRII was similar. Therefore, we conclude that IgG-dependent activation of neutrophils follows two distinct pathways: one via transmembrane FcRII, activating both the NADPH oxidase and the release of granule proteins (as was demonstrated previously by us and by others), and the other via phosphatidylinositol-linked FcRIII, activating exocytosis of granule proteins.