Subcellular distribution of glycosidases in human polymorphonuclear leucocytes

The Dynamics of Circulating Heparin-Binding Protein: Implications for Its Use as a Biomarker

Heparin-binding protein (HBP) is a promising biomarker for the development and severity of sepsis. To guide its use, it is important to understand the factors that could lead to false-positive or negative results, such as inappropriate release and inadequate clearance of HBP. HBP is presumably released only by neutrophils, and the organs responsible for its elimination are unknown. In this study, we aimed to determine whether non-neutrophil cells can be a source of circulating HBP and which organs are responsible for its removal. We found that in two cohorts of neutropenic patients, 12% and 19% of patients in each cohort, respectively, had detectable plasma HBP levels. In vitro, three leukemia-derived monocytic cell lines and healthy CD14+ monocytes constitutively released detectable levels of HBP. When HBP was injected intravenously in rats, we found that plasma levels of HBP decreased rapidly, with a distribution half-life below 10 min and an elimination half-life of 1-2 h. We measured HBP levels in the liver, spleen, kidneys, lungs, and urine using both ELISA and immunofluorescence quantitation, and found that the majority of HBP was present in the liver, and a small amount was present in the spleen. Immunofluorescence imaging indicated that HBP is associated mainly with hepatocytes in the liver and monocytes/macrophages in the spleen. The impact of hematologic malignancies and liver diseases on plasma HBP levels should be explored further in clinical studies.

The β-glucosidase assay: a new diagnostic tool for necrotizing enterocolitis. Sensitivity, specificity, and predictive values

We aimed to establish the utility of serum cytosolic β-glycosidase (CBG) assay as a NEC diagnosis tool. CBG activity has been compared in 192 NEC-free (NEC(-)) and 13 NEC-affected (NEC(+)) neonates, with modified Bell's stages II/III, born at Reina Sofia University Hospital; additional blood hematology, microbiology, and biochemical parameters have been assayed. NEC(+) neonates have higher serum CBG activity, 26.4 ± 12.4 mU/mg; 95 % CI (18.8-33.9), than NEC(-) infants, 11.0 ± 6.6 mU/mg; 95 % CI (10.1-11.9) (p < 0.0001). The CBG cutoff value in the ROC curve, 15.6 mU/mg, discriminates NEC(+)/NEC(-) infants with 84.6 % sensitivity, 85.9 % specificity, 37.9 positive predictive value and 98.2 negative predictive value, 6.11 positive likelihood ratio and 0.18 negative likelihood ratio, 33.61 DOR, and 0.89 AUC. A combined panel [CBG + aspartate aminotransferase + C-reactive protein] shows a 0.90 AUC value in multiple linear regressions.

CONCLUSIONS

The serum CBG level is a good NEC diagnosis test and a novel NEC biomarker which may become a screening tool.

WHAT IS KNOWN

•NEC affects ∼2.5 % of infants at NICU, ∼90 % of them weighing <1500 g. •NEC requires a careful differential diagnosis, being lethal if not diagnosed and treated. What is new: •CBG assay will be useful to determine infants without NEC and preventing unnecessary treatment. •CBG assay could discriminate NEC better than other gut-specific sera protein biomarkers.

Diagnostic significance of lysosomal enzymes in different types of leukemias

The activities of seven different leukocyte hydrolases were studied in 19 patients and ten controls. There was a strong positive correlation between the monocyte count and the activities of the lysosomal enzymes (N-acetyl-beta-glucosaminidase, alpha-fucosidase, beta-galactosidase, and alpha-mannosidase). High alpha-fucosidase and alpha-mannosidase activities were also found in the eosinophilic granulocytes. Using simple commercially available synthetic substrates, it is possible to study the activities of the lysosomal enzymes in different types of leukemias and to recognize the monocytic leukemias even when they present with very immature precursor cells in the peripheral blood.

Congenic analysis of the NKT cell control gene Nkt2 implicates the peroxisomal protein Pxmp4

Type 1 NKT cells play a critical role in controlling the strength and character of adaptive and innate immune responses. We have previously reported deficiencies in the numbers and function of NKT cells in the NOD mouse strain, which is a well-validated model of type 1 diabetes and systemic lupus erythematosus. Genetic control of thymic NKT cell numbers was mapped to two linkage regions: Nkt1 on distal chromosome 1 and Nkt2 on chromosome 2. Herein, we report the production and characterization of a NOD.Nkrp1(b).Nkt2b(b) congenic mouse strain, which has increased thymic and peripheral NKT cells, a decreased incidence of type 1 diabetes, and enhanced cytokine responses in vivo and increased proliferative responses in vitro following challenge with alpha-galactosylceramide. The 19 highly differentially expressed candidate genes within the congenic region identified by microarray expression analyses included Pxmp4. This gene encodes a peroxisome-associated integral membrane protein whose only known binding partner is Pex19, an intracellular chaperone and component of the peroxisomal membrane insertion machinery encoded by a candidate for the NKT cell control gene Nkt1. These findings raise the possibility that peroxisomes play a role in modulating glycolipid availability for CD1d presentation, thereby influencing NKT cell function.

Tris discriminates between the different alpha-glucosidase activities from extracts of human neutrophils

In an attempt to detect acid maltase deficiency in neutrophils from patients with type II glycogenosis, without interference from the 'renal' alpha-glucosidase activity present in these cells, we have evaluated the contribution of the renal component in the total activity measured at pH 4.0 in extracts of human neutrophils. The renal contribution is about 13-25% and renal glucosidase appears to be closely related to the enzyme present on the epithelium of small intestine, which is known to be inhibited by Tris. We have used this compound as a selective inhibitor of the renal component of alpha-glucosidase activity measured at pH 4.0 in total extracts of neutrophils. Our results demonstrate that 0.1 mol/L Tris is an inhibitor of the renal alpha-glucosidase present in neutrophils and can be used to reduce the interference from this enzyme in assays of acid maltase.

Metal content of neutrophil granules is altered in chronic inflammation

The mass fraction of certain elements was measured in isolated granulocytes and isolated granulocyte granule fractions from patients with active inflammatory arthritides (N = 6) and healthy controls (N = 6). The patients had significantly increased amounts of Ca in the granulocytes, in the specific and light azurophil granules, but normal Ca amounts in the dense azurophil granules. Sr was below the detection limit in the granulocytes and granule fraction from controls, but it appeared in high concentrations in the granulocytes and all granule fractions from the patients. The patients had considerably increased granulocyte amounts of Mn but only slightly increased Mn concentrations in the specific granules. Mn was not detectable in azurophil granules from patients and controls. A prominent accumulation of Fe was seen in the granulocytes from the patients, together with an Fe accumulation in the specific granules. Fe was below the detection limit in azurophil granules from patients and controls. The patients had reduced granulocyte Zn and reduced amounts of Zn in the dense and light azurophil granules but normal Zn amounts in the specific granules. The results obtained indicate that the granulocyte accumulation of Ca, Sr, and Fe observed during chronic inflammation is associated with corresponding granule accumulation of these metals; the considerable Mn accumulation in granulocytes during inflammation is not localized in their granules; and the granule subpopulations differ in their capacity to store certain metals.

The bactericidal effects of the respiratory burst and the myeloperoxidase system isolated in neutrophil cytoplasts

Neutrophil polymorphonuclear leucocytes kill bacteria by oxygen-dependent and oxygen-independent mechanisms. Many potentially toxic mechanisms have been described, but the complexity of the phagosomal environment and the synergy between oxidative and non-oxidative systems hamper the investigation of individual bactericidal mechanism in whole cells. Neutrophil cytoplasts are greatly depleted of granule proteins and permit the investigation of the bactericidal effects of the respiratory burst in isolation. In this study they have been used to examine the role of the respiratory burst and myeloperoxidase in oxygen-dependent killing of Staphylococcus aureus. Cytoplasts generated oxygen radicals at comparable rates to human neutrophils and phagocytosed but did not kill S. aureus. The selective reconstitution of the myeloperoxidase-hydrogen peroxide-halide system by coating bacteria with myeloperoxidase conferred on cytoplasts the ability to kill intracellular bacteria. However, extracellular killing by diffusible bactericidal factors was not detected in this system.

Degradation of gonococcal peptidoglycan by granule extract from human neutrophils: demonstration of N-acetylglucosaminidase activity that utilizes peptidoglycan substrates

The degradation of purified Neisseria gonorrhoeae peptidoglycan (PG) by granule extract derived from normal human polymorphonuclear leukocytes was examined. Hen egg lysozyme-resistant, extensively O-acetylated [3H]PG (O-PG) from strain FA19 and lysozyme-sensitive, non-O-acetylated [14C]PG (non-O-PG) from strain RD5 (each containing label in both glucosamine and muramic acid) were mixed and incubated with granule extract at pHs 4.5, 5.5, and 6.5. The rate of degradation of O-PG was uniformly slower than that of non-O-PG in the same tube, but ultimately, even the O-PG was rendered completely soluble. Molecular-sieve high-performance liquid chromatography revealed that both PGs were degraded by granule extract at the pH values tested to disaccharide peptide monomers and peptide-cross-linked oligomers, reflecting the action of human lysozyme. Of particular interest was the appearance of a peak containing free N-acetylglucosamine which was quite prominent in reaction mixtures at pH 4.5, less prominent at pH 5.5, and not detectable at pH 6.5. Free N-acetylglucosamine was not released from control PG samples at any pH in the absence of granule extract. Treatment of purified gonococcal PG monomers with granule extract at pH 4.5 yielded exclusively free N-acetylglucosamine and muramyl peptides with no N-acetylglucosamine. These data suggest that granule extract contains a previously undescribed pH-dependent N-acetylglucosaminidase with specificity for PG as well as an N-acetylmuramidase activity that degrades O-PG less efficiently than it does non-O-PG.

Rapid simultaneous assessment of neutrophil superoxide generation and lysosomal enzyme release

A rapid method for the simultaneous measurement of neutrophil superoxide generation and beta-glucuronidase release is described. Assay of beta-glucuronidase using a fluorescent substrate is shown to be valid in the presence of reduced or unreduced ferricytochrome C, a prerequisite for the simultaneous assessment of this enzyme activity and O-2 generation.

Different molecular forms of a glycoprotein antigen found on azurophilic granule membranes of cultured human HL60 promyelocytes and on the plasma membrane of a myeloblastoid variant line

In previous immunohistological studies an antigen designated D46 was identified on the surface of an agranular, myeloblastoid cell line (HL60-D). It was not detected on the surface of either parental HL60 cells or variants with aberrant primary granules (HL60-A7). In these promyelocytes it was found to be intracytoplasmic, in a granular pattern. In the work presented here, this antigen and other granule-related glycoproteins were studied by radiolabeling, subcellular fractionation and gel electrophoresis. The major findings include the following: the anti-D46 antibody precipitated one major and one minor glycosylated component, each of which migrated with a different electrophoretic mobility, depending on whether it was derived from cells with or without granules. Incorporation of radioactive amino acids, but not monosaccharides, revealed an additional component of lower mobility. The D46 antigen(s) was recovered in the detergent-rich phase of a Triton X-114 extract of granules, suggesting that it is an integral membrane protein. As assessed by the relative activities of marker enzymes, the granules of both the HL60 and HL60-A7 cell lines exhibited a heterogeneous pattern of sedimentation in density gradients. The electrophoretic patterns of the major [2-3H]mannose-labeled glycoproteins of the granule-enriched fractions were similar, except for one diffuse band of 110-170 kD which was not detected in HL60-A7. These studies provide direct evidence for heterogeneity of enzymatic and membrane constituents of primary myeloid granules, and give the first indication that there may be glycoprotein changes associated with certain ultra-structural defects that occur in abnormal promyelocytes. They suggest also, in the example of the D46 antigen; that some glycoproteins may exist in different forms when localized to either the granules or the plasma membrane.

The development of cytochrome b-245 in maturing human macrophages

Cytochrome b-245, the putative terminal component of the specialized cidal oxidase system of phagocytes, was measured in human monocytes in culture. There was a dramatic synthesis of the cytochrome, which increased by 27.3 +/- 2.0 pmol/day per 10(7) cells. This represents an increase of about 40%/day in the early stages and an overall 7-fold increase after 16 days. The protein content increased 3-fold over the same period, resulting in a doubling of the specific content of the cytochrome b. The newly synthesized cytochrome b was identified as that specifically located in the microbicidal oxidase electron-transport chain, as titration demonstrated that, at day 16 of maturation, 70% of the total membrane cytochrome b had a very low midpoint potential (-260 to -220 mV), characteristic of that found in this oxidase system. This cytochrome distributed with the plasma membrane on analytical subcellular fractionation, and a close relationship was observed between the maturation-induced increase in the concentration of this molecule and the capacity of the cells to produce superoxide.

Elastase in the different primary granules of the human neutrophil

Elastase in the human neutrophil is associated with various subpopulations of primary granules of different density. The proportion of this enzyme that is extracted with acetate pH 4.2 and cetyltrimethylammonium bromide varies in the different subpopulations. Nevertheless, the electrophoretic mobility and relative proportions of elastase isoenzymes is the same in both extracts from the different subpopulations. On stimulation of neutrophils with N-formylmethionylleucylphenylalanine, elastase is not released from the least dense subpopulation, whereas other two subpopulations do undergo degranulation to approximately the same extent. However, the release of elastase from these two denser granules differs after they are isolated and treated with calcium.

Nonoxidative antimicrobial reactions of leukocytes

Increasingly abundant evidence supports the hypothesis that PMNs and perhaps alveolar macrophages have antimicrobial mechanisms independent of the presences of molecular oxygen for effective action against an array of bacteria and against some fungi. Eosinophils have mechanisms toxic for schistosomula and Trichinella larvae. In all instances the antimicrobial substances isolated have been cationic proteins and, in PMNs, associated with the azurophil cytoplasmic granules of the PMNs. Several of these substances have thus far demonstrated no enzymic function. Two of these substances are serine proteases but in one, chymotrypsin-like protein, the antimicrobial action depends on the cationic properties of the protein and is independent of the proteolytic action of the substance. In most instances, these proteins are cationic due to relatively large proportions of arginine. In two instances, a large proportion of lysine is present. All have high proportions (about 50%) of hydrophobic amino acid. Such proteins occur in the PMNs of man, rabbit, guinea pig, rat, cow, and chicken. The present view is that they are most active against gram-negative bacteria. At least two of them-37-kd and 57-kd proteins (Shafer and Spitznagel, 1983)-act on S. typhimurium in a manner analogous to that of polymyxin B through binding to lipid A. Currently available results shows that anaerobic PMNs have substantial antimicrobial capacity. Whether this capacity is due to the O2-independent mechanisms discussed in this chapter remains to be established with greater certainty.

Demonstration of the existence, and partial characterization, of a cell-surface beta-hexosaminidase from rat splenocytes

Rat splenocytes are shown to exhibit cell-surface located beta-N-acetylglucosaminidase and beta-galactosidase activities. Preincubation experiments, solubilization experiments and chemical cross-linking experiments show that these enzymatic activities are indeed cell-surface localized. The solubilization and partial purification of the beta-N-acetylglucosaminidase activity is reported. Kinetic studies of the partially purified material with a variety of competitive inhibitors at several pH values suggest that at physiological pH the cell surface beta-N-acetylglucosaminidase may function as a carbohydrate binding protein rather than as a glycosidase.

Differential distribution of distinct forms of myeloperoxidase in different azurophilic granule subpopulations from human neutrophils

Myeloperoxidase (MPO), a characteristic enzyme of human polymorphonuclear neutrophils (PMN), is localized in specialized lysosomal or azurophilic granules, and can be resolved into three distinct forms (I, II, III) by ion-exchange chromatography. Granules were isolated from single donor PMN and fractionated with centrifugation into two different azurophilic subpopulations (high and low density) by banding in a continuous sucrose density gradient. Ion-exchange chromatography of granule extracts indicated that the lower density granules contained mainly MPO forms II and III while the higher density granules appeared to contain all three forms, but in much reduced amounts. Sodium dodecylsulfate polyacrylamide gel electrophoresis showed that, the mobilities of the heavy subunits of MPO appeared to be inversely related to the density of the granule population from which they were extracted. These observations suggest that the different forms of MPO may have distinct functional roles and/or are a possible reflection of maturational differences among the granule subpopulations.

Morphometric cytochemistry of catalase and myeloperoxidase-containing granules in the rabbit polymorphonuclear leukocyte

Recently developed morphometric and statistical techniques were applied to the study of heterogeneity of the granule population of rabbit polymorphonuclear leukocytes. The cytochemical activities of myeloperoxidase and catalase were differentiated by incubation at pH 7.6, and pH 9.7 to 10.5, respectively. Each activity was found in more than one granule. Statistical evaluation suggested that in addition to the primary granule, two myeloperoxidase-containing granules and two catalase-containing granules existed. Although the presence of catalase activity has been described in the immature polymorphonuclear leukocyte previously, this is the first report indicating cytochemical reactivity in mature polymorphs.

Iodination by stimulated human neutrophils. Studies on its stoichiometry, subcellular localization and relevance to microbial killing

Myeloperoxidase of phagocytic leucocytes is thought to utilize H2O2 to oxidize halides, which then react with and kill ingested microbes. This hypothesis was based largely on the incorporation of radiolabelled iodide into cells that had phagocytosed bacteria. The present studies investigated the stoichiometry of these reactions and the subcellular localization and electrophoretic pattern of the cellular components that became iodinated. 1. The stoichiometry of the reactions are such that only a small proportion (less than 0.3%) of the total oxygen consumed is utilized for iodination. Iodination after stimulation with the soluble stimulus phorbol myristate acetate (PMA), which is not known to involve the azurophil granules and their contained myeloperoxidase, was comparable with that occurring after bacterial ingestion. 2. Analytical subcellular fractionation of cells that had phagocytosed bacteria localized about 25% of the radioactivity to the membranes, and most of the residual radioactivity distributed with the bacteria and dense granules. In cells stimulated with PMA, more of the radioactivity was associated with the membranes, but about half was still associated with the dense granules. 3. Autoradiographs after dodecyl sulphate/polyacrylamide-gel electrophoresis of cells stimulated with opsonized bacteria gave a similar distribution of iodinated components to that obtained with cells that had been stimulated with PMA or iodinated with Iodogen. These patterns of iodination were very different from those obtained when bacteria alone were iodinated with Iodogen or myeloperoxidase and H2O2. Preparations in which bacteria had been phagocytosed did not show evidence of iodination of bacterial proteins or coating opsonins. Thus positive evidence for the iodination of bacteria has not been produced, and the role of iodination in the microbicidal process of neutrophils remains to be established.

Characterization of canine neutrophil granules

The purpose of this study was to isolate distinct populations of canine neutrophil granules and to compare them with neutrophil granules from other species. Size, shape, density, and content of canine neutrophil granules were determined. Neutrophils obtained by Ficoll-Hypaque sedimentation were homogenized, and granule populations were separated by isopycnic centrifugation on a linear sucrose gradient (rho, 1.14 to 1.22 g/ml). The most dense granule population (rho, 1.197 g/ml) contained all of the myeloperoxidase, beta-glucuronidase, and elastase, more than half of the acid beta-glycerophosphatase, and most of the lysozyme. The population with intermediate density (rho, 1.179 g/ml) contained lactoferrin, vitamin B12-binding protein, and the remainder of the acid beta-glycerophosphatase and lysozyme. The least dense granule population did not contain a major peak of any of the enzymes or binding proteins tested but was distinguished by density and morphology. The size and shape of the granules were determined from scanning electron micrographs and assessment of shape was aided by transmission electron micrographs. By these methods three populations of canine neutrophil granules were characterized and named: myeloperoxidase granules, vitamin B12-binding protein granules, and low-density granules.

Bactericidal activity in fractionated granule contents from human polymorphonuclear leukocytes: studies with leukocytes from normal individuals

Sephadex G-100 chromatographic fractions of granule extracts from normal human polymorphonuclear leukocytes, exhibiting differences from fractions previously obtained from leukemic polymorphonuclear leukocytes, possessed cationic proteins with distinct bactericidal activity against cell wall mutants of Salmonella typhimurium LT2.

Kinetics of fusion of the cytoplasmic granules with phagocytic vacuoles in human polymorphonuclear leukocytes. Biochemical and morphological studies

This study on human neutrophils was conducted to measure the kinetics of degranulation of the different cytoplasmic granules into phagocytic vacuoles, and to relate the timing of these events to the burst of respiration that accompanies phagocytosis by these cells. Purified neutrophils were incubated with latex particles opsonized with human immunoglobulin (Ig)G, and phagocytosis was stopped at timed intervals. The cells were examined by electron microscopy to document the sequence of degranulation of the cytoplasmic granules. The azurophil granules and lyosomes were identified by histochemical staining for peroxidase and acid phosphatase, respectively. Phagocytic vacuoles were separated from cell homogenates by floatation on sucrose gradients and assayed for contained lactoferrin, myeloperoxidase, and acid hydrolases. The conclusions drawn from the biochemical and morphological studies were in agreement and indicated: particle uptake and vacuole closure can be completed within 20 s; both the specific and azurophil granules fuse with the phagocytic vacuole much earlier than is generally appreciated, with half-saturation times of 39 s (99% confidence limits, 15-72); oxygen consumption has kinetics similar to those of the fusion of these granules with the phagosome; degranulation of the acid hydrolases beta-glucuronidase, N-acetyl-beta-glucosaminidase (biochemical assays), and acid phosphatase (biochemical assay and electron microscopic cytochemistry) have kinetics of degranulation that are similar to each other but totally different from and much slower than that of myeloperoxidase with half-saturation times of between 354 and 682 s (99% confidence limits, 246-883). This suggests that the acid hydrolases are not co-located with myeloperoxidase in the azurophil granule but are contained in distinct lysosomes, or "tertiary granules".

Bactericidal activity of fractionated granule contents from human polymorphonuclear leukocytes: antagonism of granule cationic proteins by lipopolysaccharide

Granule extracts from human polymorphonuclear leukocytes (PMN) were prepared with 0.2 M (pH 4.0) acetate. A fraction (valley AB) with distinctive bactericidal activity against cell wall mutants of Salmonella typhimurium LT-2 was obtained after fractionation of the granule extracts by Sephadex G-100 column chromatography. The smooth parent LT-2 strain was less sensitive to the bactericidal action. Susceptibility of the rough mutants to bactericidal action increased as sugar residues decreased in the lipopolysaccharide (LPS) (Re greater than Rd2 greater than Rd1 greater than Rc greater than Ra). Cationic protein(s) responsible for bactericidal activity could be selectively removed from the fraction by absorption with whole LT-2 cells or purified LPS. Loss of cationic protein species was confirmed by cationic polyacrylamide gel electrophoresis. Purified LPS from LT-2 or the deep rough mutant TA2168 inhibited the antimicrobial activity of the killing fraction in in vitro assays. A minor protein species (vAB1) from the valley AB fraction had an apparent molecular weight of 36,000 to 37,000 and represented a major bactericidal activity of the fraction. Small amounts of the isolated vAB1 protein were bactericidal for the smooth parent LT-2 strain.