Elastase in the different primary granules of the human neutrophil

Structural and functional diversity of neutrophil glycosylation in innate immunity and related disorders

The granulated neutrophils are abundant innate immune cells that utilize bioactive glycoproteins packed in cytosolic granules to fight pathogenic infections, but the neutrophil glycobiology remains poorly understood. Facilitated by technological advances in glycoimmunology, systems glycobiology and glycoanalytics, a considerable body of literature reporting on novel aspects of neutrophil glycosylation has accumulated. Herein, we summarize the building knowledge of the structural and functional diversity displayed by N- and O-linked glycoproteins spatiotemporally expressed and sequentially brought-into-action across the diverse neutrophil life stages during bone marrow maturation, movements to, from and within the blood circulation and microbicidal processes at the inflammatory sites in peripheral tissues. It transpires that neutrophils abundantly decorate their granule glycoproteins including neutrophil elastase, myeloperoxidase and cathepsin G with peculiar glyco-signatures not commonly reported in other areas of human glycobiology such as hyper-truncated chitobiose core- and paucimannosidic-type N-glycans and monoantennary complex-type N-glycans. Sialyl Lewis^x, Lewis^x, poly-N-acetyllactosamine extensions and core 1-/2-type O-glycans are also common neutrophil glyco-signatures. Granule-specific glycosylation is another fascinating yet not fully understood feature of neutrophils. Recent literature suggests that unconventional biosynthetic pathways and functions underpin these prominent neutrophil-associated glyco-phenotypes. The impact of glycosylation on key neutrophil effector functions including extravasation, degranulation, phagocytosis and formation of neutrophil extracellular traps during normal physiological conditions and in innate immune-related diseases is discussed. We also highlight new technologies that are expected to further advance neutrophil glycobiology and briefly discuss the untapped diagnostic and therapeutic potential of neutrophil glycosylation that could open avenues to combat the increasingly prevalent innate immune disorders.

A neutrophil multitarget functional bioassay to detect anti-inflammatory natural products

A multitarget functional bioassay was optimized as a method for detecting substances interacting with the inflammatory process of activated neutrophil granulocytes, mainly to release elastase detected by p-nitroanilide (pNA) formation. Using this bioassay, 100 fractionated extracts of 96 plants were screened, with results presented in a manner that links recorded biological activity to phylogenetic information. The plants were selected to represent a major part of the angiosperms, with emphasis on medicinal plants, Swedish anti-inflammatory plants, and plants known to contain peptides. Of the tested extracts, 41% inhibited pNA formation more than 60%, and 3% stimulated formation. The extract of Digitalis purpurea enhanced pNA formation, and digitoxin, the active compound, was isolated and identified. Plant extracts that exhibited potent nonselective inhibition (>80% inhibition) were evaluated further for direct inhibition of isolated elastase and trypsin enzyme. The inhibitory effect of most tested extracts on the isolated enzyme elastase was similar to that of PAF- and fMLP-induced pNA formation. Compared to trypsin, inhibition of elastase by extracts of Rubus idaeus and Tabernaemontana dichotoma was significantly higher (80% and 99%, respectively). Inhibition of trypsin by the extract of Reseda luteola was high (97%). Orders such as Lamiales and Brassicales were shown to include a comparably high proportion of plants with inhibitory extracts.

(99m)Tc-HMPAO (Ceretec) is stored in and released from the granules of eosinophil granulocytes

(99m)Tc-HMPAO (Ceretec) labelling of leucocytes is used clinically for the detection of inflammatory processes in the body. This study investigated the mechanisms by which (99m)Tc-HMPAO is taken up by eosinophils and neutrophils. Blood cells were labelled with (99m)Tc-HMPAO and the cells separated by means of their densities in Percoll gradients. For other purposes, eosinophils and neutrophils were purified by means of the MACS system and, after labelling these pure cellular preparations, the cells were ultrasonicated and the organelles separated on sucrose density gradients by means of ultracentrifugation. Organelles were characterized by their morphology on electron microscopy. Granulocytes were stimulated to secrete their granule constituents by means of exposure to complement-coated particles. ECP (eosinophil cationic protein) and MPO (myeloperoxidase) were measured using specific immunoassays. The uptake of (99m)Tc-HMPAO was 15--25-fold higher in eosinophils than in other leucocytes. (99m)Tc-HMPAO was predominantly stored in the secretory granules of eosinophils and released from the eosinophil, upon activation, together with ECP. A second storage compartment was a very light density organelle of unknown nature. These results indicated that, among leucocytes, (99m)Tc-HMPAO is preferentially taken up by eosinophils and stored in the secretory granules, which has to be taken into consideration when evaluating images based on this technique. Our findings suggest that (99m)Tc-HMPAO (Ceretec) may be used as a tool to follow eosinophil turnover and activity in disease.

Polymorphonuclear neutrophils release 35S-labelled proteoglycans into cartilage during frustrated phagocytosis

Rabbit peritoneal polymorphonuclear neutrophils (PMN), incubated in medium containing [35S]sulphate, incorporated 35S into proteoglycan and protein fractions. Approximately 46% of the 35S-labelled macromolecules associated with the PMN cells after 1 h of incubation were recovered in a cytoplasmic granule extract, the majority being present in azurophil granules. Analysis of the azurophil granule fraction showed that approximately 90% of the 35S-labelled macromolecules were proteoglycans. When challenged with heat-aggregated rabbit gamma-globulin in the presence of cytochalasin B and cGMP, PMN were induced to release granular enzymes but did not release 35S-labelled proteoglycans into the incubation medium. When incubated with articular cartilage slices, PMN released their granule 35S-labelled proteoglycan into the medium and into the cartilage matrix. Granule enzymes and 35S-labelled granule proteoglycan were extracted from the cartilage tissue after incubation and 35S-labelled macromolecules were detected in the cartilage tissue by autoradiography.

Preferential localisation of elastase in cytosol of human myeloid leukemia HL-60 cells

The subcellular distribution of the elastase in human myeloid leukemia HL-60 cells was studied in comparison with that in normal leukocytes. On differential centrifugation, most of the elastase activity of HL-60 cell lysates was recovered in the 105,000 x g supernatant, while that of human peripheral blood leukocyte lysates was recovered in the 500 x g precipitate (azurophil granule-rich fraction). Moreover, on Percoll density gradient centrifugation, the elastase activity in HL-60 cell extracts was recovered in the lightest fraction with none in the azurophil granule-rich fractions, whereas most of the activity in leukocyte extracts was recovered in the azurophil granule-rich fractions. This subcellular localization of elastase did not change when HL-60 cells differentiated into monocytes and granulocytes by induction with 12-O-tetradecanoyl phorbol-13-acetate and retinoic acid, respectively. Furthermore, on Sephadex G-75 gel filtration, the elastase activity in HL-60 cell extracts was eluted earlier than that in leukocyte extracts. The size estimation indicated that the elastase of HL-60 cells was 36-30 kDa, corresponding to the size of an elastase precursor reported. The relevance of a large form of the elastase in HL-60 cells to its subcellular localization is discussed.

PMN elastases: a comparison of the specificity of human isozymes and the enzyme from other species toward substrates and inhibitors

The human elastases isolated from polymorphonuclear neutrophils (PMN) and purulent sputum displayed identical kinetic constants toward substrates and inhibitors. The elastases from the two sources yield identical N-terminal sequences and were recognized by antiserum prepared against human sputum elastase (HSE) isozyme-4 (I-4). The data support the proposal put forth by Twumasi and Liener (1977, J. Biol. Chem. 252, 1917-1926) that the human elastase from sputum is of PMN origin. PMN elastases from other species displayed kinetic constants toward both substrates and inhibitors significantly different from the human enzyme. Therefore, extrapolation of inhibitor profiles from these elastases to the human source should be avoided. Four groups of isozymes were resolved from HSE by FPLC. Only the most basic isozyme (I-4) was obtained as a single species. The isozymes displayed identical macroscopic kinetic constants toward several substrates and two classes of inhibitors. The similar partition ratios observed with a cephalosporin-derived inhibitor suggest that the microscopic rate constants are also identical. The data support the proposal suggested by Baugh and Travis (1976, Biochemistry 15, 836-841) that HLE isozymes differ only in carbohydrate content. Whatever the source of human PMN elastase heterogeneity, it does not result in heterogeneous catalytic properties. In addition, a new protein was identified in elastase preparations derived from human sputum. This protein displayed homology to serine proteases and properties suggesting that it is identical to azurocidin.

Interleukin 1 alpha acts as an autocrine growth factor for RPMI 1788, an Epstein-Barr virus-transformed human B cell line

The Epstein-Barr virus-transformed B cell line RPMI 1788 constitutively produces autocrine growth factors with molecular masses of 17 kDa, 24 kDa and 35 kDa. All three molecular forms were completely neutralized with anti-interleukin (IL) 1 alpha antiserum. Although IL 1 alpha and IL 1 beta mRNA were both equally detectable by Northern blotting, no IL 1 beta activity was found in partially purified RPMI 1788 supernatant. The growth of low density-seeded RPMI 1788 cells is specifically dependent on the presence of either IL 1 alpha or IL 1 beta. Since no other cytokine was found to be capable of sustaining proliferation, this cell line is suitable for the identification and quantification of IL 1, even in the presence of other cytokines.

Stimulation of prostaglandin release by Ca2+-mobilizing agents from the perfused rat liver. A comparative study on the action of ATP, UTP, phenylephrine, vasopressin and nerve stimulation

Several Ca2+-mobilizing agents were tested for their potential to elicit the net release of prostaglandins from the isolated perfused rat liver. Among these ATP and UTP only led to an efficient stimulation of PGD2 and PGE2 synthesis. 20 microM ATP or 20 microM UTP increased the release of PGD2 8-fold and that of PGE2 2 to 3-fold. In total, at least 40 times more PGD2 than PGE2 left the liver after stimulation. The time course of prostaglandin release was similar for both nucleotides. Vasopressin had almost no effect on the release of both prostaglandins and on portal vein pressure. But phenylephrine and nerve stimulation while raising the PGD2 efflux only slightly caused an elevation of PGE2 outflow and portal pressure.

Bactericidal proteins and neutral proteases in diabetes neutrophils

Reduced bacterial killing by polymorphonuclear leucocytes has been reported in patients with diabetes mellitus. Whether this is due to reduced content of bactericidal granular proteins has not been determined. We therefore immunochemically measured the content of myeloperoxidase, lactoferrin, lysozyme, cathepsin G and elastase in polymorphonuclear leucocytes from 50 insulin-treated diabetic patients. The peroxidase activity was also measured. Normal contents of myeloperoxidase and lactoferrin as well as normal peroxidase activity were found. The average contents of cathepsin G, elastase and lysozyme were 2.5, 3.2 and 2.6 micrograms/10(6) polymorphonuclear leucocytes, respectively, and thus 14, 45 and 18% higher than the contents of normal polymorphonuclear leucocytes. The results indicate that reduced intracellular killing of bacteria demonstrated in previous studies in diabetic patients does not appear to be related to a reduction in the content of bactericidal proteins.