Methods for quantitation of human neutrophil proteins, a survey

Alpha 1-acid glycoprotein is upregulated in severe COVID-19 patients and decreases neutrophil NETs in SARS-CoV-2 infection

Orosomucoid, or alpha-1 acid glycoprotein (AGP), is a major acute-phase protein expressed in response to systemic injury and inflammation. AGP has been described as an inhibitor of neutrophil migration on sepsis, particularly its immunomodulation effects. AGP's biological functions in coronavirus disease 2019 (COVID-19) are not understood. We sought to investigate the role of AGP in severe COVID-19 infection patients and neutrophils infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Epidemiological data, AGP levels, and other laboratory parameters were measured in blood samples from 56 subjects hospitalized in the ICU with SARS-CoV-2 infection. To evaluate the role of AGP in NETosis in neutrophils, blood samples from health patients were collected, and neutrophils were separated and infected with SARS-CoV-2. Those neutrophils were treated with AGP or vehicle, and NETosis was analyzed by flow cytometry. AGP was upregulated in severe COVID-19 patients (p<0.05). AGP level was positively correlated with IL-6 and C-reactive protein (respectively, p=0.005, p=0.002) and negatively correlated with lactate (p=0.004). AGP treatment downregulated early and late NETosis (respectively, 35.7% and 43.5%) in neutrophils infected with SARS-CoV-2 and up-regulated IL-6 supernatant culture expression (p<0.0001). Our data showed increased AGP in COVID-19 infection and contributed to NETosis regulation and increased IL-6 production, possibly related to the Cytokine storm in COVID-19.

Subcellular fractionation of human neutrophils and analysis of subcellular markers

The neutrophil has long been recognized for its impressive number of cytoplasmic granules that harbor proteins indispensable for innate immunity. Analysis of isolated granules has provided important information on how the neutrophil grades its response to match the challenges it meets on its passage from blood to tissues. Nitrogen cavitation was developed as a method for disruption of cells on the assumption that sudden reduction of the partial pressure of nitrogen would lead to aeration of nitrogen dissolved in the lipid bilayer of plasma membranes. We find that cells are broken by the shear stress that is associated with passage through the outlet valve under high pressure and that this results in disruption of the neutrophil cell membrane while granules remain intact. The unique properties of Percoll as a sedimentable density medium with no inherent tonicity or viscosity are used for creation of continuous density gradients with shoulders in the density profile created to optimize the physical separation of granule subsets and light membranes. Immunological methods (sandwich enzyme-linked immunosorbent assays) are used for quantitation of proteins that are characteristic constituents of the granule subsets of neutrophils.

Evaluation of bactericidal activity of human biological fluids by flow cytofluorimetry

The ability of biological fluids to kill microbes is an important feature of the human immune system. Following incubation of fluorescein isothiocyanate-labeled Staphylococcus aureus with biological specimens and subsequent staining with propidium iodide, the proportions of killed bacteria were estimated by flow cytometry. FACScan is a simple, quick and reliable method to evaluate bactericidal activity of biological fluids. The results of the cytometric method correlated well with the results of the classic microbiological method. The proposed method is highly informative for evaluating bactericidal activity of sera in immunocompromised patients.

Application of intracellular alkaline phosphatase activity measurement in detection of neutrophil adherence in vitro

We have proposed the use of the fluorimetric method with 4-methylumbelliferyl phosphate (4-MUP) specific substrate for the alkaline phosphatase determination in the neutrophil adhesion assay. We provide evidence that the endogenous neutrophil alkaline phosphatase (NAP) activity evaluation is reliable to quantify neutrophil adhesion at a wide range of cell numbers (10(4)-10(6)). The results obtained by fluorimetric NAP activity test correlate to the results of adherence evaluated using the MTT reduction assay. The fluorimetric NAP activity test may be applied for resting as well as activated neutrophils without the risk of the activators interferences into the test. The alkaline phosphatase survey with the use of 4-MUP substrate is recommended herein as a sensitive, repeatable, simple, and reliable method of the neutrophil adherence determination in vitro.

Subcellular fractionation of human neutrophils and analysis of subcellular markers

The neutrophil has long been recognized for its impressive number of cytoplasmic granules that harbor proteins indispensable for innate immunity. Analysis of isolated granules has provided important information on how the neutrophil grades its response to match the challenges it meets on its passage from blood to tissues. Nitrogen cavitation was developed as a method for disruption of cells on the assumption that sudden reduction of the partial pressure of nitrogen would lead to aeration of nitrogen dissolved in the lipid bilayer of plasma membranes. We find that cells are broken by the shear stress that is associated with passage through the outlet valve under high pressure, and that this results in disruption of neutrophils while leaving granules intact. The unique properties of Percoll as a sedimentable density medium with no inherent tonicity or viscosity are exploited for the creation of continuous density gradients with shoulders in the density profile created to optimize the physical separation of granule subsets and light membranes. Immunological methods (sandwich enzyme-linked immunosorbent assays) are used for quantitation of proteins that are characteristic constituents of the granule subsets of neutrophils.

Human myeloperoxidase catalyzes an oscillating peroxidase-oxidase reaction

We have studied the peroxidase-oxidase reaction catalyzed by human myeloperoxidase in an open system where both substrates-molecular oxygen and NADH-are supplied continuously to the reaction mixture. The reaction shows oscillatory kinetics at pH values around 5, provided that the reaction medium in addition to the enzyme and the substrates also contains an aromatic electron mediator such as melatonin or 4-hydroxybenzoic acid and chloride ions at concentrations >1mM. The experimental findings can be simulated by a detailed model of the reaction. The results are important for our understanding of oxidant production in neutrophils.

Urokinase-deficient and urokinase receptor-deficient mice have impaired neutrophil antimicrobial activation in vitro

Leukocytes express both urokinase-type plasminogen activator (uPA) and the urokinase receptor (uPAR, CD87). We have shown that neutrophil recruitment to the lung during P. aeruginosa pneumonia is impaired in uPAR-deficient (uPAR-/-) mice but is normal in uPA-/- mice. However, both uPA-/- mice and uPAR-/- mice have impaired lung clearance of P. aeruginosa compared with wild-type (WT) mice. To determine the role of uPA and uPAR in antibacterial host defense, we compared neutrophil bacterial-phagocytosis, respiratory burst, and degranulation among uPA-/-, uPAR-/-, and WT mice. Neutrophil phagocytosis was significantly diminished comparing uPA-/- and uPAR-/- mice with WT mice at all time points. The generation of superoxide by both uPA-/- and uPAR-/- neutrophils was about half of that seen in WT neutrophils. Degranulation of azurophilic granules was significantly diminished in uPA-/- neutrophils compared with either uPAR-/- or WT neutrophils. By contrast, agonist-stimulated release of specific granules was not diminished in either uPA-/- or uPAR-/- mice compared with WT. We conclude that the uPA/uPAR system modulates several of the crucial steps in neutrophil activation that result in bacterial killing and effective innate host defense.

Changes in neutrophil surface-receptor expression after stimulation with FMLP, endotoxin, interleukin-8 and activated complement compared to degranulation

Neutrophil activation induces changes in the expression of surface receptors and may lead to degranulation. Surface expression of beta2-integrins, l-selectin, complement receptor 1 (CR-1), decay-accelerating factor (DAF), C5a receptor, intercellular adhesion molecule-1 (ICAM-1) and ICAM-3 was compared by flow cytometry on isolated neutrophils stimulated with phorbol 12-myristate 13-acetate (PMA), N-formyl-methionyl-leucyl-phenylalanine (FMLP), endotoxin or interleukin-8 and on neutrophils in whole blood anti-coagulated with the thrombin inhibitor lepirudin and stimulated with cobra venom factor to induce complement activation. Myeloperoxidase and lactoferrin in the supernatants were quantified in enzyme immunoassays. With high enough doses, all stimulants induced significant upregulation of beta2-integrins, CR-1 and DAF and downregulation of l-selectin. ICAM-3 was either unchanged or somewhat downregulated. Only FMLP and PMA induced significant upregulation of ICAM-1. Combined measurement of beta2-integrins and l-selectin permitted graded evaluation of early neutrophil activation. Measurement of degranulation showed no differences compared to unstimulated controls due to substantial spontaneous degranulation of isolated neutrophils by rewarming from 4 degrees C and incubation at 37 degrees C. Spontaneous activation was less in ethylenediaminetetraacetic acid-anti-coagulated blood, but calcium chelation may also inhibit the stimulated responses. There was large activation of unstimulated neutrophils in lepirudin-anti-coagulated blood at 37 degrees C, obscuring changes induced by stimulation, which may render this anti-coagulant unsuitable for studies of neutrophils.

Magnetic bead isolation of neutrophil plasma membranes and quantification of membrane-associated guanine nucleotide binding proteins

A protocol for isolation of neutrophil plasma membranes utilizing a plasma membrane marker antibody, anti-CD15, attached to superparamagnetic beads was developed. Cells were initially disrupted by nitrogen cavitation and then incubated with anti-CD15 antibody-conjugated superparamagnetic beads. The beads were then washed to remove unbound cellular debris and cytosol. Recovered plasma membranes were quantified by immunodetection of G(beta2) in Western blots. This membrane marker-based separation yielded highly pure plasma membranes. This protocol has advantages over standard density sedimentation protocols for isolating plasma membrane in that it is faster and easily accommodates cell numbers as low as 10(6). These methods were coupled with immunodetection methods and an adenosine 5(')-diphosphate-ribosylation assay to measure the amount of membrane-associated G(ialpha) proteins available for receptor coupling in neutrophils either stimulated with N-formyl peptides or treated to differing degrees with pertussis toxin. As expected, pertussis toxin treatment decreased the amount of membrane G protein available for signaling although total membrane G protein was not affected. In addition, activation of neutrophils with N-formyl peptides resulted in an approximately 50% decrease in G protein associated with the plasma membrane.

Granulocyte concentrates: how can we assess their quality?

The use of granulocyte transfusions to treat and prevent life-threatening infection in patients lacking neutrophil numbers or function may become increasingly important in aiding advances in the treatment of haematological malignancies. A critical factor in determining the outcome of granulocyte transfusion is the number of cells transfused, and collection of sufficiently high concentration of cells from donors remains challenging. A number of tests of granulocyte function can be performed in vitro to assess the quality of granulocyte concentrates, which may be useful in helping to optimize granulocyte collection, processing and storage methods. Studies that have examined neutrophil function in granulocyte concentrates to date have tended to focus on the assessment of viability, chemotaxis, phagocytosis and oxidative killing. How useful in vitro tests of neutrophil function are in predicting neutrophil function following granulocyte transfusion remains to be established in conjunction with well-designed clinical trials.

A model of the oscillatory metabolism of activated neutrophils

We present a two-compartment model to explain the oscillatory behavior observed experimentally in activated neutrophils. Our model is based mainly on the peroxidase-oxidase reaction catalyzed by myeloperoxidase with melatonin as a cofactor and NADPH oxidase, a major protein in the phagosome membrane of the leukocyte. The model predicts that after activation of a neutrophil, an increase in the activity of the hexose monophosphate shunt and the delivery of myeloperoxidase into the phagosome results in oscillations in oxygen and NAD(P)H concentration. The period of oscillation changes from >200 s to 10-30 s. The model is consistent with previously reported oscillations in cell metabolism and oxidant production. Key features and predictions of the model were confirmed experimentally. The requirement of the hexose monophosphate pathway for 10 s oscillations was verified using 6-aminonicotinamide and dexamethasone, which are inhibitors of glucose-6-phosphate dehydrogenase. The role of the NADPH oxidase in promoting oscillations was confirmed by dose-response studies of the effect of diphenylene iodonium, an inhibitor of the NADPH oxidase. Moreover, the model predicted an increase in the amplitude of NADPH oscillations in the presence of melatonin, which was confirmed experimentally. Successful computer modeling of complex chemical dynamics within cells and their chemical perturbation will enhance our ability to identify new antiinflammatory compounds.

Hypothermia augments polymorphonuclear leukocyte degranulation and interleukin-8 production from human umbilical vein endothelial cells and increases lipopolysaccharide-induced polymorphonuclear leukocyte-endothelial cell interaction when followed by normothermia

OBJECTIVE

To determine if hypothermia followed by normothermia (rewarmed to 37 degrees C) changes the inflammatory response of polymorphonuclear leukocytes (PMNs) and human umbilical vein endothelial cells (HUVEC).

DESIGN

Prospective, controlled, in vitro study.

SETTING

University laboratory.

PARTICIPANTS

PMNs from 4 healthy volunteers and HUVEC.

MEASUREMENTS AND MAIN RESULTS

PMNs and HUVEC were incubated for 3 hours at 20 degrees C, 30 degrees C, or 37 degrees C followed by 37 degrees C again. PMN degranulation, cytokine production from HUVEC, and PMN-HUVEC interaction were compared among the 3 experimental temperatures. Interleukin (IL)-8-induced PMN degranulation measured by myeloperoxidase concentrations was significantly higher in the 20 degrees C and 30 degrees C groups than the 37 degrees C groups. Bacterial lipopolysaccharide (LPS)-induced IL-8 production from HUVEC, measured by enzyme-linked immunosorbent assay, was significantly higher in the 20 degrees C group than the other 2 groups; however, tumor necrosis factor-alpha was not detectable in any of the groups. LPS-induced cell injury measured by cellular (51)Cr release was significantly higher in the 20 degrees C and 30 degrees C groups than in the 37 degrees C groups. This injury was significantly inhibited by IL-8 antibody.

CONCLUSION

Hypothermic (20 degrees C and 30 degrees C) incubation followed by rewarming augmented IL-8-induced PMN degranulation and LPS-induced IL-8 production from HUVEC and LPS-induced PMN-endothelial interaction. IL-8 plays an important role in this increased injury. This increased inflammatory response may support the positive outcomes of normothermic CPB.

Secretion of heparin-binding protein from human neutrophils is determined by its localization in azurophilic granules and secretory vesicles

Human neutrophils have an important role in host defense against microbial infection. At different stages of an infectious process, neutrophils progressively up-regulate receptors and release various effector molecules. These are stored in several distinct types of granules with varying propensity to be secreted. Heparin-binding protein (HBP), also known as CAP37 or azurocidin, is a multifunctional, inactive serine-protease homologue. The present work shows that HBP is released from neutrophils on stimulation with secretagogues that do not trigger the secretion of azurophilic granule content. Therefore, the subcellular localization of HBP was investigated in more detail. Immunofluorescence microscopy revealed that HBP was localized close to the plasma membrane. Further analysis by fractionation of postnuclear supernatants from cavitated neutrophils showed that HBP is stored in azurophilic granules and secretory vesicles but that it is also detected to a minor extent in the plasma membrane. These findings were confirmed by immunoelectron microscopy showing that HBP colocalized with marker proteins of azurophilic granules and secretory vesicles. The presence of HBP in secretory vesicles possibly depends on the stage of cell differentiation, since the promyelocytic cell line HL-60 contains less HBP than mature neutrophils, stored exclusively in the less easily mobilized azurophilic granules. Our findings suggest that HBP can be synthesized or targeted to easily mobilized compartments at a late stage of neutrophil maturation. The ability of neutrophils to secrete HBP from secretory vesicles may be important for proinflammatory functions of this protein, such as the alteration of vascular permeability.

Groups IV, V, and X phospholipases A2s in human neutrophils: role in eicosanoid production and gram-negative bacterial phospholipid hydrolysis

The bacterial tripeptide formyl-Met-Leu-Phe (fMLP) induces the secretion of enzyme(s) with phospholipase A(2) (PLA(2)) activity from human neutrophils. We show that circulating human neutrophils express groups V and X sPLA(2) (GV and GX sPLA(2)) mRNA and contain GV and GX sPLA(2) proteins, whereas GIB, GIIA, GIID, GIIE, GIIF, GIII, and GXII sPLA(2)s are undetectable. GV sPLA(2) is a component of both azurophilic and specific granules, whereas GX sPLA(2) is confined to azurophilic granules. Exposure to fMLP or opsonized zymosan results in the release of GV but not GX sPLA(2) and most, if not all, of the PLA(2) activity in the extracellular fluid of fMLP-stimulated neutrophils is due to GV sPLA(2). GV sPLA(2) does not contribute to fMLP-stimulated leukotriene B(4) production but may support the anti-bacterial properties of the neutrophil, because 10-100 ng per ml concentrations of this enzyme lead to Gram-negative bacterial membrane phospholipid hydrolysis in the presence of human serum. By use of a recently described and specific inhibitor of cytosolic PLA(2)-alpha (group IV PLA(2)alpha), we show that this enzyme produces virtually all of the arachidonic acid used for the biosynthesis of leukotriene B(4) in fMLP- and opsonized zymosan-stimulated neutrophils, the major eicosanoid produced by these pro-inflammatory cells.