Isolation of bovine neutrophils with biomagnetic beads: comparison with standard Percoll density gradient isolation methods

Paralytic Impact of Centrifugation on Human Neutrophils

Centrifugation is a common step in most of the popular protocols for the isolation of neutrophils from whole blood. Inconsistent results from previous studies on neutrophils may originate from an underestimation of the centrifugation effect, as in consequence impaired, not native cells, being investigated. We hypothesize, that centrifugation significantly impairs major neutrophil functions. However, there is no data yet whether the application of g-force itself or the product of g-force and duration of centrifugation (="g-time") defines the impact on neutrophils. Neutrophils were isolated from whole blood via centrifugation with different g-times and subsequently analyzed via live cell imaging for migration, as well as via flow cytometry for oxidative burst and surface antigen expression. Chemotactic migration was significantly reduced with increasing g-time. Oxidative burst decreased likewise the higher the g-time applied. Expression of CD11b was no longer upregulated in response to an n-formylmethionine-leucyl-phenylalanine (fMLP) stimulus in neutrophils having experienced high g-time during the isolation process. We conclude that centrifugation "paralyzes" neutrophils in the form of a significant decrease in functionality. Future investigations on neutrophil granulocytes should reduce the g-time load as far as possible.

Methods of Granulocyte Isolation from Human Blood and Labeling with Multimodal Superparamagnetic Iron Oxide Nanoparticles

This in vitro study aimed to find the best method of granulocyte isolation for subsequent labeling with multimodal nanoparticles (magnetic and fluorescent properties) to enable detection by optical and magnetic resonance imaging (MRI) techniques. The granulocytes were obtained from venous blood samples from 12 healthy volunteers. To achieve high purity and yield, four different methods of granulocyte isolation were evaluated. The isolated granulocytes were labeled with multimodal superparamagnetic iron oxide nanoparticles (M-SPIONs) coated with dextran, and the iron load was evaluated qualitatively and quantitatively by MRI, near-infrared fluorescence (NIRF) and inductively coupled plasma mass spectrometry (ICP-MS). The best method of granulocyte isolation was Percoll with Ficoll, which showed 95.92% purity and 94% viability. After labeling with M-SPIONs, the granulocytes showed 98.0% purity with a yield of 3.5 × 10⁶ cells/mL and more than 98.6% viability. The iron-loading value in the labeled granulocytes, as obtained by MRI, was 6.40 ± 0.18 pg/cell. Similar values were found with the ICP-MS and NIRF imaging techniques. Therefore, our study shows that it is possible to isolate granulocytes with high purity and yield and labeling with M-SPIONs provides a high internalized iron load and low toxicity to cells. Therefore, these M-SPION-labeled granulocytes could be a promising candidate for future use in inflammation/infection detection by optical and MRI techniques.

Comparison Between K3EDTA and Lithium Heparin as Anticoagulant to Isolate Bovine Granulocytes From Blood

Granulocytes play a key role in the defense against invading pathogens. To study granulocyte functions, the isolation of a pure and active cell population from fresh blood is required. Anticoagulants and red blood cells (RBCs) lysis used in the isolation procedure may influence cell harvest, cell marker expression, and pre-activation of cells. In this study, the influence of the anticoagulants K₃EDTA or lithium heparin and the effect of different RBCs lysis methods on bovine granulocyte population from fresh blood of healthy cows after density gradient centrifugation were investigated. Venous blood from healthy cows was collected in K₃EDTA and lithium heparin tubes. Density gradient centrifugation to separate granulocytes from other cells was conducted using Biocoll. Then, RBCs were lysed with hypotonic water or 0.2% sodium chloride (NaCl). Immediately after isolation, harvest, viability, size, granularity, purity, and CD11b expression as a marker for granulocytes was analyzed by flow cytometry. In addition, as a marker for activation and reactivity of the granulocytes, we stimulated cells with phorbol-myristate-acetate to evaluate the release of reactive oxygen species. Furthermore, extracellular trap (ET) formation was investigated by confocal immunofluorescence microscopy in untreated control cells and cells treated with the cholesterol-depleting agent methyl-β-cyclodextrin. We did not find a significant difference in percentage of dead cells when comparing the two anticoagulants or the different RBCs lysis methods. However, the percentage of granulocytes in the harvested population was significantly less using lithium heparin blood as anticoagulant compared to K₃EDTA. The granulocytes harvested from lithium heparin blood and water lysis exhibited higher clumping and pre-activation of unstimulated control cells as indicated by isolation of doublet cells, increased CD11b expression, and increased oxidative burst and higher amount of ET-releasing cells. Furthermore, the combination of K₃EDTA as anticoagulant and NaCl as RBCs lysis method revealed the lowest variability and highest difference between untreated and methyl-β-cyclodextrin-treated cells when quantifying ET formation. In conclusion, density gradient centrifugation of K₃EDTA blood resulted in higher purity of bovine granulocytes compared to lithium heparin blood. In contrast to water lysis, NaCl lysis method is recommended to avoid pre-activation of cells which may occur during hypotonic water lysis.

Molecular analysis of the bovine anaphylatoxin C5a receptor

Recruitment of phagocytes to inflammatory sites involves the coordinated action of several chemoattractants, including the anaphylatoxin C5a. While the C5a receptor (C5aR) has been well characterized in humans and rodents, little is known about the bovine C5aR. Here, we report cloning of bovine C5R1, the gene encoding bovine C5aR. We also analyzed genomic sequence upstream of the C5R1 translation start site. Although the bovine C5aR amino acid sequence was well conserved among species, significant differences in conserved features were found, including major differences in the N terminus, intracellular loop 3, and transmembrane domain VII. Analysis of C5aR expression by flow cytometry and confocal microscopy demonstrated high levels of C5aR on all bovine neutrophils and a subset of bovine monocytes. C5aR was not expressed on resting or activated bovine lymphocytes, although C5aR message was present in these cells. C5aR was also expressed on a small subset of bovine mammary epithelial cells. Pharmacological analysis of bovine C5aR-mediated responses showed that bovine C5a and C5adesArg both induced dose-dependent calcium fluxes and chemotaxis in bovine neutrophils, with similar efficacy for both agonists. Treatment of bovine neutrophils with C5a or C5adesArg resulted in homologous desensitization of bovine C5aR and cross-desensitization to interleukin 8 (IL-8) and platelet-activating factor (PAF); whereas, treatment with IL-8 or PAF did not cross-desensitize the cells to C5a or C5adesArg. Overall, these studies provide important information regarding distinct structural and functional features that may contribute to the unique pharmacological properties of bovine C5aR.

Cell isolation and expansion using Dynabeads

This chapter describes the use of Dynabeads for cell isolation and expansion. Dynabeads are uniform polystyrene spherical beads that have been made magnetisable and superparamagnetic, meaning they are only magnetic in a magnetic field. Due to this property, the beads can easily be resuspended when the magnetic field is removed. The invention of Dynabeads made, by Professor John Ugelstad, has revolutionized the separation of many biological materials. For example, the attachment of target-specific antibodies to the surface of the beads allows capture and isolation of intact cells directly from a complex suspension such as blood. This is all accomplished under the influence of a simple magnetic field without the need for column separation techniques or centrifugation. In general, magnetic beads coated with specific antibodies can be used either for isolation or depletion of various cell types. Positive or negative cell isolation can be performed depending on the nature of the starting sample, the cell surface markers and the downstream application in question. Positive cell isolation is the method of choice for unprocessed samples, such as whole blood, and for downstream molecular applications. Positive cell isolation can also be used for any downstream application after detachment and removal of the beads. Negative cell isolation is the method of choice when it is critical that cells of interest remain untouched, i.e., no antibodies have been bound to any cell surface markers on the cells of interest. Some cell populations can only be defined by multiple cell surface markers. Such populations of cells can be isolated by the combination of negative and positive cell isolation. By coupling Dynabeads with antibodies directed against cell surface activation molecules, the beads can be used both for isolation and expansion of the cells. Dynabeads are currently used in two major clinical applications: 1) In the Isolex 300i Magnetic Cell Selection System for CD34 Stem Cell Isolation--2) For ex vivo T cell isolation and expansion using Dynabeads ClinExVivo CD3/CD28 for clinical trials in novel adoptive immunotherapy.

Contribution of respiratory burst activity to innate immune function and the effects of disease status and agent on chemiluminescence responses by ruminant phagocytes in vitro

The mechanisms of interaction between phagocytes and different bacteria that help resolve lung infections or contribute to lung pathology are poorly defined. Alveolar phagocytes (resident macrophages and recruited neutrophils) make a major contribution to innate immunity by mounting a respiratory burst that helps kill internalised bacteria. However, this ability may be altered during or after exposure to infection. This review considers the application and limitations of a variety of analytical methods for oxygen-dependent mechanisms of respiratory burst in phagocytes initiated by soluble and particulate activators. Particular reference is given to the study in vitro of phagocytes from healthy and diseased ruminants during either natural infection with Mycobacterium avium paratuberculosis or experimental infection with Pasteurella multocida or Mannheimia haemolytica.

Inhibition of actin polymerization by peroxynitrite modulates neutrophil functional responses

Peroxynitrite, a potent oxidant generated in inflammatory tissues, can nitrate tyrosine residues on a variety of proteins. Based on previous studies suggesting that actin might be a potential target for peroxynitrite-mediated nitration in neutrophils, we investigated the effects of peroxynitrite on actin function. We show here that peroxynitrite and the peroxynitrite generator (SIN-1) modified actin in a concentration-dependent manner, resulting in an inhibition of globular-actin polymerization and filamentous-actin depolymerization in vitro. The effects of peroxynitrite were inhibited by the pyrrolopyrimidine antioxidant PNU-101033E, which has been shown previously to specifically block peroxynitrite-mediated tyrosine nitration. Furthermore, spectrophotometric and immunoblot analysis of peroxynitrite-treated actin demonstrated a concentration-dependent increase in nitrotyrosine, which was also blocked by PNU-101033E. Activation of neutrophils in the presence of a nitric oxide donor (S-nitroso-N-acetylpenicillamine) resulted in nitration of exogenously added actin. Nitrated actin was also found in peroxynitrite-treated neutrophils, suggesting that actin may be an important intracellular target during inflammation. To investigate this issue, we analyzed the effect of peroxynitrite treatment on a number of actin-dependent neutrophil processes. Indeed, neutrophil actin polymerization, migration, phagocytosis, and respiratory burst activity were all inhibited by SIN-1 treatment in a concentration-dependent manner. Therefore, the ability of peroxynitrite to inhibit actin dynamics has a significant effect on actin-dependent, cellular processes in phagocytic cells and may modulate their host defense function.

Effect of fibrin sealant composition on human neutrophil chemotaxis

The use of fibrin sealants offers one of the most physiologically compatible approaches to preventing postoperative adhesions. Although a number of fibrin sealant formulations have been developed, little is known about how the various components of these preparations affect the wound-healing process. Because one of the key steps in wound healing is the migration of phagocytic leukocytes, such as neutrophils, into the site of injury, we performed studies to characterize systematically the effects of various fibrin sealant components on neutrophil chemotaxis. Using a transwell chemotaxis assay, we found that increasing fibrin concentration resulted in an inhibition of the ability of the cells to migrate through the clots in a dose-dependent manner, and at fibrin clot concentrations >2.0 mg/mL chemotaxis was completely blocked. Factor XIII crosslinking of the clots also had a significant impact on neutrophil chemotaxis, and sealant preparations deficient in Factor XIII allowed neutrophil migration at much higher fibrin concentrations. The presence of various other fibrin sealant components such as plasminogen and fibrinolysis inhibitors (aprotinin and tranexamic acid) did not have any significant effects on the ability of neutrophils to migrate through fibrin clots as compared to control clots without these components. Overall, these studies show that the composition of fibrin sealant preparations can significantly affect neutrophil migration into the site of injury, which could possibly influence the wound healing process.

Ultrastructural examination of cytoskeletal linkage of L-selectin and comparison of L-selectin cytoskeletal association to that of other human and bovine lymphocyte surface antigens

L-selectin is constitutively expressed on most leukocytes and is responsible for the initial events in cell trafficking termed tethering and rolling. Recently, L-selectin has been shown to associate with the actin-based cytoskeleton under a variety of conditions. In an effort to better understand L-selectin cytoskeletal association and the ultrastructural nature of the cytoskeleton itself, we provide a comparison of the cytoskeletal association of various human and bovine surface proteins in relation to L-selectin. Electron microscopic examination of the cytoskeleton provided further data on the ultrastructure of freshly isolated peripheral lymphocytes as well as demonstrated L-selectin localization to the periphery of the cytoskeleton following low dose detergent treatment of the cell. Clusters of colloidal-gold-stained L-selectin were found on the surface of the detergent-treated lymphocytes, even though these particles completely lacked microvilli. By flow cytometry, we have defined three distinct patterns of cytoskeletal association; constitutive, inductive, and mAb crosslink-induced, and assigned human and bovine CD2, CD3, CD4, CD5, CD8, CD18, CD19, CD44, CD45RA, CD45RO, alphabeta TCR, gammadelta TCR, E-selectin ligands, and L-selectin surface antigens to one of these respective patterns. SDS-PAGE analyses confirmed most of the flow cytometry results. Depending upon its conformation, L-selectin fell into the inductive or mAb crosslink-induced pattern of association, similar to E-selectin ligand(s). Our data provide additional insight into the functional role of L-selectin and the cytoskeleton in immunological events.

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.

Selective recruitment of T-cell subsets to the udder during staphylococcal and streptococcal mastitis: analysis of lymphocyte subsets and adhesion molecule expression

During bacterial infection of the bovine mammary gland, large numbers of leukocytes migrate into the udder, resulting in the establishment of a host response against the pathogen. Currently, the specific leukocyte populations mediating this immune response are not well defined. In the studies described here, we analyzed blood and milk from healthy cows and cows with naturally occurring mastitis to determine if distinct alphabeta and gammadelta T-lymphocyte subsets were involved in the response of the udder to a mastitis pathogen and if the type of mastitis pathogen influenced the subset composition of these responding leukocytes. Although blood samples from cows with confirmed staphylococcal and streptococcal mastitis were characterized by increased numbers of gammadelta T cells, the most dramatic changes in leukocyte distributions occurred in milk samples from these cows, with a 75% increase in alphabeta T-cell levels and a 100% increase in gammadelta T-cell levels relative to the levels in milk samples from healthy animals. Interestingly, the increase in alphabeta T-cell numbers observed in milk from cows with staphylococcal mastitis was primarily due to increased numbers of CD4(+) T cells, while the increase in alphabeta T-cell numbers observed in cows with streptococcal mastitis was due to a parallel increase in both CD4(+) and CD8(+) T-cell numbers. The increased numbers of gammadelta T cells in milk from cows with staphylococcal and streptococcal mastitis were due to a selective recruitment of a distinct gammadelta T-cell subset (GD3.1(+)), while no change in the numbers of GD197(+) gammadelta T cells was observed. We also analyzed adhesion protein expression on blood and milk leukocytes and found that, in comparison to the situation for healthy cows, L-selectin was down-regulated and CD18 was up-regulated on leukocytes from cows with mastitis. Thus, shedding of L-selectin and up-regulation of CD18 by neutrophils may provide a sensitive indicator of early inflammatory responses during bovine mastitis. Overall, these studies suggest that distinct alphabeta and gammadelta T-cell subsets are involved in the host defense of the udder against mastitis infection and that selective recruitment of these T-cell subsets depends on the infectious agent involved.