Reorganization of the human neutrophil plasma membrane is associated with functional priming: implications for neutrophil preparations

Neutrophil Membrane Nanovesicles Alleviate the Renal Function Indicators in Acute Kidney Injury Caused by Septic Rats

This study aims to explore the efficacy of neutrophil membrane nanovesicles (NMNVs) in the treatment of acute kidney injury caused by sepsis (S-AKI). Moreover, its effects on renal function indicators in plasma [creatinine (CREA), urea (UREA)], oxidative stress factor [malondialdehyde (MDA)], inflammatory factor [myeloperoxidase (MPO), histone H4 (H4), and macrophage inflammatory protein-2 (MIP-2)] are studied. Sixty SPF grade adult male Wistar rats in a healthy state under natural infection were randomly divided into blank, LSP, and experimental groups, with 20 rats in each group. After 7 days of adaptive feeding, a S-AKI model was established in the control group and the experimental group. The control group was treated with red blood cell membrane nanovesicles (RBC-NVs), the experimental group was treated with NMNVs, and the blank group was normal rats. The clinical treatment and changes in renal function indicators of the tested rats were observed and recorded. The total effective rate of treatment in the experimental group was higher than that in the controlling group (P < 0.05). Moreover, 1 h after the construction of the S-AKI model, the CREA, UREA, MDA, MPO, H4, MIP-2 in the controlling group and experimental group were higher than those in the blank group. At 7 and 14 h after constructing S-AKI model, the CREA, UREA, MDA, MPO, H4, and MIP-2 in the controlling and experimental groups decreased. However, the above indicators in the experimental group were lower than those in the controlling group (P < 0.05), and the comparison between this group and the blank group showed P > 0.05. In summary, the efficacy of NMNV in treating S-AKI is significant, as it can reduce CREA, UREA, MDA, MPO, as well as H4 and MIP-2, effectively controlling disease progression.

Isolation of Human Neutrophils from Venous Blood

Venous blood provides a ready source of large numbers of unstimulated granulocytes and mononuclear cells. Exploiting the differences in the relative densities of the leukocytes circulating in venous blood, one can separate leukocytes from erythrocytes as well as isolate the individual leukocyte populations in high purity for use in ex vivo studies. For selected functional studies, such as transcriptional analysis or cytokine quantitation, addition of an immunomagnetic negative selection step to the standard isolation protocol can yield highly purified human neutrophils.

Transmigrating neutrophils shape the mucosal microenvironment through localized oxygen depletion to influence resolution of inflammation

Acute intestinal inflammation involves early accumulation of neutrophils (PMNs) followed by either resolution or progression to chronic inflammation. Based on recent evidence that mucosal metabolism influences disease outcomes, we hypothesized that transmigrating PMNs influence the transcriptional profile of the surrounding mucosa. Microarray studies revealed a cohort of hypoxia-responsive genes regulated by PMN-epithelial crosstalk. Transmigrating PMNs rapidly depleted microenvironmental O2 sufficiently to stabilize intestinal epithelial cell hypoxia-inducible factor (HIF). By utilizing HIF reporter mice in an acute colitis model, we investigated the relative contribution of PMNs and the respiratory burst to "inflammatory hypoxia" in vivo. CGD mice, lacking a respiratory burst, developed accentuated colitis compared to control, with exaggerated PMN infiltration and diminished inflammatory hypoxia. Finally, pharmacological HIF stabilization within the mucosa protected CGD mice from severe colitis. In conclusion, transcriptional imprinting by infiltrating neutrophils modulates the host response to inflammation, via localized O2 depletion, resulting in microenvironmental hypoxia and effective inflammatory resolution.

Isolation of human neutrophils from venous blood

Venous blood provides a ready source of large numbers of unstimulated granulocytes and mononuclear cells. Exploiting the differences in the relative densities of the leukocytes circulating in venous blood, one can separate leukocytes from erythrocytes as well as isolate the individual leukocyte populations in high purity for use in ex vivo studies.

Proteomic approaches to understanding the role of the cytoskeleton in host-defense mechanisms

The cytoskeleton is a cellular scaffolding system whose functions include maintenance of cellular shape, enabling cellular migration, division, intracellular transport, signaling and membrane organization. In addition, in immune cells, the cytoskeleton is essential for phagocytosis. Following the advances in proteomics technology over the past two decades, cytoskeleton proteome analysis in resting and activated immune cells has emerged as a possible powerful approach to expand our understanding of cytoskeletal composition and function. However, so far there have only been a handful of studies of the cytoskeleton proteome in immune cells. This article considers promising proteomics strategies that could augment our understanding of the role of the cytoskeleton in host-defense mechanisms.

Flow cytometric differentiation of avian leukocytes and analysis of their intracellular cytokine expression

A flow cytometric method for the identification of chicken blood leukocyte subpopulations and thrombocytes was developed. An anti-chicken CD45 phycoerythrin-labelled antibody was used to separate leukocytes from red blood cell nuclei. Leukocytes and thrombocytes were identified using a combination of their CD45-positivity and their typical side scatter properties. The identity of the CD45-positive cells was confirmed by sorting the subpopulations and subsequent light microscopic evaluation. In these differentiated cell populations, intracellular expression analysis of the proinflammatory cytokines interleukin-1beta and interleukin-6 was subsequently optimized on whole blood after in vitro stimulation with lipopolysaccharide from Escherichia coli strain O127:B8.

Lipoxin A4 counterregulates GM-CSF signaling in eosinophilic granulocytes

Eosinophils are granulated leukocytes that are involved in many inflammation-associated pathologies including airway inflammation in asthma. Resolution of eosinophilic inflammation and return to homeostasis is in part due to endogenous chemical mediators, for example, lipoxins, resolvins, and protectins. Lipoxins are endogenous eicosanoids that demonstrate antiinflammatory activity and are synthesized locally at sites of inflammation. In view of the importance of lipoxins (LXs) in resolving inflammation, we investigated the molecular basis of LXA(4) action on eosinophilic granulocytes stimulated with GM-CSF employing the eosinophilic leukemia cell line EoL-1 as well as peripheral blood eosinophils. We report herein that LXA(4) (1-100 nM) decreased protein tyrosine phosphorylation in EoL-1 cells stimulated with GM-CSF. Additionally, the expression of a number of GM-CSF-induced cytokines was inhibited by LXA(4) in a dose-dependent manner. Furthermore, using a proteomics approach involving mass spectrometry and immunoblot analysis we identified 11 proteins that were tyrosine phosphorylated after GM-CSF stimulation and whose phosphorylation was significantly inhibited by LXA(4) pretreatment. Included among these 11 proteins were alpha-fodrin (nonerythroid spectrin) and actin. Microscopic imaging showed that treatment of EoL-1 cells or blood eosinophils with GM-CSF resulted in the reorganization of actin and the translocation of alpha-fodrin from the cytoplasm to the plasma membrane. Importantly, alpha-fodrin translocation was prevented by LXA(4) but actin reorganization was not. Thus, the mechanism of LXA(4) action likely involves prevention of activation of eosinophilic granulocytes by GM-CSF through inhibition of protein tyrosine phosphorylation and modification of some cytoskeletal components.

Anti-proteinase 3 antibodies both stimulate and prime human neutrophils

BACKGROUND

Anti-neutrophil cytoplasmic antibodies (ANCA) against proteinase 3 (PR3) are postulated to injure vascular endothelium by inducing cytokine-primed neutrophils to release proteolytic enzymes and generate reactive oxygen species. Anti-PR3 induce exocytosis, and since priming is associated with upregulation of plasma membrane proteins by exocytosis of intracellular granules, we tested the hypothesis that anti-PR3 prime neutrophils in the absence of cytokines.

METHODS

Isolated human neutrophils were incubated with or without anti-PR3. Superoxide release was determined by measuring the reduction of ferricytochrome C. Exocytosis of secretory vesicles and specific granules was determined by measuring the expression of CD35 and CD66b, respectively, using flow cytometry.

RESULTS

Anti-PR3 (15 mug/mL) directly stimulated superoxide production and enhanced FMLP-stimulated superoxide production. Anti-PR3 (0.5 mug/mL) did not stimulate superoxide production but did enhance FMLP-stimulated superoxide production. Incubation of neutrophils with anti-PR3 resulted in time-dependent exocytosis of secretory vesicles and specific granules. Anti-PR3-induced exocytosis, but not superoxide production, was dependent on p38 mitogen-activated protein kinase. Conclusions. These data demonstrate that anti-PR3 can directly stimulate production of reactive oxygen species by neutrophils without cytokine priming, and that anti-PR3 prime neutrophils for increased FMLP-stimulated reactive oxygen species production. Anti-PR3 also induce exocytosis via a mechanism separate from their effect on reactive oxygen species production. These findings suggest that anti-PR3 ANCA may activate neutrophils and cause endothelial cell injury by multiple pathways, including some that are independent of priming by a second agent.

Lysophospholipid acyltransferases: novel potential regulators of the inflammatory response and target for new drug discovery

Molecular and biochemical analyses of membrane phospholipids have revealed that, in addition to their physico-chemical properties, the metabolites of phospholipids play a crucial role in the recognition, signalling and responses of cells to a variety of stimuli. Such responses are mediated in large part by the removal and/or addition of different acyl chains to provide different phospholipid molecular species. The reacylation reactions, catalysed by specific acyltransferases control phospholipid composition and the availability of the important mediators free arachidonic acid and lysophospholipids. Lysophospholipid acyltransferases are therefore key control points for cellular responses to a variety of stimuli including inflammation. Regulation or manipulation of lysophospholipid acyltransferases may thus provide important mechanisms for novel anti-inflammatory therapies. This review will highlight mammalian lysophospholipid acyltransferases with particular reference to the potential role of lysophosphatidylcholine acyltransferase and its substrates in sepsis and other inflammatory conditions and as a potential target for novel anti-inflammatory therapies.

C-Terminal Tail Phosphorylation of N-Formyl Peptide Receptor: Differential Recognition of Two Neutrophil Chemoattractant Receptors by Monoclonal Antibodies NFPR1 and NFPR2

The N-formyl peptide receptor (FPR), a G protein-coupled receptor that binds proinflammatory chemoattractant peptides, serves as a model receptor for leukocyte chemotaxis. Recombinant histidine-tagged FPR (rHis-FPR) was purified in lysophosphatidyl glycerol (LPG) by Ni(2+)-NTA agarose chromatography to >95% purity with high yield. MALDI-TOF mass analysis (>36% sequence coverage) and immunoblotting confirmed the identity as FPR. The rHis-FPR served as an immunogen for the production of 2 mAbs, NFPR1 and NFPR2, that epitope map to the FPR C-terminal tail sequences, 305-GQDFRERLI-313 and 337-NSTLPSAEVE-346, respectively. Both mAbs specifically immunoblotted rHis-FPR and recombinant FPR (rFPR) expressed in Chinese hamster ovary cells. NFPR1 also recognized recombinant FPRL1, specifically expressed in mouse L fibroblasts. In human neutrophil membranes, both Abs labeled a 45-75 kDa species (peak M(r) approximately 60 kDa) localized primarily in the plasma membrane with a minor component in the lactoferrin-enriched intracellular fractions, consistent with FPR size and localization. NFPR1 also recognized a band of M(r) approximately 40 kDa localized, in equal proportions to the plasma membrane and lactoferrin-enriched fractions, consistent with FPRL1 size and localization. Only NFPR2 was capable of immunoprecipitation of rFPR in detergent extracts. The recognition of rFPR by NFPR2 is lost after exposure of cellular rFPR to f-Met-Leu-Phe (fMLF) and regained after alkaline phosphatase treatment of rFPR-bearing membranes. In neutrophils, NFPR2 immunofluorescence was lost upon fMLF stimulation. Immunoblotting approximately 60 kDa species, after phosphatase treatment of fMLF-stimulated neutrophil membranes, was also enhanced. We conclude that the region 337-346 of FPR becomes phosphorylated after fMLF activation of rFPR-expressing Chinese hamster ovary cells and neutrophils.