Phagocytosis In Human Neutrophils Research Articles

Intraphagosomal Free Ca2+ Changes during Phagocytosis.

Phagocytosis (and endocytosis) is an unusual cellular process that results in the formation of a novel subcellular organelle, the phagosome. This phagosome contains not only the internalised target of phagocytosis but also the external medium, creating a new border between extracellular and intracellular environments. The boundary at the plasma membrane is, of course, tightly controlled and exploited in ionic cell signalling events. Although there has been much work on the control of phagocytosis by ions, notably, Ca2+ ions influxing across the plasma membrane, increasing our understanding of the mechanism enormously, very little work has been done exploring the phagosome/cytosol boundary. In this paper, we explored the changes in the intra-phagosomal Ca2+ ion content that occur during phagocytosis and phagosome formation in human neutrophils. Measuring Ca2+ ion concentration in the phagosome is potentially prone to artefacts as the intra-phagosomal environment experiences changes in pH and oxidation. However, by excluding such artefacts, we conclude that there are open Ca2+ channels on the phagosome that allow Ca2+ ions to "drain" into the surrounding cytosol. This conclusion was confirmed by monitoring the translocation of the intracellularly expressed YFP-tagged C2 domain of PKC-γ. This approach marked regions of membrane at which Ca2+ influx occurred, the earliest being the phagocytic cup, and then the whole cell. This paper therefore presents data that have novel implications for understanding phagocytic Ca2+ signalling events, such as peri-phagosomal Ca2+ hotspots, and other phenomena.

Mercury-containing preparations attenuate neutrophil extracellular trap formation in mice and humans through inhibiting the ERK1/2 pathway

Ethnopharmacological relevanceNeutrophil extracellular trap (NET) formation plays a crucial role in wound healing disorders, including chronic skin ulcers and diabetic foot ulcers (DFUs). Over the years, traditional Chinese topical medications, such as Cinnabar (composed of HgS and soluble mercury salt) and hydrargyria oxydum rubrum (containing HgO and soluble mercury salt), have been utilized for treating these ailments. Nevertheless, the fundamental processes remain mostly ambiguous. Aim of the studyThis study sought to investigate the potential effects of topical mercury-containing preparations on the process of NET formation. Materials and methodsNeutrophils isolated from healthy individuals and mouse models of type 1 and type 2 diabetes were cultured with phorbol 12-myristate 13-acetate (PMA), both with and without the mercury-containing preparations (MCP). The formation of NETs was monitored using confocal and scanning electron microscopes. Immunofluorescence and fluorescent probes were employed to assess the levels of citrulline histone H3 (Cit-H3) and intracellular reactive oxygen species (ROS), respectively. The impact of MCP extracts on cytokine expression, peptidylarginine deiminase 4 (PAD4), and myeloperoxidase (MPO) was measured through Luminex and ELISA assays. Phagocytosis of human neutrophils was analyzed using Flow Cytometry. Finally, the phosphorylation levels of ERK were detected by western blotting. ResultsTreatment with MCP led to a reduction in PAD4, Cit-H3, and MPO expressions in neutrophils, consequently inhibiting PMA-induced NET formation. MCP treatment also dampened ERK1/2 activation in neutrophils. Furthermore, MCP exhibited inhibitory effects on the secretion of the cytokine IL-8 and ROS production while enhancing neutrophil phagocytosis. ConclusionOur findings suggest that MCP can mitigate the release of NETs, likely by suppressing the ERK1/2 signaling pathway.

Disrupting the Dok3-Card9 Interaction with Synthetic Peptides Enhances Antifungal Effector Functions of Human Neutrophils.

Invasive fungal disease is an emerging and serious public health threat globally. The expanding population of susceptible individuals, together with the rapid emergence of multidrug-resistant fungi pathogens, call for the development of novel therapeutic strategies beyond the limited repertoire of licensed antifungal drugs. Card9 is a critical signaling molecule involved in antifungal defense; we have previously identified Dok3 to be a key negative regulator of Card9 activity in neutrophils. In this study, we identified two synthetic peptides derived from the coiled-coil domain of Card9, which can specifically block Dok3-Card9 binding. We showed that these peptides are cell-permeable, non-toxic, and can enhance antifungal cytokine production and the phagocytosis of human neutrophils upon fungal infection. Collectively, these data provide a proof of concept that disrupting the Dok3-Card9 interaction can boost the antifungal effector functions of neutrophils; they further suggest the potential utility of these peptide inhibitors as an immune-based therapeutic to fight fungal infection.

Purified complement C3b triggers phagocytosis and activation of human neutrophils via complement receptor 1

The complement system provides vital immune protection against infectious agents by labeling them with complement fragments that enhance phagocytosis by immune cells. Many details of complement-mediated phagocytosis remain elusive, partly because it is difficult to study the role of individual complement proteins on target surfaces. Here, we employ serum-free methods to couple purified complement C3b onto E. coli bacteria and beads and then expose human neutrophils to these C3b-coated targets. We examine the neutrophil response using a combination of flow cytometry, confocal microscopy, luminometry, single-live-cell/single-target manipulation, and dynamic analysis of neutrophil spreading on opsonin-coated surfaces. We show that purified C3b can potently trigger phagocytosis and killing of bacterial cells via Complement receptor 1. Comparison of neutrophil phagocytosis of C3b- versus antibody-coated beads with single-bead/single-target analysis exposes a similar cell morphology during engulfment. However, bulk phagocytosis assays of C3b-beads combined with DNA-based quenching reveal that these are poorly internalized compared to their IgG1 counterparts. Similarly, neutrophils spread slower on C3b-coated compared to IgG-coated surfaces. These observations support the requirement of multiple stimulations for efficient C3b-mediated uptake. Together, our results establish the existence of a direct pathway of phagocytic uptake of C3b-coated targets and present methodologies to study this process.

Analysis of Human and Mouse Neutrophil Phagocytosis by Flow Cytometry.

Neutrophils are primary phagocytes that recognize their targets through surface chemistry, either through pattern recognition receptor (PPR) interaction with pathogen-associated molecular patterns (PAMPs) or through immunoglobulin (Ig) or complement mediated recognition. Opsonization can be important for target recognition and phagocytosis by neutrophils. Therefore, phagocytosis assays performed using neutrophils in whole blood, compared to isolated cells, will differ due to the presence of opsonizing blood serum components, as well as other blood components like platelets. Powerful and sensitive flow cytometry-based methods are presented to measure phagocytosis by human blood neutrophils and mouse peritoneal neutrophils.

Interferon-β regulates proresolving lipids to promote the resolution of acute airway inflammation.

Aberrant immune responses, including hyperresponsiveness to Toll-like receptor (TLR) ligands, underlie acute respiratory distress syndrome (ARDS). Type I interferons confer antiviral activities and could also regulate the inflammatory response, whereas little is known about their actions to resolve aberrant inflammation. Here we report that interferon-β (IFN-β) exerts partially overlapping, but also cooperative actions with aspirin-triggered 15-epi-lipoxin A4 (15-epi-LXA4) and 17-epi-resolvin D1 to counter TLR9-generated cues to regulate neutrophil apoptosis and phagocytosis in human neutrophils. In mice, TLR9 activation impairs bacterial clearance, prolongs Escherichia coli-evoked lung injury, and suppresses production of IFN-β and the proresolving lipid mediators 15-epi-LXA4 and resolvin D1 (RvD1) in the lung. Neutralization of endogenous IFN-β delays pulmonary clearance of E. coli and aggravates mucosal injury. Conversely, treatment of mice with IFN-β accelerates clearance of bacteria, restores neutrophil phagocytosis, promotes neutrophil apoptosis and efferocytosis, and accelerates resolution of airway inflammation with concomitant increases in 15-epi-LXA4 and RvD1 production in the lungs. Pharmacological blockade of the lipoxin receptor ALX/FPR2 partially prevents IFN-β-mediated resolution. These findings point to a pivotal role of IFN-β in orchestrating timely resolution of neutrophil and TLR9 activation-driven airway inflammation and uncover an IFN-β-initiated resolution program, activation of an ALX/FPR2-centered, proresolving lipids-mediated circuit, for ARDS.

Dysregulated Neutrophil Iron Homeostasis in β-Thalassemia Impairs Phagocytosis and Reactive Oxygen Species Production

IntroductionBeta thalassemia is an inherited disorder characterised by ineffective erythropoiesis leading to anemia and secondary iron overload. Neutrophils are the first line of innate immune defence against infection is dysfunctional in thalassemia patients. Iron is required for the oxidative response of neutrophils to allow the production of reactive oxygen species (ROS). However, the role of iron contributing to the neutrophil dysfunction is unclear. This is the first study to characterise the neutrophil iron metabolism in β-thalassemia and its association with oxidative burst capacity, phagocytosis, and systemic iron homeostasis.MethodSixteen thalassemia patients and fourteen healthy individuals were recruited in the department of Haematology, Christian Medical College, Vellore, India. Neutrophils were purified from human whole blood collected in EDTA tube, using neutrophil magnetic isolation kit (Miltenyi Biotec). Purified population (>95%) was confirmed by the presence of the surface marker CD62L evaluated using flow cytometry. Haematological parameters were analysed according to standard methods. Serum ferritin, iron, soluble transferrin receptor were measured using immunoassay. Serum hepcidin was measured using ELISA. Neutrophil RNA was isolated using trizol method and was reverse transcribed into complementary DNA using QIAGEN kit. The relative quantification of iron related genes were measured using real-time PCR. In oxidative burst assay, neutrophils were incubated with dihydrorhodamine 123 (DHR) and stimulated with Phorbol 12-Myristate 13-Acetate (PMA). Respiratory burst of the cell was analysed by flow cytometry. Phagocytosis and acidification capacity of human neutrophils were quantified using the pHrodo Green Staphylococcus aureus BioParticles kit (Thermo Fisher). Acquisition was performed using the Beckman Coulter(Navios) flow cytometer and analysed using kaluza software. Statistical analysis was performed using SPSS software.ResultsWe investigated a cohort of β thalassemia Major (n=5), intermedia (n=6) and sickle beta thalassemia (n=5) patients who were on regular iron chelation therapy. The demographic and biochemical parameters are tabulated in Table 1. Serum iron, ferritin levels and transferrin saturation were significantly increased in thalassemia cohort as compared to healthy donors (Fig1a). There was no significant association between ferritin and hepcidin levels. The percentage of neutrophils in thalassemia was significantly reduced incomparision to healthy donors (p=0.032). Oxidative burst capacity of neutrophils from thalassemia major and intermedia patients were significantly decreased (p=0.002) compared to healthy donors upon stimulation with PMA (Fig1b). Neutrophil phagocytosis capacity indicated by the relative amounts of phagocytized fluorescein S.aureus particles were significantly lower in thalassemia patients compared with controls, after 15min/30min incubation (Fig1c). The recognition capacity of neutrophils towards bioparticles significantly decreased at 45-minute incubation in patients (p=0.017) (Fig1d). Serum iron overload and transferrin saturation had negative association with neutrophil phagocytosis capacity (r=-0.714; p=0.045 & r=-0.857; p=0.014), respectively. Neutrophil iron related gene expression was analysed and found significantly lower expression of FPN 1A (FPN1 containing iron regulatory element (IRE)), DMT1B without IRE region and IRP2 respectively (p=0.029, p=0.029 & p=0.016) (Fig1e). FPN1B without IRE region was upregulated in thalassemia patients (p=0.016). Serum ferritin had positive correlation with FPN1B (r=0.786; p=0.036). Soluble transferrin receptor had negative association with DMT1A (containing IRE region) and IRP2 respectively (r=-0.900; p=0.037 and r=-0.750; p=0.052).Aberrant neutrophil function was found in all thalassemia patients. Although oxidative burst activity was decreased in thalassemia major and intermedia patients, sickle β-thalassemia patients had normal burst activity. Systemic iron status had inverse correlation with phagocytosis capacity of neutrophils. Dysregulation of iron transporters in neutrophils was indicated by decreased expression of DMT1 and augmented FPN1B expression, despite systemic iron overload. These findings have to be explored in a larger cohort to elucidate the clinical significance. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Histidine-Rich Glycoprotein Stimulates Human Neutrophil Phagocytosis and Prolongs Survival through CLEC1A.

Histidine-rich glycoprotein (HRG) is a multifunctional plasma protein and maintains the homeostasis of blood cells and vascular endothelial cells. In the current study, we demonstrate that HRG and recombinant HRG concentration dependently induced the phagocytic activity of isolated human neutrophils against fluorescence-labeled Escherichia coli and Staphylococcus aureus through the stimulation of CLEC1A receptors, maintaining their spherical round shape. The phagocytosis-inducing effects of HRG were inhibited by a specific anti-HRG Ab and enhanced by opsonization of bacteria with diluted serum. HRG and C5a prolonged the survival time of isolated human neutrophils, in association with a reduction in the spontaneous production of extracellular ROS. In contrast, HRG maintained the responsiveness of neutrophils to TNF-α, zymosan, and E. coli with regard to reactive oxygen species production. The blocking Ab for CLEC1A and recombinant CLEC1A-Fc fusion protein significantly inhibited the HRG-induced neutrophil rounding, phagocytic activity, and prolongation of survival time, suggesting the involvement of the CLEC1A receptor in the action of HRG on human neutrophils. These results as a whole indicated that HRG facilitated the clearance of E. coli and S. aureus by maintaining the neutrophil morphology and phagocytosis, contributing to the antiseptic effects of HRG in vivo.

E‐Cigarette Use Increases Susceptibility to Bacterial Infection by Impairment of Human Neutrophil Chemotaxis, Phagocytosis and NET Formation

Although E‐cigarettes are frequently portrayed as a safer alternative to conventional cigarettes, a growing body of evidence suggests that the use of these devices may adversely affect host defense against infection. Neutrophils, critical effector cells of the innate immune system and early responders to sites of infection, may represent a particularly important cellular target of E‐cigarette vapor components. Using primary human neutrophils isolated from healthy donors, we evaluated the impact of electronic vapor extract (EVE) exposure on multiple aspects of neutrophil cellular physiology, including chemotaxis, reactive oxygen species (ROS) production, generation of Neutrophil Extracellular Traps (NETs) and phagocytosis. Using a transwell chamber approach, we found that exposure to E‐cigarette vapor‐infused media (EVE) reduced neutrophil chemotaxis in response to the chemoattractant f‐Met‐Leu‐Phe (fMLP) by up to 4.2 fold (p < 0.001). Staining with the fluorescent actin probe rhodamine phalloidin revealed aberrant actin cytoskeleton polarization in EVE‐treated, fMLP‐stimulated neutrophils. Neutrophil membrane fluidity was also altered by EVE exposure, with holotomographic microscopy revealing alterations in cellular morphology in EVE‐treated neutrophils. ROS production was reduced in EVE‐treated neutrophils, and ROS‐dependent production of bactericidal extracellular traps was reduced by up to 3.5 fold (p < 0.01). Interestingly, this reduction in NET production (NETosis) was observed in neutrophils treated with EVE produced using propylene glycol‐based E‐cigarette liquid formulations both with and without nicotine. The rate of neutrophil phagocytosis, quantified using fluorescent E. coli/S. aureus bioparticles, was also reduced by up to 47% in EVE‐treated neutrophils (p < 0.05). To determine how such alterations of immune cell function might affect host response to infection, a physiologic mouse model of chronic E‐cigarette exposure and sepsis was utilized. In this model, E‐cigarette vapor inhalation led to reduced neutrophil migration into infected spaces and a higher burden of Pseudomonas aeruginosa. Taken together, these findings provide evidence that E‐cigarette use adversely impacts the innate immune system, potentially placing E‐cigarette users at higher risk for dysregulated inflammatory responses and invasive bacterial infections.

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Human Neutrophil Granule Exocytosis in Response to Mycobacterium smegmatis.

Mycobacterium smegmatis rarely causes disease in the immunocompetent, but reported cases of soft tissue infection describe abscess formation requiring surgical debridement for resolution. Neutrophils are the first innate immune cells to accumulate at sites of bacterial infection, where reactive oxygen species and proteolytic enzymes are used to kill microbial invaders. As these phagocytic cells play central roles in protection from most bacteria, we assessed human neutrophil phagocytosis and granule exocytosis in response to serum opsonized or non-opsonized M. smegmatis mc2. Although phagocytosis was enhanced by serum opsonization, M. smegmatis did not induce exocytosis of secretory vesicles or azurophilic granules at any time point tested, with or without serum opsonization. At early time points, opsonized M. smegmatis induced significant gelatinase granule exocytosis compared to non-opsonized bacteria. Differences in granule release between opsonized and non-opsonized M. smegmatis decreased in magnitude over the time course examined, with bacteria also evoking specific granule exocytosis by six hours after addition to cultured primary single-donor human neutrophils. Supernatants from neutrophils challenged with opsonized M. smegmatis were able to digest gelatin, suggesting that complement and gelatinase granule exocytosis can contribute to neutrophil-mediated tissue damage seen in these rare soft tissue infections.

The Potential of Telomeric G-quadruplexes Containing Modified Oligoguanosine Overhangs in Activation of Bacterial Phagocytosis and Leukotriene Synthesis in Human Neutrophils.

Human neutrophils are the first line of defense against bacterial and viral infections. They eliminate pathogens through phagocytosis, which activate the 5-lipoxygenase (5-LOX) pathway resulting in synthesis of leukotrienes. Using HPLC analysis, flow cytometry, and other biochemical methods, we studied the effect of synthetic oligodeoxyribonucleotides (ODNs) able to fold into G-quadruplex structures on the main functions of neutrophils. Designed ODNs contained four human telomere TTAGGG repeats (G4) including those with phosphorothioate oligoguanosines attached to the end(s) of G-quadruplex core. Just modified analogues of G4 was shown to more actively than parent ODN penetrate into cells, improve phagocytosis of Salmonella typhimurium bacteria, affect 5-LOX activation, the cytosol calcium ion level, and the oxidative status of neutrophils. As evident from CD and UV spectroscopy data, the presence of oligoguanosines flanking G4 sequence leads to dramatic changes in G-quadruplex topology. While G4 folds into a single antiparallel structure, two main folded forms have been identified in solutions of modified ODNs: antiparallel and dominant, more stable parallel. Thus, both the secondary structure of ODNs and their ability to penetrate into the cytoplasm of cells are important for the activation of neutrophil cellular effects. Our results offer new clues for understanding the role of G-quadruplex ligands in regulation of integral cellular processes and for creating the antimicrobial agents of a new generation.

E-cigarette use increases susceptibility to bacterial infection by impairment of human neutrophil chemotaxis, phagocytosis, and NET formation.

E-cigarettes are portrayed as safer relative to conventional tobacco. However, burgeoning evidence suggests that E-cigarettes may adversely affect host defenses. However, the precise mechanisms by which E-cigarette vapor alters innate immune cell function have not been fully elucidated. We determined the effects of E-cigarette exposure on the function and responses to infectious challenge of the most abundant innate immune cell, the neutrophil, using isolated human neutrophils and a mouse model of gram-negative infection. Our results revealed that human neutrophils exposed to E-cigarette vapor had 4.2-fold reductions in chemotaxis toward the bacterial cell-well component f-Met-Leu-Phe (P < 0.001). F-actin polarization and membrane fluidity were also adversely affected by E-cigarette vapor exposure. E-cigarette-exposed human neutrophils exhibited a 48% reduction in production of reactive oxygen species (ROS; P < 0.001). Given the central role of ROS in neutrophil extracellular trap (NET) production, NET production was quantified, and E-cigarette vapor exposure was found to reduce NETosis by 3.5-fold (P < 0.01); formulations with and without nicotine containing propylene glycol exhibiting significant suppressive effects. However, noncanonical NETosis was unaffected. In addition, exposure to E-cigarette vapor lowered the rate of phagocytosis of bacterial bioparticles by 47% (P < 0.05). In our physiological mouse model of chronic E-cigarette exposure and sepsis, E-cigarette vapor inhalation led to reduced neutrophil migration in infected spaces and a higher burden of Pseudomonas. These findings provide evidence that E-cigarette use adversely impacts the innate immune system and may place E-cigarette users at higher risk for dysregulated inflammatory responses and invasive bacterial infections.

Phagocytosis and Motility in Human Neutrophils is Competent but Compromised by Pharmacological Inhibition of Ezrin Phosphorylation.

Ezrin links the cortical cytoskeleton to the plasma membrane and plays a role in regulating changes in cell shape. Recently, NSC668394 has been shown to inhibit a key step for its activity, i.e. phosphorylation at threonine 567. In neutrophils, another key regulatory step is the Ca2+-mediated cleavage of ezrin by calpain. In this paper, we use NSC668394 as a pharmacological inhibitor to investigate the interplay between these two steps in regulating changes in neutrophil shape. NSC668394 reduced the amount of peripherally located ezrin in neutrophils, and increased Ca2+-dependent ezrin cleavage. Neutrophils with NSC668394-inhibited ezrin phosphorylation remained both phagocytic and chemotactically competent. However, phagocytosis was slightly impaired and chemotaxis could not be maintained over longer periods. The characteristic chemotactic morphology which neutrophils adopt was also aberrant. Although phosphorylation of ezrin plays a minor role in limiting the rapid changes in cell shape in neutrophils, inhibition of ezrin phosphorylation by NSC668394 prevented multiple and prolonged shape changes during extended chemotaxis. The susceptibility of prolonged chemotaxis to inhibition by NSC668394 may point to a useful target for anti-inflammatory therapy. Inhibition of neutrophil chemotaxis towards chronically inflamed sites without compromising their ability to undergo phagocytosis is a much sought after the effect of anti-neutrophil therapy.

Inhibitory effects of α, β-unsaturated carbonyl-based compounds and their pyrazoline derivatives on the phagocytosis of human neutrophils

A series of α, β-unsaturated carbonyl-based compounds (curcumin analogs and chalcone derivatives) and their pyrazoline derivatives were investigated for their in vitro inhibitory effects on the phagocytosis of human neutrophils. The effects of the compounds on the chemotactic migration, CD11a/18 expression, phagocytic activity, and reactive oxygen species (ROS) production by human whole blood cells (WBC) and isolated human polymorphonuclear neutrophils (PMNs) were assessed by using 24-well cell migration assay kit, flow cytometer, Phagotest assay kit, and luminol/lucigenin-based chemiluminescence assay, respectively. Compounds 4, 5, 6, 13, 23, 33, 39, and 41 showed strong inhibitory activity against PMNs chemotaxis with IC50 values, ranging from 0.22–1.68 µM which were much lower than those of ibuprofen and curcumin (IC50 values 11.02 and 5.0 µM, respectively). All compounds showed low or moderate inhibition of cell adhesion molecule expression except for compound 15, while compounds 4, 5, 8, and 21 at 100, 25, and 6.25 μg/mL showed strong inhibition of opsonized bacteria engulfment by neutrophils with the highest suppressive effects exhibited by compound 21 at 37.4%. Compounds 4, 11, 13, 14, 24, 25, 27, 33, and 34 significantly suppressed ROS generation by PMNs and WBC. Compounds with N-methyl 4-piperidone and 4-piperidone linkers (4, 13, 14, 23, 24) and 2-pyrazoline-1-carboxamide and 2-pyrazoline-1-carbothioamide derivatives showed strong inhibition on chemotactic and phagocytic activities, and ROS production. The results suggest that some of the α, β-unsaturated carbonyl-based compounds strongly modulated the innate immune responses of phagocytes at different steps, highlighting their potential as a source of new immunomodulatory agents.

Baccharis dracunculifoliaDC (Asteraceae) selectively modulates the effector functions of human neutrophils

To examine whether the hydroalcoholic extract from Baccharis dracunculifolia leaves (BdE) modulates the human neutrophil oxidative metabolism, degranulation, phagocytosis and microbial killing capacity. In-vitro assays based on chemiluminescence, spectrophotometry, flow cytometry and polarimetry were used, as well as docking calculations. At concentrations that effectively suppressed the neutrophil oxidative metabolism elicited by soluble and particulate stimuli (<10 μg/ml), without clear signs of cytotoxicity, BdE (1) inhibited NADPH oxidase and myeloperoxidase activity; (2) scavenged H2 O2 and HOCl; (3) weakly inhibited phagocytosis; and (4) did not affect neutrophil degranulation and microbial killing capacity, the expression levels of TLR2, TLR4, FcγRIIa, FcγRIIIb and CR3 and the activity of elastase and lysozyme. Caffeic acid, one of the major B. dracunculifolia secondary metabolites, did not inhibit phagocytosis but interfered in the myeloperoxidase-H2 O2 -HOCl system by scavenging H2 O2 and HOCl, and interacting with the catalytic residues His-95, Arg-239 and Gln-91. BdE selectively modulates the effector functions of human neutrophils, inhibits the activity of key enzymes and scavenges physiological oxidant species. Caffeic acid contributes to lower the levels of oxidant species. Our findings help to unravel the mechanisms by which these natural products exert immunomodulatory action towards neutrophils.

Multi-functional mechanisms of immune evasion by the streptococcal complement inhibitor C5a peptidase.

The complement cascade is crucial for clearance and control of invading pathogens, and as such is a key target for pathogen mediated host modulation. C3 is the central molecule of the complement cascade, and plays a vital role in opsonization of bacteria and recruitment of neutrophils to the site of infection. Streptococcal species have evolved multiple mechanisms to disrupt complement-mediated innate immunity, among which ScpA (C5a peptidase), a C5a inactivating enzyme, is widely conserved. Here we demonstrate for the first time that pyogenic streptococcal species are capable of cleaving C3, and identify C3 and C3a as novel substrates for the streptococcal ScpA, which are functionally inactivated as a result of cleavage 7 amino acids upstream of the natural C3 convertase. Cleavage of C3a by ScpA resulted in disruption of human neutrophil activation, phagocytosis and chemotaxis, while cleavage of C3 generated abnormally-sized C3a and C3b moieties with impaired function, in particular reducing C3 deposition on the bacterial surface. Despite clear effects on human complement, expression of ScpA reduced clearance of group A streptococci in vivo in wildtype and C5 deficient mice, and promoted systemic bacterial dissemination in mice that lacked both C3 and C5, suggesting an additional complement-independent role for ScpA in streptococcal pathogenesis. ScpA was shown to mediate streptococcal adhesion to both human epithelial and endothelial cells, consistent with a role in promoting bacterial invasion within the host. Taken together, these data show that ScpA is a multi-functional virulence factor with both complement-dependent and independent roles in streptococcal pathogenesis.

Analysis of Human and Mouse Neutrophil Phagocytosis by Flow Cytometry.

Neutrophils are primary phagocytes that recognize their targets through surface chemistry, either through Pattern Recognition Receptor (PPR) interaction with Pathogen-Associated Molecular Patterns (PAMPs) or through immunoglobulin (Ig) or complement mediated recognition. Opsonization can be important for target recognition, and phagocytosis by neutrophils in whole blood can be greatly enhanced due to the presence of blood serum components and platelets. Powerful and sensitive flow cytometry based methods are presented to measure phagocytosis by human blood neutrophils and mouse peritoneal neutrophils.

Ultraviolet light A irradiation induces immunosuppression associated with the generation of reactive oxygen species in human neutrophils

Ultraviolet blood irradiation has been used as a physical therapy to treat many nonspecific diseases in clinics; however, the underlying mechanisms remain largely unclear. Neutrophils, the first line of host defense, play a crucial role in a variety of inflammatory responses. In the present work, we investigated the effects of ultraviolet light A (UVA) on the immune functions of human neutrophils at the single-cell level by using an inverted fluorescence microscope. N-Formyl-methionyl-leucyl-phenylalanine (FMLP), a classic physiological chemotactic peptide, was used to induce a series of immune responses in neutrophils in vitro. FMLP-induced calcium mobilization, migration, and phagocytosis in human neutrophils was significantly blocked after treatment with 365[Formula: see text]nm UVA irradiation, demonstrating the immunosuppressive effects of UVA irradiation on neutrophils. Similar responses were also observed when the cells were pretreated with H2O2, a type of reactive oxygen species (ROS). Furthermore, UVA irradiation resulted in an increase in NAD(P)H, a member of host oxidative stress in cells. Taken together, our data indicate that UVA irradiation results in immunosuppression associated with the production of ROS in human neutrophils.

Immunomodulatory effects of Santolina chamaecyparissus leaf extracts on human neutrophil functions

Context: Santolina chamaecyparissus L. (Asteraceae) is an aromatic plant wide spread in the Mediterranean region. It is used in folk medicine for its anti-inflammatory properties.Objective: The effects of S. chamaecyparissus aqueous extract (SCAE) and polyphenolic extract (SCPE) on human polymorphonuclear neutrophil (PMN) degranulation, chemotaxis, phagocytosis, and microbicidal capacity were examined in vitro.Materials and methods: Aqueous and polyphenolic extracts were prepared from S. chamaecyparissus leaves. The elastase release was used as a marker for measuring PMN degranulation, while chemotaxis was performed using a 48-microwell chemotaxis chamber. The phagocytosis and the microbicidal capacity were evaluated using fresh cultures of Candida albicans.Results: The treatment of neutrophils with different concentrations (10–200 µg/ml) of SCAE and SCPE caused a significant (p < 0.001) and dose-dependent inhibitory effect on elastase release in fMLP/Cytochalasin B (CB)-stimulated neutrophils. Indeed, 100 µg/ml of SCAE exerted an inhibitory effect of 51.97 ± 6.2%, whereas SCPE at the same concentration abolished completely PMN degranulation. Moreover, both extracts inhibited markedly (p < 0.01) fMLP-induced chemotactic migration. At 200 µg/ml, SCAE and SCPE exerted an inhibitory effect of 54.61 ± 7.3% and 57.71 ± 7.44%, respectively. In addition, a decline in both phagocytosis and microbicidal capacity against Candida albicans was observed when PMNs were exposed to 100 and 200 µg/ml of SCAE or SCPE.Conclusion: The exerted effects on neutrophil functions support the anti-inflammatory activity and show new mechanisms of action and effectiveness of S. chamaecyparissus leaf extracts. This plant may be considered as an interesting source of anti-inflammatory and immunomodulatory agents.