Role of the phospholipid binding sites, PX of p47phox and PB region of Rac1, in the formation of the phagocyte NADPH oxidase complex NOX2

In phagocytes, superoxide anion (O2-), the precursor of reactive oxygen species, is produced by the NADPH oxidase complex to kill pathogens. Phagocyte NADPH oxidase consists of the transmembrane cytochrome b558 (cyt b558) and four cytosolic components: p40phox, p47phox, p67phox, and Rac1/2. The phagocyte activation by stimuli leads to activation of signal transduction pathways. This is followed by the translocation of cytosolic components to the membrane and their association with cyt b558 to form the active enzyme. To investigate the roles of membrane-interacting domains of the cytosolic proteins in the NADPH oxidase complex assembly and activity, we used giant unilamellar phospholipid vesicles (GUV). We also used the neutrophil-like cell line PLB-985 to investigate these roles under physiological conditions. We confirmed that the isolated proteins must be activated to bind to the membrane. We showed that their membrane binding was strengthened by the presence of the other cytosolic partners, with a key role for p47phox. We also used a fused chimera consisting of p47phox(aa 1-286), p67phox(aa 1-212) and Rac1Q61L, as well as mutated versions in the p47phox PX domain and the Rac polybasic region (PB). We showed that these two domains have a crucial role in the trimera membrane-binding and in the trimera assembly to cyt b558. They also have an impact on O2.- production in vitro and in cellulo: the PX domain strongly binding to GUV made of a mix of polar lipids; and the PB region strongly binding to the plasma membrane of neutrophils and resting PLB-985 cells.

Multifunctional role of the ubiquitin proteasome pathway in phagocytosis

Phagocytosis is a specialized form of endocytosis where large cells and particles (>0.5μm) are engulfed by the phagocytic cells, and ultimately digested in the phagolysosomes. This process not only eliminates unwanted particles and pathogens from the extracellular sources, but also eliminates apoptotic cells within the body, and is critical for maintenance of tissue homeostasis. It is believed that both endocytosis and phagocytosis share common pathways after particle internalization, but specialized features and differences between these two routes of internalization are also likely. The recruitment and removal of each protein/particle during the maturation of endocytic/phagocytic vesicles has to be tightly regulated to ensure their timely action. Ubiquitin proteasome pathway (UPP), degrades unwanted proteins by post-translational modification of proteins with chains of conserved protein Ubiquitin (Ub), with subsequent recognition of Ub chains by the 26S proteasomes and substrate degradation by this protease. This pathway utilizes different Ub linkages to modify proteins to regulate protein-protein interaction, localization, and activity. Due to its vast number of targets, it is involved in many cellular pathways, including phagocytosis. This chapters describes the basic steps and signaling in phagocytosis and different roles that UPP plays at multiple steps in regulating phagocytosis directly, or through its interaction with other phagosomal proteins. How aberrations in UPP function affect phagocytosis and their association with human diseases, and how pathogens exploit this pathway for their own benefit is also discussed.

Bacterial Binding, Phagocytosis, and Killing Capacity: Measurements Using Colony Forming Units

Herein, we provide a colony forming unit (CFU)-based counting method for quantitating the bacterial binding, phagocytosis, and killing capacity of phagocytes. Although these functions can be measured by immunofluorescence- and dye-based assays, quantitating CFUs are comparatively inexpensive and easy to perform. The protocol described below is easily modified for use with different phagocytes (e.g., macrophages, neutrophils, cell lines), types of bacteria, or opsonic conditions.

Non-autonomous cell death induced by the Draper phagocytosis receptor requires signaling through the JNK and SRC pathways

The last step of cell death is cell clearance, a process critical for tissue homeostasis. For efficient cell clearance to occur, phagocytes and dead cells need to reciprocally signal to each other. One important phenomenon that is under-investigated, however, is that phagocytes not only engulf corpses but contribute to cell death progression. The aims of this study were to determine how the phagocytic receptor Draper non-autonomously induces cell death, using the Drosophila ovary as a model system. We found that Draper, expressed in epithelial follicle cells, requires its intracellular signaling domain to kill the adjacent nurse cell population. Kinases Src42A, Shark and JNK (Bsk) were required for Draper-induced nurse cell death. Signs of nurse cell death occurred prior to apparent engulfment and required the caspase Dcp-1, indicating that it uses a similar apoptotic pathway to starvation-induced cell death. These findings indicate that active signaling by Draper is required to kill nurse cells via the caspase Dcp-1, providing novel insights into mechanisms of phagoptosis driven by non-professional phagocytes.

A Novel CEBPE Variant Causes Severe Infections and Profound Neutropenia

PURPOSE

Specific granule deficiency (SGD) is a rare inborn error of immunity resulting from loss-of-function variants in CEBPE gene (encoding for transcription factor C/EBPε). Although this genetic etiology has been known for over two decades, only a few patients with CEBPE variant-proven SGD (type I) have been reported. Herein, we describe two siblings with a novel homozygous CEBPE deletion who were noted to have profound neutropenia on initial evaluation. We aimed to evaluate the immunohematological consequences of this novel variant, including profound neutropenia.

METHODS

Light scatter characteristics of granulocytes were examined on various automated hematology analyzers. Phagocyte immunophenotype, reactive oxygen species generation, and Toll-like receptor (TLR) signaling were assessed using flow cytometry. Relative expression of genes encoding various granule proteins was studied using RT-PCR. Western blot analysis and luciferase reporter assay were performed to explore variant C/EBPε expression and function.

RESULTS

Severe infections occurred in both siblings. Analysis of granulocyte light scatter plots revealed automated hematology analyzers can provide anomalously low neutrophil counts due to abnormal neutrophil morphology. Neutrophils displayed absence/marked reduction of CD15/CD16 expression and overexpression (in a subset) of CD14/CD64. Three distinct populations of phagocytes with different oxidase activities were observed. Impaired shedding of CD62-ligand was noted on stimulation with TLR-4, TLR-2/6, and TLR-7/8 agonists. We demonstrated the variant C/EBPε to be functionally deficient.

CONCLUSION

Homozygous c.655_665del variant in CEBPE causes SGD. Anomalous automated neutrophil counts may be reported in patients with SGD type I. Aberrant TLR signaling might be an additional pathogenetic mechanism underlying immunodeficiency in SGD type I.

Macropinocytosis in Phagocyte Function and Immunity

Phagocytes play critical roles in the maintenance of organismal homeostasis and immunity. Central to their role is their ability to take up and process exogenous material via the related processes of phagocytosis and macropinocytosis. The mechanisms and functions underlying macropinocytosis have remained severely understudied relative to phagocytosis. In recent years, however, there has been a renaissance in macropinocytosis research. Phagocytes can engage in various forms of macropinocytosis including an "induced" form and a "constitutive" form. This chapter, however, will focus on constitutive macropinocytosis and its role in the maintenance of immunity. Functions previously attributed to macropinocytosis, including antigen presentation and immune surveillance, will be revisited in light of recent revelations and emerging concepts will be highlighted.

Particle uptake driven phagocytosis in macrophages and neutrophils enhances bacterial clearance

Humans are exposed to numerous synthetic foreign particles in the form of drug delivery systems and diagnostic agents. Specialized immune cells (phagocytes) clear these particles by phagocytosing and attempting to degrade them. The process of recognition and internalization of the particles may trigger changes in the function of phagocytes. Some of these changes, especially the ability of a particle-loaded phagocyte to take up and neutralize pathogens, remains poorly studied. Herein, we demonstrate that the uptake of non-stimulatory cargo-free particles enhances the phagocytic ability of monocytes, macrophages and neutrophils. The enhancement in phagocytic ability was independent of particle properties, such as size or the base material constituting the particle. Additionally, we show that the increased phagocytosis was not a result of cellular activation or cellular heterogeneity but was driven by changes in cell membrane fluidity and cellular compliance. A consequence of the enhanced phagocytic activity was that particulate-laden immune cells neutralize E. coli faster in culture. Moreover, when administered in mice as a prophylactic, particulates enable faster clearance of E. coli and Staphylococcus epidermidis. Together, we demonstrate that the process of uptake induces cellular changes that favor additional phagocytic events. This study provides insights into using non-stimulatory cargo-free particles to engineer immune cell functions for applications involving faster clearance of phagocytosable particulates.

Examining Neutrophil-Candida auris Interactions with Human Neutrophils Ex Vivo

Neutrophils play a key role in controlling invasive fungal infections. These phagocytes engage and kill fungal pathogens through a variety of effector mechanisms. Here, we describe how to isolate human neutrophils for ex vivo study of neutrophil-Candida auris interactions. We detail assays to measure fungal killing, phagocytosis, and reactive oxygen species production.

Fine definition of the epitopes on the human gp91phox/NOX2 for the monoclonal antibodies CL-5 and 48

Superoxide-producing NADPH oxidase, gp91^phox/NOX2, in phagocytes plays a critical role in the host defenses against pathogens. Moreover, gp91^phox/NOX2 contributes to the oxidative stress in endothelial cells. Therefore, investigating the level of gp91^phox/NOX2 with immunoblotting is important for estimating the amount of superoxide produced. Here, we showed that the epitopes in human gp91^phox/NOX2 recognized by monoclonal antibodies (mAbs) CL-5 and 48 were in amino acids 132-147 and 136-144, respectively. Although the epitopes were close to the N-glycosylation sites, N-glycan maturation did not affect mAbs recognition. When Pro-136 was substituted with Arg, the corresponding mouse residue, human gp91^phox/NOX2 was not recognized by mAbs CL-5 and 48; however, the substitution did not affect gp91^phox/NOX2-based oxidase activity. This finding explains why these mAbs specifically recognize the human but not mouse gp91^phox/NOX2. Hence, these mAbs are useful for investigating the level of gp91^phox/NOX2 without amino acid substitutions in the epitopes.

Zinc accelerates respiratory burst termination in human PMN

The respiratory burst of phagocytes is essential for human survival. Innate immune defence against pathogens relies strongly on reactive oxygen species (ROS) production by the NADPH oxidase (NOX2). ROS kill pathogens while the translocation of electrons across the plasma membrane via NOX2 depolarizes the cell. Simultaneously, protons are released into the cytosol. Here, we compare freshly isolated human polymorphonuclear leukocytes (PMN) to the granulocytes-like cell line PLB 985. We are recording ROS production while inhibiting the charge compensating and pH regulating voltage-gated proton channel (H_V1). The data suggests that human PMN and the PLB 985 generate ROS via a general mechanism, consistent of NOX2 and H_V1. Additionally, we advanced a mathematical model based on the biophysical properties of NOX2 and H_V1. Our results strongly suggest the essential interconnection of H_V1 and NOX2 during the respiratory burst of phagocytes. Zinc chelation during the time course of the experiments postulates that zinc leads to an irreversible termination of the respiratory burst over time. Flow cytometry shows cell death triggered by high zinc concentrations and PMA. Our data might help to elucidate the complex interaction of proteins during the respiratory burst and contribute to decipher its termination.

Genome-Scale Transcript Analyses of Human Neutrophils

Transcriptome analyses of unicellular and multicellular organisms have changed fundamental understanding of biological and pathological processes across multiple scientific disciplines. Over the past 15 years, studies of polymorphonuclear leukocyte (PMN or neutrophil) gene expression on a global scale have provided new insight into the molecular processes that promote resolution of infections in humans. Herein we present methods to analyze gene expression in human neutrophils using Affymetrix oligonucleotide microarrays and next-generation sequencing. Notably, the procedures utilize commercially available reagents and materials and thus represent a standardized approach for evaluating PMN transcript levels.

Signal Inhibitory Receptor on Leukocytes-1 is highly expressed on lung monocytes, but absent on mononuclear phagocytes in skin and colon

Signal Inhibitory Receptor on Leukocytes-1 (SIRL-1) is expressed on human blood monocytes and granulocytes and inhibits myeloid effector functions. On monocytes, but not granulocytes, SIRL-1 expression is low or absent in individuals with the single nucleotide polymorphism (SNP) rs612529C. The expression of SIRL-1 in tissue and the influence of rs612529 hereon is currently unknown. Here, we used flow cytometry to determine SIRL-1 expression on immune cells in human blood and three barrier tissues; skin, colon and lung. SIRL-1 was expressed by virtually all neutrophils and eosinophils in these tissues. In contrast, SIRL-1 was not expressed by monocyte-derived cells in skin and colon, whereas it was highly expressed by lung classical monocytes. Lung monocytes from individuals with a rs612529C allele had decreased SIRL-1 expression, consistent with the genotype association in blood. Within the different monocyte subsets in blood and lung, SIRL-1 expression was highest in classical monocytes and lowest in nonclassical monocytes. SIRL-1 was not expressed by dendritic cells in blood and barrier tissues. Together, these results indicate that SIRL-1 is differentially expressed on phagocyte subsets in blood and barrier tissues, and that its expression on monocytes is genotype- and tissue-specific. Immune regulation of monocytes by SIRL-1 may be of particular importance in the lung.

IRF5 Signaling in Phagocytes Is Detrimental to Neonatal Hypoxic Ischemic Encephalopathy

Immune responses to neonatal hypoxic ischemic encephalopathy (HIE) exacerbate brain injury. Phagocytes, including microglia, play a central role in the immune response, but how the activation of phagocytes is regulated remains elusive. Previously, we have reported that interferon regulatory factor 5 (IRF5) signaling is closely correlated with a pro-inflammatory microglial phenotype in adult mice after stroke. The present study investigated IRF5's regulatory role in post-HIE inflammation. Male IRF5 conditional knockout (CKO) and IRF5^fl/fl postnatal day 10 (P10) pups were subjected to the Rice-Vannucci model (RVM) to induce HIE. Outcomes including morphological and neurobehavioral changes were evaluated at day 7 after HIE. Microglia/macrophage phenotypes and inflammatory responses were evaluated by flow cytometry (FC), RT-PCR, and multiplex cytokine assays. Lenti-IRF5 virus was administered in microglia-neuron co-cultures to evaluate the effects of microglial IRF5 upregulation in ischemic neurons exposed to oxygen-glucose deprivation (OGD). Deletion of phagocytic IRF5 resulted in significantly decreased IRF5 expression, attenuated pro-inflammatory and enhanced anti-inflammatory responses to HIE, and improved outcomes compared with IRF5^fl/fl control pups. In vitro lentivirus transfection experiments revealed that overexpression of IRF5 in microglia amplified pro-inflammatory signals and exacerbated OGD-induced neuronal apoptosis and neurite fragmentation. IRF5 signaling mediates microglial pro-inflammatory activation and also affects anti-inflammatory responses. Phagocytic IRF5 signaling is detrimental in HIE and is a potential therapeutic target for post-ischemic inflammation.

Acetaminophen Inhibits the Neutrophil Oxidative Burst: Implications for Diagnostic Testing

BACKGROUND

Chronic granulomatous disease is a primary immunodeficiency characterized by recurrent bacterial and fungal infections, granuloma formation, and inflammatory disease. Impaired neutrophil oxidative function is an essential diagnostic criterion. In vitro exposure of neutrophils to acetaminophen, a commonly used over-the-counter medication, has been associated with reduced neutrophil oxidative function. The clinical implications of acetaminophen intake for dihydrorhodamine (DHR) testing remain unknown.

OBJECTIVE

To evaluate the effect of in vivo administration of therapeutic doses of acetaminophen on DHR diagnostic testing.

METHODS

We performed DHR testing in 15 healthy adults before and after administering a single dose of acetaminophen. We retrospectively reviewed 195 DHR test results from hospitalized patients who had received acetaminophen, nonsteroidal anti-inflammatory drug, or corticosteroid before testing.

RESULTS

DHR testing result was abnormal in 100% (n = 15) of healthy adults 2 hours after acetaminophen intake. We identified 195 instances of DHR testing less than or equal to 72 hours after acetaminophen ingestion in hospitalized patients who did not have chronic granulomatous disease. DHR results were abnormal in 43 of 195 cases (22.1%). Frequency of false-positive testing was increased in patients who received acetaminophen within 24 hours of testing, and in patients who received more than 1 dose of acetaminophen. Nonsteroidal anti-inflammatory drug and corticosteroid intakes were not associated with abnormal DHR result.

CONCLUSIONS

Patients treated with acetaminophen have decreased neutrophil oxidative burst as measured by DHR testing. To avoid falsely abnormal testing for chronic granulomatous disease, patients should be advised to avoid acetaminophen for at least 24 hours before DHR testing.

Importance of methodology in the evaluation of renal mononuclear phagocytes and analysis of a model of experimental nephritis with Shp1 conditional knockout mice

Tissue resident mononuclear phagocytes (Mophs), comprising monocytes, macrophages, and dendritic cells (DCs), play important roles under physiological and pathological conditions. The presence of these cells in the kidney has been known for decades, and studies of renal Mophs (rMophs) are currently underway. Since no unified procedure has been identified to isolate rMophs, results of flow cytometric analysis of rMophs have been inconsistent among studies. We therefore first evaluated a preparative method for rMophs using collagenous digestion. The yield of rMophs greatly increased after the collagenase digestion. In particular, F4/80high rMophs, which were positive for CD11c, a specific marker of DCs, dramatically increased. In addition, since neutrophils are sometimes mixed among rMophs in the analysis of flow cytometry, we established a gating strategy for eliminating neutrophils. To determine the contribution of rMophs to the development of autoimmune nephritis, we analyzed an experimental model of autoimmune nephritis that was applied to Shp1 conditional knockout mice (Shp1 CKO). This knockout strain is generated by crossing a mouse line carrying floxed Shp1 allele to mice expressing Cre recombinase under the control of the CD11c promoter. Shp1 CKO therefore specifically lack Shp1 in cells expressing CD11c. As a result, Shp1 CKO were susceptible to that experimental glomerulonephritis and F4/80high rMophs of Shp1 CKO increased dramatically. In conclusion, our preparative methods for collagenase digestion and gating strategy for neutrophils are necessary for the analysis of rMophs, and Shp1 suppresses the development of autoimmune nephritis through the control of rMophs.

Molecular Mechanisms of Calcium Signaling During Phagocytosis

Calcium (Ca²⁺) is a ubiquitous second messenger involved in the regulation of numerous cellular functions including vesicular trafficking, cytoskeletal rearrangements and gene transcription. Both global as well as localized Ca²⁺ signals occur during phagocytosis, although their functional impact on the phagocytic process has been debated. After nearly 40 years of research, a consensus may now be reached that although not strictly required, Ca²⁺ signals render phagocytic ingestion and phagosome maturation more efficient, and their manipulation make an attractive avenue for therapeutic interventions. In the last decade many efforts have been made to identify the channels and regulators involved in generating and shaping phagocytic Ca²⁺ signals. While molecules involved in store-operated calcium entry (SOCE) of the STIM and ORAI family have taken center stage, members of the canonical, melastatin, mucolipin and vanilloid transient receptor potential (TRP), as well as purinergic P2X receptor families are now recognized to play significant roles. In this chapter, we review the recent literature on research that has linked specific Ca²⁺-permeable channels and regulators to phagocytic function. We highlight the fact that lipid mediators are emerging as important regulators of channel gating and that phagosomal ionic homeostasis and Ca²⁺ release also play essential parts. We predict that improved methodologies for measuring these factors will be critical for future advances in dissecting the intricate biology of this fascinating immune process.

Inflammatory responses relate to distinct bronchoalveolar lavage lipidome in community-acquired pneumonia patients: a pilot study

Background

Community-acquired pneumonia (CAP) is a leading cause of morbidity and mortality worldwide. Antibiotics are losing their effectiveness due to the emerging infectious diseases, the scarcity of novel antibiotics, and the contributions of antibiotic misuse and overuse to resistance. Characterization of the lipidomic response to pneumonia and exploring the “lipidomic phenotype” can provide new insight into the underlying mechanisms of pathogenesis and potential avenues for diagnostic and therapeutic treatments.

Methods

Lipid profiles of bronchoalveolar lavage fluid (BALF) samples were generated through untargeted lipidomic profiling analysis using high-performance liquid chromatography with mass spectrometry (HPLC-MS). Principal component analysis (PCA) was applied to identify possible sources of variations among samples. Partitioning clustering analysis (k-means) was employed to evaluate the existence of distinct lipidomic clusters.

Results

PCA showed that BALF lipidomes differed significantly between CAP (n = 52) and controls (n = 68, including 35 healthy volunteers and 33 patients with non-infectious lung diseases); while no clear separation was found between severe CAP and non-severe CAP cases. Lactosylceramides were the most prominently elevated lipid constituent in CAP. Clustering analysis revealed three separate lipid profiles; subjects in each cluster exhibited significant differences in disease severity, incidence of hypoxemia, percentages of phagocytes in BALF, and serum concentrations of albumin and total cholesterol (all p < 0.05). In addition, SM (d34:1) was negatively related to macrophage (adjusted r = − 0.462, p < 0.0001) and PE (18:1p/20:4) was positively correlated with polymorphonuclear neutrophil (PMN) percentages of BALF (adjusted r = 0.541, p < 0.0001). The 30-day mortality did not differ amongst three clusters (p < 0.05).

Conclusions

Our data suggest that specific lower airway lipid composition is related to different intensities of host inflammatory responses, and may contribute to functionally relevant shifts in disease pathogenesis in CAP individuals. These findings argue for the need to tailor therapy based on specific lipid profiles and related inflammatory status.

Trial registration

ClinicalTrials.gov (NCT03093220). Registered on 28 March 2017 (retrospectively registered).

Electronic supplementary material

The online version of this article (10.1186/s12931-019-1028-8) contains supplementary material, which is available to authorized users.

Die in pieces: How Drosophila sheds light on neurite degeneration and clearance

Dendrites and axons are delicate neuronal membrane extensions that undergo degeneration after physical injuries. In neurodegenerative diseases, they often degenerate prior to neuronal death. Understanding the mechanisms of neurite degeneration has been an intense focus of neurobiology research in the last two decades. As a result, many discoveries have been made in the molecular pathways that lead to neurite degeneration and the cell-cell interactions responsible for the subsequent clearance of neuronal debris. Drosophila melanogaster has served as a prime in vivo model system for identifying and characterizing the key molecular players in neurite degeneration, thanks to its genetic tractability and easy access to its nervous system. The knowledge learned in the fly provided targets and fuel for studies in other model systems that have further enhanced our understanding of neurodegeneration. In this review, we will introduce the experimental systems developed in Drosophila to investigate injury-induced neurite degeneration, and then discuss the biological pathways that drive degeneration. We will also cover what is known about the mechanisms of how phagocytes recognize and clear degenerating neurites, and how recent findings in this area enhance our understanding of neurodegenerative disease pathology.

Salmonella and Reactive Oxygen Species: A Love-Hate Relationship

Salmonella enterica represents an enterobacterial species including numerous serovars that cause infections at, or initiated at, the intestinal epithelium. Many serovars also act as facultative intracellular pathogens with a tropism for phagocytic cells. These bacteria not only survive in phagocytes but also undergo de facto replication therein. Phagocytes, through the activities of phagocyte NADPH-dependent oxidase and inducible nitric oxide synthase, are very proficient in converting molecular oxygen to reactive oxygen (ROS) and nitrogen species (RNS). These compounds represent highly efficient effectors of the innate immune defense. Salmonella is by no means resistant to these effectors, which may stand in contrast to the host niches chosen. To cope with this paradox, these bacteria rely on an array of detoxification and repair systems. Combination these systems allows for a high enough tolerance to ROS and RNS to enable establishment of infection. In addition, salmonella possesses protein factors that have the potential to dampen the infection-associated inflammation, which evidently results in a reduced exposure to ROS and RNS. This review attempts to summarize the activities and strategies by which salmonella tries to cope with ROS and RNS and how the bacterium can make use of these innate defense factors.

Delayed kinetics of phagocytosis related respiratory burst in blood is a distinctive feature of moderate exacerbation of bronchial asthma

Atopic bronchial asthma based on allergy history and chronic inflammation is hazardous to patients due to the risk of exacerbation. The sign of severe exacerbation is considered an abundant number and high activity of granulocytes in respiratory system and blood. Relationships between the ability of cells in blood to produce reactive radicals and their metabolites and the severity of asthma remain largely unclear. Kinetics of respiratory burst evoked by microbe particles in blood samples of patients was studied to reveal the most significant predictors distinguishing states of moderate exacerbation and out of exacerbation. Asthmatic patients with exacerbation (n = 18) or out of exacerbation (n = 62) and healthy individuals (n = 43) were characterized on respiratory function, cell count in blood and kinetics of generation of reactive radicals and their metabolites during phagocytosis. Mean values of respiratory parameters forced expiratory volume in 1 s and peak expiratory flow rate in patients with exacerbation were significantly differed compared with same of patients out of exacerbation and healthy individuals. Mean values of cell count in blood did not significantly differed in patients with exacerbation and out of exacerbation. Receiver operating characteristic analysis showed that both cell count and respiratory indexes did not discriminate patients with exacerbation from out of exacerbation. A delayed response to opsonized zymosan was revealed in patients with exacerbation compared to other examinees: lengthened lag-time and T_max, reduced production of reactive species. T_max was the most statistically significant predictor to discriminate bronchial asthma exacerbation from bronchial asthma out of exacerbation (area under curve >90%, p < 10^-5) and controls (area under curve >80%, p < 10^-5). Thus kinetic parameters of the phagocyte response to opsonized zymosan in the whole blood are the best predictors of bronchial asthma exacerbation in comparison with respiratory parameters and blood cell count. This test can be used for immunological monitoring of bronchial asthma status to prevent exacerbation.

Cold water immersion or LED therapy after training sessions: effects on exercise-induced muscle damage and performance in rats

Cryotherapy and phototherapy have been suggested as recovery methods due to their anti-inflammatory effects. They may also induce mitochondrial biogenesis, thus favoring endurance training adaptation. The aim of this study was to evaluate the anti-inflammatory and ergogenic effects of phototherapy or cold water immersion (CWI) applied daily after exercise in rats. Thirty-five rats were divided into five groups: control (CO), non-exercised (CE), passive recovery (PR), cold water immersion (CWI), and LED therapy (LED). The CO and CE groups were not submitted to training; however, the CE were submitted to an exhaustion test after the training period. Low-intensity swimming training (21 sessions, 45 min) was performed followed by passive recovery (PR), CWI (10 °C, 5 min), or infrared irradiation (940 nm, 4 J/cm²). Forty-eight hours after the final training session, the CE, PR, CWI, and LED animals were submitted to an exhaustion test. The animals were euthanized 24 h later and submitted to hematological, creatine kinase (CK), and C-reactive protein (PCR) analysis. Gastrocnemius and soleus muscles were submitted to histological analysis. No differences in blood cell counts, CK, and PCR were detected between groups. The CE group presented an increased number of areas with necrosis in the gastrocnemius and soleus muscles. The PR group presented the highest frequency of areas with edema and inflammation followed by CWI and LED groups. None of the recovery methods improved the performance in the exhaustion test. Successive applications of recovery methods do not improve exercise performance, but downmodulate the inflammation and prevent muscle necrosis.

Development of a macrophage-targeting and phagocytosis-inducing bio-nanocapsule-based nanocarrier for drug delivery

Macrophage hyperfunction or dysfunction is tightly associated with various diseases, such as osteoporosis, inflammatory disorder, and cancers. However, nearly all conventional drug delivery system (DDS) nanocarriers utilize endocytosis for entering target cells; thus, the development of macrophage-targeting and phagocytosis-inducing DDS nanocarriers for treating these diseases is required. In this study, we developed a hepatitis B virus (HBV) envelope L particle (i.e., bio-nanocapsule (BNC)) outwardly displaying a tandem form of protein G-derived IgG Fc-binding domain and protein L-derived IgG Fab-binding domain (GL-BNC). When conjugated with the macrophage-targeting ligand, mouse IgG2a (mIgG2a), the GL-BNC itself, and the liposome-fused GL-BNC (i.e., GL-virosome) spontaneously initiated aggregation by bridging between the Fc-binding domain and Fab-binding domain with mIgG2a. The aggregates were efficiently taken up by macrophages, whereas this was inhibited by latrunculin B, a phagocytosis-specific inhibitor. The mIgG2a-GL-virosome containing doxorubicin exhibited higher cytotoxicity toward macrophages than conventional liposomes and other BNC-based virosomes. Thus, GL-BNCs and GL-virosomes may constitute promising macrophage-targeting and phagocytosis-inducing DDS nanocarriers.

STATEMENT OF SIGNIFICANCE

We have developed a novel macrophage-targeting and phagocytosis-inducing bio-nanocapsule (BNC)-based nanocarrier named GL-BNC, which comprises a hepatitis B virus envelope L particle outwardly displaying protein G-derived IgG Fc- and protein L-derived IgG Fab-binding domains in tandem. The GL-BNC alone or liposome-fused form (GL-virosomes) could spontaneously aggregate when conjugated with macrophage-targeting IgGs, inducing phagocytosis by the interaction between IgG Fc of aggregates and FcγR on phagocytes. Thereby these aggregates were efficiently taken up by macrophages. GL-virosomes containing doxorubicin exhibited higher cytotoxicity towards macrophages than ZZ-virosomes and liposomes. Our results suggested that GL-BNCs and GL-virosomes would serve as promising drug delivery system nanocarriers for targeting delivery to macrophages.

Molecular and functional characterization of the voltage-gated proton channel in zebrafish neutrophils

Voltage‐gated proton channels (Hv1/VSOP) are expressed in various cells types, including phagocytes, and are involved in diverse physiological processes. Although hvcn1, the gene encoding Hv1, has been identified across a wide range of species, most of the knowledge about its physiological function and expression profile is limited to mammals. In this study, we investigated the basic properties of DrHv1, the Hv1 ortholog in zebrafish (Danio rerio) which is an excellent animal model owing to the transparency, as well as its functional expression in native cells. Electrophysiological analysis using a heterologous expression system confirmed the properties of a voltage‐gated proton channel are conserved in DrHv1 with differences in threshold and activation kinetics as compared to mouse (Mus musculus) Hv1 (mHv1). RT‐PCR analysis revealed that hvcn1 is expressed in zebrafish neutrophils, as is the case in mammals. Subsequent electrophysiological analysis confirmed the functional expression of DrHv1 in zebrafish neutrophils, which suggests Hv1 function in phagocytes is conserved among vertebrates. We also found that DrHv1 is comparatively resistant to extracellular Zn²⁺, which is a potent inhibitor of mammalian Hv1, and this phenomenon appears to reflect variation in the Zn²⁺‐coordinating residue (histidine) within the extracellular linker region in mammalian Hv1. Notably, the serum Zn²⁺ concentration is much higher in zebrafish than in mouse, raising the possibility that Zn²⁺ sensitivity was acquired in accordance with a change in the serum Zn²⁺ concentration. This study highlights the biological variation and importance of Hv1 in different animal species.

Microglial dynamics after axotomy-induced retinal ganglion cell death

BACKGROUND

Microglial cells (MCs) are the sentries of the central nervous system. In health, they are known as surveying MCs because they examine the tissue to maintain the homeostasis. In disease, they activate and, among other functions, become phagocytic to clean the cellular debris. In this work, we have studied the behavior of rat retinal MCs in two models of unilateral complete intraorbital optic nerve axotomy which elicit a different time course of retinal ganglion cell (RGC) loss.

METHODS

Albino Sprague-Dawley rats were divided into these groups: (a) intact (no surgery), (b) fluorogold (FG) tracing from the superior colliculi, and (c) FG tracing + crush or transection of the left optic nerve. The retinas were dissected from 2 days to 2 months after the lesions (n = 4-12 group/lesion and time point) and then were subjected to Brn3a and Iba1 double immunodetection. In each intact retina, the total number of Brn3a+RGCs and Iba+MCs was quantified. In each traced retina (b and c groups), FG-traced RGCs and phagocytic microglial cells (PMCs, FG+Iba+) were also quantified. Topographical distribution was assessed by neighbor maps.

RESULTS

In intact retinas, surveying MCs are homogenously distributed in the ganglion cell layer and the inner plexiform layer. Independently of the axotomy model, RGC death occurs in two phases, one quick and one protracted, and there is a lineal and topographical correlation between the appearance of PMCs and the loss of traced RGCs. Furthermore, the clearance of FG+RGCs by PMCs occurs 3 days after the actual loss of Brn3a expression that marks RGC death. In addition, almost 50% of MCs from the inner plexiform layer migrate to the ganglion cell layer during the quick phase of RGC loss, returning to the inner plexiform layer during the slow degeneration phase. Finally, in contrast to what happens in mice, in rats, there is no microglial phagocytosis in the contralateral uninjured retina.

CONCLUSIONS

Axotomy-induced RGC death occurs earlier than RGC clearance and there is an inverse correlation between RGC loss and PMC appearance, both numerically and topographically, suggesting that phagocytosis occurs as a direct response to RGC death rather than to axonal damage.

Accelerated reactivity of blood granulocytes in patients with atopic bronchial asthma out of exacerbation

Reactive oxygen species (ROS) are important in bronchial asthma (BA) pathogenesis owing to accumulation of activated granulocytes in the lungs. But the ROS-producing activity of the cells is insufficiently understood in the blood of BA patients. This study analyzes the kinetics of phagocyte respiratory burst in the blood to improve the methods of BA patients monitoring. Patients with atopic BA out of exacerbation (n=60) and healthy controls (n=43) were recruited. The time-course of respiratory response to opsonized zymosan (OZ) was recorded in the whole blood using luminol-dependent chemiluminescence (CL), and its activation kinetics (lag-time, rate, amplitude, ROS production) was calculated. The discriminative power of ROS generation kinetics was defined by Receiver Operating Characteristic (ROC) curve analysis. Standard physiological respiratory parameters of patients did not differ from the controls. More rapid response to OZ was recorded in BA patient samples versus the controls. The primed state of phagocytes in the blood of BA patients was corroborated by significant weakening formyl peptide priming effect. The adhesion of granulocytes to cultured human endothelial cells was two-fold higher in BA patients versus controls. ROC curve analysis exhibited good discriminative effectiveness of the CL kinetics to compare BA individuals with the controls. The highest power (86% sensitivity and 90% specificity) was achieved at a linear combination of the parameters. We assume that the assessment of phagocyte reactivity based on the analysis of the response kinetic profile is a good test for monitoring of the state in BA patients.

Imaging the pharmacology of nanomaterials by intravital microscopy: Toward understanding their biological behavior

Therapeutic nanoparticles (NPs) can deliver cytotoxic chemotherapeutics and other drugs more safely and efficiently to patients; furthermore, selective delivery to target tissues can theoretically be accomplished actively through coating NPs with molecular ligands, and passively through exploiting physiological "enhanced permeability and retention" features. However, clinical trial results have been mixed in showing improved efficacy with drug nanoencapsulation, largely due to heterogeneous NP accumulation at target sites across patients. Thus, a clear need exists to better understand why many NP strategies fail in vivo and not result in significantly improved tumor uptake or therapeutic response. Multicolor in vivo confocal fluorescence imaging (intravital microscopy; IVM) enables integrated pharmacokinetic and pharmacodynamic (PK/PD) measurement at the single-cell level, and has helped answer key questions regarding the biological mechanisms of in vivo NP behavior. This review summarizes progress to date and also describes useful technical strategies for successful IVM experimentation.

Selective Biological Responses of Phagocytes and Lungs to Purified Histones

Histones invoke strong proinflammatory responses in many different organs and cells. We assessed biological responses to purified or recombinant histones, using human and murine phagocytes and mouse lungs. H1 had the strongest ability in vitro to induce cell swelling independent of requirements for toll-like receptors (TLRs) 2 or 4. These responses were also associated with lactate dehydrogenase release. H3 and H2B were the strongest inducers of [Ca2+]i elevations in phagocytes. Cytokine and chemokine release from mouse and human phagocytes was predominately a function of H2A and H2B. Double TLR2 and TLR4 knockout (KO) mice had dramatically reduced cytokine release induced in macrophages exposed to individual histones. In contrast, macrophages from single TLR-KO mice showed few inhibitory effects on cytokine production. Using the NLRP3 inflammasome protocol, release of mature IL-1β was predominantly a feature of H1. Acute lung injury following the airway delivery of histones suggested that H1, H2A, and H2B were linked to alveolar leak of albumin and the buildup of polymorphonuclear neutrophils as well as the release of chemokines and cytokines into bronchoalveolar fluids. These results demonstrate distinct biological roles for individual histones in the context of inflammation biology and the requirement of both TLR2 and TLR4.

Bacterial Binding, Phagocytosis, and Killing: Measurements Using Colony Forming Units

Herein we provide a colony forming unit (CFU)-based counting method for quantitating the bacterial binding, phagocytosis, and killing capacity of phagocytes. Although these functions can be measured by immunofluorescence and dye-based assays, quantitating CFUs is comparatively inexpensive and easy to perform. The protocol described below is easily modified for use with different phagocytes (e.g., macrophages, neutrophils, cell lines), types of bacteria or opsonic conditions.

Mycobacterium tuberculosis: Readouts of Bacterial Fitness and the Environment Within the Phagosome

Macrophages fulfill most of their microbicidal duties in their phagosomes following uptake of microbes. However, some microbes, such as Mycobacterium tuberculosis, have evolved mechanisms to subvert the normal maturation process of their phagocytic compartment to limit the hostility of this environment. The experimental analysis of this process and its subsequent impact on bacterial fitness is technically demanding and has required the development of a broad range of readouts to correlate function and outcome. In this chapter we detail two technically divergent platforms to measure the environment within the phagosomal compartment that contains Mtb in the short term, and more long-term readouts of bacterial fitness and Mtb's reaction to host-derived stresses. The readouts are all fluorescence-based and are adaptable to measurement by a range of platforms, including spectrofluorometry, confocal microscopy, and flow cytometry.

The cytochemical and ultrastructural characteristics of phagocytes in the Pacific oyster Crassostrea gigas

Phagocytes have been proved to play vital roles in the innate immune response. However, the cellular characteristics of phagocytes in invertebrates, especially in molluscs, remain largely unknown. In the present study, fluorescence activated cell sorting (FACS) was employed to sort the phagocytes from the non-phagocytic haemocytes of the Pacific oyster Crassostrea gigas. The cytochemical staining analysis revealed that phagocytes were positive staining for α-naphthyl acetate esterase and myeloperoxidase, while negative staining for toluidine blue and periodic acid-Schiff. The non-phagocytic haemocytes exhibited positive staining for periodic acid-Schiff, weak positive staining for toluidine blue, but negative staining for α-naphthyl acetate esterase and myeloperoxidase. In addition, phagocytes exhibited ultrastructural cellular features similar to those of macrophages, with large cell diameter, rough cell membrane and extended pseudopodia revealed by the scanning electron microscopy, while the non-phagocytic haemocytes exhibited small cell diameter, smooth cell surface and round spherical shape. Transmission electron microscopy further demonstrated that phagocytes were abundant of cytoplasmic bodies and mitochondria, while non-phagocytic haemocytes were characterized as the comparatively large cell nucleus with contorted and condensed heterochromatin adherent to the nuclear envelope. Moreover, compared with non-phagocytic haemocytes, phagocytes exhibited significantly higher levels of intracellular cytokines, including tumor necrosis factor, interferon-like protein and interleukin-17, and significantly higher abundance of lysosome and reactive oxygen species, which were of great importance to the activation of immune response and pathogen clearance. Taken together, these findings revealed the different cytochemical and ultrastructural features between phagocytes and non-phagocytic haemocytes in C. gigas, which would provide an important clue to investigate the mechanism of phagocytosis underlying the innate immune response.

The disintegrin, trimucrin, suppresses LPS-induced activation of phagocytes primarily through blockade of NF-κB and MAPK activation

In addition to antiplatelet activity, disintegrin, a small-mass RGD-containing polypeptide, has been shown to exert anti-inflammatory effects but the mechanism involved remains unclear. In this study, we report that trimucrin, a disintegrin from the venom of Trimeresurus mucrosquamatus, inhibits lipopolysaccharide (LPS)-induced stimulation of THP-1 and RAW 264.7 cells. We also investigate the underlying mechanism. Trimucrin decreased the release of proinflammatory cytokines including tumor necrosis factor α (TNFα), interleukin-6 (IL-6), nitric oxide, and reactive oxygen species (ROS), and inhibited the adhesion and migration of LPS-activated phagocytes. Trimucrin significantly blocked the expression of nuclear factor kappaB (NF-κB)-related downstream inducible enzymes such as inducible nitric oxide synthase (iNOS) and COX-2. In addition, its anti-inflammatory effect was associated with the decreased mitogen-activated protein kinase (MAPK) phosphorylation. Furthermore, trimucrin concentration dependently inhibited LPS-induced phosphorylation of focal adhesion kinase (FAK), PI3K, and Akt. Trimucrin also reversed the DNA-binding activity of NF-κB by suppressing the LPS-induced nuclear translocation of p65 and the cytosolic IκB release. Flow cytometric analyses showed that trimucrin bound to cells in a concentration-dependent manner. The anti-αVβ3 mAb also specifically decreased the binding of fluorescein isothiocyanate (FITC)-conjugated trimucrin. Binding assays demonstrated that integrin αVβ3 was the binding site for trimucrin on THP-1 and RAW 264.7 cells. In conclusion, we showed that trimucrin decreases the inflammatory reaction through the attenuation of iNOS expression and nitric oxide (NO) production by blocking MAP kinase and the NF-κB activation in LPS-stimulated THP-1 and RAW 264.7 cells.

Neutrophil NET formation is regulated from the inside by myeloperoxidase-processed reactive oxygen species

AIM

Neutrophil extracellular traps (NETs) are mesh-like DNA fibers clad with intracellular proteins that are cast out from neutrophils in response to certain stimuli. The process is thought to depend on reactive oxygen species (ROS) generated by the phagocyte NADPH-oxidase and the ROS-modulating granule enzyme myeloperoxidase (MPO), but when, how, and where these factors contribute is so far uncertain. The neutrophil NADPH-oxidase can be activated at different cellular sites and ROS may be produced and processed by MPO within intracellular granules, even in situations where a phagosome is not formed, e.g., upon stimulation with phorbol myristate acetate (PMA).

OBJECTIVES

We investigated the subcellular location of ROS production and processing by MPO in the context of PMA-induced NET formation.

RESULTS

Complete neutralization of extracellular ROS was not sufficient to block NET formation triggered by PMA, indicating that intragranular ROS are critical for NETosis. Employing a set of novel MPO-inhibitors, inhibition of NET formation correlated with inhibition of intragranular MPO activity. Also, extracellular addition of MPO was not sufficient to rescue NET formation in completely MPO-deficient neutrophils and specific neutralization by luminol of MPO-processed ROS within intracellular granules led to a complete block of PMA-triggered NET formation.

CONCLUSION

We show for the first time that inhibition of intragranular MPO activity, or neutralization of intragranular MPO-processed ROS by luminol effectively block NET formation. Our data demonstrate that ROS must be formed and processed by MPO in order to trigger NET formation, and that these events have to occur within intracellular granules.

Measuring the phagocytic activity of cells

Phagocytosis is a critical biological activity through which the host can protect itself from infectious and non-infectious environmental particles and remove unwanted host cells in order to maintain tissue homeostasis. Phagocytosis is an ancient, conserved process that is apparent in all multicellular organisms. The process of phagocytosis requires the recognition of ligands on particles by specific receptors expressed by the phagocyte that promote internalization via reorganization of cytoskeletal elements and directed formation of the phagosome. Subsequent phagosome-lysosome fusion delivers the contents for destruction and recycling in the acidic compartment. Significantly, receptor engagement and uptake can also trigger intracellular signaling pathways that initiate appropriate innate immune and pro-inflammatory or anti-inflammatory responses dependent upon the nature of the particle. The important benefits of phagocytosis to host survival are exemplified by the detrimental effects to health that occur when phagocytic efficiency is diminished. In an overview, we discuss the different experimental approaches or options that can be considered when investigating and determining the characteristics and quantification of phagocytic activity. These criteria will include choice of phagocytic cell type, selection, and method of labeling of particle for monitoring internalization, targeting of particles to specific receptors, and quantification of ingestion either at the single cell or at the population level. We provide two detailed examples of phagocytosis assays.

Cell death and autophagy in tuberculosis

Mycobacterium tuberculosis has succeeded in infecting one-third of the human race though inhibition or evasion of innate and adaptive immunity. The pathogen is a facultative intracellular parasite that uses the niche provided by mononuclear phagocytes for its advantage. Complex interactions determine whether the bacillus will or will not be delivered to acidified lysosomes, whether the host phagocyte will survive infection or die, and whether the timing and mode of cell death works to the advantage of the host or the pathogen. Here we discuss cell death and autophagy in TB. These fundamental processes of cell biology feature in all aspects of TB pathogenesis and may be exploited to the treatment or prevention of TB disease.

An improved flow cytometry assay to monitor phagosome acidification

Phago-lysosome formation is important for cell-autonomous immunity to intracellular pathogens, antigen presentation and metabolism. A hallmark feature of phago-lysosomal compartments is that they undergo progressive luminal acidification controlled by the activation of vacuolar V-ATPase. Acidification is required for many enzymatic processes taking place in phago-lysosomes, like proteolysis, and supports the microbicidal activity of macrophages. Here we present a new quantitative methodology to assess phagosome acidification by flow cytometry based on the use of bi-fluorescent particles. This method relies on the use of UV polystyrene beads labelled with the acid sensor pHrodo-succinimidyl ester (pHrodo(TM) SE red) and enables us to dissociate particle association with phagocytes from their engulfment in acidified compartments. This methodology is well suited to monitor the acidification of phagosomes formed in vivo after fluorescent bead administration.

Characterization of betaine aldehyde dehydrogenase (BetB) as an essential virulence factor of Brucella abortus

The pathogenic mechanisms of Brucellosis used to adapt to the harsh intracellular environment of the host cell are not fully understood. The present study investigated the in vitro and in vivo characteristics of B. abortus betaine aldehyde dehydrogenase (BetB) (Gene Bank ID: 006932) using a betB deletion mutant constructed from virulent B. abortus 544. In test under stress conditions, including osmotic- and acid stress-resistance, the betB mutant had a lower osmotic-resistance than B. abortus wild-type. In addition, the betB mutant showed higher internalization rates compared to the wild-type strain; however, it also displayed replication failures in HeLa cells and RAW 264.7 macrophages. During internalization, compared to the wild-type strain, the betB mutant was more adherent to the host surface and showed enhanced phosphorylation of protein kinases, two processes that promote phagocytic activity, in host cells. During intracellular trafficking, colocalization of B. abortus-containing phagosomes with LAMP-1 was elevated in betB mutant-infected cells compared to the wild-type cells. In mice, the betB mutant was predominantly cleared from spleens compared to the wild-type strain after 2 weeks post-infection, and the vaccination test with the live betB mutant showed effective protection against challenge infection with the virulent wild-type strain. These findings suggested that the B. abortus betB gene substantially affects the phagocytic pathway in human phagocytes and in host cells in mice. Furthermore, this study highlights the potential use of the B. abortus betB mutant as a live vaccine for the control of brucellosis.

Peroxiredoxin-6 and NADPH oxidase activity

Peroxiredoxins (Prdxs) are a family of proteins which catalyze the reduction of H2O2 through the interaction of active site cysteine residues. Conserved within all plant and animal kingdoms, the function of these proteins is related to protection from oxidation or participation of signaling through degradation of H2O2. Peroxiredoxin 6 (Prdx6), a protein belonging to the class of 1-cys Prdxs, was identified in polymorphonuclear leukocytes or neutrophils, defined by amino acid sequence and activity, and found associated with a component of the NADPH oxidase (Nox2), p67(phox). Prdx6 plays an important role in neutrophil function and supports the optimal activity of Nox2. In this chapter, methods are described for determining the Prdx activity of Prdx6. In addition, the approach for assessing the effect of Prdx6 on Nox2 in the SDS-activated, cell-free system of NADPH oxidase activity is presented. Finally, the techniques for suppressing Prdx6 expression in phox-competent K562 cells and cultured myeloid cells with siRNA and shRNA methods are described. With these approaches, the role of Prdx6 in Nox2 activity can be explored with intact cells. The biochemical mechanisms of the Prdx6 effect on the NADPH oxidase can be investigated with the experimental strategies described.

The scoop on the fly brain: glial engulfment functions in Drosophila

Glial cells provide support and protection for neurons in the embryonic and adult brain, mediated in part through the phagocytic activity of glia. Glial cells engulf apoptotic cells and pruned neurites from the developing nervous system, and also clear degenerating neuronal debris from the adult brain after neural trauma. Studies indicate that Drosophila melanogaster is an ideal model system to elucidate the mechanisms of engulfment by glia. The recent studies reviewed here show that many features of glial engulfment are conserved across species and argue that work in Drosophila will provide valuable cellular and molecular insight into glial engulfment activity in mammals.