Mechanisms of phagocytosis

PKC-α is involved in the signaling of phagocytosis induced by two snake venom secretory PLA2S in macrophages

Phagocytosis, an essential process for host defense, requires the coordination of a variety of signaling reactions. MT-II, an enzymatically inactive Lys49 phospholipase A2 (PLA2) homolog, and MT-III, a catalytically-active Asp49 PLA2, are known to activate phagocytosis in macrophages. In this study, the signaling pathways mediating phagocytosis, focusing on protein kinases, were investigated. Macrophages from male Swiss mice peritoneum were obtained 96 h after intraperitoneal thioglycolate injection. Phagocytosis was evaluated using non-opsonized zymosan particles in the presence or absence of specific inhibitors, as well as PKC and PKC-α localization by confocal microscopy. Moreover, protein kinase C (PKC) activity was assessed by γP32 ATP in macrophages stimulated by both PLA2s. Data showed that both sPLA2s increased phagocytosis. Cytochalasin D, staurosporine/H7, wortmannin, and herbimycin, inhibitors of actin polymerization, PKC, phosphoinositide 3-kinase (PI3K), and protein tyrosine kinase (PTK), respectively, significantly reduced phagocytosis induced by both PLA2s. PKC activity was increased in macrophages stimulated by both PLA2s. Actin polymerization and talin were evidenced by immunofluorescence and talin was recruited 5 min after both PLA2s stimulation. PKC and PKC-α localization within the cell were increased after 60 min of MT-II and MT-III stimulation. These data suggest that the effect of both PLA2s depends on actin cytoskeleton rearrangements and the activation of PKC, PI3K, and PTK signaling events required for phagocytosis.

Extracellular vesicles (EVs)' journey in recipient cells: from recognition to cargo release

Extracellular vesicles (EVs) are nano-sized bilayer vesicles that are shed or secreted by virtually every cell type. A variety of biomolecules, including proteins, lipids, coding and non-coding RNAs, and mitochondrial DNA, can be selectively encapsulated into EVs and delivered to nearby and distant recipient cells, leading to alterations in the recipient cells, suggesting that EVs play an important role in intercellular communication. EVs play effective roles in physiology and pathology and could be used as diagnostic and therapeutic tools. At present, although the mechanisms of exosome biogenesis and secretion in donor cells are well understood, the molecular mechanism of EV recognition and uptake by recipient cells is still unclear. This review summarizes the current understanding of the molecular mechanisms of EVs' biological journey in recipient cells, from recognition to uptake and cargo release. Furthermore, we highlight how EVs escape endolysosomal degradation after uptake and thus release cargo, which is crucial for studies applying EVs as drug-targeted delivery vehicles. Knowledge of the cellular processes that govern EV uptake is important to shed light on the functions of EVs as well as on related clinical applications.

Clearance phagocytosis by the retinal pigment epithelial during photoreceptor outer segment renewal: Molecular mechanisms and relation to retinal inflammation

Mammalian photoreceptor outer segment renewal is a highly coordinated process that hinges on timed cell signaling between photoreceptor neurons and the adjacent retinal pigment epithelial (RPE). It is a strictly rhythmic, synchronized process that underlies in part circadian regulation. We highlight findings from recently developed methods that quantify distinct phases of outer segment renewal in retinal tissue. At light onset, outer segments expose the conserved "eat-me" signal phosphatidylserine exclusively at their distal, most aged tip. A coordinated two-receptor efferocytosis process follows, in which ligands bridge outer segment phosphatidylserine with the RPE receptors αvβ5 integrin, inducing cytosolic signaling toward Rac1 and focal adhesion kinase/MERTK, and with MERTK directly, additionally inhibiting RhoA/ROCK and thus enabling F-actin dynamics favoring outer segment fragment engulfment. Photoreceptors and RPE persist for life with each RPE cell in the eye servicing dozens of overlying photoreceptors. Thus, RPE cells phagocytose more often and process more material than any other cell type. Mutant mice with impaired outer segment renewal largely retain functional photoreceptors and retinal integrity. However, when anti-inflammatory signaling in the RPE via MERTK or the related TYRO3 is lacking, catastrophic inflammation leads to immune cell infiltration that swiftly destroys the retina causing blindness.

Natural Gallic Acid and Methyl Gallate Induces Apoptosis in Hela Cells through Regulation of Intrinsic and Extrinsic Protein Expression

Induction of apoptosis is one of the targeted approaches in cancer therapies. As previously reported, natural products can induce apoptosis in in vitro cancer treatments. However, the underlying mechanisms of cancer cell death are poorly understood. The present study aimed to elucidate cell death mechanisms of gallic acid (GA) and methyl gallate (MG) from Quercus infectoria toward human cervical cancer cell lines (HeLa). The antiproliferative activity of GA and MG was characterised by an inhibitory concentration using 50% cell populations (IC₅₀) by an MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Cervical cancer cells, HeLa, were treated with GA and MG for 72 h and calculated for IC₅₀ values. The IC₅₀ concentration of both compounds was used to elucidate the apoptotic mechanism using acridine orange/propidium iodide (AO/PI) staining, cell cycle analysis, the Annexin-V FITC dual staining assay, apoptotic proteins expressions (p53, Bax and Bcl-2) and caspase activation analysis. GA and MG inhibited the growth of HeLa cells with an IC₅₀ value of 10.00 ± 0.67 µg/mL and 11.00 ± 0.58 µg/mL, respectively. AO/PI staining revealed incremental apoptotic cells. Cell cycle analysis revealed an accumulation of cells at the sub-G1 phase. The Annexin-V FITC assay showed that cell populations shifted from the viable to apoptotic quadrant. Moreover, p53 and Bax were upregulated, whereas Bcl-2 was markedly downregulated. Activation of caspase 8 and 9 showed an ultimate apoptotic event in HeLa cells treated with GA and MG. In conclusion, GA and MG significantly inhibited HeLa cell growth through apoptosis induction by the activation of the cell death mechanism via extrinsic and extrinsic pathways.

TLR2 and 4 signaling pathways are altered in macrophages from V30M TTR mice with down-regulated expression of chemokines

Hereditary amyloid transthyretin (ATTRv) amyloidosis is a fatal neurodegenerative disorder, first identified in Portugal. The most common transthyretin (TTR) mutation in ATTRv results from an exchange of a methionine for a valine at position 30 (V30M). ATTRv is characterized by the extracellular deposition of aggregates and fibrils of mutant forms of TTR, particularly in the nerves and ganglia of the peripheral nervous system (PNS). This phenotype is often accompanied by the lack of inflammatory infiltrates, despite the importance of macrophages in removal of TTR deposits in ATTRv patients. The mechanisms underlying this impairment of inflammatory responses in ATTRv patients are poorly understood. Here, we show a significant down-regulation in the expression of several chemokines by bone marrow-derived macrophages (BMDM) generated from V30M TTR mice upon stimulation with toll-like receptor 4 (TLR4) and TLR2 agonists. The phosphorylation of the MAP kinase p38, important for TLR4 and TLR2 signaling pathways, was also down-regulated in V30M macrophages, as compared with wild-type (WT) ones. The present study contributes with new insights to unravel the molecular mechanisms underlying the lack of inflammatory immune responses observed in ATTRv patients and may help in the development of new immune therapeutic strategies for the disease.

The spatial resolution limit of phagocytosis

Antibody-opsonized bacteria interact with Fc receptors in macrophages and trigger signaling cascades, which induce phagocytosis. The signaling pathways ultimately lead to actin polymerization that induces the protrusion of the membrane around the bacterium until it is completely engulfed. Although many proteins involved in the phagocytic cup formation have already been identified, it is still unclear how far the initial stimulus created by the bacterium-cell contact propagates in the cell. We hypothesize that this spreading distance is closely related to the spatial resolution limit of phagocytosis, the smallest distance in which two stimuli can be differentiated. Here, we probe this resolution limit by using holographic optical tweezers to attach pairs of immunoglobulin G-coated polystyrene microparticles (as models for opsonized bacteria) to murine macrophages in distances ranging from zero to several micrometers. By using 2-μm-sized particles, we found that the particles can be internalized jointly into one phagosome if they are attached to the cell very close together, but that they are taken up separately if they are attached far from each other. To explain this, we developed a model of the signaling process, which predicts the probabilities for separate uptake for different particle sizes and distances using cellular parameters including the average receptor distance. We tested the model by measuring the separate uptake probabilities for particles with a diameter of 1 to 3 μm and for cells with reduced numbers of Fcγ receptors and found very good agreement. Our model shows that the phagocytic uptake behavior can be explained by assuming an effective phagocytic signaling range of about 500 nm. Interestingly, this value corresponds to the lower size limit of phagocytosis. Our work provides quantitative access to spatial parameters of cellular signaling during phagocytosis and thereby contributes to a more quantitative understanding of cellular information processing.

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.

The Multiple Faces of Nitric Oxide in Chronic Granulomatous Disease: A Comprehensive Update

Nitric oxide (NO), a signaling molecule, regulates multiple biological functions, including a variety of physiological and pathological processes. In this regard, NO participates in cutaneous inflammations, modulation of mitochondrial functions, vascular diseases, COVID-19, neurologic diseases, and obesity. It also mediates changes in the skeletal muscle function. Chronic granulomatous disease (CGD) is a primary immunodeficiency disorder characterized by the malfunction of phagocytes caused by mutations in some of the genes encoding subunits of the superoxide-generating phagocyte NADPH (NOX). The literature consulted shows that there is a relationship between the production of NO and the NADPH oxidase system, which regulates the persistence of NO in the medium. Nevertheless, the underlying mechanisms of the effects of NO on CGD remain unknown. In this paper, we briefly review the regulatory role of NO in CGD and its potential underlying mechanisms.

Study of tribological properties of human buccal epithelium cell membranes using probe microscopy

In this work demostrates a unique method for determining the absolute value of the friction force of a nanoobject on the surface of a cell membrane using atomic force microscopy. The tribological properties of membranes of adult human buccal epithelium cells in the presence of a protective adsorption buffer layer of ~ 100 nm on their surface were studied using atomic force microscopy in the contact scanning mode. Local mapping of the tribological characteristics of the surface was carried out, viz. friction F_L = F_L(x, y) and adhesion F_adh = F_adh(x, y) forces were measured. Studies of the friction force F_fr on the membrane surface at the nanolevel showed that its value varies discretely with an interval equal to l_LF ≈ 100 nm. It was shown that such discreteness is determined by the interval l_LF of the action of adhesive forces F_adh and indicates the fractal nature of the functional dependence of the friction force on the coordinate F_fr = F_fr(x). Thus, for nano-objects with dimensions ≤ l_LF, the absolute value of F_fr decreases according to a power law with an increase in the size of the object, which contradicts the similar dependence of the friction force for macro-objects in the global approximation.

Recent advances in the intracellular delivery of macromolecule therapeutics

This review summarizes the uptake pathway of intracellular delivery vehicles for macromolecule therapeutics, and provides in-depth discussions and prospects about intracellular delivery of macromolecule therapeutics.

Cellular uptake of polylactide particles induces size dependent cytoskeletal remodeling in antigen presenting cells

Phagocytosis of particulate vaccine delivery systems is a critical immune mechanism involved in antigen capture and processing by macrophages and dendritic cells. The internalization and degradation of the particles involve a complex sequence of events. This process coordinates lipids, signaling proteins, and the cytoskeleton. Dynamic changes in the actin cytoskeleton are essential for phagocytosis and antigen presentation. Knowledge regarding the correlation of surface properties, attached ligand density and geometric size of particles with the efficiency of phagocytosis may facilitate their design and application. To investigate this, polylactide biodegradable particles with different diameters (2-4 μm and 200-300 nm) were exposed to murine macrophages and dendritic cells and the effect of size on a series of cellular responses was evaluated. Cellular uptake studies using microscopy and flow cytometry showed size dependent internalization of particles, with nanoparticles accumulating in cells at a faster rate. The particles induced homoaggregation of cells and also showed cytoskeletal remodeling that could be inhibited by cytochalasin-D. Scanning electron microscopy images showed the time dependent formation of phagocytic cups and invaginations that promote particle uptake. The particles were observed to co-localized with the endo-lysosomal compartments after phagocyotosis. In our experiments, particle mediated immunoactivation, antigen processing and cytokine secretion have shown a good correlation with the uptake process. These findings would allow a better understanding of the process of particle uptake and may be instrumental in the rational design of optimal vaccine delivery systems.

Importance of particle size of oligomannose-coated liposomes for induction of Th1 immunity

Oligomannose-coated liposomes (OMLs) comprised of dipalmitoylphosphatidylcholine, cholesterol and Man3-DPPE at a molar ratio of 1:1:0.1 and particle diameters of about 1000 nm can induce liposome-encased antigen-specific strong Th1 immunity. In this study, we evaluated the effect of particle sizes of OMLs on induction of Th1 immune responses in mice. Spleen cells obtained from mice immunized with antigen-encapsulating OMLs with 1000- and 800-nm diameters secreted remarkably high levels of IFN-γ upon in vitro stimulation. In addition, sera of mice that received these OMLs had significantly higher titers of antigen-specific IgG2a than those of IgG1, which are commonly associated with Th1 responses. In contrast, treatment with antigen-encapsulating OMLs with 400- and 200-nm diameters failed to induce IFN-γ secretion from spleen cells, although these OMLs did elicit elevation of antigen-specific IgGs. In addition, the titers of serum antigen-specific IgG2a were the same as those of IgG1 in mice that received 400-nm OMLs. Resident peritoneal mononuclear phagocytes (MNPs) treated with OMLs of diameter ≥ 600 nm secreted IL-12, which is essential for induction of Th1 immune responses, while those treated with OMLs of ≤ 400 nm failed to produce this cytokine. However, 400-nm OMLs did induce enhanced expression of MHC class II and costimulatory molecules on MNPs, similarly to OMLs of ≥ 600 nm. Taken together, these results strongly indicate that OMLs of diameter ≥ 600 nm are required to induce Th1 immune responses against OML-encased antigens, although OMLs of diameter ≤ 400 nm can activate MNPs.

Acute RhoA/Rho Kinase Inhibition Is Sufficient to Restore Phagocytic Capacity to Retinal Pigment Epithelium Lacking the Engulfment Receptor MerTK

The diurnal phagocytosis of spent photoreceptor outer segment fragments (POS) by retinal pigment epithelial (RPE) cells is essential for visual function. POS internalization by RPE cells requires the assembly of F-actin phagocytic cups beneath surface-tethered POS and Mer tyrosine kinase (MerTK) signaling. The activation of the Rho family GTPase Rac1 is necessary for phagocytic cup formation, and Rac1 is activated normally in MerTK-deficient RPE. We show here that mutant RPE lacking MerTK and wild-type RPE deprived of MerTK ligand both fail to form phagocytic cups regardless of Rac1 activation. However, in wild-type RPE in vivo, a decrease in RhoA activity coincides with the daily phagocytosis burst, while RhoA activity in MerTK-deficient RPE is constant. Elevating RhoA activity blocks phagocytic cup formation and phagocytosis by wild-type RPE. Conversely, inhibiting RhoA effector Rho kinases (ROCKs) rescues both F-actin assembly and POS internalization of primary RPE if MerTK or its ligand are lacking. Most strikingly, acute ROCK inhibition is sufficient to induce the formation and acidification of endogenous POS phagosomes by MerTK-deficient RPE ex vivo. Altogether, RhoA pathway inactivation is a necessary and sufficient downstream effect of MerTK phagocytic signaling such that the acute manipulation of cytosolic ROCK activity suffices to restore phagocytic capacity to MerTK-deficient RPE.

Study of Uptake Mechanisms of Halloysite Nanotubes in Different Cell Lines

Purpose

Halloysite nanotubes (HNTs) are a natural aluminosilicate clay with a chemical formula of Al₂Si₂O₅(OH)₄×nH₂O and a hollow tubular structure. Due to their peculiar structure, HNTs can play an important role as a drug carrier system. Currently, the mechanism by which HNTs are internalized into living cells, and what is the transport pathway, is still unclear. Therefore, this study aimed at establishing the in vitro mechanism by which halloysite nanotubes could be internalized, using phagocytic and non-phagocytic cell lines as models.

Methods

The HNT/CURBO hybrid system, where a fluorescent probe (CURBO) is confined in the HNT lumen, has been used as a model to study the transport pathway mechanisms of HNTs. The cytocompatibility of HNT/CURBO on cell lines model was investigated by MTS assay. In order to identify the internalization pathway involved in the cellular uptake, we performed various endocytosis-inhibiting studies, and we used fluorescence microscopy to verify the nanomaterial internalization by cells. We evaluated the haemolytic effect of HNT/CURBO placed in contact with human red blood cells (HRBCs), by reading the absorbance value of the supernatant at 570 nm.

Results

The HNT/CURBO is highly biocompatible and does not have an appreciable haemolytic effect. The results of the inhibition tests have shown that the internalization process of nanotubes occurs in an energy-dependent manner in both the investigated cell lines, although they have different characteristics. In particular, in non-phagocytic cells, clathrin-dependent and independent endocytosis are involved. In phagocytic cells, in addition to phagocytosis and clathrin-dependent endocytosis, microtubules also participate in the halloysite cellular trafficking. Upon internalization by cells, HNT/CURBO is localized in the cytoplasmic area, particularly in the perinuclear region.

Conclusion

Understanding the cellular transport pathways of HNTs can help in the rational design of novel drug delivery systems and can be of great value for their applications in biotechnology.

Administration of GDF3 Into Septic Mice Improves Survival via Enhancing LXRα-Mediated Macrophage Phagocytosis

The defective eradication of invading pathogens is a major cause of death in sepsis. As professional phagocytic cells, macrophages actively engulf/kill microorganisms and play essential roles in innate immune response against pathogens. Growth differentiation factor 3 (GDF3) was previously implicated as an important modulator of inflammatory response upon acute sterile injury. In this study, administration of recombinant GDF3 protein (rGDF3) either before or after CLP surgery remarkably improved mouse survival, along with significant reductions in bacterial load, plasma pro-inflammatory cytokine levels, and organ damage. Notably, our in vitro experiments revealed that rGDF3 treatment substantially promoted macrophage phagocytosis and intracellular killing of bacteria in a dose-dependent manner. Mechanistically, RNA-seq analysis results showed that CD5L, known to be regulated by liver X receptor α (LXRα), was the most significantly upregulated gene in rGDF3-treated macrophages. Furthermore, we observed that rGDF3 could promote LXRα nuclear translocation and thereby, augmented phagocytosis activity in macrophages, which was similar as LXRα agonist GW3965 did. By contrast, pre-treating macrophages with LXRα antagonist GSK2033 abolished beneficial effects of rGDF3 in macrophages. In addition, rGDF3 treatment failed to enhance bacteria uptake and killing in LXRα-knockout (KO) macrophages. Taken together, these results uncover that GDF3 may represent a novel mediator for controlling bacterial infection.

Complement Receptors and Their Role in Leukocyte Recruitment and Phagocytosis

The complement system is deeply embedded in our physiology and immunity. Complement activation generates a multitude of molecules that converge simultaneously on the opsonization of a target for phagocytosis and activation of the immune system via soluble anaphylatoxins. This response is used to control microorganisms and to remove dead cells, but also plays a major role in stimulating the adaptive immune response and the regeneration of injured tissues. Many of these effects inherently depend on complement receptors expressed on leukocytes and parenchymal cells, which, by recognizing complement-derived molecules, promote leukocyte recruitment, phagocytosis of microorganisms and clearance of immune complexes. Here, the plethora of information on the role of complement receptors will be reviewed, including an analysis of how this functionally and structurally diverse group of molecules acts jointly to exert the full extent of complement regulation of homeostasis.

Complex Factors and Challenges that Affect the Pharmacology, Safety and Efficacy of Nanocarrier Drug Delivery Systems

Major developments in nanomedicines, such as nanoparticles (NPs), nanosomes, and conjugates, have revolutionized drug delivery capabilities over the past four decades. Although nanocarrier agents provide numerous advantages (e.g., greater solubility and duration of systemic exposure) compared to their small-molecule counterparts, there is considerable inter-patient variability seen in the systemic disposition, tumor delivery and overall pharmacological effects (i.e., anti-tumor efficacy and unwanted toxicity) of NP agents. This review aims to provide a summary of fundamental factors that affect the disposition of NPs in the treatment of cancer and why they should be evaluated during preclinical and clinical development. Furthermore, this chapter will highlight some of the translational challenges associated with elements of NPs and how these issues can only be addressed by detailed and novel pharmacology studies.

Multivalent Antibody-Recruiting Macromolecules: Linking Increased Binding Affinity with Enhanced Innate Immune Killing

Antibody-recruiting molecules (ARMs) are a novel class of immunotherapeutics. They are capable of introducing antibodies onto disease-relevant targets such as cancer cells, bacterial cells or viruses. This can induce antibody-mediated immune responses such as antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC) and antibody-dependent phagocytosis (ADCP), which can kill the pathogen. In contrast to the classic ARMs, multivalent ARMs could offer the advantage of increasing the efficiency of antibody recruitment and subsequent innate immune killing. Such compounds consist of multiple target-binding termini (TBT) and/or antibody-binding termini (ABT). Those multivalent interactions are able to convert low binding affinities into increased binding avidities. This minireview summarizes the current status of multivalent ARMs and gives insight into possible benefits, hurdles still to be overcome and future perspectives.

Macrophage polarization in intestinal inflammation and gut homeostasis

Gut homeostasis is a process that requires a prudent balance of host responses to the beneficial enteric microbial community and the pathogenic stimuli that can arise. The lack of this balance in the intestine can result in inflammatory bowel diseases, where the immune system dysfunctions leading to exacerbated inflammatory responses. In this process, macrophages are considered to play a pivotal role. In this review, we describe the important role of macrophages in maintaining intestinal homeostasis and we discuss how altered macrophage function may lead to inflammatory bowel diseases. The plasticity of macrophages during the gut inflammatory response shows the broad role of these cells in orchestrating not only the onset of inflammation but also its termination as well as healing and repair. Indeed, the state of macrophage polarization can be the key factor in defining the resolution or the progression of inflammation and disease. Here, we discuss the different populations of macrophages and their implication in development, propagation, control and resolution of inflammatory bowel diseases.

Mechanobiology of Macrophages: How Physical Factors Coregulate Macrophage Plasticity and Phagocytosis

In addition to their early-recognized functions in host defense and the clearance of apoptotic cell debris, macrophages play vital roles in tissue development, homeostasis, and repair. If misregulated, they steer the progression of many inflammatory diseases. Much progress has been made in understanding the mechanisms underlying macrophage signaling, transcriptomics, and proteomics, under physiological and pathological conditions. Yet, the detailed mechanisms that tune circulating monocytes/macrophages and tissue-resident macrophage polarization, differentiation, specification, and their functional plasticity remain elusive. We review how physical factors affect macrophage phenotype and function, including how they hunt for particles and pathogens, as well as the implications for phagocytosis, autophagy, and polarization from proinflammatory to prohealing phenotype. We further discuss how this knowledge can be harnessed in regenerative medicine and for the design of new drugs and immune-modulatory drug delivery systems, biomaterials, and tissue scaffolds.

The road to lysosome-related organelles: Insights from Hermansky-Pudlak syndrome and other rare diseases

Lysosome-related organelles (LROs) comprise a diverse group of cell type-specific, membrane-bound subcellular organelles that derive at least in part from the endolysosomal system but that have unique contents, morphologies and functions to support specific physiological roles. They include: melanosomes that provide pigment to our eyes and skin; alpha and dense granules in platelets, and lytic granules in cytotoxic T cells and natural killer cells, which release effectors to regulate hemostasis and immunity; and distinct classes of lamellar bodies in lung epithelial cells and keratinocytes that support lung plasticity and skin lubrication. The formation, maturation and/or secretion of subsets of LROs are dysfunctional or entirely absent in a number of hereditary syndromic disorders, including in particular the Hermansky-Pudlak syndromes. This review provides a comprehensive overview of LROs in humans and model organisms and presents our current understanding of how the products of genes that are defective in heritable diseases impact their formation, motility and ultimate secretion.

Geometry and dynamics of lipid membranes: The Scriven-Love number

The equations governing lipid membrane dynamics in planar, spherical, and cylindrical geometries are presented here. Unperturbed and first-order perturbed equations are determined and nondimensionalized. In membrane systems with a nonzero base flow, perturbed in-plane and out-of-plane quantities are found to vary over different length scales. A new dimensionless number, named the Scriven-Love number, and the well-known Föppl-von Kármán number result from a scaling analysis. The Scriven-Love number compares out-of-plane forces arising from the in-plane, intramembrane viscous stresses to the familiar elastic bending forces, while the Föppl-von Kármán number compares tension to bending forces. Both numbers are calculated in past experimental works, and span a wide range of values in various biological processes across different geometries. In situations with large Scriven-Love and Föppl-von Kármán numbers, the dynamical response of a perturbed membrane is dominated by out-of-plane viscous and surface tension forces-with bending forces playing a negligible role. Calculations of non-negligible Scriven-Love numbers in various biological processes and in vitro experiments show in-plane intramembrane viscous flows cannot generally be ignored when analyzing lipid membrane behavior.

TLR3 stimulation induces melanosome endo/phagocytosis through RHOA and CDC42 in human epidermal keratinocyte

BACKGROUND

Keratinocytes and melanocytes in human epidermis express Toll-like receptors (TLR) and induce immune responses. We previously reported that TLR3 stimulation increases melanosome transport from perinuclear to cell membrane in melanocytes and enhanced release of melanosome from melanocytes, which were followed by increase in melanosome uptake into keratinocytes.

OBJECTIVE

In this study, we investigated whether TLR3 stimuli directly affect keratinocytes to enhance melanosome uptake.

METHODS

To observe keratinocyte's melanosome uptake ability precisely without melanocytes influences, we isolated melanosomes from human melanocytes and applied isolated melanosomes to keratinocytes stimulated by Poly(I:C).

RESULTS

Poly(I:C)-stimulated keratinocytes enhanced uptake of isolated melanosome-rich globules five-times as much as control. Poly(I:C) increases the RNA and protein expressions of RHOA and CDC42, which are small GTP-binding proteins inducing the endocytosis. Pull-down assay showed that Poly(I:C) increased the GTP-binding RHOA and CDC42, suggesting TLR3 stimulation activated RHOA and CDC42. The knockdown of TLR3 suppressed RHOA and CDC42 induction by Poly(I:C). Consistently, the knockdown of RHOA and CDC42 significantly suppressed the melanosome-rich globules uptake by Poly(I:C)-stimulated keratinocytes.

CONCLUSION

Because RHOA and CDC42 activation induces endocytosis by modification of actin stress fiber and filopodia formation, respectively, these results suggested that TLR3 stimulation enhances melanosome uptake into keratinocytes through endocytosis mechanisms. Combining with the data of our previous publications, TLR3, which signal is activated by sensing viral molecules, enhance pigmentation by controlling both melanin transport system by RAB GTPases induction in melanocytes and uptake system by RHOA and CDC42 in keratinocytes.

Therapeutic potential of low-cost nanocarriers produced by green synthesis: macrophage uptake of superparamagnetic iron oxide nanoparticles

Aim: The primary goal of this work was to synthesize low-cost superparamagnetic iron oxide nanoparticles (SPIONs) with the aid of coconut water and evaluate the ability of macrophages to internalize them. Our motivation was to determine potential therapeutic applications in drug-delivery systems associated with magnetic hyperthermia. Materials & methods: We used the following characterization techniques: x-ray and electron diffractions, electron microscopy, spectrometry and magnetometry. Results: The synthesized SPIONs, roughly 4 nm in diameter, were internalized by macrophages, likely via endocytic/phagocytic pathways. They were randomly distributed throughout the cytoplasm and mainly located in membrane-bound compartments. Conclusion: Nanoparticles presented an elevated intrinsic loss power value and were not cytotoxic to mammalian cells. Thus, we suggest that low-cost SPIONs have great therapeutic potential.

Membrane-Mimetic Dendrimersomes Engulf Living Bacteria via Endocytosis

There is much interest in developing vesicular microcompartments from natural and synthetic amphiphiles, enabling programmable interactions with living matter. Of particular interest is the development of vesicles capable of endocytosis of living bacteria. Despite the complexity of this process, theoretical studies predict that the endocytosis of prolate micro-objects is possible without the need of active cell machinery if the energy released upon bacterial adhesion to the membrane surpasses the energy required to bend the membrane. Nonetheless, natural liposomes and synthetic polymersomes fail to sufficiently recapitulate membrane properties to perform this advanced function. Here we report the engulfment of living bacteria into endosomes by cell-like dendrimersomes assembled from Janus dendrimers. Full engulfment occurred in less than a minute after contact. The process is driven by the adhesion of the bacterium to the dendrimersome's membrane by ultraweak interactions, comparable to those utilized by nature. The key to success relies on the combination of high flexibility and stability of the dendrimersomes. The key properties of the dendrimersomes are programmed into the molecular structures of their building blocks. The ability to support endocytosis highlights opportunities for the design and programming of dendrimersomes in biomedical research.

Binding and uptake of single and dual-opsonized targets by macrophages

Our current understanding of phagocytosis is largely derived from studies of individual receptor-ligand interactions and their downstream signaling pathways. Because phagocytes are exposed to a variety of ligands on heterogeneous target particles in vivo, it is important to observe the engagement of multiple receptors simultaneously and the triggered involvement of downstream signaling pathways. Potential crosstalk between the two well-characterized opsonic receptors, FcγR and CR3, was briefly explored in the early 1970s, where macrophages were challenged with dual-opsonized targets. However, subsequent studies on receptor crosstalk were primarily restricted to using single opsonins on different targets, typically at saturating opsonin conditions. Beyond validating these initial explorations on receptor crosstalk, we identify the early signaling mechanisms that underlie the binding and phagocytosis during the simultaneous activation of both opsonic receptors, through the presence of a dual-opsonized target (immunoglobulin G [IgG] and C3bi), compared with single receptor activation. For this purpose, we used signaling protein inhibitor studies as well as live cell brightfield and fluorescent imaging to fully understand the role of tyrosine kinases, F-actin dynamics and internalization kinetics for FcγR and CR3. Importantly, opsonic receptors were studied together and in isolation, in the context of sparsely opsonized targets. We observed enhanced particle binding and a synergistic effect on particle internalization during the simultaneous activation of FcγR and CR3 engaged with sparsely opsonized targets. Inhibition of early signaling and cytoskeletal molecules revealed a differential involvement of Src kinase for FcγR- vs CR3- and dual receptor-mediated phagocytosis. Src activity recruits Syk kinase and we observed intermediate levels of Syk phosphorylation in dual-opsonized particles compared with those opsonized with IgG or C3bi alone. These results likely explain the intermediate levels of F-actin that is recruited to sites of dual-opsonized particle uptake and the notoriously delayed internalization of C3bi-opsonized targets by macrophages.

Immunostimulatory Effects Triggered by Self-Assembled Microspheres with Tandem Repeats of Polymerized RNA Strands

Self-assembled RNA particles have been exploited widely to maximize the therapeutic potential of RNA. However, the immune response via RNA particles is not fully understood. In addition, the investigation of the immunogenicity from RNA-based particles is required owing to inherent immunostimulatory effects of RNA for clinical translation. To examine the immune stimulating potency, rationally designed microsized RNA particles, called RNA microspheres (RMSs), are generated with single or double strands via rolling circle transcription. The RMSs show an exceptional stability in the presence of serum, while they are selectively degraded under endolysosomal conditions. With precisely controlled size, both RMSs are successfully taken up by macrophages. Unlike the nature of RNA fragments, RMSs induce only basal-level expression of inflammatory cytokines as well as type I interferon from macrophages, suggesting that RMSs are immunocompatible in the therapeutic dose range. Taken together, this study could help accelerate clinical translation and broaden the applicability of the self-assembled RNA-based particles without being limited by their potential immunotoxicity, while a systematic controllability study observing the release of RNA fragments from RMSs would provide self-assembled RNA-based structures with a great potential for immunomodulation.

From Phagocytes to Immune Defense: Roles for Coronin Proteins in Dictyostelium and Mammalian Immunity

Microbes have interacted with eukaryotic cells for as long as they have been co-existing. While many of these interactions are beneficial for both the microbe as well as the eukaryotic cell, several microbes have evolved into pathogenic species. For some of these pathogens, host cell invasion results in irreparable damage and thus host cell destruction, whereas others use the host to avoid immune detection and elimination. One of the latter pathogens is Mycobacterium tuberculosis, arguably one of the most notorious pathogens on earth. In mammalian macrophages, M. tuberculosis manages to survive within infected macrophages by avoiding intracellular degradation in lysosomes using a number of different strategies. One of these is based on the recruitment and phagosomal retention of the host protein coronin 1, that is a member of the coronin protein family and a mammalian homolog of coronin A, a protein identified in Dictyostelium. Besides mediating mycobacterial survival in macrophages, coronin 1 is also an important regulator of naïve T cell homeostasis. How, exactly, coronin 1 mediates its activity in immune cells remains unclear. While in lower eukaryotes coronins are involved in cytoskeletal regulation, the functions of the seven coronin members in mammals are less clear. Dictyostelium coronins may have maintained multiple functions, whereas the mammalian coronins may have evolved from regulators of the cytoskeleton to modulators of signal transduction. In this minireview, we will discuss the different studies that have contributed to understand the molecular and cellular functions of coronin proteins in mammals and Dictyostelium.

SWAP70 is a universal GEF-like adaptor for tethering actin to phagosomes

We recently identified a key role for SWAP70 as the tethering factor stabilizing F-actin filaments on the surface of phagosomes in human dendritic cells by interacting both with Rho-family GTPases and the lipid phosphatidylinositol (3,4)-bisphosphate. In this study, we aimed to investigate whether this role of SWAP70 was general among immune phagocytes. Our data reveal that SWAP70 is recruited to early phagosomes of macrophages and dendritic cells from both human and mouse. The putative inhibitor of SWAP70 sanguinarine blocked phagocytosis and F-actin polymerization, supporting a key role for SWAP70 in phagocytosis as demonstrated previously with knock-down. Moreover, SWAP70 was recently shown to sequester the F-actin severing protein cofilin and we investigated this relationship in phagocytosis. Our data show an increased activation of cellular cofilin upon siRNA knockdown of SWAP70. Finally, we explored whether SWAP70 would be recruited to the immune synapse between dendritic cells and T cells required for antigen presentation, as the formation of such synapses depends on F-actin. However, we observed that SWAP70 was depleted at immune synapses and specifically was recruited to phagosomes. Our data support an essential and specific role for SWAP70 in tethering and stabilizing F-actin to the phagosomal surface in a wide range of phagocytes.

SWAP70 Organizes the Actin Cytoskeleton and Is Essential for Phagocytosis

Actin plays a critical role during the early stages of pathogenic microbe internalization by immune cells. In this study, we identified a key mechanism of actin filament tethering and stabilization to the surface of phagosomes in human dendritic cells. We found that the actin-binding protein SWAP70 is specifically recruited to nascent phagosomes by binding to the lipid phosphatidylinositol (3,4)-bisphosphate. Multi-color super-resolution stimulated emission depletion (STED) microscopy revealed that the actin cage surrounding early phagosomes is formed by multiple concentric rings containing SWAP70. SWAP70 colocalized with and stimulated activation of RAC1, a known activator of actin polymerization, on phagosomes. Genetic ablation of SWAP70 impaired actin polymerization around phagosomes and resulted in a phagocytic defect. These data show a key role for SWAP70 as a scaffold for tethering the peripheral actin cage to phagosomes.

Glycogen synthase kinase-3 (GSK3) regulates TNF production and haemocyte phagocytosis in the immune response of Chinese mitten crab Eriocheir sinensis

Glycogen synthase kinase-3 (GSK3) is a serine/threonine protein kinase firstly identified as a regulator of glycogen synthesis. Recently, it has been proved to be a key regulator of the immune reaction. In the present study, a GSK3 homolog gene (designated as EsGSK3) was cloned from Chinese mitten crab, Eriocheir sinensis. The open reading frame (ORF) was 1824 bp, which encoded a predicted polypeptide of 607 amino acids. There was a conserved Serine/Threonine Kinase domain and a DNA binding domain found in EsGSK3. Phylogenetic analysis showed that EsGSK3 was firstly clustered with GSK3-β from oriental river prawn Macrobrachium nipponense in the invertebrate branch, while GSK3s from vertebrates formed the other distinct branch. EsGSK3 mRNA transcripts could be detected in all tested tissues of the crab including haepatopancreas, eyestalk, muscle, gonad, haemocytes and haematopoietic tissue with the highest expression level in haepatopancreas. And EsGSK3 protein was mostly detected in the cytoplasm of haemocyte by immunofluorescence analysis. The expression levels of EsGSK3 mRNA increased significantly at 6 h after Aeromonas hydrophila challenge (p < 0.05) in comparison with control group, and then gradually decreased to the initial level at 48 h (p > 0.05). The mRNA expression of lipopolysaccharide-induced tumor necrosis factor (TNF)-α factor (EsLITAF) was also induced by A. hydrophila challenge. However, the mRNA expression of EsLITAF and TNF-α production was significantly suppressed after EsGSK3 was blocked in vivo with specific inhibitor lithium, while the phagocytosis of crab haemocytes was significantly promoted. These results collectively demonstrated that EsGSK3 could regulate the innate immune responses of E. sinensis by promoting TNF-α production and inhibiting haemocyte phagocytosis.

The interaction of an amino-modified ZrO2 nanomaterial with macrophages-an in situ investigation by Raman microspectroscopy

Metal oxide nanoparticles (NP) are applied in the fields of biomedicine, pharmaceutics, and in consumer products as textiles, cosmetics, paints, or fuels. In this context, the functionalization of the NP surface is a common method to modify and modulate the product performance. A chemical surface modification of NP such as an amino-functionalization can be used to achieve a positively charged and hydrophobic surface. Surface functionalization is known to affect the interaction of nanomaterials (NM) with cellular macromolecules and the responses of tissues or cells, like the uptake of particles by phagocytic cells. Therefore, it is important to assess the possible risk of those modified NP for human health and environment. By applying Raman microspectroscopy, we verified in situ the interaction of amino-modified ZrO2 NP with cultivated macrophages. The results demonstrated strong adhesion properties of the NP to the cell membrane and internalization into the cells. The intracellular localization of the NP was visualized via Raman depth scans of single cells. After the cells were treated with sodium azide (NaN3) and 2-deoxy-glucose to inhibit the phagocytic activity, NP were still detected inside cells to comparable percentages. The observed tendency of amino-modified ZrO2 NP to interact with the cultivated macrophages may influence membrane integrity and cellular functions of alveolar macrophages in the respiratory system. Graphical abstract Detection of ZrO2 NM at subcellular level.

Macrophages, Foreign Body Giant Cells and Their Response to Implantable Biomaterials

All biomaterials, when implanted in vivo, elicit cellular and tissue responses. These responses include the inflammatory and wound healing responses, foreign body reactions, and fibrous encapsulation of the implanted materials. Macrophages are myeloid immune cells that are tactically situated throughout the tissues, where they ingest and degrade dead cells and foreign materials in addition to orchestrating inflammatory processes. Macrophages and their fused morphologic variants, the multinucleated giant cells, which include the foreign body giant cells (FBGCs) are the dominant early responders to biomaterial implantation and remain at biomaterial-tissue interfaces for the lifetime of the device. An essential aspect of macrophage function in the body is to mediate degradation of bio-resorbable materials including bone through extracellular degradation and phagocytosis. Biomaterial surface properties play a crucial role in modulating the foreign body reaction in the first couple of weeks following implantation. The foreign body reaction may impact biocompatibility of implantation devices and may considerably impact short- and long-term success in tissue engineering and regenerative medicine, necessitating a clear understanding of the foreign body reaction to different implantation materials. The focus of this review article is on the interactions of macrophages and foreign body giant cells with biomaterial surfaces, and the physical, chemical and morphological characteristics of biomaterial surfaces that play a role in regulating the foreign body response. Events in the foreign body response include protein adsorption, adhesion of monocytes/macrophages, fusion to form FBGCs, and the consequent modification of the biomaterial surface. The effect of physico-chemical cues on macrophages is not well known and there is a complex interplay between biomaterial properties and those that result from interactions with the local environment. By having a better understanding of the role of macrophages in the tissue healing processes, especially in events that follow biomaterial implantation, we can design novel biomaterials-based tissue-engineered constructs that elicit a favorable immune response upon implantation and perform for their intended applications.

Theoretical and computational investigations of nanoparticle-biomembrane interactions in cellular delivery

With the rapid development of nanotechnology, nanoparticles have been widely used in many applications such as phototherapy, cell imaging, and drug/gene delivery. A better understanding of how nanoparticles interact with bio-system (especially cells) is of great importance for their potential biomedical applications. In this review, the current status and perspective of theoretical and computational investigations is presented on the nanoparticle-biomembrane interactions in cellular delivery. In particular, the determining parameters (including the properties of nanoparticles, cell membranes and environments) that govern the cellular uptake of nanoparticles (direct penetration and endocytosis) are discussed. Further, some special attention is paid to their interactions beyond the translocation of nanoparticles across membranes (e.g., nanoparticles escaping from endosome and entering into nucleus). Finally, a summary is given, and the challenging problems of this field in the future are identified.

The Pallbearer E3 ligase promotes actin remodeling via RAC in efferocytosis by degrading the ribosomal protein S6

Clearance of apoptotic cells (efferocytosis) is achieved through phagocytosis by professional or amateur phagocytes. It is critical for tissue homeostasis and remodeling in all animals. Failure in this process can contribute to the development of inflammatory autoimmune or neurodegenerative diseases. We found previously that the PALL-SCF E3-ubiquitin ligase complex promotes apoptotic cell clearance, but it remained unclear how it did so. Here we show that the F-box protein PALL interacts with phosphorylated ribosomal protein S6 (RpS6) to promote its ubiquitylation and proteasomal degradation. This leads to RAC2 GTPase upregulation and activation and F-actin remodeling that promotes efferocytosis. We further show that the specific role of PALL in efferocytosis is driven by its apoptotic cell-induced nuclear export. Finding a role for RpS6 in the negative regulation of efferocytosis provides the opportunity to develop new strategies to regulate this process.

The cellular and proteomic response of primary and immortalized murine Kupffer cells following immune stimulation diverges from that of monocyte-derived macrophages

Kupffer cells (KCs) are the first line of defense in the liver against pathogens, yet several microbes successfully target the liver, bypass immune surveillance, and effectively develop in this tissue. Our current, albeit poor, understanding of KC-pathogen interactions has been largely achieved through the study of primary cells, requiring isolation from large numbers of animals. To facilitate the study of KC biology, an immortalized rat KC line 1, RKC1, was developed. We performed a comparative global proteomic analysis of RKC1 and primary rat KCs (PRKC) to characterize their respective responses to lipopolysaccharide-mediated immune stimulation. We identified patent differences in the proteomic response profile of RKC1 and PRKC to lipopolysaccharide. We observed that PRKC upregulated more immune function pathways and exhibited marked changes in cellular morphology following stimulation. We consequently analyzed the cytoskeletal signaling pathways of these cells in light of the fact that macrophages are known to induce cytoskeletal changes in response to pathogens. Our findings suggest that KCs respond differently to inflammatory stimulus than do monocyte-derived macrophages, and such data may provide insight into how pathogens, such as the malaria parasite, may have evolved mechanisms of liver entry through KCs without detection.

Response gene to complement 32 protein promotes macrophage phagocytosis via activation of protein kinase C pathway

Macrophage phagocytosis plays an important role in host defense. The molecular mechanism, especially factors regulating the phagocytosis, however, is not completely understood. In the present study, we found that response gene to complement 32 (RGC-32) is an important regulator of phagocytosis. Although RGC-32 is induced and abundantly expressed in macrophage during monocyte-macrophage differentiation, RGC-32 appears not to be important for this process because RGC-32-deficient bone marrow progenitor can normally differentiate to macrophage. However, both peritoneal macrophages and bone marrow-derived macrophages with RGC-32 deficiency exhibit significant defects in phagocytosis, whereas RGC-32-overexpressed macrophages show increased phagocytosis. Mechanistically, RGC-32 is recruited to macrophage membrane where it promotes F-actin assembly and the formation of phagocytic cups. RGC-32 knock-out impairs F-actin assembly. RGC-32 appears to interact with PKC to regulate PKC-induced phosphorylation of F-actin cross-linking protein myristoylated alanine-rich protein kinase C substrate. Taken together, our results demonstrate for the first time that RGC-32 is a novel membrane regulator for macrophage phagocytosis.

Cellular effects of bacterial N-3-Oxo-dodecanoyl-L-Homoserine lactone on the sponge Suberites domuncula (Olivi, 1792): insights into an intimate inter-kingdom dialogue

Sponges and bacteria have lived together in complex consortia for 700 million years. As filter feeders, sponges prey on bacteria. Nevertheless, some bacteria are associated with sponges in symbiotic relationships. To enable this association, sponges and bacteria are likely to have developed molecular communication systems. These may include molecules such as N-acyl-_L-homoserine lactones, produced by Gram-negative bacteria also within sponges. In this study, we examined the role of N-3-oxododecanoyl-_L-homoserine lactone (3-oxo-C₁₂-HSL) on the expression of immune and apoptotic genes of the host sponge Suberites domuncula. This molecule seemed to inhibit the sponge innate immune system through a decrease of the expression of genes coding for proteins sensing the bacterial membrane: a Toll-Like Receptor and a Toll-like Receptor Associated Factor 6 and for an anti-bacterial perforin-like molecule. The expression of the pro-apoptotic caspase-like 3/7 gene decreased as well, whereas the level of mRNA of anti-apoptotic genes Bcl-2 Homolog Proteins did not change. Then, we demonstrated the differential expression of proteins in presence of this 3-oxo-C₁₂-HSL using 3D sponge cell cultures. Proteins involved in the first steps of the endocytosis process were highlighted using the 2D electrophoresis protein separation and the MALDI-TOF/TOF protein characterization: α and β subunits of the lysosomal ATPase, a cognin, cofilins-related proteins and cytoskeleton proteins actin, α tubulin and α actinin. The genetic expression of some of these proteins was subsequently followed. We propose that the 3-oxo-C₁₂-HSL may participate in the tolerance of the sponge apoptotic and immune systems towards the presence of bacteria. Besides, the sponge may sense the 3-oxo-C₁₂-HSL as a molecular evidence of the bacterial presence and/or density in order to regulate the populations of symbiotic bacteria in the sponge. This study is the first report of a bacterial secreted molecule acting on sponge cells and regulating the symbiotic relationship.

Macrophages lift off surface-bound bacteria using a filopodium-lamellipodium hook-and-shovel mechanism

To clear pathogens from host tissues or biomaterial surfaces, phagocytes have to break the adhesive bacteria-substrate interactions. Here we analysed the mechanobiological process that enables macrophages to lift-off and phagocytose surface-bound Escherichia coli (E. coli). In this opsonin-independent process, macrophage filopodia hold on to the E. coli fimbriae long enough to induce a local protrusion of a lamellipodium. Specific contacts between the macrophage and E. coli are formed via the glycoprotein CD48 on filopodia and the adhesin FimH on type 1 fimbriae (hook). We show that bacterial detachment from surfaces occurrs after a lamellipodium has protruded underneath the bacterium (shovel), thereby breaking the multiple bacterium-surface interactions. After lift-off, the bacterium is engulfed by a phagocytic cup. Force activated catch bonds enable the long-term survival of the filopodium-fimbrium interactions while soluble mannose inhibitors and CD48 antibodies suppress the contact formation and thereby inhibit subsequent E. coli phagocytosis.

A comparative study: In vitro effects of EPA and DHA on immune functions of head-kidney macrophages isolated from large yellow croaker (Larmichthys crocea)

Comparative effects of different concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on immune responses of head-kidney macrophages isolated from large yellow croaker were studied in vitro. After exposing to serum-free medium for 1 day, cultured cells were incubated in medium supplemented with graded levels of EPA or DHA (0, 5, 25, 100, 200 and 1000 μM, respectively) in the form of fatty acid bovine serum albumin (FA-BSA) complex for 12 h, 24 h and 36 h, respectively. Control samples were incubated in the absence of EPA or DHA (2% bovine serum albumin, BSA). Following stimulation, cell viability, lipid peroxidation, secretary phopholipase A2 (sPLA2) and prostaglandin E2 (PGE2) production as well as some immune parameters including phagocytosis, respiratory burst activity and interleukin 1β (IL-1β) production were determined. Results showed that EPA and DHA affected cell viability in dose-dependent and time-dependent manners. In particular, cell viability was significantly decreased after 24 h and 36 h incubation with 1000 μM EPA or DHA (P < 0.05). Higher levels of EPA (200 and 1000 μM) caused a significant increase in the production of malondialdehyde (MDA) (P < 0.05), while DHA did not significantly affect the MDA production. EPA significantly increased the intracellular superoxide anion synthesis which, on the contrary, was significantly reduced by DHA. Phagocytosis percentage (PP) values were significantly higher in treatments with 5 μM DHA (P < 0.05), but significantly decreased by 200 and 1000 μM EPA and DHA compared to the control group (P < 0.05). Decreased PGE2 production was produced by cells treated with relatively low doses of EPA or DHA. When high levels of stimulants (1000 μM EPA or DHA) were used, PGE2 levels were elevated and reached a significant level (P < 0.05). Both EPA and DHA significantly inhibited the production of sPLA2, where DHA exerted the more potent inhibitory effects than EPA. No pronounced effect was observed on IL-1β production among all the treatments, and IL-1β level in cell culture supernatant was fairly low (only approximately 6 pg/ml). Those findings suggested that EPA and DHA could influence the immunity and physiological conditions of macrophages from head kidney of large yellow croaker in vitro.

Shotgun proteomics of coelomic fluid from the purple sea urchin, Strongylocentrotus purpuratus

The purple sea urchin has a complex immune system that is likely mediated by gene expression in coelomocytes (blood cells). A broad array of potential immune receptors and immune response proteins has been deduced from their gene models. Here we use shotgun mass spectrometry to describe 307 proteins with possible immune function in sea urchins including proteins involved in the complement pathway and numerous SRCRs. The relative abundance of dual oxidase 1, ceruloplasmin, ferritin and transferrin suggests the production of reactive oxygen species in coelomocytes and the sequestration of iron. Proteins such as selectin, cadherin, talin, galectin, amassin and the Von Willebrand factor may be involved in generating a strong clotting reaction. Cell signaling proteins include a guanine nucleotide binding protein, the Rho GDP dissociation factor, calcium storage molecules and a variety of lipoproteins. However, based on this dataset, the expression of TLRs, NLRs and fibrinogen domain containing proteins in coelomic fluid and coelomocytes could not be verified.

Hemocytic immune responses triggered by CpG ODNs in shrimp Litopenaeus vannamei

CpG oligodeoxynucleotides (CpG ODNs), also called bacterial DNA or synthetic oligodeoxynucleotides, can induce apparent immunity protection against various pathogens, and they are widely used as functional immunostimulant or vaccine adjuvant in mammals. In the present study, CpG-rich plasmid pUC57-CpG was constructed and employed to stimulate the shrimp Litopenaeus vannamei, and the total hemocyte count, percentage of apoptotic hemocytes, regeneration of circulating hemocytes, the ability of phagocytosis and generation of reactive oxygen species (ROS) were measured to reveal the possible protection mechanism of CpG ODNs. After the injection of pUC57-CpG, the total hemocyte count significantly decreased (p < 0.01) to 2.56 × 10(7) cell/mL at the first day post stimulation, while the apoptosis increased (p < 0.01), which was 1.72-fold of that in control group. At the same time, the regeneration of circulating hemocytes fluctuated in a similar trend, and a significant increase was observed at the first day post stimulation. The phagocytotic activity including the percentage of phagocytosis and phagocytotic index, experienced an upward tend during the whole experimental period and the ROS level increased by 22% (p < 0.05) compared to that in the control group at first day post stimulation. These results together suggested that pUC57-CpG could promote the apoptosis and regeneration of circulating hemocytes, and enhance the phagocytosis and ROS production, which might contribute to the boosted immunity against the infection of pathogens.

The effects of oral consumption of selenium nanoparticles on chemotactic and respiratory burst activities of neutrophils in comparison with sodium selenite in sheep

The present study was designed to compare the effects of nano-selenium and of sodium selenite on the chemotactic and respiratory burst activities of neutrophils in sheep. Fifteen sheep were randomly divided into three groups. Groups 1 and 2 received selenium nanoparticles (1 mg/kg) or sodium selenite (1 mg/kg) orally, respectively, for ten consecutive days, and the third group was considered as the control. To determine the chemotactic and respiratory burst activities of the neutrophils, the leading front assay and the NBT test were used on heparinized blood samples that were collected at different intervals (days 0, 10th, 20th, and 30th). The results obtained showed that the chemotactic activities in groups 1 and 2 increased significantly on the 10th, 20th, and 30th day, compared to day 0, and on the 20th day in comparison with the 10th day, while in group 2, there was a significant decrease on the 30th day compared to the 20th day. The chemotactic activities in group 1 were significantly higher than in group 2 on the 10th day and in the control group on the 10th, 20th, and 30th day, but the chemotactic activities in group 2 were significantly higher than those in the control group only on the 20th day. On the 30th day into the experiment, the respiratory bursts in groups 1 and 2 were significantly stronger in comparison with those at day 0. Overall, nano-selenium increased the chemotactic and respiratory burst activities more significantly than sodium selenite, which is suggestive of a stronger stimulatory effect of the Se nanoparticles on intracellular activities.