Monocytes, particularly nonclassical ones, lose their opsonic and nonopsonic phagocytosis capacity during pediatric cerebral malaria.

Introduction: Innate immunity is crucial to reducing parasite burden and contributing to survival in severe malaria. Monocytes are key actors in the innate response and, like macrophages, are plastic cells whose function and phenotype are regulated by the signals from the microenvironment. In the context of cerebral malaria (CM), monocyte response constitutes an important issue to understand. We previously demonstrated that decreased percentages of nonclassical monocytes were associated with death outcomes in CM children. In the current study, we postulated that monocyte phagocytosis function is impacted by the severity of malaria infection. Methods: To study this hypothesis, we compared the opsonic and nonopsonic phagocytosis capacity of circulant monocytes from Beninese children with uncomplicated malaria (UM) and CM. For the CM group, samples were obtained at inclusion (D0) and 3 and 30 days after treatment (D3, D30). The phagocytosis capacity of monocytes and their subsets was characterized by flow cytometry and transcriptional profiling by studying genes known for their functional implication in infected-red blood cell (iRBC) elimination or immune escape. Results: Our results confirm our hypothesis and highlight the higher capacity of nonclassical monocytes to phagocyte iRBC. We also confirm that a low number of nonclassical monocytes is associated with CM outcome when compared to UM, suggesting a mobilization of this subpopulation to the cerebral inflammatory site. Finally, our results suggest the implication of the inhibitory receptors LILRB1, LILRB2, and Tim3 in phagocytosis control. Discussion: Taken together, these data provide a better understanding of the interplay between monocytes and malaria infection in the pathogenicity of CM.

Recombinant SpTransformer proteins are functionally diverse for binding and phagocytosis by three subtypes of sea urchin phagocytes.

Introduction: The California purple sea urchin, Strongylocentrotus purpuratus, relies solely on an innate immune system to combat the many pathogens in the marine environment. One aspect of their molecular defenses is the SpTransformer (SpTrf) gene family that is upregulated in response to immune challenge. The gene sequences are highly variable both within and among animals and likely encode thousands of SpTrf isoforms within the sea urchin population. The native SpTrf proteins bind foreign targets and augment phagocytosis of a marine Vibrio. A recombinant (r)SpTrf-E1-Ec protein produced by E. coli also binds Vibrio but does not augment phagocytosis. Methods: To address the question of whether other rSpTrf isoforms function as opsonins and augment phagocytosis, six rSpTrf proteins were expressed in insect cells. Results: The rSpTrf proteins are larger than expected, are glycosylated, and one dimerized irreversibly. Each rSpTrf protein cross-linked to inert magnetic beads (rSpTrf::beads) results in different levels of surface binding and phagocytosis by phagocytes. Initial analysis shows that significantly more rSpTrf::beads associate with cells compared to control BSA::beads. Binding specificity was verified by pre-incubating the rSpTrf::beads with antibodies, which reduces the association with phagocytes. The different rSpTrf::beads show significant differences for cell surface binding and phagocytosis by phagocytes. Furthermore, there are differences among the three distinct types of phagocytes that show specific vs. constitutive binding and phagocytosis. Conclusion: These findings illustrate the complexity and effectiveness of the sea urchin innate immune system driven by the natSpTrf proteins and the phagocyte cell populations that act to neutralize a wide range of foreign pathogens.

Disulfiram Inhibits Opsonin-Independent Phagocytosis and Migration of Human Long-Lived In Vitro Cultured Phagocytes from Multiple Inflammatory Diseases.

Disulfiram (DSF), an anti-alcoholism medicine, exerts treatment effects in patients suffering from persistent Borreliosis and also exhibits anti-cancer effects through its copper chelating derivatives and induction of oxidative stress in mitochondria. Since chronic/persistent borreliosis is characterized by increased amounts of pro-inflammatory macrophages, this study investigated opsonin-independent phagocytosis, migration, and surface marker expression of in vivo activated and in vitro cultured human monocyte-derived phagocytes (macrophages and dendritic cells) with and without DSF treatment. Phagocytosis of non-opsonized Dynabeads® M-450 and migration of macrophages and dendritic cells were monitored using live cell analyzer Juli™ Br for 24 h, imaging every 3.5 min. To simultaneously monitor phagocyte function, results were analyzed by a newly developed software based on the differential phase contrast images of cells before and after ingestion of Dynabeads. DSF decreased the phagocytic capacities exhibited by in vitro enriched and long-lived phagocytes. Although no chemotactic gradient was applied to the test system, vigorous spontaneous migration was observed. We therefore set up an algorithm to monitor and quantify both phagocytosis and migration simultaneously. DSF not only reduced phagocytosis in a majority of these long-lived phagocytes but also impaired their migration. Despite these selective effects by DSF, we found that DSF reduced the expression densities of surface antigens CD45 and CD14 in all of our long-lived phagocytes. In cells with a high metabolic activity and high mitochondrial contents, DSF led to cell death corresponding to mitochondrial oxidative stress, whereas metabolically inactive phagocytes survived our DSF treatment protocol. In conclusion, DSF affects the viability of metabolically active phagocytes by inducing mitochondrial stress and secondly attenuates phagocytosis and migration in some long-lived phagocytes.

Discovery and Preclinical Activity of BMS-986351, an Antibody to SIRPα That Enhances Macrophage-mediated Tumor Phagocytosis When Combined with Opsonizing Antibodies.

In normal cells, binding of the transmembrane protein CD47 to signal regulatory protein-α (SIRPα) on macrophages induces an antiphagocytic signal. Tumor cells hijack this pathway and overexpress CD47 to evade immune destruction. Macrophage antitumor activity can be restored by simultaneously blocking the CD47-SIRPα signaling axis and inducing a prophagocytic signal via tumor-opsonizing antibodies. We identified a novel, fully human mAb (BMS-986351) that binds SIRPα with high affinity. BMS-986351 demonstrated broad binding coverage across SIRPα polymorphisms and potently blocked CD47-SIRPα binding at the CD47 binding site in a dose-dependent manner. In vitro, BMS-986351 increased phagocytic activity against cell lines from solid tumors and hematologic malignancies, and this effect was markedly enhanced when BMS-986351 was combined with the opsonizing antibodies cetuximab and rituximab. A phase I dose-escalation/-expansion study of BMS-986351 for the treatment of advanced solid and hematologic malignancies is underway (NCT03783403). SIGNIFICANCE: Increasing the phagocytotic capabilities of tumor-associated macrophages by modulating macrophage-tumor cell surface signaling via the CD47-SIRPα axis is a novel strategy. Molecules targeting CD47 have potential but its ubiquitous expression necessitates higher therapeutic doses to overcome potential antigen sink effects. The restricted expression pattern of SIRPα may limit toxicities and lower doses of the SIRPα antibody BMS-986351 may overcome target mediated drug disposition while maintaining the desired pharmacology.

Identification of a capsular polysaccharide from Enterococcus faecium U0317 using a targeted approach to discover immunogenic carbohydrates for vaccine development.

Enterococcus faecium, a gram-positive opportunistic pathogen, has become a major concern for nosocomial infections due to its resistance to several antibiotics, including vancomycin. Finding novel alternatives for treatment prevention, such as vaccines, is therefore crucial. In this study, we used various techniques to discover a novel capsular polysaccharide. Firstly, we identified an encapsulated E. faecium strain by evaluating the opsonophagocytic activity of fifteen strains with antibodies targeting the well-known lipoteichoic acid antigen. This activity was attributed to an unknown polysaccharide. We then prepared a crude cell wall glycopolymer and fractionated it, guided by immunodot-blot analysis. The most immunoreactive fractions were used for opsonophagocytic inhibition assays. The fraction containing the inhibitory polysaccharide underwent structural characterization using NMR and chemical analyses. The elucidated structure presents a branched repeating unit, with the linear part being: →)-ß-d-Gal-(1 â†’ 4)-ß-d-Glc-(1 â†’ 4)-ß-d-Gal-(1 â†’ 4)-ß-d-GlcNAc-(1→, further decorated with a terminal α-d-Glc and a d-phosphoglycerol moiety, attached to O-2 and O-3 of the 4-linked Gal unit, respectively. This polysaccharide was conjugated to BSA and the synthetic glycoprotein used to immunize mice. The resulting sera exhibited good opsonic activity, suggesting its potential as a vaccine antigen. In conclusion, our effector-function-based approach successfully identified an immunogenic capsular polysaccharide with promising applications in immunotherapy.

Evasion of opsonization of macromolecules using novel surface-modification and biological-camouflage-mediated techniques for next-generation drug delivery.

Opsonization plays a pivotal role in hindering controlled drug release from nanoformulations due to macrophage-mediated nanoparticle destruction. While first and second-generation delivery systems, such as lipoplexes (50-150 nm) and quantum dots, hold immense potential in revolutionizing disease treatment through spatiotemporal controlled drug delivery, their therapeutic efficacy is restricted by the selective labeling of nanoparticles for uptake by reticuloendothelial system and mononuclear phagocyte system via various molecular forces, such as electrostatic, hydrophobic, and van der Waals bonds. This review article presents novel insights into surface-modification techniques utilizing macromolecule-mediated approaches, including PEGylation, di-block copolymerization, and multi-block polymerization. These techniques induce stealth properties by generating steric forces to repel micromolecular-opsonins, such as fibrinogen, thereby mitigating opsonization effects. Moreover, advanced biological methods, like cellular hitchhiking and dysopsonic protein adsorption, are highlighted for their potential to induce biological camouflage by adsorbing onto the nanoparticulate surface, leading to immune escape. These significant findings pave the way for the development of long-circulating next-generation nanoplatforms capable of delivering superior therapy to patients. Future integration of artificial intelligence-based algorithms, integrated with nanoparticle properties such as shape, size, and surface chemistry, can aid in elucidating nanoparticulate-surface morphology and predicting interactions with the immune system, providing valuable insights into the probable path of opsonization.

Biological significance of C-reactive protein, the ancient acute phase functionary.

C-reactive protein (CRP) is one of the major members of the family of acute phase proteins (APP). Interest in this CRP was the result of a seminal discovery of its pattern of response to pneumococcal infection in humans. CRP has the unique property of reacting with phosphocholine-containing substances, such as pneumococcal C-polysaccharide, in the presence of Ca2+. The attention regarding the origin of CRP and its multifunctionality has gripped researchers for several decades. The reason can be traced to the integrated evolution of CRP in the animal kingdom. CRP has been unequivocally listed as a key indicator of infectious and inflammatory diseases including autoimmune diseases. The first occurrence of CRP in the evolutionary ladder appeared in arthropods followed by molluscs and much later in the chordates. The biological significance of CRP has been established in the animal kingdom starting from invertebrates. Interestingly, the site of synthesis of CRP is mainly the liver in vertebrates, while in invertebrates it is located in diverse tissues. CRP is a multifunctional player in the scenario of innate immunity. CRP acts as an opsonin in the area of complement activation and phagocytosis. Interestingly, CRP upregulates and downregulates both cytokine production and chemotaxis. Considering various studies of CRP in humans and non-human animals, it has been logically proposed that CRP plays a common role in animals. CRP also interacts with Fcγ receptors and triggers the inflammatory response of macrophages. CRP in other animals such as primates, fish, echinoderms, arthropods, and molluscs has also been studied in some detail which establishes the evolutionary significance of CRP. In mammals, the increase in CRP levels is an induced response to inflammation or trauma; interestingly, in arthropods and molluscs, CRP is constitutively expressed and represents a major component of their hemolymph. Investigations into the primary structure of CRP from various species revealed the overall relatedness between vertebrate and invertebrate CRP. Invertebrates lack an acquired immune response; they are therefore dependent on the multifunctional role of CRP leading to the evolutionary success of the invertebrate phyla.

Competition of opsonins and dysopsonins on the nanoparticle surface.

The biological behavior and fate of nanoparticles are dependent on their retention time in the blood circulation system. The protein corona components, especially opsonins, and dysopsonins, adsorbed on the nanoparticle surface determine their blood circulation time. The protein corona formation is a dynamic process that involves the competition between different proteins to be adsorbed on the nanoparticles. Therefore, studying how proteins compete and are oriented on the nanoparticle surface is essential. We hypothesized that the presence of opsonins (immunoglobulin (IgG)) might affect the adsorption of dysopsonins (human serum albumin (HSA)) and vice versa. Using the molecular dynamics simulations, we showed that the adsorption of HSA on the GO surface after the IgG adsorption is more probable than the opposite order of adsorption. It was also observed that the higher lateral diffusion of the HSA compared to the IgG helped the system reach a more stable configuration while the initial adsorption of the HSA limits the lateral diffusion of IgG. Therefore, replacing IgG adsorbed on the GO surface with HSA is plausible while the reverse process is less likely to occur. This study revealed that albumin might extend the blood circulation time of GO by replacing opsonins (IgG).

A genome-wide genetic screen identifies CYRI-B as a negative regulator of CEACAM3-mediated phagocytosis.

Opsonin-independent phagocytosis mediated by human carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) has evolved to control a subset of human-restricted bacterial pathogens. CEACAM3 engagement triggers rapid GTP-loading of the small GTPase Rac as a master regulator of cytoskeletal rearrangements and lamellipodia-driven internalization. To identify components of the CEACAM3-initiated signaling cascade, we performed a genome-wide CRISPR/Cas9-based screen in human myeloid cells. Following infection with fluorescently labeled bacteria, cells exhibiting elevated phagocytosis (gain-of-function) as well as cells showing reduced phagocytosis (loss-of-function) were sorted and enrichment of individual single-guide RNAs (sgRNAs) was determined by next generation sequencing. Concentrating on genes whose targeting by three distinct sgRNAs consistently resulted in a gain-of-function phenotype, we identified the Rac-GTP-sequestering protein CYRI-B as a negative regulator of CEACAM3-mediated phagocytosis. Clonal HL-60 cell lines with CYRI-B knockout showed enhanced CEACAM3-downstream signaling, such as Rac GTP loading and phosphorylation of PAK kinases, leading to increased phagocytosis of bacteria. Complementation of the CYRI-B knockout cells reverted the knockout phenotype. Our results unravel components of CEACAM3-initiated opsonin-independent phagocytosis on a genome-wide level and highlight CYRI-B as a negative regulator of CEACAM3-initiated signaling in myeloid cells.

Quasi-opsonin conjugated lipase-sensitive micelles activate macrophages against facultative intracellular bacterial infection.

Drug resistance caused by facultative intracellular bacteria such as Salmonella typhimurium (S. typhimurium) is still a tough challenge. Bacteria phagocytosed by macrophages have evolved a variety of mechanisms to defend against host attack, and the poor entry of antibiotics into infected macrophages is conducive to the survival of intracellular bacteria. In this report, we prepared a quasi-opsonized chloramphenicol (Chl)-loaded micellar system (B-mLBP-M/Chl) assembled by a bacterial lipase-sensitive polymer with a conjugate of lipopolysaccharide-binding protein (LBP) analog and biotin (B) as a ligand, which could eliminate drug-resistant S. typhimurium with quasi-opsonization via 3 steps: (i) target and release antibiotics on bacteria lipase, (ii) opsonize S. typhimurium to be digested by the macrophage, and (iii) activate the macrophage for fighting. The B-mLBP-M/Chl could target bacterial LPS through mLBP by simulating the N-terminal sequence of native LBP, exhibiting a high ability to target the localized infection site in mice. It could also activate the phagocytosis of macrophages via coupled biotin, cooperating with antibiotics and effectively improving the survival of mice with little pathological damage to tissues. Moreover, compared with native opsonin, B-mLBP does not cause an excessive inflammatory response and could recover homeostasis after exerting the quasi-opsonization by regulating the levels of pro-inflammatory cytokines and anti-inflammatory cytokines. With a universal target site for Gram-negative bacteria and macrophage activation, this B-mLBP-M/Chl could be applied to other bacterial infections in the future. In particular, this analog may also serve as a useful template to design safe artificial opsonin, which could be a ligand for drug delivery systems or prodrugs.

Opsonização

The process of recognizing and targeting particles by binding with OPSONINS (e.g., IgM, C1 and IgG) for phagocytosis or for antibody-dependent cell cytotoxicity.

El proceso de reconocer y dirigir partículas mediante la unión con PROTEÍNAS OPSONINAS (por ejemplo, IgM, C1 e IgG) para la fagocitosis o para la citotoxicidad celular dependiente de anticuerpos.

Processo de reconhecer e direcionar partículas pela ligação a PROTEÍNAS OPSONIZANTES (por exemplo, IgM, C1 e IgG) para o desencadeamento da fagocitose ou para a citotoxidade dependente de anticorpos.

Proteínas Opsonizantes

Proteins that bind to particles and cells to increase susceptibility to PHAGOCYTOSIS, especially ANTIBODIES bound to EPITOPES that attach to FC RECEPTORS. COMPLEMENT C3B may also participate.

Proteinas que se unen a partículas y células, para aumentar la susceptibilidad a la FAGOCITOSIS, especialmente ANTICUERPOS unidos a EPITOPES que se unen a RECEPTORES FC. También puede participar el COMPLEMENTO C3B.

Proteínas que se ligam a partículas e células para aumentar a susceptibilidade à FAGOCITOSE, em particular os ANTICORPOS ligados aos EPITOPOS que se ligam aos RECEPTORES FC. Também pode participar o COMPLEMENTO C3B.

Role of Surface Charge of Nanoscale Ultrasound Contrast Agents in Complement Activation and Phagocytosis.

Purpose: To prepare nanoscale ultrasound contrast agents (Nano-UCAs) and examine the role of their surface charge in complement activation and phagocytosis. Materials and Methods: We analyzed serum proteins present in the corona formed on Nano-UCAs and evaluated two important protein markers of complement activation (C3 and SC5b-9). The effect of surface charge on phagocytosis was further assessed using THP-1 macrophages. Results: When Nano-UCAs were incubated with human serum, they were opsonized by various blood proteins, especially C3. Highly charged Nano-UCAs, whether positive or negative, were favorably opsonized by complement proteins and phagocytized by macrophages. Conclusion: Charged Nano-UCAs show a higher tendency to activated complement system, and are efficiently engulfed by macrophages. The present results provide meaningful insights into the role of the surface charge of nanoparticles in the activation of the innate immune system, which is important not only for the design of targeted Nano-UCAs, but also for the effectiveness and safety of other theranostic agents.

A Maleimide-Terminally Modified PEGylated Liposome Induced the Accelerated Blood Clearance Independent of the Production of Anti-PEG IgM Antibodies.

PEGylated liposomes (PL) lose their long-circulating characteristic when administered repeatedly, called the accelerated blood clearance (ABC) phenomenon. The ABC phenomenon is generally thought to occur when the anti-polyethylene glycol (PEG) antibody (anti-PEG immunoglobulin M (IgM)) expressed in the spleen B cells triggered by the first dose of PL binds to the second and subsequent doses of PL, leading to activation of the complement system. MAL-PEG-DSPE, a PEG lipid with a maleimide (MAL) group at the PEG terminal, is used in various studies as a linker for ligand-bound liposomes such as antibody-modified liposomes. However, most ABC phenomenon research used PL with a terminal methoxy group (PL-OCH3). In this study, we prepared MAL-PEG-DSPE liposomes (PL-MAL) to evaluate the effect of PL-MAL on the ABC phenomenon induction compared to PL-OCH3. Pharmacokinetic, anti-PEG IgM secretion and complement activation analyses of these liposomes were conducted in mice. Interestingly, despite C3 bound to the surface of the initially administered PL-MAL, the administered PL-MAL showed high blood retention, demonstrating the same results as PL-OCH3. On the other hand, although the secretion of anti-PEG IgM induced by PL-MAL was lower than PL-OCH3, the second dose of PL-MAL rapidly disappeared from the blood. These results suggest that the antibody produced from the first dose of PL-MAL binds to the second dose of PL-MAL, thereby activating C3 to act as an opsonin which promotes phagocytic uptake. In conclusion, PL-MAL induced the ABC phenomenon independent of the production of IgM antibodies against PEG. This study provides valuable findings for further studies using ligand-bound liposomes.

The role of the complement system in kidney glomerular capillary thrombosis.

The complement system is part of the innate immune system. The crucial step in activating the complement system is the generation and regulation of C3 convertase complexes, which are needed to generate opsonins that promote phagocytosis, to generate C3a that regulates inflammation, and to initiate the lytic terminal pathway through the generation and activity of C5 convertases. A growing body of evidence has highlighted the interplay between the complement system, coagulation system, platelets, neutrophils, and endothelial cells. The kidneys are highly susceptible to complement-mediated injury in several genetic, infectious, and autoimmune diseases. Atypical hemolytic uremic syndrome (aHUS) and lupus nephritis (LN) are both characterized by thrombosis in the glomerular capillaries of the kidneys. In aHUS, congenital or acquired defects in complement regulators may trigger platelet aggregation and activation, resulting in the formation of platelet-rich thrombi in the kidneys. Because glomerular vasculopathy is usually noted with immunoglobulin and complement accumulation in LN, complement-mediated activation of tissue factors could partly explain the autoimmune mechanism of thrombosis. Thus, kidney glomerular capillary thrombosis is mediated by complement dysregulation and may also be associated with complement overactivation. Further investigation is required to clarify the interaction between these vascular components and develop specific therapeutic approaches.

Human Cell-Camouflaged Nanomagnetic Scavengers Restore Immune Homeostasis in a Rodent Model with Bacteremia.

Bloodstream infection caused by antimicrobial resistance pathogens is a global concern because it is difficult to treat with conventional therapy. Here, scavenger magnetic nanoparticles enveloped by nanovesicles derived from blood cells (MNVs) are reported, which magnetically eradicate an extreme range of pathogens in an extracorporeal circuit. It is quantitatively revealed that glycophorin A and complement receptor (CR) 1 on red blood cell (RBC)-MNVs predominantly capture human fecal bacteria, carbapenem-resistant (CR) Escherichia  coli, and extended-spectrum beta-lactamases-positive (ESBL-positive) E. coli, vancomycin-intermediate Staphylococcus aureus (VISA), endotoxins, and proinflammatory cytokines in human blood. Additionally, CR3 and CR1 on white blood cell-MNVs mainly contribute to depleting the virus envelope proteins of Zika, SARS-CoV-2, and their variants in human blood. Supplementing opsonins into the blood significantly augments the pathogen removal efficiency due to its combinatorial interactions between pathogens and CR1 and CR3 on MNVs. The extracorporeal blood cleansing enables full recovery of lethally infected rodent animals within 7 days by treating them twice in series. It is also validated that parameters reflecting immune homeostasis, such as blood cell counts, cytokine levels, and transcriptomics changes, are restored in blood of the fatally infected rats after treatment.

Blockade of the Adenylate Cyclase Toxin Synergizes with Opsonizing Antibodies to Protect Mice against Bordetella pertussis.

Bordetella produces an array of virulence factors, including the adenylate cyclase toxin (ACT), which is essential, immunogenic in humans, and highly conserved. Despite mediating immune-evasive functions as a leukotoxin, ACT's potential role as a protective antigen is unclear. To better understand the contributions of humoral anti-ACT immunity, we evaluated protection against Bordetella pertussis by antibodies binding structurally defined ACT epitopes in a mouse pneumonia model. An ACT-neutralizing antibody, but not a nonneutralizing antibody or an isotype control, significantly increased mouse survival after lethal challenge with B. pertussis. When modified to impair Fc effector functions, the neutralizing antibody retained protective capabilities, indicating that protection was mediated by the blockade of the interactions of ACT with its αMß2 integrin receptor. After infection with a lower bacterial dose, ACT neutralization synergistically reduced lung bacterial colonization levels when combined with an opsonic antibody binding the surface antigen pertactin. Notably, protection was significantly enhanced when antibodies were administered intranasally as opposed to systemically, indicating that local immune responses are key to antibody-mediated protection against ACT and pertactin. These data reconcile previous conflicting reports to indicate that neutralizing anti-ACT antibodies support the phagocytosis of opsonized B. pertussis and thereby contribute to pertussis protection in vivo. IMPORTANCE Despite high vaccine coverage in developed countries, the incidence of pertussis has increased in recent decades, often leading to severe consequences for sensitive groups, including infants. For this reason, improving the efficacy of pertussis vaccines is critical, and the addition of new antigens is a leading strategy to achieve this goal. The Bordetella pertussis adenylate cyclase toxin (ACT) acts to disarm host immunity and is considered a promising vaccine candidate since it is found in all Bordetella species. In this work, we show that antibodies neutralizing ACT offer protection against pertussis. Using a murine infection model, we show that antibodies neutralizing ACT can contribute to protection against infection through synergistic interactions with antibodies recognizing current vaccine antigens. Our data can help guide the design of future vaccines, whereby the inclusion of ACT-based immunogens might increase protection against pertussis infection.

Complement-Opsonized NIR-IIb Emissive Immunotracers for Dynamically Monitoring Neutrophils in Inflammation-Related Diseases.

Real-time monitoring of neutrophil dynamics is crucial for timely diagnosis and effective treatment of inflammation-related diseases, which requires a reliable tracer for in vivo tracking of neutrophils. However, immunotracers for neutrophils are extremely limited because of the difficulty in labeling the cells. Inspired by the natural biological function of the complement system, a strategy of enhancing the complement C3 opsonization of lanthanide-doped nanoparticles (LnNPs) by modulating their surface chemistry, thus developing a near infrared-IIb emissive nanotracer for neutrophils, is reported herein. Four kinds of surface-modified LnNPs are fabricated, among which phospholipids DOPG-modified LnNPs (LnNPs@PG) with weak antifouling ability and hydroxyl groups adsorb more complement C3 proteins and form covalent linkages with C3b active fragments under inflammation conditions, inducing enhanced complement C3 opsonization. Therefore, LnNPs@PG with enhanced complement C3 opsonization are capable of efficiently labeling inflammation-stimulated neutrophils in vivo through complement-receptors-mediated phagocytosis and achieve dynamic monitoring neutrophils during cutaneous wound healing and cerebral ischemia/reperfusion.

Phagocytosis mediated by the human granulocyte receptor CEACAM3 is limited by the receptor-type protein tyrosine phosphatase PTPRJ.

Carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) is a human granulocyte receptor mediating the efficient phagocytosis of a subset of human-restricted bacterial pathogens. Its function depends on phosphorylation of a tyrosine-based sequence motif, but the enzyme(s) responsible for reversing this modification are unclear. Here, we identify the receptor-type protein tyrosine phosphatase PTPRJ as a negative regulator of CEACAM3-mediated phagocytosis. We show depletion of PTPRJ results in a gain-of-function phenotype, while overexpression of a constitutively active PTPRJ phosphatase strongly reduces bacterial uptake via CEACAM3. We also determined that recombinant PTPRJ directly dephosphorylates the cytoplasmic tyrosine residues of purified full-length CEACAM3 and recognizes synthetic CEACAM3-derived phosphopeptides as substrates. Dephosphorylation of CEACAM3 by PTPRJ is also observed in intact cells, thereby limiting receptor-initiated cytoskeletal re-arrangements, lamellipodia formation, and bacterial uptake. Finally, we show that human phagocytes deficient for PTPRJ exhibit exaggerated lamellipodia formation and enhanced opsonin-independent phagocytosis of CEACAM3-binding bacteria. Taken together, our results highlight PTPRJ as a bona fide negative regulator of CEACAM3-initiated phagocyte functions, revealing a potential molecular target to limit CEACAM3-driven inflammatory responses.

Treponema pallidum delays the apoptosis of human polymorphonuclear neutrophils through the intrinsic and extrinsic pathways.

Treponema pallidum is a "stealth pathogen" responsible for infectious sexually transmitted diseases. Although neutrophils are usually present in skin lesions of early syphilis, the role of these cells in T. pallidum infection has barely been investigated. Neutrophils are short-lived cells that undergo constitutive apoptosis, and phagocytosis usually accelerates this process. Here, we demonstrated that human polymorphonuclear neutrophils (hPMNs) could phagocytose T. pallidum in vitro. An unexpected discovery was that T. pallidum inhibited hPMNs apoptosis markedly in an opsonin-independent manner. Furthermore, this phenomenon was not affected by bacterial viability, as detected by annexin V, morphology studies, and TUNEL staining. Exploration of the underlying mechanism showed that expression of the cleaved forms of caspase-3, -8, and -9 and effector caspase activity were diminished significantly in T. pallidum-infected hPMNs. T. pallidum also impaired staurosporine- and anti-Fas-induced signaling for neutrophil apoptosis. Of note, these effects were accompanied by inducing the autocrine production of the anti-apoptotic cytokine IL-8. Taken together, our data revealed that T. pallidum could inhibit the apoptosis of hPMNs through intrinsic and extrinsic pathways and provide new insights for understanding the pathogenicity mechanisms of T. pallidum.