Patterns, Receptors, and Signals: Regulation of Phagosome Maturation

Comparative proteome analysis revealed potential biomarkers and the underlying immune mechanisms in Vibrio-resistant hybrid grouper, Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂

Vibrio alginolyticus is the causative agent of vibriosis, a common bacterial infection in grouper aquaculture that is associated with the development of haemorrhagic and non-haemorrhagic ulcerations on the fish. In the present study, comparative proteome analysis was performed on serum samples from Vibrio-resistant and Vibrio-susceptible grouper. Samples were analysed using high-throughput LC-MS/MS and identified 2770 unique peptides that corresponded to 344 proteins. Subsequent analysis identified 21 proteins that were significantly up-regulated in the resistant group compared to the control and the susceptible groups. Those proteins are associated with immunostimulatory effects, signalling and binding cascade, metabolism, and maintaining tissue integrity and physiological condition. Besides, potential protein biomarkers related to the immune system were identified, which could be associated with the disease-resistant phenotype. These data provide insights into the underlying immune mechanism of hybrid groupers upon Vibrio sp. infection.

Carbon Dot-Loaded Apoptotic Vesicles Improve the Liver Kupffer Cell-Mediated Antibacterial Effect to Synergistically Alleviate Sepsis

Sepsis is a lethal systemic inflammatory disease against infection that lacks effective therapeutic approaches. Liver resident macrophage Kupffer cell (KC)-initiated bacterial clearance is crucial for the host to defend against infection. However, it remains unclear whether this process also governs the antibacterial therapy of sepsis that would be used to improve therapeutic outcomes. Here, we found that copper-doped carbon dots (Cu-CDs) exhibited superior antibacterial capabilities in vitro but displayed limited therapeutic effects in septic mice due to their limited ability to target the liver and restore KC antimicrobial capacity. Thus, we developed a composite nanodrug of copper-doped carbon dot-loaded apoVs (CC-apoVs) that combined the antibacterial ability of Cu-CDs and liver KC targeting features of apoV. Moreover, intravenous injection of CC-apoVs markedly alleviated the systemic infection and decreased the mortality of septic mice compared to Cu-CD and apoV infusion alone. Mechanistically, CC-apoV injection rescued impaired liver KCs during sepsis and enhanced their ability to capture and kill bloodborne bacteria. In addition, apoV-promoted macrophage killing of bacteria could be blocked by the inhibition of small GTPase Rab5. This study reveals a liver KC-targeted therapeutic strategy for sepsis and provides a nanodrug CC-apoV to improve the host antibacterial defense and amplify the therapeutic effect of the nanodrug.

Transcriptome-based network analysis reveals hub immune genes and pathways of hepatopancreas against LPS in Amphioctopus fangsiao

The hepatopancreas is the biggest digestive organ in Amphioctopus fangsiao (A. fangsiao), but also undertakes critical functions like detoxification and immune defense. Generally, pathogenic bacteria or endotoxin from the gut microbiota would be arrested and detoxified in the hepatopancreas, which could be accompanied by the inevitable immune responses. In recent years, studies related to cephalopods immune have been increasing, but the molecular mechanisms associated with the hepatopancreatic immunity are still unclear. In this study, lipopolysaccharide (LPS), a major component of the cell wall of Gram-negative bacteria, was used for imitating bacteria infection to stimulate the hepatopancreas of A. fangsiao. To investigate the immune process happened in A. fangsiao hepatopancreas, we performed transcriptome analysis of hepatopancreas tissue after LPS injection, and identified 2,615 and 1,943 differentially expressed genes (DEGs) at 6 and 24 h post-injection, respectively. GO and KEGG enrichment analysis showed that these DEGs were mainly involved in immune-related biological processes and signaling pathways, including ECM-receptor interaction signaling pathway, Phagosome signaling pathway, Lysosome signaling pathway, and JAK-STAT signaling pathways. The function relationships between these DEGs were further analyzed through protein-protein interaction (PPI) networks. It was found that Mtor, Mapk14 and Atm were the three top interacting DEGs under LPS stimulation. Finally, 15 hub genes involving multiple KEGG signaling pathways and PPI relationships were selected for qRT-PCR validation. In this study, for the first time we explored the molecular mechanisms associated with hepatopancreatic immunity in A. fangsiao using a PPI networks approach, and provided new insights for understanding hepatopancreatic immunity in A. fangsiao.

Optimizing Spectronaut Search Parameters to Improve Data Quality with Minimal Proteome Coverage Reductions in DIA Analyses of Heterogeneous Samples

Data-independent acquisition has seen breakthroughs that enable comprehensive proteome profiling using short gradients. As the proteome coverage continues to increase, the quality of the data generated becomes much more relevant. Using Spectronaut, we show that the default search parameters can be easily optimized to minimize the occurrence of false positives across different samples. Using an immunological infection model system to demonstrate the impact of adjusting search settings, we analyzed Mus musculus macrophages and compared their proteome to macrophages spiked withCandida albicans. This experimental system enabled the identification of "false positives" as Candida albicans peptides and proteins should not be present in the Mus musculus-only samples. We show that adjusting the search parameters reduced "false positive" identifications by 89% at the peptide and protein level, thereby considerably increasing the quality of the data. We also show that these optimized parameters incurred a moderate cost, only reducing the overall number of "true positive" identifications across each biological replicate by <6.7% at both the peptide and protein level. We believe the value of our updated search parameters extends beyond a two-organism analysis and would be of great value to any DIA experiment analyzing heterogeneous populations of cell types or tissues.

C-C motif chemokine receptor 2 and 7 synergistically control inflammatory monocyte recruitment but the infecting virus dictates monocyte function in the brain

Inflammatory monocytes (iMO) are recruited from the bone marrow to the brain during viral encephalitis. C-C motif chemokine receptor (CCR) 2 deficiency substantially reduces iMO recruitment for most, but not all encephalitic viruses. Here we show CCR7 acts synergistically with CCR2 to control this process. Following Herpes simplex virus type-1 (HSV-1), or La Crosse virus (LACV) infection, we find iMO proportions are reduced by approximately half in either Ccr2 or Ccr7 knockout mice compared to control mice. However, Ccr2/Ccr7 double knockouts eliminate iMO recruitment following infection with either virus, indicating these receptors together control iMO recruitment. We also find that LACV induces a more robust iMO recruitment than HSV-1. However, unlike iMOs in HSV-1 infection, LACV-recruited iMOs do not influence neurological disease development. LACV-induced iMOs have higher expression of proinflammatory and proapoptotic but reduced mitotic, phagocytic and phagolysosomal transcripts compared to HSV-1-induced iMOs. Thus, virus-specific activation of iMOs affects their recruitment, activation, and function.

Expression of ALS-PFN1 impairs vesicular degradation in iPSC-derived microglia

Microglia play a pivotal role in neurodegenerative disease pathogenesis, but the mechanisms underlying microglia dysfunction and toxicity remain to be elucidated. To investigate the effect of neurodegenerative disease-linked genes on the intrinsic properties of microglia, we studied microglia-like cells derived from human induced pluripotent stem cells (iPSCs), termed iMGs, harboring mutations in profilin-1 (PFN1) that are causative for amyotrophic lateral sclerosis (ALS). ALS-PFN1 iMGs exhibited evidence of lipid dysmetabolism, autophagy dysregulation and deficient phagocytosis, a canonical microglia function. Mutant PFN1 also displayed enhanced binding affinity for PI3P, a critical signaling molecule involved in autophagic and endocytic processing. Our cumulative data implicate a gain-of-toxic function for mutant PFN1 within the autophagic and endo-lysosomal pathways, as administration of rapamycin rescued phagocytic dysfunction in ALS-PFN1 iMGs. These outcomes demonstrate the utility of iMGs for neurodegenerative disease research and implicate microglial vesicular degradation pathways in the pathogenesis of these disorders.

Cyberlindnera jadinii yeast as a functional protein source: Modulation of immunoregulatory pathways in the intestinal proteome of zebrafish (Danio rerio)

Yeasts contain bioactive components that can enhance fish immune robustness and disease resistance. Our study focused on analyzing intestinal immunoregulatory pathways in zebrafish (Danio rerio) using iTRAQ and 2D LC-MS/MS to quantify intestinal proteins. Zebrafish were fed either control diet (C) or diet supplemented with autolyzed Cyberlindnera jadinii (ACJ). KEGG analysis revealed that ACJ yeast diet induced increased abundance of proteins related to arginine and proline metabolism, phagosome, C-lectin receptor signaling, ribosome and PPAR signaling pathways, which can modulate and enhance innate immune responses. ACJ yeast diet also showed decreased abundance of proteins associated with inflammatory pathways, including apoptosis, necroptosis and ferroptosis. These findings indicate boosted innate immune response and control of inflammation-related pathways in zebrafish intestine. Our findings in the well annotated proteome of zebrafish enabled a detailed investigation of intestinal responses and provide insight into health-beneficial effects of yeast species C. jadinii, which is relevant for aquaculture species.

VAMP5 promotes Fcγ receptor-mediated phagocytosis and regulates phagosome maturation in macrophages

Phagosome formation and maturation reportedly occur via sequential membrane fusion events mediated by synaptosomal-associated protein of 23 kDa (SNAP23), a plasma membrane-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family. Vesicle-associated membrane protein 5 (VAMP5), also a plasmalemma SNARE, interacts with SNAP23; however, its precise function in phagocytosis in macrophages remains elusive. To elucidate this aspect, we investigated the characteristics of macrophages in the presence of VAMP5 overexpression or knockdown and found that VAMP5 participates in Fcγ receptor-mediated phagosome formation, although not directly in phagosome maturation. Overexpressed VAMP5 was localized to the early phagosomal membrane but no longer localized to the lysosomal-associated membrane protein 1-positive maturing phagosomal membrane. Analyses using compound-based selective inhibitors demonstrated that VAMP5 dissociation from early phagosomes occurs in a clathrin- and dynamin-dependent manner and is indispensable for SNAP23 function in subsequent membrane fusion during phagosome maturation. Accordingly, to the best of our knowledge, we demonstrate, for the first time, that VAMP5 exerts an immunologically critical function during phagosome formation and maturation via SNARE-based membrane trafficking in macrophages.

Molecular Mechanisms of Intracellular Delivery of Nanoparticles Monitored by an Enzyme-Induced Proximity Labeling

Achieving increasingly finely targeted drug delivery to organs, tissues, cells, and even to intracellular biomacromolecules is one of the core goals of nanomedicines. As the delivery destination is refined to cellular and subcellular targets, it is essential to explore the delivery of nanomedicines at the molecular level. However, due to the lack of technical methods, the molecular mechanism of the intracellular delivery of nanomedicines remains unclear to date. Here, we develop an enzyme-induced proximity labeling technology in nanoparticles (nano-EPL) for the real-time monitoring of proteins that interact with intracellular nanomedicines. Poly(lactic-co-glycolic acid) nanoparticles coupled with horseradish peroxidase (HRP) were fabricated as a model (HRP(+)-PNPs) to evaluate the molecular mechanism of nano delivery in macrophages. By adding the labeling probe biotin-phenol and the catalytic substrate H2O2 at different time points in cellular delivery, nano-EPL technology was validated for the real-time in situ labeling of proteins interacting with nanoparticles. Nano-EPL achieves the dynamic molecular profiling of 740 proteins to map the intracellular delivery of HRP (+)-PNPs in macrophages over time. Based on dynamic clustering analysis of these proteins, we further discovered that different organelles, including endosomes, lysosomes, the endoplasmic reticulum, and the Golgi apparatus, are involved in delivery with distinct participation timelines. More importantly, the engagement of these organelles differentially affects the drug delivery efficiency, reflecting the spatial-temporal heterogeneity of nano delivery in cells. In summary, these findings highlight a significant methodological advance toward understanding the molecular mechanisms involved in the intracellular delivery of nanomedicines.

Combating bacterial infections with host defense peptides: Shifting focus from bacteria to host immunity

The increasing prevalence of multidrug-resistant bacterial infections necessitates the exploration of novel paradigms for anti-infective therapy. Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), have garnered extensive recognition as immunomodulatory molecules that leverage natural host mechanisms to enhance therapeutic benefits. The unique immune mechanism exhibited by certain HDPs that involves self-assembly into supramolecular nanonets capable of inducing bacterial agglutination and entrapping is significantly important. This process effectively prevents microbial invasion and subsequent dissemination and significantly mitigates selective pressure for the evolution of microbial resistance, highlighting the potential of HDP-based antimicrobial therapy. Recent advancements in this field have focused on developing bio-responsive materials in the form of supramolecular nanonets. A comprehensive overview of the immunomodulatory and bacteria-agglutinating activities of HDPs, along with a discussion on optimization strategies for synthetic derivatives, is presented in this article. These optimized derivatives exhibit improved biological properties and therapeutic potential, making them suitable for future clinical applications as effective anti-infective therapeutics.

Propulsive cell entry diverts pathogens from immune degradation by remodeling the phagocytic synapse

Phagocytosis is a critical immune function for infection control and tissue homeostasis. During phagocytosis, pathogens are internalized and degraded in phagolysosomes. For pathogens that evade immune degradation, the prevailing view is that virulence factors are required to disrupt the biogenesis of phagolysosomes. In contrast, we present here that physical forces from motile pathogens during cell entry divert them away from the canonical degradative pathway. This altered fate begins with the force-induced remodeling of the phagocytic synapse formation. We used the parasite Toxoplasma gondii as a model because live Toxoplasma actively invades host cells using gliding motility. To differentiate the effects of physical forces from virulence factors in phagocytosis, we employed magnetic forces to induce propulsive entry of inactivated Toxoplasma into macrophages. Experiments and computer simulations show that large propulsive forces hinder productive activation of receptors by preventing their spatial segregation from phosphatases at the phagocytic synapse. Consequently, the inactivated parasites are engulfed into vacuoles that fail to mature into degradative units, similar to the live motile parasite's intracellular pathway. Using yeast cells and opsonized beads, we confirmed that this mechanism is general, not specific to the parasite used. These results reveal new aspects of immune evasion by demonstrating how physical forces during active cell entry, independent of virulence factors, enable pathogens to circumvent phagolysosomal degradation.

Model-based assessment of neutrophil-mediated phagocytosis and digestion of bacteria across in vitro and in vivo studies

Neutrophil granulocytes are key components of the host response against pathogens, and severe neutropenia, with neutrophil counts below 0.5 × 106 cells/mL, renders patients increasingly vulnerable to infections. Published in vitro (n = 7) and in vivo (n = 5) studies with time-course information on bacterial and neutrophil counts were digitized to characterize the kinetics of neutrophil-mediated bacterial killing and inform on the immune systems' contribution to the clearance of bacterial infections. A mathematical model for the in vitro dynamics of bacteria and the kinetics of neutrophil-mediated phagocytosis and digestion was developed, which was extended to in vivo studies in immune-competent and immune-compromised mice. Neutrophil-mediated bacterial killing was described by two first-order processes-phagocytosis and digestion-scaled by neutrophil concentration, where 50% of the maximum was achieved at neutrophil counts of 1.19 × 106 cells/mL (phagocytosis) and 6.55 × 106 cells/mL (digestion). The process efficiencies diminished as the phagocytosed bacteria to total neutrophils ratio increased (with 50% reduction at a ratio of 3.41). Neutrophil in vivo dynamics were captured through the characterization of myelosuppressive drug effects and postinoculation neutrophil influx into lungs and by system differences (27% bacterial growth and 9.3% maximum capacity, compared with in vitro estimates). Predictions showed how the therapeutically induced reduction of neutrophil counts enabled bacterial growth, especially when falling below 0.5 × 106 cells/mL, whereas control individuals could deal with all tested bacterial burdens (up to 109  colony forming units/g lung). The model-based characterization of neutrophil-mediated bacterial killing simultaneously predicted data across in vitro and in vivo studies and may be used to inform the capacity of host-response at the individual level.

Transcriptomic Profiling of Influenza A Virus-Infected Mouse Lung at Recovery Stage Using RNA Sequencing

Influenza A virus (IAV) is known to cause mild to severe respiratory illness. Under some conditions, the infection can lead to pneumonia (viral or bacterial), acute respiratory distress syndrome, and other complications that can be fatal, especially in vulnerable populations such as the elderly, young children, and individuals with underlying health conditions. Despite previous studies, little is known about the host immune response and neuroimmune interactions in IAV infection. Using RNA sequencing, we performed transcriptomic analysis of murine lung tissue 21 days post infection (dpi) with IAV (H1N1) in order to find the differentially expression genes (DEGs) related to the host immune response and neuroimmune interactions inside the lung during recovery. Among 792 DEGs, 434 genes were up-regulated, whereas 358 genes were down-regulated. The most prominent molecular functions of the up-regulated genes were related to the immune response and tissue repair, whereas a large proportion of the down-regulated genes were associated with neural functions. Although further molecular/functional studies need to be performed for these DEGs, our results facilitate the understanding of the host response (from innate immunity to adaptive immunity) and neuroimmune interactions in infected lungs at the recovery stage of IAV infection. These genes might have potential uses as mechanistic/diagnostic biomarkers and represent possible targets for anti-IAV therapies.

Polyphosphate uses mTOR, pyrophosphate, and Rho GTPase components to potentiate bacterial survival in Dictyostelium

IMPORTANCE

Although most bacteria are quickly killed after phagocytosis by a eukaryotic cell, some pathogenic bacteria escape death after phagocytosis. Pathogenic Mycobacterium species secrete polyP, and the polyP is necessary for the bacteria to prevent their killing after phagocytosis. Conversely, exogenous polyP prevents the killing of ingested bacteria that are normally killed after phagocytosis by human macrophages and the eukaryotic microbe Dictyostelium discoideum. This suggests the possibility that in these cells, a signal transduction pathway is used to sense polyP and prevent killing of ingested bacteria. In this report, we identify key components of the polyP signal transduction pathway in D. discoideum. In cells lacking these components, polyP is unable to inhibit killing of ingested bacteria. The pathway components have orthologs in human cells, and an exciting possibility is that pharmacologically blocking this pathway in human macrophages would cause them to kill ingested pathogens such as Mycobacterium tuberculosis.

Noteworthy perspectives on microglia in neuropsychiatric disorders

Microglia are so versatile that they not only provide immune surveillance for central nervous system, but participate in neural circuitry development, brain blood vessels formation, blood-brain barrier architecture, and intriguingly, the regulation of emotions and behaviors. Microglia have a profound impact on neuronal survival, brain wiring and synaptic plasticity. As professional phagocytic cells in the brain, they remove dead cell debris and neurotoxic agents via an elaborate mechanism. The functional profile of microglia varies considerately depending on age, gender, disease context and other internal or external environmental factors. Numerous studies have demonstrated a pivotal involvement of microglia in neuropsychiatric disorders, including negative affection, social deficit, compulsive behavior, fear memory, pain and other symptoms associated with major depression disorder, anxiety disorder, autism spectrum disorder and schizophrenia. In this review, we summarized the latest discoveries regarding microglial ontogeny, cell subtypes or state spectrum, biological functions and mechanistic underpinnings of emotional and behavioral disorders. Furthermore, we highlight the potential of microglia-targeted therapies of neuropsychiatric disorders, and propose outstanding questions to be addressed in future research of human microglia.

Harnessing host-pathogen interactions for innovative drug discovery and host-directed therapeutics to tackle tuberculosis

Tuberculosis (TB) is a highly contagious bacterial infection caused by Mycobacterium tuberculosis (Mtb), which has been ranked as the second leading cause of death worldwide from a single infectious agent. As an intracellular pathogen, Mtb has well adapted to the phagocytic host microenvironment, influencing diverse host processes such as gene expression, trafficking, metabolism, and signaling pathways of the host to its advantage. These responses are the result of dynamic interactions of the bacteria with the host cell signaling pathways, whereby the bacteria attenuate the host cellular processes for their survival. Specific host genes and the mechanisms involved in the entry and subsequent stabilization of M. tuberculosis intracellularly have been identified in various genetic and chemical screens recently. The present understanding of the co-evolution of Mtb and macrophage system presented us the new possibilities for exploring host-directed therapeutics (HDT). Here, we discuss the host-pathogen interaction for Mtb, including the pathways adapted by Mtb to escape immunity. The review sheds light on different host-directed therapies (HDTs) such as repurposed drugs and vitamins, along with their targets such as granuloma, autophagy, extracellular matrix, lipids, and cytokines, among others. The article also examines the available clinical data on these drug molecules. In conclusion, the review presents a perspective on the current knowledge in the field of HDTs and the need for additional research to overcome the challenges associated HDTs.

pH-gated nanoparticles selectively regulate lysosomal function of tumour-associated macrophages for cancer immunotherapy

Tumour-associated macrophages (TAMs), as one of the most abundant tumour-infiltrating immune cells, play a pivotal role in tumour antigen clearance and immune suppression. M2-like TAMs present a heightened lysosomal acidity and protease activity, limiting an effective antigen cross-presentation. How to selectively reprogram M2-like TAMs to reinvigorate anti-tumour immune responses is challenging. Here, we report a pH-gated nanoadjuvant (PGN) that selectively targets the lysosomes of M2-like TAMs in tumours rather than the corresponding organelles from macrophages in healthy tissues. Enabled by the PGN nanotechnology, M2-like TAMs are specifically switched to a M1-like phenotype with attenuated lysosomal acidity and cathepsin activity for improved antigen cross-presentation, thus eliciting adaptive immune response and sustained tumour regression in tumour-bearing female mice. Our findings provide insights into how to specifically regulate lysosomal function of TAMs for efficient cancer immunotherapy.

SLC38A5 aggravates DC-mediated psoriasiform skin inflammation via potentiating lysosomal acidification

Amino acid (aa) metabolism is closely correlated with the pathogenesis of psoriasis; however, details on aa transportation during this process are barely known. Here, we find that SLC38A5, a sodium-dependent neutral aa transporter that counter-transports protons, is markedly upregulated in the psoriatic skin of both human patients and mouse models. SLC38A5 deficiency significantly ameliorates the pathogenesis of psoriasis, indicating a pathogenic role of SLC38A5. Surprisingly, SLC38A5 is almost exclusively expressed in dendritic cells (DCs) when analyzing the psoriatic lesion and mainly locates on the lysosome. Mechanistically, SLC38A5 potentiates lysosomal acidification, which dictates the cleavage and activation of TLR7 with ensuing production of pro-inflammatory cytokines such as interleukin-23 (IL-23) and IL-1β from DCs and eventually aggravates psoriatic inflammation. In summary, this work uncovers an auxiliary mechanism in driving lysosomal acidification, provides inspiring insights for DC biology and psoriasis etiology, and reveals SLC38A5 as a promising therapeutic target for treating psoriasis.

Bi-functional particles for real-time phagosome acidification and proteolysis multiplex assay in macrophages

Phagosome acidification and proteolysis are essential processes in the immune response to contain and eliminate pathogens. In recent years, there has been an increased desire for a rapid and accurate method of assessing these processes in real-time. Here, we outline the development of a multiplexed assay that allows simultaneous monitoring of phagosome acidification and proteolysis in the same sample using silica beads conjugated to pHrodo and DQ BSA. We describe in detail how to prepare the bi-functional particles and show proof of concept using differentially activated macrophages. This multiplexed spectrophotometric assay allows rapid and accurate assessment of phagosome acidification and proteolysis in real-time and could provide valuable information for understanding the immune response to pathogen invasion.

The dynamics of Mycobacterium tuberculosis phagosome and the fate of infection

Phagosomes are vesicles produced by phagocytosis of phagocytes, which are crucial in immunity against Mycobacterium tuberculosis (Mtb) infection. After the phagocyte ingests the pathogen, it activates the phagosomes to recruit a series of components and process proteins, to phagocytose, degrade and kill Mtb. Meanwhile, Mtb can resist acid and oxidative stress, block phagosome maturation, and manipulate host immune response. The interaction between Mtb and phagocytes leads to the outcome of infection. The dynamic of this process can affect the cell fate. This article mainly reviews the development and maturation of phagosomes, as well as the dynamics and modifications of Mtb effectors and phagosomes components, and new diagnostic and therapeutic markers involved in phagosomes.

Tenofovir alters the immune microenvironment of pregnant women with hepatitis B virus infection: Evidence from single-cell RNA sequencing

BACKGROUND

Mother-to-child is the main route of the transmission of hepatitis B virus (HBV) infection. Tenofovir fumarate (TDF) antiviral treatment has become the most extensive choice worldwide. However, the effects of TDF treatment on the immune function of pregnant women remains unclear. Here we investigate the effect of TDF treatment on the immune microenvironment of pregnant women with HBV infection using single-cell RNA sequencing (scRNA-seq).

METHODS

Three HBV-infected pregnant women were treated with TDF and six samples were collected before and after the treatment. In total, 68,200 peripheral blood mononuclear cells (PBMCs) were extracted for 10 × scRNA-seq. The cells were clustered using t-distributed stochastic neighbor embedding (t-SNE) and unbiased computational informatics analysis.

RESULTS

The analysis identified four-cell subtypes, including T cells, monocytes, natural killer (NK) cells, and B cells, and unraveled the developmental trajectory and maturation of CD4⁺ T and CD8⁺ T cell subtypes. The cellular state and molecular features of the effector/memory T cells revealed a significant increase in the inflammatory state of CD4⁺ T cells and the cytotoxic characteristics of CD8⁺ T cells. Additionally, after TDF treatment, the monocytes showed a tendency for M1 polarization, and the cytotoxicity of NK cells was enhanced. Furthermore, the analysis of intercellular communication revealed the interaction of various subtypes of cells and the heterogeneous expression of key signal pathways.

CONCLUSIONS

The findings of this study reveal significant differences in cellular subtypes and molecular characteristics of PBMCs of pregnant women with HBV infection before and after TDF treatment and demonstrate the recovery of immune response after treatment. These findings could help develop immune intervention measures to control HBV during pregnancy and the puerperium period.

Propulsive cell entry diverts pathogens from immune degradation by remodeling the phagocytic synapse

Phagocytosis is a critical immune function for infection control and tissue homeostasis. This process is typically described as non-moving pathogens being internalized and degraded in phagolysosomes. For pathogens that evade immune degradation, the prevailing view is that virulence factors that biochemically disrupt the biogenesis of phagoslysosomes are required. In contrast, here we report that physical forces exerted by pathogens during cell entry divert them away from the canonical phagolysosomal degradation pathway, and this altered intracellular fate is determined at the time of phagocytic synapse formation. We used the eukaryotic parasite Toxoplasma gondii as a model because live Toxoplasma uses gliding motility to actively invade into host cells. To differentiate the effect of physical forces from that of virulence factors in phagocytosis, we developed a strategy that used magnetic forces to induce propulsive entry of inactivated Toxoplasma into macrophage cells. Experiments and computer simulations collectively reveal that large propulsive forces suppress productive activation of receptors by hindering their spatial segregation from phosphatases at the phagocytic synapse. Consequently, the inactivated parasites, instead of being degraded in phagolysosomes, are engulfed into vacuoles that fail to mature into degradative units, following an intracellular pathway strikingly similar to that of the live motile parasite. Using opsonized beads, we further confirmed that this mechanism is general, not specific to the parasite used. These results reveal previously unknown aspects of immune evasion by demonstrating how physical forces exerted during active cell entry, independent of virulence factors, can help pathogens circumvent phagolysosomal degradation.

Update of cellular responses to the efferocytosis of necroptosis and pyroptosis

Cell death is a basic physiological process that occurs in all living organisms. A few key players in these mechanisms, as well as various forms of cell death programming, have been identified. Apoptotic cell phagocytosis, also known as apoptotic cell clearance, is a well-established process regulated by a number of molecular components, including 'find-me', 'eat-me' and engulfment signals. Efferocytosis, or the rapid phagocytic clearance of cell death, is a critical mechanism for tissue homeostasis. Despite having similar mechanism to phagocytic clearance of infections, efferocytosis differs from phagocytosis in that it induces a tissue-healing response and is immunologically inert. However, as field of cell death has rapid expanded, much attention has recently been drawn to the efferocytosis of additional necrotic-like cell types, such as necroptosis and pyroptosis. Unlike apoptosis, this method of cell suicide allows the release of immunogenic cellular material and causes inflammation. Regardless of the cause of cell death, the clearance of dead cells is a necessary function to avoid uncontrolled synthesis of pro-inflammatory molecules and inflammatory disorder. We compare and contrast apoptosis, necroptosis and pyroptosis, as well as the various molecular mechanisms of efferocytosis in each type of cell death, and investigate how these may have functional effects on different intracellular organelles and signalling networks. Understanding how efferocytic cells react to necroptotic and pyroptotic cell uptake can help us understand how to modulate these cell death processes for therapeutic purposes.

Lung macrophages utilize unique cathepsin K-dependent phagosomal machinery to degrade intracellular collagen

Resident tissue macrophages are organ-specialized phagocytes responsible for the maintenance and protection of tissue homeostasis. It is well established that tissue diversity is reflected by the heterogeneity of resident tissue macrophage origin and phenotype. However, much less is known about tissue-specific phagocytic and proteolytic macrophage functions. Here, using a quantitative proteomics approach, we identify cathepsins as key determinants of phagosome maturation in primary peritoneum-, lung-, and brain-resident macrophages. The data further uncover cathepsin K (CtsK) as a molecular marker for lung phagosomes required for intracellular protein and collagen degradation. Pharmacological blockade of CtsK activity diminished phagosomal proteolysis and collagenolysis in lung-resident macrophages. Furthermore, profibrotic TGF-β negatively regulated CtsK-mediated phagosomal collagen degradation independently from classical endocytic-proteolytic pathways. In humans, phagosomal CtsK activity was reduced in COPD lung macrophages and non-COPD lung macrophages exposed to cigarette smoke extract. Taken together, this study provides a comprehensive map of how peritoneal, lung, and brain tissue environment shapes phagosomal composition, revealing CtsK as a key molecular determinant of lung phagosomes contributing to phagocytic collagen clearance in lungs.

From a cell model to a fish trial: Immunomodulatory effects of heat-killed Lactiplantibacillus plantarum as a functional ingredient in aquafeeds for salmonids

Paraprobiotics (dead/inactivated probiotics) are promising candidates in functional feeds to promote growth performance, modulate intestinal microbiota and enhance immune response of fish. During industrial production, fish are exposed to several stressful conditions such as handling, sub-optimal nutrition and diseases that can lead to reduced growth, increased mortalities and large economical losses. Such problems can be mitigated by use of functional feeds, leading to more-sustainable aquaculture and improved animal welfare. Lactiplantibacillus plantarum strain L-137 is a common bacterium found in fermented Southeast Asian dish made from fish and rice. The benefits of its heat-killed form (HK L-137) related to growth performance and immunomodulation have been studied in farmed fish such as Nile Tilapia (Oreochromis niloticus), striped catfish (Pangasianodon hypophthalmus) and bighead catfish (Clarias macrocephalus). To study if such benefits can also be observed in salmonids, we worked both at in vitro level using an intestinal epithelium cell line from rainbow trout (Oncorhynchus mykiss; RTgutGC) stimulated with HK L-137 (Feed LP20™) and at in vivo level with pre-smolt Atlantic salmon (Salmo salar) fed HK L-137 at different inclusion levels (20, 100 and 500 mg of Feed LP20™ kg-1 feed). In RTgutGC, the results showed that the barrier function of the cell monolayer was strengthened along with an increased production of IL-1β and a decreased production of Anxa1, indicating a modulation of the immune response. Interestingly, a similar trend was detected at the in vivo level in distal intestine from fish fed the highest inclusion level of HK L-137. Here, a lower production of Anxa1 was also detected (after a 61-day feeding period) in addition to an increase of total plasma IgM in the same group. Furthermore, the RNA-seq analysis showed that HK L-137 was able to modulate the gene expression of pathways related to molecular function, biological process and cellular component in distal intestine, without compromising fish performance and gut microbiota. Taken together, our study has shown that HK L-137 can modulate physiological response of Atlantic salmon, making fish more robust against stressful conditions during production.

Aspergillus fumigatus hijacks human p11 to redirect fungal-containing phagosomes to non-degradative pathway

The decision whether endosomes enter the degradative or recycling pathway in mammalian cells is of fundamental importance for pathogen killing, and its malfunctioning has pathological consequences. We discovered that human p11 is a critical factor for this decision. The HscA protein present on the conidial surface of the human-pathogenic fungus Aspergillus fumigatus anchors p11 on conidia-containing phagosomes (PSs), excludes the PS maturation mediator Rab7, and triggers binding of exocytosis mediators Rab11 and Sec15. This reprogramming redirects PSs to the non-degradative pathway, allowing A. fumigatus to escape cells by outgrowth and expulsion as well as transfer of conidia between cells. The clinical relevance is supported by the identification of a single nucleotide polymorphism in the non-coding region of the S100A10 (p11) gene that affects mRNA and protein expression in response to A. fumigatus and is associated with protection against invasive pulmonary aspergillosis. These findings reveal the role of p11 in mediating fungal PS evasion.

Enrichr in silico analysis of MS-based extracted candidate proteomic biomarkers highlights pathogenic pathways in systemic sclerosis

Systemic sclerosis (SSc) is a rheumatic disease characterised by vasculopathy, inflammation and fibrosis. Its aetiopathogenesis is still unknown, and the pathways/mechanisms of the disease are not clarified. This study aimed to perform in silico analysis of the already Mass Spectrometry (MS)-based discovered biomarkers of SSc to extract possible pathways/mechanisms implicated in the disease. We recorded all published candidate MS-based found biomarkers related to SSc. We then selected a number of the candidate biomarkers using specific criteria and performed pathway and cellular component analyses using Enrichr. We used PANTHER and STRING to assess the biological processes and the interactions of the recorded proteins, respectively. Pathway analysis extracted several pathways that are associated with the three different stages of SSc pathogenesis. Some of these pathways are also related to other diseases, including autoimmune diseases. We observe that these biomarkers are located in several cellular components and implicated in many biological processes. STRING analysis showed that some proteins interact, creating significant clusters, while others do not display any evidence of an interaction. All these data highlight the complexity of SSc, and further investigation of the extracted pathways/biological processes and interactions may help study the disease from a different angle.

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.

Isolation of Polystyrene Bead-Induced Phagosomes for Western Blotting

The engulfment of "self" and "non-self" particles by immune and non-immune cells is crucial for maintaining homeostasis and combatting infection. Engulfed particles are contained within vesicles termed phagosomes that undergo dynamic fusion and fission events, which ultimately results in the formation of phagolysosomes that degrade the internalized cargo. This process is highly conserved and plays an important role in maintaining homeostasis, and disruptions in this are implicated in numerous inflammatory disorders. Given its broad role in innate immunity, it is important to understand how different stimuli or changes within the cell can shape the phagosome architecture. In this chapter, we describe a robust protocol for the isolation of polystyrene bead-induced phagosomes using sucrose density gradient centrifugation. This process results in a highly pure sample that can be used in downstream applications, namely, Western blotting.

Examining the Kinetics of Phagocytosis-Coupled Inflammasome Activation in Murine Bone Marrow-Derived Dendritic Cells

In the present chapter, we describe procedures to assess NLRP3 and NLRC4 inflammasome assembly by immunofluorescence microscopy or live cell imaging, together with inflammasome activation by biochemical and immunological techniques upon phagocytosis. We also include a step-by-step guide to automating the counting of inflammasome "specks" after imaging. While our focus resides on murine bone marrow-derived dendritic cells differentiated in the presence of granulocyte-macrophage colony-stimulating factor, which results in a cell population that resembles inflammatory dendritic cells, the strategies described herein may apply to other phagocytes as well.

Targeting of phagolysosomes containing conidia of the fungus Aspergillus fumigatus with polymeric particles

Conidia of the airborne human-pathogenic fungus Aspergillus fumigatus are inhaled by humans. In the lung, they are phagocytosed by alveolar macrophages and intracellularly processed. In macrophages, however, conidia can interfere with the maturation of phagolysosomes to avoid their elimination. To investigate whether polymeric particles (PPs) can reach this intracellular pathogen in macrophages, we formulated dye-labeled PPs with a size allowing for their phagocytosis. PPs were efficiently taken up by RAW 264.7 macrophages and were found in phagolysosomes. When macrophages were infected with conidia prior to the addition of PPs, we found that they co-localized in the same phagolysosomes. Mechanistically, the fusion of phagolysosomes containing PPs with phagolysosomes containing conidia was observed. Increasing concentrations of PPs increased fusion events, resulting in 14% of phagolysosomes containing both conidia and PPs. We demonstrate that PPs can reach conidia-containing phagolysosomes, making these particles a promising carrier system for antimicrobial drugs to target intracellular pathogens. KEY POINTS: • Polymer particles of a size larger than 500 nm are internalized by macrophages and localized in phagolysosomes. • These particles can be delivered to Aspergillus fumigatus conidia-containing phagolysosomes of macrophages. • Enhanced phagolysosome fusion by the use of vacuolin1 can increase particle delivery.

Effects of morphology and size of nanoscale drug carriers on cellular uptake and internalization process: a review

In the field of targeted drug delivery, the effects of size and morphology of drug nanocarriers are of great importance and need to be discussed in depth. To be concise, among all the various shapes of nanocarriers, rods and tubes with a narrow cross-section are the most preferred shapes for the penetration of a cell membrane. In this regard, several studies have focused on methods to produce nanorods and nanotubes with controlled optimized size and aspect ratio (AR). Additionally, a non-spherical orientation could affect the cellular uptake process while a tangent angle of less than 45° is better at penetrating the membrane, and Ω = 90° is beneficial. Moreover, these nanocarriers show different behaviors when confronting diverse cells whose fields should be investigated in future studies. In this survey, a comprehensive classification based on carrier shape is first submitted. Then, the most commonly used methods for control over the size and shape of the carriers are reviewed. Finally, influential factors on the cellular uptake and internalization processes and related analytical methods for evaluating this process are discussed.

Transcriptome analysis of the immunomodulatory effects of Salvia miltiorrhiza polysaccharide on hemocyte immune response in Procambarus clarkii

Natural plant polysaccharide as immune modulator is considered an effective strategy for healthy aquaculture to reduce medicine treatment. Salvia miltiorrhiza polysaccharides (SMP) had applications to regulate immune activity and enhance antioxidant in vertebrates, but the potential function has been rarely reported in crustaceans. In this study, the immunological effects of SMP on hemocytes of Procambarus clarkii were analyzed. Results showed that total superoxide dismutase (T-SOD), phenoloxidase (PO) activity and respiratory burst were up-regulated after SMP treatment. After high-throughput sequencing, 2170 differentially expressed genes (DEGs) including 1294 up-regulated and 876 down-regulated genes were identified. KEGG function enrichment analysis indicated that DEGs are involved in crustaceans cellular immune-related signaling pathways, including lysosome, phagosome and endocytosis. Transcriptome mining and qRT-PCR showed that SMP up-regulated humoral immunity factors gene expression. Diets supplemented with 0.8% SMP significantly up-regulated the total number of hemocytes (THC), T-SOD and PO activity, improved the survival of crayfish after Citrobacter freundii infection. This study suggested that SMP could improve the cellular and humoral immunity of P. clarkii. Furthermore, this finding supplied a molecular foundation for further comprehending the immunopotentiator effects of plant polysaccharides in crustaceans.

A Nanomedicine Structure-Activity Framework for Research, Development, and Regulation of Future Cancer Therapies

Despite their clinical success in drug delivery applications, the potential of theranostic nanomedicines is hampered by mechanistic uncertainty and a lack of science-informed regulatory guidance. Both the therapeutic efficacy and the toxicity of nanoformulations are tightly controlled by the complex interplay of the nanoparticle's physicochemical properties and the individual patient/tumor biology; however, it can be difficult to correlate such information with observed outcomes. Additionally, as nanomedicine research attempts to gradually move away from large-scale animal testing, the need for computer-assisted solutions for evaluation will increase. Such models will depend on a clear understanding of structure-activity relationships. This review provides a comprehensive overview of the field of cancer nanomedicine and provides a knowledge framework and foundational interaction maps that can facilitate future research, assessments, and regulation. By forming three complementary maps profiling nanobio interactions and pathways at different levels of biological complexity, a clear picture of a nanoparticle's journey through the body and the therapeutic and adverse consequences of each potential interaction are presented.

The E3 ubiquitin ligase RNF115 regulates phagosome maturation and host response to bacterial infection

Phagocytosis is a key process in innate immunity and homeostasis. After particle uptake, newly formed phagosomes mature by acquisition of endolysosomal enzymes. Macrophage activation by interferon gamma (IFN-γ) increases microbicidal activity, but delays phagosomal maturation by an unknown mechanism. Using quantitative proteomics, we show that phagosomal proteins harbour high levels of typical and atypical ubiquitin chain types. Moreover, phagosomal ubiquitylation of vesicle trafficking proteins is substantially enhanced upon IFN-γ activation of macrophages, suggesting a role in regulating phagosomal functions. We identified the E3 ubiquitin ligase RNF115, which is enriched on phagosomes of IFN-γ activated macrophages, as an important regulator of phagosomal maturation. Loss of RNF115 protein or ligase activity enhanced phagosomal maturation and increased cytokine responses to bacterial infection, suggesting that both innate immune signalling from the phagosome and phagolysosomal trafficking are controlled through ubiquitylation. RNF115 knock-out mice show less tissue damage in response to S. aureus infection, indicating a role of RNF115 in inflammatory responses in vivo. In conclusion, RNF115 and phagosomal ubiquitylation are important regulators of innate immune functions during bacterial infections.

Macrophage-Membrane-Camouflaged Nonviral Gene Vectors for the Treatment of Multidrug-Resistant Bacterial Sepsis

Sepsis is a life-threatening disease caused by systemic bacterial infections, with high morbidity and mortality worldwide. As the standard treatment for sepsis, antibiotic therapy faces the challenge of impaired macrophages and drug-resistant bacteria. In this study, we developed a membrane-camouflaged metal-organic framework (MOF) system for plasmid DNA (pDNA) delivery to combat sepsis. The antimicrobial gene LL37 was efficiently encapsulated in the pH-sensitive MOF, and the nanoparticles were decorated with macrophage membranes in a compatible manner. Macrophage membrane coating allows targeted delivery of LL37 to macrophages and creates macrophage factories for the continuous generation of antimicrobial peptides. Compared to naked nanoparticles, primary bone marrow mesenchymal macrophage membrane-modified nanoparticles greatly improved the survival rate of immunodeficient septic mice through the synergistic effect of efficient gene therapy and inflammatory cytokine sequestration. This study demonstrates an effective membrane biomimetic strategy for efficiently delivering pDNA, offering an excellent option for overcoming sepsis.

Phenotypic adaptation of Mycobacterium tuberculosis to host-associated stressors that induce persister formation

Mycobacterium tuberculosis exhibits a remarkable ability to interfere with the host antimicrobial response. The pathogen exploits elaborate strategies to cope with diverse host-induced stressors by modulating its metabolism and physiological state to prolong survival and promote persistence in host tissues. Elucidating the adaptive strategies that M. tuberculosis employs during infection to enhance persistence is crucial to understanding how varying physiological states may differentially drive disease progression for effective management of these populations. To improve our understanding of the phenotypic adaptation of M. tuberculosis, we review the adaptive strategies employed by M. tuberculosis to sense and coordinate a physiological response following exposure to various host-associated stressors. We further highlight the use of animal models that can be exploited to replicate and investigate different aspects of the human response to infection, to elucidate the impact of the host environment and bacterial adaptive strategies contributing to the recalcitrance of infection.

Kinetics of phagosome maturation is coupled to their intracellular motility

Immune cells degrade internalized pathogens in phagosomes through sequential biochemical changes. The degradation must be fast enough for effective infection control. The presumption is that each phagosome degrades cargos autonomously with a distinct but stochastic kinetic rate. However, here we show that the degradation kinetics of individual phagosomes is not stochastic but coupled to their intracellular motility. By engineering RotSensors that are optically anisotropic, magnetic responsive, and fluorogenic in response to degradation activities in phagosomes, we monitored cargo degradation kinetics in single phagosomes simultaneously with their translational and rotational dynamics. We show that phagosomes that move faster centripetally are more likely to encounter and fuse with lysosomes, thereby acidifying faster and degrading cargos more efficiently. The degradation rates increase nearly linearly with the translational and rotational velocities of phagosomes. Our results indicate that the centripetal motion of phagosomes functions as a clock for controlling the progression of cargo degradation.

Nanoparticle entry into cells; the cell biology weak link

Nanoparticles (NP) are attractive options for the therapeutic delivery of active pharmaceutical drugs, proteins and nucleic acids into cells, tissues and organs. Research into the development and application of NP most often starts with a diverse group of scientists, including chemists, bioengineers and material and pharmaceutical scientists, who design, fabricate and characterize NP in vitro (Stage 1). The next step (Stage 2) generally investigates cell toxicity as well as the processes by which NP bind, are internalized and deliver their cargo to appropriate model tissue culture cells. Subsequently, in Stage 3, selected NP are tested in animal systems, mostly mouse. Whereas the chemistry-based development and analysis in Stage 1 is increasingly sophisticated, the investigations in Stage 2 are not what could be regarded as 'state-of-the-art' for the cell biology field and the quality of research into NP interactions with cells is often sub-standard. In this review we describe our current understanding of the mechanisms by which particles gain entry into mammalian cells via endocytosis. We summarize the most important areas for concern, highlight some of the most common mis-conceptions, and identify areas where NP scientists could engage with trained cell biologists. Our survey of the different mechanisms of uptake into cells makes us suspect that claims for roles for caveolae, as well as macropinocytosis, in NP uptake into cells have been exaggerated, whereas phagocytosis has been under-appreciated.

Receptor for advanced glycation end-products (RAGE) mediates phagocytosis in nonprofessional phagocytes

In mammals, both professional phagocytes and nonprofessional phagocytes (NPPs) can perform phagocytosis. However, limited targets are phagocytosed by NPPs, and thus, the mechanism remains unclear. We find that spores of the yeast Saccharomyces cerevisiae are internalized efficiently by NPPs. Analyses of this phenomenon reveals that RNA fragments derived from cytosolic RNA species are attached to the spore wall, and these fragments serve as ligands to induce spore internalization. Furthermore, we show that a multiligand receptor, RAGE (receptor for advanced glycation end-products), mediates phagocytosis in NPPs. RAGE-mediated phagocytosis is not uniquely induced by spores but is an intrinsic mechanism by which NPPs internalize macromolecules containing RAGE ligands. In fact, artificial particles labeled with polynucleotides, HMGB1, or histone (but not bovine serum albumin) are internalized in NPPs. Our findings provide insight into the molecular basis of phagocytosis by NPPs, a process by which a variety of macromolecules are targeted for internalization.

The multiligand receptor RAGE (receptor for advanced glycation end-products) mediates phagocytosis in non-professional phagocytes (NPPs), for example through the use of RNA fragments as ligands for internalization.

Manipulation and exploitation of host immune system by pathogenic Mycobacterium tuberculosis for its advantage

Mycobacterium tuberculosis (Mtb) can become a long-term infection by evading the host immune response. Coevolution of Mtb with humans has resulted in its ability to hijack the host's immune systems in a variety of ways. So far, every Mtb defense strategy is essentially dependent on a subtle balance that, if shifted, can promote Mtb proliferation in the host, resulting in disease progression. In this review, the authors summarize many important and previously unknown mechanisms by which Mtb evades the host immune response. Besides recently found strategies by which Mtb manipulates the host molecular regulatory machinery of innate and adaptive immunity, including the intranuclear regulatory machinery, costimulatory molecules, the ubiquitin system and cellular intrinsic immune components will be discussed. A holistic understanding of these immune-evasion mechanisms is of foremost importance for the prevention, diagnosis and treatment of tuberculosis and will lead to new insights into tuberculosis pathogenesis and the development of more effective vaccines and treatment regimens.

LC3-Associated Phagocytosis in Bacterial Infection

LC3-associated phagocytosis (LAP) is a noncanonical autophagy process reported in recent years and is one of the effective mechanisms of host defense against bacterial infection. During LAP, bacteria are recognized by pattern recognition receptors (PRRs), enter the body, and then recruit LC3 onto a single-membrane phagosome to form a LAPosome. LC3 conjugation can promote the fusion of the LAPosomes with lysosomes, resulting in their maturation into phagolysosomes, which can effectively kill the identified pathogens. However, to survive in host cells, bacteria have also evolved strategies to evade killing by LAP. In this review, we summarized the mechanism of LAP in resistance to bacterial infection and the ways in which bacteria escape LAP. We aim to provide new clues for developing novel therapeutic strategies for bacterial infectious diseases.

Titania nanospikes activate macrophage phagocytosis by ligand-independent contact stimulation

Macrophage phagocytosis is an important research target to combat various inflammatory or autoimmune diseases; however, the phenomenon has never been controlled by artificial means. Titania nanospikes created by alkaline etching treatment can tune macrophage polarization toward a M1-like type and might regulate macrophage phagocytosis. This in vitro study aimed to determine whether the two-dimensional titania nanosurfaces created by alkaline etching treatment activated the macrophage phagocytosis by nanospike-mediated contact stimulation. On two-dimensional pure titanium sheets, alkaline etching treatments with different protocols created superhydrophilic nanosurfaces with hydroxyl function groups and moderate or dense nanospikes. Both types of titania nanosurfaces promoted the phagocytic activity of the mouse macrophage-like cell line, J774A.1, through upregulation of M1 polarization markers and phagocytosis-related receptors, such as toll-like receptors (TLR2 and 4). In contrast, the hydrophobic smooth or micro-roughened titanium surfaces did not activate macrophage phagocytosis or the expression of related receptors. These phenomena remained unchanged even under the antibody blockade of macrophage TLR2 but were either suppressed or augmented for each surface excited by ultraviolet irradiation. Titania nanospikes induced paxillin expression and provided physical stimuli to macrophages, the extent of which was positively correlated with TLR expression levels. Ligand stimulation with lipopolysaccharide did not upregulate macrophage TLR expression but further enhanced M1 marker expression by titania nanosurfaces. These results showed that the two-dimensional titania nanosurfaces activated macrophage phagocytosis by enhancing expression of phagocytosis-related receptors through nanospike-mediated contact stimulation, in assistance with physical surface properties, in a ligand-independent manner.

The NCF1 variant aggravates autoimmunity by facilitating the activation of plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are a professional type I IFN producer that play critical roles in the pathogenesis of autoimmune diseases. However, both genetic regulation of the function of pDCs and their relationships with autoimmunity are largely undetermined. Here, we investigated the causality of the neutrophil cytosolic factor 1 (NCF1) missense variant, which is one of the most significant associated risk variants for lupus, and found that the substitution of arginine (R) for histidine (H) at position 90 in the NCF1 protein (NCF1 p.R90H) led to excessive activation of pDCs. A mechanism study demonstrated that p.R90H reduced the affinity of NCF1 for phospholipids, thereby impairing endosomal localization of NCF1. As NCF1 is a subunit of the NADPH oxidase 2 (NOX2) complex, this impairment led to an acidified endosomal pH and facilitated downstream TLR signaling. Consistently, the homozygous knockin mice manifested aggravated lupus progression in a pDC-dependent lupus model. More important, pharmaceutical intervention revealed that hydroxychloroquine (HCQ) could antagonize the detrimental function of NCF1 p.R90H in the lupus model and systemic lupus erythematosus samples, supporting the idea that NCF1 p.R90H could be identified as a genetic biomarker for HCQ application. Therefore, our study provides insights into the genetic control of pDC function and a paradigm for applying genetic variants to improve targeted therapy for autoimmune diseases.

Molecularly Imprinted Polymers Exhibit Low Cytotoxic and Inflammatory Properties in Macrophages In Vitro

Molecularly imprinted polymers (MIPs) against sialic acid (SA) have been developed as a detection tool to target cancer cells. Before proceeding to in vivo studies, a better knowledge of the overall effects of MIPs on the innate immune system is needed. The aim of this study thus was to exemplarily assess whether SA-MIPs lead to inflammatory and/or cytotoxic responses when administered to phagocytosing cells in the innate immune system. The response of monocytic/macrophage cell lines to two different reference particles, Alhydrogel and PLGA, was compared to their response to SA-MIPs. In vitro culture showed a cellular association of SA-MIPs and Alhydrogel, as analyzed by flow cytometry. The reference particle Alhydrogel induced secretion of IL-1β from the monocytic cell line THP-1, whereas almost no secretion was provoked for SA-MIPs. A reduced number of both THP-1 and RAW 264.7 cells were observed after incubation with SA-MIPs and this was not caused by cytotoxicity. Digital holographic cytometry showed that SA-MIP treatment affected cell division, with much fewer cells dividing. Thus, the reduced number of cells after SA-MIP treatment was not linked to SA-MIPs cytotoxicity. In conclusion, SA-MIPs have a low degree of inflammatory properties, are not cytotoxic, and can be applicable for future in vivo studies.

Efferocytosis requires periphagosomal Ca2+-signaling and TRPM7-mediated electrical activity

Efficient clearance of apoptotic cells by phagocytosis, also known as efferocytosis, is fundamental to developmental biology, organ physiology, and immunology. Macrophages use multiple mechanisms to detect and engulf apoptotic cells, but the signaling pathways that regulate the digestion of the apoptotic cell cargo, such as the dynamic Ca²⁺ signals, are poorly understood. Using an siRNA screen, we identify TRPM7 as a Ca²⁺-conducting ion channel essential for phagosome maturation during efferocytosis. Trpm7-targeted macrophages fail to fully acidify or digest their phagosomal cargo in the absence of TRPM7. Through perforated patch electrophysiology, we demonstrate that TRPM7 mediates a pH-activated cationic current necessary to sustain phagosomal acidification. Using mice expressing a genetically-encoded Ca²⁺ sensor, we observe that phagosome maturation requires peri-phagosomal Ca²⁺-signals dependent on TRPM7. Overall, we reveal TRPM7 as a central regulator of phagosome maturation during macrophage efferocytosis.

Efficient removal of apoptotic cells by phagocytosis underlies tissue development, wound repair, host defense and organ homeostasis. Here, authors identify TRPM7 as a regulator of cargo acidification and Ca2+ signaling during apoptotic cell clearance.

Recent Advances in Host-Directed Therapies for Tuberculosis and Malaria

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, and malaria, caused by parasites from the Plasmodium genus, are two of the major causes of death due to infectious diseases in the world. Both diseases are treatable with drugs that have microbicidal properties against each of the etiologic agents. However, problems related to treatment compliance by patients and emergence of drug resistant microorganisms have been a major problem for combating TB and malaria. This factor is further complicated by the absence of highly effective vaccines that can prevent the infection with either M. tuberculosis or Plasmodium. However, certain host biological processes have been found to play a role in the promotion of infection or in the pathogenesis of each disease. These processes can be targeted by host-directed therapies (HDTs), which can be administered in conjunction with the standard drug treatments for each pathogen, aiming to accelerate their elimination or to minimize detrimental side effects resulting from exacerbated inflammation. In this review we discuss potential new targets for the development of HDTs revealed by recent advances in the knowledge of host-pathogen interaction biology, and present an overview of strategies that have been tested in vivo, either in experimental models or in patients.