The life cycle of phagosomes: formation, maturation, and resolution

Differential phagocytic expression of IC-21 macrophages and their scavenging receptors during inflammatory induction by oxysterol: A microscopic approach

Phagocytosis by macrophages dates back to a long history in science, this present study deals with new approaches that have been analyzed and standardized towards the interesting aspects of primary and secondary macrophages. The distinct morphological differences in primary and secondary phagocytic cells were observed and the phagocytic response of secondary macrophages under the influence of 7-ketocholesterol and lipopolysaccharide was analyzed. The primary peritoneal and secondary IC-21 cells unveiled explicit differences in nuclear numbers shapes and sizes of the granules present within the cytoplasmic region. Further, potent inducers 7KCh and LPS influenced an effective activation of IC-21 macrophages and resulted in ROS generation, irregulated protein expressions of CD86, CD68, and CD206 with enhanced phagocytic responses towards goat, cow, and human RBC targets with significant phagocytic rate and index were observed. Moreover, a remarkable observation of target specificity and aggregations with IC-21 phagocytic macrophages revealed the notion that specific membrane receptors and secretory molecules (lysosomes) are primarily involved in their phagocytic mechanism. RESEARCH HIGHLIGHTS: IC-21 macrophages are peritoneal origin from mice but the primary peritoneal macrophages and cell line show distinct differences. IC-21 macrophages express target-specific phagocytosis. Phagocytosis in IC-21 macrophages is regulated by CD markers (68, 86, and 206).

Loss of Gre factors leads to phenotypic heterogeneity and cheating in Escherichia coli populations under nitric oxide stress

Nitric oxide (·NO) is one of the toxic metabolites that bacteria can be exposed to within phagosomes. Gre factors, which are also known as transcript cleavage factors or transcription elongation factors, relieve back-tracked transcription elongation complexes by cleaving nascent RNAs, which allows transcription to resume after stalling. Here we discovered that loss of both Gre factors in Escherichia coli, GreA and GreB, significantly compromised ·NO detoxification due to ·NO-induced phenotypic heterogeneity in ΔgreAΔgreB populations, which did not occur in wild-type cultures. Under normal culturing conditions, both wild-type and ΔgreAΔgreB synthesized transcripts uniformly, whereas treatment with ·NO led to bimodal transcript levels in ΔgreAΔgreB that were unimodal in wild-type. Interestingly, exposure to another toxic metabolite of phagosomes, hydrogen peroxide (H2O2), produced analogous results. Furthermore, we showed that loss of Gre factors led to cheating under ·NO stress where transcriptionally deficient cells benefited from the detoxification activities of the transcriptionally proficient subpopulation. Collectively, these results show that loss of Gre factor activities produces phenotypic heterogeneity under ·NO and H2O2 stress that can yield cheating between subpopulations.IMPORTANCEToxic metabolite stress occurs in a broad range of contexts that are important to human health, microbial ecology, and biotechnology, whereas Gre factors are highly conserved throughout the bacterial kingdom. Here we discovered that loss of Gre factors in E. coli leads to phenotypic heterogeneity under ·NO and H2O2 stress, which we further show with ·NO results in cheating between subpopulations. Collectively, these data suggest that Gre factors play a role in coping with toxic metabolite stress, and that loss of Gre factors can produce cheating between neighbors.

Current methodologies available to evaluate the virulence potential among Listeria monocytogenes clonal complexes

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans, the severity of which depends on multiple factors, including intrinsic characteristics of the affected individuals and the pathogen itself. Additionally, emerging evidence suggests that epigenetic modifications may also modulate host susceptibility to infection. Therefore, different clinical outcomes can be expected, ranging from self-limiting gastroenteritis to severe central nervous system and maternal-neonatal infections, and bacteremia. Furthermore, L. monocytogenes is a genetically and phenotypically diverse species, resulting in a large variation in virulence potential between strains. Multilocus sequence typing (MLST) has been widely used to categorize the clonal structure of bacterial species and to define clonal complexes (CCs) of genetically related isolates. The combination of MLST and epidemiological data allows to distinguish hypervirulent CCs, which are notably more prevalent in clinical cases and typically associated with severe forms of the disease. Conversely, other CCs, termed hypovirulent, are predominantly isolated from food and food processing environments and are associated with the occurrence of listeriosis in immunosuppressed individuals. Reports of genetic traits associated with this diversity have been described. The Food and Agriculture Organization (FAO) is encouraging the search for virulence biomarkers to rapidly identify the main strains of concern to reduce food waste and economical losses. The aim of this review is to comprehensively collect, describe and discuss the methodologies used to discriminate the virulence potential of L. monocytogenes CCs. From the exploration of in vitro and in vivo models to the study of expression of virulence genes, each approach is critically explored to better understand its applicability and efficiency in distinguishing the virulence potential of the pathogen.

Macrophage variants in laboratory research: most are well done, but some are RAW

Macrophages play a pivotal role in the innate immune response. While their most characteristic function is phagocytosis, it is important not to solely characterize macrophages by this activity. Their crucial roles in body development, homeostasis, repair, and immune responses against pathogens necessitate a broader understanding. Macrophages exhibit remarkable plasticity, allowing them to modify their functional characteristics in response to the tissue microenvironment (tissue type, presence of pathogens or inflammation, and specific signals from neighboring cells) swiftly. While there is no single defined "macrophage" entity, there is a diverse array of macrophage types because macrophage ontogeny involves the differentiation of progenitor cells into tissue-resident macrophages, as well as the recruitment and differentiation of circulating monocytes in response to tissue-specific cues. In addition, macrophages continuously sense and respond to environmental cues and tissue conditions, adjusting their functional and metabolic states accordingly. Consequently, it is of paramount importance to comprehend the heterogeneous origins and functions of macrophages employed in in vitro studies, as each available in vitro macrophage model is associated with specific sets of strengths and limitations. This review centers its attention on a comprehensive comparison between immortalized mouse macrophage cell lines and primary mouse macrophages. It provides a detailed analysis of the strengths and weaknesses inherent in these in vitro models. Finally, it explores the subtle distinctions between diverse macrophage cell lines, offering insights into numerous factors beyond the model type that can profoundly influence macrophage function.

Pathobiology of Fungal Endophthalmitis: A Major Review

Fungal endophthalmitis is a chronic inflammatory condition of the eye's posterior segment that can lead to irreversible vision loss. While relatively rare in western countries, its incidence is notably higher in Asia, particularly India. The condition's prevalence is exacerbated by factors such as intravenous drug use, antibiotics, and ocular surgeries. Fungal endophthalmitis can be categorized as endogenous, arising from systemic infection, or exogenous, linked to external sources such as trauma or surgery. The fungal agents responsible vary by region, with Candida species common in the West and Aspergillus and Fusarium species more prevalent in India. Management typically involves vitrectomy and intravitreal antifungal drugs such as amphotericin B and voriconazole, though treatment is often complicated by multidrug resistance and culture-negative cases. Recent proteomic and transcriptomic analyses have highlighted the early and sustained activation of the host immune response during infection involving key inflammatory and oxidative stress-related proteins. Given the potential for excessive inflammation to cause retinal damage, targeted immunotherapies are crucial. Immunomodulation, which aims to balance the immune response, shows promise in preserving vision while effectively combating the infection. Key targets for immunomodulation include pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, IL-17), chemokines (CCL2, CXCL8), Toll-like receptors (TLR2, TLR4), and the complement system. Additionally, modulating the activity of macrophages, neutrophils, regulatory T cells, and Th17 cells, as well as targeting inflammasomes, can help control inflammation. Biologic agents and small molecule inhibitors offer further avenues for precise immune response modulation. This review underscores the importance of a comprehensive understanding of host-pathogen interactions in the development of effective therapies for fungal endophthalmitis.

Bactericidal ability of target acidic phospholipids and phagocytosis of CDC42 GTPase-mediated cytoskeletal rearrangement underlie functional conservation of CXCL12 in vertebrates

Chemokine CXCL12 plays a crucial role in both direct bactericidal activity and phagocytosis in humans. However, the mechanisms and evolutionary functions of these processes in vertebrates remain largely unknown. In this study, we found that the direct bactericidal activity of CXCL12 is highly conserved across various vertebrate lineages, including Arctic lamprey (Lampetra japonica), Basking shark (Cetorhinus maximus), grass carp (Ctenopharyngodon idella), Western clawed frog (Xenopus tropicalis), Green anole (Anolis carolinensis), chicken (Gallus gallus), and human (Homo sapiens). CXCL12 also has been shown to promote phagocytosis in lower and higher vertebrates. We then employed C. idella CXCL12a (CiCXCL12a) as a model to further investigate its immune functions and underlying mechanisms. CiCXCL12a exerts direct broad-spectrum antibacterial activity by targeting bacterial acidic phospholipids, resulting in bacterial cell membrane perforation, and eventual lysis. Monocytes/macrophages are attracted to the infection sites for phagocytosis through the rapid production of CiCXCL12a during bacterial infection. CiCXCL12a induces CDC42 and CDC42 GTPase activation, which in turn mediates F-actin polymerization and cytoskeletal rearrangement. The interaction between F-actin and Aeromonas hydrophila facilitates bacterial internalization into monocytes/macrophages. Additionally, A. hydrophila is colocalized within early endosomes, late endosomes and lysosomes, ultimately degrading within phagolysosomes. CiCXCL12a also activates PI3K-AKT, JAK-STAT5 and MAPK-ERK signaling pathways. Notably, only the PI3K-AKT signaling pathway inhibits LPS-induced monocyte/macrophage apoptosis. Thus, CiCXCL12a plays key roles in reducing tissue bacterial loads, attenuating organ injury, and decreasing mortality rates. Altogether, our findings elucidate the conserved mechanisms underlying CXCL12-mediated bactericidal activity and phagocytosis, providing novel perspectives into the immune functions of CXCL12 in vertebrates.

Fc-FcγR interactions during infections: From neutralizing antibodies to antibody-dependent enhancement

Advances in antibody technologies have resulted in the development of potent antibody-based therapeutics with proven clinical efficacy against infectious diseases. Several monoclonal antibodies (mAbs), mainly against viruses such as SARS-CoV-2, HIV-1, Ebola virus, influenza virus, and hepatitis B virus, are currently undergoing clinical testing or are already in use. Although these mAbs exhibit potent neutralizing activity that effectively blocks host cell infection, their antiviral activity results not only from Fab-mediated virus neutralization, but also from the protective effector functions mediated through the interaction of their Fc domains with Fcγ receptors (FcγRs) on effector leukocytes. Fc-FcγR interactions confer pleiotropic protective activities, including the clearance of opsonized virions and infected cells, as well as the induction of antiviral T-cell responses. However, excessive or inappropriate activation of specific FcγR pathways can lead to disease enhancement and exacerbated pathology, as seen in the context of dengue virus infections. A comprehensive understanding of the diversity of Fc effector functions during infection has guided the development of engineered antiviral antibodies optimized for maximal effector activity, as well as the design of targeted therapeutic approaches to prevent antibody-dependent enhancement of disease.

Cellular Uptake of Phase-Separating Peptide Coacervates

Peptide coacervates self-assembling via liquid-liquid phase separation are appealing intracellular delivery vehicles of macromolecular therapeutics (proteins, DNA, mRNA) owing to their non-cytotoxicity, high encapsulation capacity, and efficient cellular uptake. However, the mechanisms by which these viscoelastic droplets cross the cellular membranes remain unknown. Here, using multimodal imaging, data analytics, and biochemical inhibition assays, identify the key steps by which droplets enter the cell. find that the uptake follows a non-canonical pathway and instead integrates essential features of macropinocytosis and phagocytosis, namely active remodeling of the actin cytoskeleton and appearance of filopodia-like protrusions. Experiments using giant unilamellar vesicles show that the coacervates attach to the bounding membrane in a charge- and cholesterol-dependent manner but do not breach the lipid bilayer barrier. Cell uptake in the presence of small molecule inhibitors - interfering with actin and tubulin polymerization - confirm the active role of cytoskeleton remodeling, most prominently evident in electron microscopy imaging. These findings suggest a peculiar internalization mechanism for viscoelastic, glassy coacervate droplets combining features of non-specific uptake of fluids by macropinocytosis and particulate uptake of phagocytosis. The broad implications of this study will enable to enhance the efficacy and utility of coacervate-based strategies for intracellular delivery of macromolecular therapeutics.

Transcriptomic responses to shifts in light and nitrogen in two congeneric diatom species

Light and nitrogen availability are basic requirements for photosynthesis. Changing in light intensity and nitrogen concentration may require adaptive physiological and life process changes in phytoplankton cells. Our previous study demonstrated that two Thalassiosira species exhibited, respectively, distinctive physiological responses to light and nitrogen stresses. Transcriptomic analyses were employed to investigate the mechanisms behind the different physiological responses observed in two diatom species of the genus Thalassiosira. The results indicate that the congeneric species are different in their cellular responses to the same shifting light and nitrogen conditions. When conditions changed to high light with low nitrate (HLLN), the large-celled T. punctigera was photodamaged. Thus, the photosynthesis pathway and carbon fixation related genes were significantly down-regulated. In contrast, the small-celled T. pseudonana sacrificed cellular processes, especially amino acid metabolisms, to overcome the photodamage. When changing to high light with high nitrate (HLHN) conditions, the additional nitrogen appeared to compensate for the photodamage in the large-celled T. punctigera, with the tricarboxylic acid cycle (TCA cycle) and carbon fixation significantly boosted. Consequently, the growth rate of T. punctigera increased, which suggest that the larger-celled species is adapted for forming post-storm algal blooms. The impact of high light stress on the small-celled T. pseudonana was not mitigated by elevated nitrate levels, and photodamage persisted.

Bacteria extracellular vesicle as nanopharmaceuticals for versatile biomedical potential

Bacteria extracellular vesicles (BEVs), characterized as the lipid bilayer membrane-surrounded nanoparticles filled with molecular cargo from parent cells, play fundamental roles in the bacteria growth and pathogenesis, as well as facilitating essential interaction between bacteria and host systems. Notably, benefiting from their unique biological functions, BEVs hold great promise as novel nanopharmaceuticals for diverse biomedical potential, attracting significant interest from both industry and academia. Typically, BEVs are evaluated as promising drug delivery platforms, on account of their intrinsic cell-targeting capability, ease of versatile cargo engineering, and capability to penetrate physiological barriers. Moreover, attributing to considerable intrinsic immunogenicity, BEVs are able to interact with the host immune system to boost immunotherapy as the novel nanovaccine against a wide range of diseases. Towards these significant directions, in this review, we elucidate the nature of BEVs and their role in activating host immune response for a better understanding of BEV-based nanopharmaceuticals' development. Additionally, we also systematically summarize recent advances in BEVs for achieving the target delivery of genetic material, therapeutic agents, and functional materials. Furthermore, vaccination strategies using BEVs are carefully covered, illustrating their flexible therapeutic potential in combating bacterial infections, viral infections, and cancer. Finally, the current hurdles and further outlook of these BEV-based nanopharmaceuticals will also be provided.

Triggers, cascades, and endpoints: connecting the dots of coral bleaching mechanisms

The intracellular coral-dinoflagellate symbiosis is the engine that underpins the success of coral reefs, one of the most diverse ecosystems on the planet. However, the breakdown of the symbiosis and the loss of the microalgal symbiont (i.e. coral bleaching) due to environmental changes are resulting in the rapid degradation of coral reefs globally. There is an urgent need to understand the cellular physiology of coral bleaching at the mechanistic level to help develop solutions to mitigate the coral reef crisis. Here, at an unprecedented scope, we present novel models that integrate putative mechanisms of coral bleaching within a common framework according to the triggers (initiators of bleaching, e.g. heat, cold, light stress, hypoxia, hyposalinity), cascades (cellular pathways, e.g. photoinhibition, unfolded protein response, nitric oxide), and endpoints (mechanisms of symbiont loss, e.g. apoptosis, necrosis, exocytosis/vomocytosis). The models are supported by direct evidence from cnidarian systems, and indirectly through comparative evolutionary analyses from non-cnidarian systems. With this approach, new putative mechanisms have been established within and between cascades initiated by different bleaching triggers. In particular, the models provide new insights into the poorly understood connections between bleaching cascades and endpoints and highlight the role of a new mechanism of symbiont loss, i.e. 'symbiolysosomal digestion', which is different from symbiophagy. This review also increases the approachability of bleaching physiology for specialists and non-specialists by mapping the vast landscape of bleaching mechanisms in an atlas of comprehensible and detailed mechanistic models. We then discuss major knowledge gaps and how future research may improve the understanding of the connections between the diverse cascade of cellular pathways and the mechanisms of symbiont loss (endpoints).

Innate immune signal transduction pathways to fungal infection: Components and regulation

Candida species are significant causes of mucosal and systemic infections in immune compromised populations, including HIV-infected individuals and cancer patients. Drug resistance and toxicity have limited the use of anti-fungal drugs. A good comprehension of the nature of the immune responses to the pathogenic fungi will aid in the developing of new approaches to the treatment of fungal diseases. In recent years, extensive research has been done to understand the host defending systems to fungal infections. In this review, we described how pattern recognition receptors senses the cognate fungal ligands and the cellular and molecular mechanisms of anti-fungal innate immune responses. Furthermore, particular focus is placed on how anti-fungal signal transduction cascades are being activated for host defense and being modulated to better treat the infections in terms of immunotherapy. Understanding the role that these pathways have in mediating host anti-fungal immunity will be crucial for future therapeutic development.

Recent advances in molecular mechanisms of skin wound healing and its treatments

The skin, being a multifaceted organ, performs a pivotal function in the complicated wound-healing procedure, which encompasses the triggering of several cellular entities and signaling cascades. Aberrations in the typical healing process of wounds may result in atypical scar development and the establishment of a persistent condition, rendering patients more vulnerable to infections. Chronic burns and wounds have a detrimental effect on the overall quality of life of patients, resulting in higher levels of physical discomfort and socio-economic complexities. The occurrence and frequency of prolonged wounds are on the rise as a result of aging people, hence contributing to escalated expenditures within the healthcare system. The clinical evaluation and treatment of chronic wounds continue to pose challenges despite the advancement of different therapeutic approaches. This is mainly owing to the prolonged treatment duration and intricate processes involved in wound healing. Many conventional methods, such as the administration of growth factors, the use of wound dressings, and the application of skin grafts, are used to ease the process of wound healing across diverse wound types. Nevertheless, these therapeutic approaches may only be practical for some wounds, highlighting the need to advance alternative treatment modalities. Novel wound care technologies, such as nanotherapeutics, stem cell treatment, and 3D bioprinting, aim to improve therapeutic efficacy, prioritize skin regeneration, and minimize adverse effects. This review provides an updated overview of recent advancements in chronic wound healing and therapeutic management using innovative approaches.

ATAT1 deficiency enhances microglia/macrophage-mediated erythrophagocytosis and hematoma absorption following intracerebral hemorrhage

MIcroglia/macrophage-mediated erythrophagocytosis plays a crucial role in hematoma clearance after intracerebral hemorrhage. Dynamic cytoskeletal changes accompany phagocytosis. However, whether and how these changes are associated with microglia/macrophage-mediated erythrophagocytosis remain unclear. In this study, we investigated the function of acetylated α-tubulin, a stabilized microtubule form, in microglia/macrophage erythrophagocytosis after intracerebral hemorrhage both in vitro and in vivo. We first assessed the function of acetylated α-tubulin in erythrophagocytosis using primary DiO GFP-labeled red blood cells co-cultured with the BV2 microglia or RAW264.7 macrophage cell lines. Acetylated α-tubulin expression was significantly decreased in BV2 and RAW264.7 cells during erythrophagocytosis. Moreover, silencing α-tubulin acetyltransferase 1 (ATAT1), a newly discovered α-tubulin acetyltransferase, decreased Ac-α-tub levels and enhanced the erythrophagocytosis by BV2 and RAW264.7 cells. Consistent with these findings, in ATAT1-/- mice, we observed increased ionized calcium binding adapter molecule 1 (Iba1) and Perls-positive microglia/macrophage phagocytes of red blood cells in peri-hematoma and reduced hematoma volume in mice with intracerebral hemorrhage. Additionally, knocking out ATAT1 alleviated neuronal apoptosis and pro-inflammatory cytokines and increased anti-inflammatory cytokines around the hematoma, ultimately improving neurological recovery of mice after intracerebral hemorrhage. These findings suggest that ATAT1 deficiency accelerates erythrophagocytosis by microglia/macrophages and hematoma absorption after intracerebral hemorrhage. These results provide novel insights into the mechanisms of hematoma clearance and suggest ATAT1 as a potential target for the treatment of intracerebral hemorrhage.

Neutrophils versus Protozoan Parasites: Plasmodium, Trichomonas, Leishmania, Trypanosoma, and Entameoba

Neutrophils are the most abundant polymorphonuclear granular leukocytes in human blood and are an essential part of the innate immune system. Neutrophils are efficient cells that eliminate pathogenic bacteria and fungi, but their role in dealing with protozoan parasitic infections remains controversial. At sites of protozoan parasite infections, a large number of infiltrating neutrophils is observed, suggesting that neutrophils are important cells for controlling the infection. Yet, in most cases, there is also a strong inflammatory response that can provoke tissue damage. Diseases like malaria, trichomoniasis, leishmaniasis, Chagas disease, and amoebiasis affect millions of people globally. In this review, we summarize these protozoan diseases and describe the novel view on how neutrophils are involved in protection from these parasites. Also, we present recent evidence that neutrophils play a double role in these infections participating both in control of the parasite and in the pathogenesis of the disease.

Comparative transcriptomics reveals common and strain-specific responses of human macrophages to infection with Mycobacterium tuberculosis and Mycobacterium bovis BCG

Mycobacterium tuberculosis (MTB) and Mycobacterium bovis (M. bovis) are closely related pathogenic mycobacteria known to cause chronic pulmonary infections in both humans and animals. Despite sharing nearly identical genomes and virulence factors, these two bacteria display variations in host tropism, epidemiology, and clinical presentations. M. bovis Bacillus Calmette-Guérin (BCG) is an attenuated strain of M. bovis commonly utilized as a vaccine for tuberculosis (TB). Nevertheless, the molecular underpinnings of these distinctions and the intricacies of host-pathogen interactions remain areas of ongoing research. In this study, a comparative transcriptomic analysis was conducted on human leukemia macrophages (THP-1) infected with either MTB H37Rv or M. bovis BCG (Tokyo strain) to elucidate common and strain-specific responses at the transcriptional level. RNA sequencing was utilized to characterize the transcriptomes of human primary macrophages infected with MTB or BCG at 6 and 24 h post-infection. The findings indicate that both MTB and BCG induce substantial and dynamic alterations in the transcriptomes of THP-1, with a notable overlap in the quantity and extent of differentially expressed genes (DEGs). Moreover, gene ontology (GO) enrichment analysis unveiled shared pathways related to immune response, cytokine signaling, and apoptosis. The immune response of macrophages to bacterial infections at 6 h exhibited significantly greater intensity compared to that at 24 h. Furthermore, distinct gene sets displaying notable variances between MTB and BCG infections were identified. The profound impact of MTB infection on macrophage gene expression, particularly within the initial 6 h, was evident. Additionally, downregulation of pathways such as Focal adhesion, Rap1 signaling pathway, and Regulation of actin cytoskeleton was observed. The pathways associated with inflammation reactions and cell apoptosis exhibited significant differences, with BCG triggering macrophage apoptosis and MTB enhancing the survival of intracellular bacteria. Our findings reveal that MTB and BCG provoke similar yet distinct transcriptional responses in human macrophages, indicating variations in their pathogenesis and ability to adapt to host environments. These results offer novel insights into the molecular mechanisms governing host-pathogen interactions and may contribute to a deeper understanding of TB pathogenesis.

Development of Genetically Encoded Fluorescent KSR1-Based Probes to Track Ceramides during Phagocytosis

Ceramides regulate phagocytosis; however, their exact function remains poorly understood. Here, we sought (1) to develop genetically encoded fluorescent tools for imaging ceramides, and (2) to use them to examine ceramide dynamics during phagocytosis. Fourteen enhanced green fluorescent protein (EGFP) fusion constructs based on four known ceramide-binding domains were generated and screened. While most constructs localized to the nucleus or cytosol, three based on the CA3 ceramide-binding domain of kinase suppressor of ras 1 (KSR1) localized to the plasma membrane or autolysosomes. C-terminally tagged CA3 with a vector-based (C-KSR) or glycine-serine linker (C-KSR-GS) responded sensitively and similarly to ceramide depletion and accumulation using a panel of ceramide modifying drugs, whereas N-terminally tagged CA3 (N-KSR) responded differently to a subset of treatments. Lipidomic and liposome microarray analysis suggested that, instead, N-KSR may preferentially bind glucosyl-ceramide. Additionally, the three probes showed distinct dynamics during phagocytosis. Despite partial autolysosomal degradation, C-KSR and C-KSR-GS accumulated at the plasma membrane during phagocytosis, whereas N-KSR did not. Moreover, the weak recruitment of C-KSR-GS to the endoplasmic reticulum and phagosomes was enhanced through overexpression of the endoplasmic reticulum proteins stromal interaction molecule 1 (STIM1) and Sec22b, and was more salient in dendritic cells. The data suggest these novel probes can be used to analyze sphingolipid dynamics and function in living cells.

Ninein promotes F-actin cup formation and inward phagosome movement during phagocytosis in macrophages

Phagocytosis by macrophages is a highly polarized process to destroy large target cells. Binding to particles induces extensive cortical actin-generated forces that drive the formation of elaborate pseudopods around the target particle. Postinternalization, the resultant phagosome is driven toward the cell interior on microtubules (MTs) by cytoplasmic dynein. However, it is unclear whether dynein and cargo-adaptors contribute to the earlier steps of particle internalization and phagosome formation. Here we reveal that ninein, a MT minus-end-associated protein that localizes to the centrosome, is also present at the phagocytic cup in macrophages. Ninein depletion impairs particle internalization by delaying the early F-actin recruitment to sites of particle engagement and cup formation, with no impact on F-actin dynamics beyond this initial step. Ninein forms membrane-bound clusters on phagocytic cups that do not nucleate acentrosomal MTs but instead mediate the assembly of dynein-dynactin complex at active phagocytic membranes. Both ninein depletion and pharmacological inhibition of dynein activity reduced inward displacement of bound particles into macrophages. We found that ninein and dynein motor activity were required for timely retrograde movement of phagosomes and for phagolysosome formation. Taken together, these data show that ninein, alone and with dynein, play significant roles during phagocytosis.

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.

Salmonella actively modulates TFEB in murine macrophages in a growth-phase and time-dependent manner

IMPORTANCE

Activation of the host transcription factor TFEB helps mammalian cells adapt to stresses such as starvation and infection by upregulating lysosome, autophagy, and immuno-protective gene expression. Thus, TFEB is generally thought to protect host cells. However, it may also be that pathogenic bacteria like Salmonella orchestrate TFEB in a spatio-temporal manner to harness its functions to grow intracellularly. Indeed, the relationship between Salmonella and TFEB is controversial since some studies showed that Salmonella actively promotes TFEB, while others have observed that Salmonella degrades TFEB and that compounds that promote TFEB restrict bacterial growth. Our work provides a path to resolve these apparent discordant observations since we showed that stationary-grown Salmonella actively delays TFEB after infection, while late-log Salmonella is permissive of TFEB activation. Nevertheless, the exact function of this manipulation remains unclear, but conditions that erase the conditional control of TFEB by Salmonella may be detrimental to the microbe.

Quantitative Analysis of the Inactivation Process of Internalized Bacteria in Dictyostelium Cells

The understanding of the inactivation process of ingested bacteria by phagocytes is a key focus in the field of host-pathogen interactions. Dictyostelium is a model organism that has been at the forefront of uncovering the mechanisms underlying this type of interaction. In this study, we describe an assay designed to measure the inactivation of Klebsiella aerogenes in the phagosomes of Dictyostelium discoideum.

Phagocytosis

One hundred years have passed since the death of Élie Metchnikoff (1845-1916). He was the first to observe the uptake of particles by cells and realized the importance of this process, named phagocytosis, for the host response to injury and infection. He also was a strong advocate of the role of phagocytosis in cellular immunity, and with this, he gave us the basis for our modern understanding of inflammation and the innate immune response. Phagocytosis is an elegant but complex process for the ingestion and elimination of pathogens, but it is also important for the elimination of apoptotic cells and hence fundamental for tissue homeostasis. Phagocytosis can be divided into four main steps: (i) recognition of the target particle, (ii) signaling to activate the internalization machinery, (iii) phagosome formation, and (iv) phagolysosome maturation. In this chapter, we present a general view of our current knowledge on phagocytosis performed mainly by professional phagocytes through antibody and complement receptors and discuss aspects that remain incompletely understood.

Extracellular and intracellular destruction of Pseudomonas aeruginosa by Dictyostelium discoideum phagocytes mobilize different antibacterial mechanisms

Ingestion and killing of bacteria by phagocytic cells are critical processes to protect the human body from bacterial infections. In addition, some immune cells (neutrophils, NK cells) can release microbicidal molecules in the extracellular medium to eliminate non-ingested microorganism. Molecular mechanisms involved in the resulting intracellular and extracellular killing are still poorly understood. In this study, we used the amoeba Dictyostelium discoideum as a model phagocyte to investigate the mechanisms allowing intracellular and extracellular killing of Pseudomonas aeruginosa. When a D. discoideum cell establishes a close contact with a P. aeruginosa bacterium, it can either ingest it and kill it in phagosomes, or kill it extracellularly, allowing a direct side-by-side comparison of these two killing modalities. Efficient intracellular destruction of P. aeruginosa requires the presence of the Kil2 pump in the phagosomal membrane. On the contrary, extracellular lysis is independent on Kil2 but requires the expression of the superoxide-producing protein NoxA, and the extracellular release of the AplA bacteriolytic protein. These results shed new light on the molecular mechanisms allowing elimination of P. aeruginosa bacteria by phagocytic cells.

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.

Effect of Punicalagin and Ellagic Acid on Human Fibroblasts In Vitro: A Preliminary Evaluation of Their Therapeutic Potential

BACKGROUND

Pomegranate is a fruit that contains various phenolic compounds, including punicalagin and ellagic acid, which have been attributed to anti-inflammatory, antioxidant, and anticarcinogenic properties, among others.

OBJECTIVE

To evaluate the effect of punicalagin and ellagic acid on the viability, migration, cell cycle, and antigenic profile of cultured human fibroblasts (CCD-1064Sk). MTT spectrophotometry was carried out to determine cell viability, cell culture inserts were used for migration trials, and flow cytometry was performed for antigenic profile and cell cycle analyses. Cells were treated with each phenolic compound for 24 h at doses of 10-5 to 10-9 M.

RESULTS

Cell viability was always significantly higher in treated versus control cells except for punicalagin at 10-9 M. Doses of punicalagin and ellagic acid in subsequent assays were 10-6 M or 10-7 M, which increased the cell migration capacity and upregulated fibronectin and α-actin expression without altering the cell cycle.

CONCLUSIONS

These in vitro findings indicate that punicalagin and ellagic acid promote fibroblast functions that are involved in epithelial tissue healing.

Deciphering the mechanism of action of VP343, an antileishmanial drug candidate, in Leishmania infantum

Antileishmanial chemotherapy is currently limited due to severe toxic side effects and drug resistance. Hence, new antileishmanial compounds based on alternative approaches, mainly to avoid the emergence of drug resistance, are needed. The present work aims to decipher the mechanism of action of an antileishmanial drug candidate, named VP343, inhibiting intracellular Leishmania infantum survival via the host cell. Cell imaging showed that VP343 interferes with the fusion of parasitophorous vacuoles and host cell late endosomes and lysosomes, leading to lysosomal cholesterol accumulation and ROS overproduction within host cells. Proteomic analyses showed that VP343 perturbs host cell vesicular trafficking as well as cholesterol synthesis/transport pathways. Furthermore, a knockdown of two selected targets involved in vesicle-mediated transport, Pik3c3 and Sirt2, resulted in similar antileishmanial activity to VP343 treatment. This work revealed potential host cell pathways and targets altered by VP343 that would be of interest for further development of host-directed antileishmanial drugs.

Dectin-1/CARD9 induction of the TFEB and TFE3 gene network is dispensable for phagocyte anti-Aspergillus activity in the lung

Myeloid phagocytes of the respiratory immune system, such as neutrophils, monocytes, and alveolar macrophages, are essential for immunity to Aspergillus fumigatus, the most common etiologic agent of mold pneumonia worldwide. Following the engulfment of A. fumigatus conidia, fusion of the phagosome with the lysosome is a critical process for killing conidia. TFEB and TFE3 are transcription factors that regulate lysosomal biogenesis under stress and are activated by inflammatory stimuli in macrophages, but it is unknown whether TFEB and TFE3 contribute to anti-Aspergillus immunity during infection. We found that lung neutrophils express TFEB and TFE3, and their target genes were upregulated during A. fumigatus lung infection. In addition, A. fumigatus infection induced nuclear accumulation of TFEB and TFE3 in macrophages in a process regulated by Dectin-1 and CARD9. Genetic deletion of Tfeb and Tfe3 impaired macrophage killing of A. fumigatus conidia. However, in a murine immune-competent Aspergillus infection model with genetic deficiency of Tfeb and Tfe3 in hematopoietic cells, we surprisingly found that lung myeloid phagocytes had no defects in conidial phagocytosis or killing. Loss of TFEB and TFE3 did not impact murine survival or clearance of A. fumigatus from the lungs. Our findings indicate that myeloid phagocytes activate TFEB and TFE3 in response to A. fumigatus, and while this pathway promotes macrophage fungicidal activity in vitro, genetic loss can be functionally compensated in the lung, resulting in no measurable defect in fungal control and host survival.

Pharmacological inhibition of TRPV2 attenuates phagocytosis and lipopolysaccharide-induced migration of primary macrophages

BACKGROUND AND PURPOSE

In macrophages, transient receptor potential vanilloid 2 (TRPV2) channel contributes to various cellular processes such as cytokine production, differentiation, phagocytosis and migration. Due to a lack of selective pharmacological tools, its function in immunological processes is not well understood and the identification of novel and selective TRPV2 modulators is highly desirable.

EXPERIMENTAL APPROACH

Novel and selective TRPV2 modulators were identified by screening a compound library using Ca2+ influx assays with human embryonic kidney 293 (HEK293) cells heterologously expressing rat TRPV2. Hits were further characterized and validated with Ca2+ influx and electrophysiological assays. Phagocytosis and migration of macrophages were analysed and the contribution of TRPV2 to the generation of Ca2+ microdomains was studied by total internal reflection fluorescence microscopy (TIRFM).

KEY RESULTS

The compound IV2-1, a dithiolane derivative (1,3-dithiolan-2-ylidene)-4-methyl-5-phenylpentan-2-one), is a potent inhibitor of heterologously expressed TRPV2 channels (IC50  = 6.3 ± 0.7 μM) but does not modify TRPV1, TRPV3 or TRPV4 channels. IV2-1 also inhibits TRPV2-mediated Ca2+ influx in macrophages. IV2-1 inhibits macrophage phagocytosis along with valdecoxib and after siRNA-mediated knockdown. Moreover, TRPV2 inhibition inhibits lipopolysaccharide-induced migration of macrophages whereas TRPV2 activation promotes migration. After activation, TRPV2 shapes Ca2+ microdomains predominantly at the margin of macrophages, which are important cellular regions to promote phagocytosis and migration.

CONCLUSIONS AND IMPLICATIONS

IV2-1 is a novel TRPV2-selective blocker and underline the role of TRPV2 in macrophage-mediated phagocytosis and migration. Furthermore, we provide evidence that TRPV2 activation generates Ca2+ microdomains, which may be involved in phagocytosis and migration of macrophages.

KIF16B drives MT1-MMP recycling in macrophages and promotes co-invasion of cancer cells

The matrix metalloproteinase MT1-MMP is a central effector of cellular proteolysis. Accordingly, regulation of the surface-localized pool of MT1-MMP is crucial for cell migration and invasion. Here, we identify the superprocessive kinesin KIF16B as a major driver of fast recycling of MT1-MMP to the surface of primary human macrophages. KIF16B associates with MT1-MMP on Rab14-positive vesicles, and its depletion results in strongly reduced MT1-MMP surface levels, as shown by microscopical, biochemical, and cell-sorting approaches. As a consequence, KIF16B-depleted macrophages exhibit strongly reduced matrix degradation and invasion. We further identify the cargo-binding C-terminus of KIF16B as a critical element of MT1-MMP transport, as its overexpression uncouples MT1-MMP vesicles from the endogenous motor, thus leading to a reduction of surface-associated MT1-MMP and to reduced matrix degradation and invasion. Importantly, depletion of KIF16B in primary macrophages also reduces the co-invasion of cancer cells from tumor spheroids, pointing to the KIF16B-driven recycling pathway in macrophages as an important regulatory element of the tumor microenvironment.

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.

The resolution of phagosomes

Phagocytosis is a fundamental immunobiological process responsible for the removal of harmful particulates. While the number of phagocytic events achieved by a single phagocyte can be remarkable, exceeding hundreds per day, the same phagocytic cells are relatively long-lived. It should therefore be obvious that phagocytic meals must be resolved in order to maintain the responsiveness of the phagocyte and to avoid storage defects. In this article, we discuss the mechanisms involved in the resolution process, including solute transport pathways and membrane traffic. We describe how products liberated in phagolysosomes support phagocyte metabolism and the immune response. We also speculate on mechanisms involved in the redistribution of phagosomal metabolites back to circulation. Finally, we highlight the pathologies owed to impaired phagosome resolution, which range from storage disorders to neurodegenerative diseases.

The Mycobacterium tuberculosis protein tyrosine phosphatase MptpA features a pH dependent activity overlapping the bacterium sensitivity to acidic conditions

The Mycobacterium tuberculosis low-molecular weight protein tyrosine phosphatase (MptpA) is responsible for the inhibition of phagosome-lysosome fusion and is essential for the bacterium pathogenicity. This inhibition implies that M. tuberculosis is not exposed to a strongly acidic environment in vivo, enabling successful propagation in host cells. Remarkably, MptpA has been previously structurally and functionally investigated, with special emphasis devoted to the enzyme properties at pH 8.0. Considering that the virulence of M. tuberculosis is strictly dependent on the avoidance of acidic conditions in vivo, we analysed the pH-dependence of the structural and catalytic properties of MptpA. Here we show that this enzyme undergoes pronounced conformational rearrangements when exposed to acidic pH conditions, inducing a severe decrease of the enzymatic catalytic efficiency at the expense of phosphotyrosine (pTyr). In particular, a mild decrease of pH from 6.5 to 6.0 triggers a significant increase of K0.5 of MptpA for phosphotyrosine, the phosphate group of which we determined to feature a pKa2 equal to 5.7. Surface plasmon resonance experiments confirmed that MptpA binds poorly to pTyr at pH values < 6.5. Notably, the effectiveness of the MptpA competitive inhibitor L335-M34 at pH 6 does largely outperform the inhibition exerted at neutral or alkaline pH values. Overall, our observations indicate a pronounced sensitivity of MptpA to acidic pH conditions, and suggest the search for competitive inhibitors bearing a negatively charged group featuring pKa values lower than that of the substrate phosphate group.

Host-directed therapy for bacterial infections -Modulation of the phagolysosome pathway

Bacterial infections still impose a significant burden on humanity, even though antimicrobial agents have long since been developed. In addition to individual severe infections, the f fatality rate of sepsis remains high, and the threat of antimicrobial-resistant bacteria grows with time, putting us at inferiority. Although tremendous resources have been devoted to the development of antimicrobial agents, we have yet to recover from the lost ground we have been driven into. Looking back at the evolution of treatment for cancer, which, like infectious diseases, has the similarity that host immunity eliminates the lesion, the development of drugs to eliminate the tumor itself has shifted from a single-minded focus on drug development to the establishment of a treatment strategy in which the de-suppression of host immunity is another pillar of treatment. In infectious diseases, on the other hand, the development of therapies that strengthen and support the immune system has only just begun. Among innate immunity, the first line of defense that bacteria encounter after invading the host, the molecular mechanisms of the phagolysosome pathway, which begins with phagocytosis to fusion with lysosome, have been elucidated in detail. Bacteria have a large number of strategies to escape and survive the pathway. Although the full picture is still unfathomable, the molecular mechanisms have been elucidated for some of them, providing sufficient clues for intervention. In this article, we review the host defense mechanisms and bacterial evasion mechanisms and discuss the possibility of host-directed therapy for bacterial infection by intervening in the phagolysosome pathway.

Fungal mechanisms of intracellular survival: what can we learn from bacterial pathogens?

Fungal infections represent a major, albeit neglected, public health threat with serious medical and economic burdens globally. With unacceptably high mortality rates, invasive fungal pathogens are responsible for millions of deaths each year, with a steadily increasing incidence primarily in immunocompromised individuals. The poor therapeutic options and rise of antifungal drug resistance pose further challenges in controlling these infections. These fungal pathogens have adapted to survive within mammalian hosts and can establish intracellular niches to promote survival within host immune cells. To do that, they have developed diverse methods to circumvent the innate immune system attack. This includes strategies such as altering their morphology, counteracting macrophage antimicrobial action, and metabolic adaptation. This is reminiscent of how bacterial pathogens have adapted to survive within host cells and cause disease. However, relative to the great deal of information available concerning intracellular bacterial pathogenesis, less is known about the mechanisms fungal pathogens employ. Therefore, here we review our current knowledge and recent advances in our understanding of how fungi can evade and persist within host immune cells. This review will focus on the major fungal pathogens, including Cryptococcus neoformans, Candida albicans, and Aspergillus fumigatus, among others. As we discover and understand the strategies used by these fungi, similarities with their bacterial counterparts are becoming apparent, hence we can use the abundant information from bacteria to guide our studies in fungi. By understanding these strategies, new lines of research will open that can improve the treatments of these devastating fungal diseases.

A PI(3,5)P2 reporter reveals PIKfyve activity and dynamics on macropinosomes and phagosomes

Phosphoinositide signaling lipids (PIPs) are key regulators of membrane identity and trafficking. Of these, PI(3,5)P2 is one of the least well-understood, despite key roles in many endocytic pathways including phagocytosis and macropinocytosis. PI(3,5)P2 is generated by the phosphoinositide 5-kinase PIKfyve, which is critical for phagosomal digestion and antimicrobial activity. However PI(3,5)P2 dynamics and regulation remain unclear due to lack of reliable reporters. Using the amoeba Dictyostelium discoideum, we identify SnxA as a highly selective PI(3,5)P2-binding protein and characterize its use as a reporter for PI(3,5)P2 in both Dictyostelium and mammalian cells. Using GFP-SnxA, we demonstrate that Dictyostelium phagosomes and macropinosomes accumulate PI(3,5)P2 3 min after engulfment but are then retained differently, indicating pathway-specific regulation. We further find that PIKfyve recruitment and activity are separable and that PIKfyve activation stimulates its own dissociation. SnxA is therefore a new tool for reporting PI(3,5)P2 in live cells that reveals key mechanistic details of the role and regulation of PIKfyve/PI(3,5)P2.

mTORC1 regulates phagosome digestion of symbiotic bacteria for intracellular nutritional symbiosis in a deep-sea mussel

Phagocytosis is one of the methods used to acquire symbiotic bacteria to establish intracellular symbiosis. A deep-sea mussel, Bathymodiolus japonicus, acquires its symbiont from the environment by phagocytosis of gill epithelial cells and receives nutrients from them. However, the manner by which mussels retain the symbiont without phagosome digestion remains unknown. Here, we show that controlling the mechanistic target of rapamycin complex 1 (mTORC1) in mussels leads to retaining symbionts in gill cells. The symbiont is essential for the host mussel nutrition; however, depleting the symbiont's energy source triggers the phagosome digestion of symbionts. Meanwhile, the inhibition of mTORC1 by rapamycin prevented the digestion of the resident symbionts and of the engulfed exogenous dead symbionts in gill cells. This indicates that mTORC1 promotes phagosome digestion of symbionts under reduced nutrient supply from the symbiont. The regulation mechanism of phagosome digestion by mTORC1 through nutrient signaling with symbionts is key for maintaining animal-microbe intracellular nutritional symbiosis.

Dectin-1/CARD9-induction of the TFEB and TFE3 gene network is dispensable for phagocyte anti-Aspergillus activity in the lung

Myeloid phagocytes of the respiratory immune system, such as neutrophils, monocytes, and alveolar macrophages, are essential for immunity to Aspergillus fumigatus, the most common etiologic agent of mold pneumonia worldwide. Following engulfment of A. fumigatus conidia, fusion of the phagosome with the lysosome, is a critical process for killing conidia. TFEB and TFE3 are transcription factors that regulate lysosomal biogenesis under stress and are activated by inflammatory stimuli in macrophages, but it is unknown whether TFEB and TFE3 contribute to anti-Aspergillus immunity during infection. We found that lung neutrophils express TFEB and TFE3, and their target genes were upregulated during A. fumigatus lung infection. Additionally, A. fumigatus infection induced nuclear accumulation of TFEB and TFE3 in macrophages in a process regulated by Dectin-1 and CARD9 signaling. Genetic deletion of Tfeb and Tfe3 impaired macrophage killing of A. fumigatus conidia. However, in a murine immune competent Aspergillus infection model with genetic deficiency of Tfeb and Tfe3 in hematopoietic cells, we surprisingly found that lung myeloid phagocytes had no defects in conidial phagocytosis or killing. Loss of TFEB and TFE3 did not impact murine survival or clearance of A. fumigatus from the lungs. Our findings indicate that myeloid phagocytes activate TFEB and TFE3 in response to A. fumigatus, and while this pathway promotes macrophage fungicidal activity in vitro, genetic loss can be functionally compensated at the portal of infection in the lung, resulting in no measurable defect in fungal control and host survival.

VSV-ΔG-Spike Candidate Vaccine Induces Protective Immunity and Protects K18-hACE2 Mice against SARS-CoV-2 Variants

Since the emergence of the original SARS-CoV-2, several variants were described, raising questions as to the ability of recently developed vaccine platforms to induce immunity and provide protection against these variants. Here, we utilized the K18-hACE2 mouse model to show that VSV-ΔG-spike vaccination provides protection against several SARS-CoV-2 variants: alpha, beta, gamma, and delta. We show an overall robust immune response, regardless of variant identity, leading to reduction in viral load in target organs, prevention of morbidity and mortality, as well as prevention of severe brain immune response, which follows infection with various variants. Additionally, we provide a comprehensive comparison of the brain transcriptomic profile in response to infection with different variants of SARS-CoV-2 and show how vaccination prevents these disease manifestations. Taken together, these results highlight the robust VSV-ΔG-spike protective response against diverse SARS-CoV-2 variants, as well as its promising potential against newly arising variants.

Measuring the acidification of the phagosomal lumen in live C. elegans embryos

In metazoans, the acidification of the phagosomal lumen is essential for the efficient degradation of cargoes. Here, we present a protocol for measuring the rate of acidification inside phagosomal lumen containing apoptotic cells in living C. elegans embryos. We describe steps for generating a worm population, selecting embryos, and mounting embryos on agar pads. We then detail live imaging of embryos and data analysis. This protocol is applicable to any organism in which real-time fluorescence imaging can be performed. For complete details on the use and execution of this protocol, please refer to Pena-Ramos et al. (2022).¹.

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.

Autophagy in protists and their hosts: When, how and why?

Pathogenic protists are a group of organisms responsible for causing a variety of human diseases including malaria, sleeping sickness, Chagas disease, leishmaniasis, and toxoplasmosis, among others. These diseases, which affect more than one billion people globally, mainly the poorest populations, are characterized by severe chronic stages and the lack of effective antiparasitic treatment. Parasitic protists display complex life-cycles and go through different cellular transformations in order to adapt to the different hosts they live in. Autophagy, a highly conserved cellular degradation process, has emerged as a key mechanism required for these differentiation processes, as well as other functions that are crucial to parasite fitness. In contrast to yeasts and mammals, protist autophagy is characterized by a modest number of conserved autophagy-related proteins (ATGs) that, even though, can drive the autophagosome formation and degradation. In addition, during their intracellular cycle, the interaction of these pathogens with the host autophagy system plays a crucial role resulting in a beneficial or harmful effect that is important for the outcome of the infection. In this review, we summarize the current state of knowledge on autophagy and other related mechanisms in pathogenic protists and their hosts. We sought to emphasize when, how, and why this process takes place, and the effects it may have on the parasitic cycle. A better understanding of the significance of autophagy for the protist life-cycle will potentially be helpful to design novel anti-parasitic strategies.

Large vesicle extrusions from C. elegans neurons are consumed and stimulated by glial-like phagocytosis activity of the neighboring cell

Caenorhabditis elegans neurons under stress can produce giant vesicles, several microns in diameter, called exophers. Current models suggest that exophers are neuroprotective, providing a mechanism for stressed neurons to eject toxic protein aggregates and organelles. However, little is known of the fate of the exopher once it leaves the neuron. We found that exophers produced by mechanosensory neurons in C. elegans are engulfed by surrounding hypodermal skin cells and are then broken up into numerous smaller vesicles that acquire hypodermal phagosome maturation markers, with vesicular contents gradually degraded by hypodermal lysosomes. Consistent with the hypodermis acting as an exopher phagocyte, we found that exopher removal requires hypodermal actin and Arp2/3, and the hypodermal plasma membrane adjacent to newly formed exophers accumulates dynamic F-actin during budding. Efficient fission of engulfed exopher-phagosomes to produce smaller vesicles and degrade their contents requires phagosome maturation factors SAND-1/Mon1, GTPase RAB-35, the CNT-1 ARF-GAP, and microtubule motor-associated GTPase ARL-8, suggesting a close coupling of phagosome fission and phagosome maturation. Lysosome activity was required to degrade exopher contents in the hypodermis but not for exopher-phagosome resolution into smaller vesicles. Importantly, we found that GTPase ARF-6 and effector SEC-10/exocyst activity in the hypodermis, along with the CED-1 phagocytic receptor, is required for efficient production of exophers by the neuron. Our results indicate that the neuron requires specific interaction with the phagocyte for an efficient exopher response, a mechanistic feature potentially conserved with mammalian exophergenesis, and similar to neuronal pruning by phagocytic glia that influences neurodegenerative disease.

The formation and function of the neutrophil phagosome

Neutrophils are the most abundant circulating leukocyte and are crucial to the initial innate immune response to infection. One of their key pathogen-eliminating mechanisms is phagocytosis, the process of particle engulfment into a vacuole-like structure called the phagosome. The antimicrobial activity of the phagocytic process results from a collaboration of multiple systems and mechanisms within this organelle, where a complex interplay of ion fluxes, pH, reactive oxygen species, and antimicrobial proteins creates a dynamic antimicrobial environment. This complexity, combined with the difficulties of studying neutrophils ex vivo, has led to gaps in our knowledge of how the neutrophil phagosome optimizes pathogen killing. In particular, controversy has arisen regarding the relative contribution and integration of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived antimicrobial agents and granule-delivered antimicrobial proteins. Clinical syndromes arising from dysfunction in these systems in humans allow useful insight into these mechanisms, but their redundancy and synergy add to the complexity. In this article, we review the current knowledge regarding the formation and function of the neutrophil phagosome, examine new insights into the phagosomal environment that have been permitted by technological advances in recent years, and discuss aspects of the phagocytic process that are still under debate.

Stage of infection with Mycobacterium avium subsp. paratuberculosis impacts expression of Rab5, Rab7, and CYP27B1 in macrophages within the ileum of naturally infected cows

Introduction

Macrophages are the preferential target of Mycobacterium avium subsp. paratuberculosis (MAP), the etiologic agent of ruminant paratuberculosis. Uptake of pathogens by intestinal macrophages results in their trafficking through endosomal compartments, ultimately leading to fusion with an acidic lysosome to destroy the pathogen. MAP possesses virulence factors which disrupt these endosomal pathways. Additionally, levels of serum vitamin D₃ have proven relevant to host immunity. Dynamics of endosomal trafficking and vitamin D₃ metabolism have been largely unexplored in bovine paratuberculosis.

Methods

This study aimed to characterize expression of early and late endosomal markers Rab5 and Rab7, respectively, within CD68+ macrophages in frozen mid-ileum sections harvested from cows at different stages of natural paratuberculosis infection. Additionally, factors of vitamin D₃ signaling and metabolism were characterized through expression of vitamin D₃ activating enzyme 1α-hydroxylase (CYP27B1), vitamin D₃ inactivating enzyme 24-hydroxylase (CYP24A1), and vitamin D₃ receptor (VDR) within CD68+ ileal macrophages.

Results and discussion

Cows with clinical paratuberculosis had significantly greater macrophage and MAP burden overall, as well as intracellular MAP. Total expression of Rab5 within macrophages was reduced in clinical cows; however, Rab5 and MAP colocalization was significantly greater in this group. Intracellular Rab7 colocalization with MAP was not detected in subclinical or Johne's Disease negative (JD-) control cows but was present in clinical cows. Additionally, macrophage CYP27B1 expression was significantly reduced in clinical cows. Taken together, the results from this study show disparate patterns of expression for key mediators in intracellular MAP trafficking and vitamin D metabolism for cows at different stages of paratuberculosis.

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.

Morphological Evidence for Novel Roles of Microtubules in Macrophage Phagocytosis

Although the phagocytic activity of macrophages has long been studied, the involvement of microtubules in the process is not well understood. In this study, we improved the fixation protocol and revealed a dynamically rearranging microtubule network in macrophages, consisting of a basal meshwork, thick bundles at the cell edge, and astral microtubules. Some astral microtubules extended beneath the cell cortex and continued to form bundles at the cell edge. These microtubule assemblies were mutually exclusive of actin accumulation during membrane ruffling. Although the stabilization of microtubules with paclitaxel did not affect the resting stage of the macrophages, it reduced the phagocytic activity and membrane ruffling of macrophages activated with serum-MAF, which induced rapid phagocytosis. In contrast, the destabilization of microtubules with nocodazole enhanced membrane ruffling and the internalization of phagocytic targets suggesting an inhibitory effect of the microtubule network on the remodeling of the actin network. Meanwhile, the microtubule network was necessary for phagosome maturation. Our detailed analyses of cytoskeletal filaments suggest a phagocytosis control system involving Ca²⁺ influx, the destabilization of microtubules, and activation of actin network remodeling, followed by the translocation and acidification of phagosomes on the microtubule bundles.

Quantifying Phagocytosis by Immunofluorescence and Microscopy

Phagocytosis is carried out by cells such as macrophages of the immune system, whereby particulates like bacteria and apoptotic bodies are engulfed and sequestered within phagosomes for subsequent degradation. Hence, phagocytosis is important for infection resolution and tissue homeostasis. Aided by the innate and adaptive immune system, the activation of various phagocytic receptors triggers a cascade of downstream signaling mediators that drive actin and plasma membrane remodeling to entrap the bound particulate within the phagosome. Modulation of these molecular players can lead to distinct changes in the capacity and rates of phagocytosis. Here, we present a fluorescence microscopy-based technique to quantify phagocytosis using a macrophage-like cell line. We exemplify the technique through the phagocytosis of antibody-opsonized polystyrene beads and Escherichia coli. This method can be extended to other phagocytes and phagocytic particles.

In vitro impact of platinum nanoparticles on inner ear related cell culture models

So far, it was supposed that the increase of electrical impedance following cochlear implant (CI) insertion was due to technical defects of the electrode, inflammatory and/or formation of scar tissue along the electrode. However, it was recently reported that corrosion of the platinum electrode contacts may be the reason for high impedances. It could be shown that platinum particles were stripped from the electrode surfaces. Its potential cytotoxic effects within the inner ear remains to be examined. In this study in vitro cell culture models of the mouse organ of Corti cell line (HEI-OC1) and the spiral ganglion (SG) cells derived from the cochleae neonatal rats were used to investigate the effects of the polyvinylpyrrolidone coated platinum nanoparticles (Pt-NPPVP, 3 nm) on cell metabolism, neuronal survival and neurite outgrowth. Our data revealed no decrease of the metabolic activity of the HEI-OC1 cells at Pt-NPPVP concentrations between 50-150 μg/ml. Also, staining with Calcein AM/EthD demonstrated prevalent presence of vital cells. As shown by transmission electron microscopy no Pt-NPPVP could be found at the cell surface or in the cytosol of the HEI-OC1 cells. Similarly, the SG cells exposed to 20-100 μg/ml Pt-NPPVP did not show any reduced survival rate and neurite outgrowth following staining of the neurofilament antigen even at the highest Pt-NPPVP concentration. Although the SG cells were exposed to Pt-NPPVP for further 72 h and 96 h immunocytochemical staining of the glial cells and fibroblasts presented normal cell morphology and growth independently of the cultivation period. Our data indicates that the used Pt-NPPVP do not trigger the cellular uptake and, thus, presumable do not initiate apoptotic pathways in cells of the organ of Corti cell line or the auditory nerve. The protection mechanisms to the Pt-NPPVP interactions remain to be clarified.

Quantitative Immunofluorescence to Study Phagosome Maturation and Resolution

Cells such as macrophages and neutrophils can internalize a diverse set of particulate matter, illustrated by bacteria and apoptotic bodies through the process of phagocytosis. These particles are sequestered into phagosomes, which then fuse with early and late endosomes and ultimately with lysosomes to mature into phagolysosomes, through a process known as phagosome maturation. Ultimately, after particle degradation, phagosomes then fragment to reform lysosomes through phagosome resolution. As phagosomes change, they acquire and divest proteins that are associated with the various stages of phagosome maturation and resolution. These changes can be assessed at the single-phagosome level by using immunofluorescence methods. Typically, we use indirect immunofluorescence methods that rely on primary antibodies against specific molecular markers that track phagosome maturation. Commonly, progression of phagosomes into phagolysosomes can be determined by staining cells for Lysosomal-Associated Membrane Protein I (LAMP1) and measuring the fluorescence intensity of LAMP1 around each phagosome by microscopy or flow cytometry. However, this method can be used to detect any molecular marker for which there are compatible antibodies for immunofluorescence.

Acute Inflammation in Tissue Healing

There are well-established links between acute inflammation and successful tissue repair across evolution. Innate immune reactions contribute significantly to pathogen clearance and activation of subsequent reparative events. A network of molecular and cellular regulators supports antimicrobial and tissue repair functions throughout the healing process. A delicate balance must be achieved between protection and the potential for collateral tissue damage associated with overt inflammation. In this review, we summarize the contributions of key cellular and molecular components to the acute inflammatory process and the effective and timely transition toward activation of tissue repair mechanisms. We further discuss how the disruption of inflammatory responses ultimately results in chronic non-healing injuries.