Neutrophil in Reverse Migration: Role in Sepsis

MCTR1 ameliorates LPS-induced lung injury by inhibiting neutrophil reverse transendothelial migration

OBJECTIVES

Dysregulated inflammatory responses during sepsis often result in acute lung injury (ALI). Neutrophils activated at the primary site of injury can re-enter the circulation through reverse transendothelial migration (rTEM), subsequently infiltrating other organs and contributing to systemic inflammation and multi-organ damage. The specialized pro-resolving lipid mediator (SPM) maresin conjugate in tissue regeneration 1 (MCTR1) has been shown to mitigate organ injury in sepsis. This study investigated the role of neutrophil rTEM in ALI and examined whether MCTR1 can alleviate ALI by modulating neutrophil rTEM.

METHODS

Lung injury was induced in mice by administrating lipopolysaccharide (LPS). Lung damage was assessed using H&E staining, lung wet-to-dry ratio, inflammatory mediator levels, and protein content in the bronchoalveolar lavage fluid. Neutrophil infiltration in lung tissue was evaluated by immunofluorescence, and flow cytometry was used to quantify rTEM neutrophils. Protein expression of neutrophil elastase (NE) and junctional adhesion molecule-C (JAM-C) was analyzed to assess rTEM activity. The role of CXCR4 in neutrophil rTEM was investigated using the CXCR4 inhibitor AMD3100. Additionally, bone marrow-derived neutrophils were isolated to evaluate the effects of MCTR1 on CXCR4 and GRK2 expression.

RESULTS

MCTR1 alleviated lung injury and inhibited neutrophils rTEM in LPS-induced lung injury. MCTR1 also decreased NE expression and increased JAM-C expression. The CXCR4 inhibitor AMD3100 effectively suppressed neutrophil rTEM and alleviated lung injury. Furthermore, MCTR1 inhibited CXCR4 expression and enhanced GRK2 expression.

CONCLUSIONS

MCTR1 reduces lung damage by upregulating GRK2 to inhibit CXCR4 expression, thereby suppressing neutrophil rTEM in LPS-induced lung injury.

Intravacuolar persistence in neutrophils facilitates Listeria monocytogenes spread to co-cultured cells

The bacterium Listeria monocytogenes (Lm) causes listeriosis in humans and ruminants. Acute lesions are predominantly infiltrated by polymorphonuclear neutrophils (PMNs), considered to be the efficient bactericidal arm of innate immunity. However, recent evidence suggests that PMNs cannot achieve antilisterial sterilizing immunity and that Lm may persist within PMNs. Despite this, interactions between PMNs and Lm remain poorly understood. In this study, we characterized the listericidal activity and interaction dynamics of bovine PMNs with Lm ex vivo. Phagocytosed Lm failed to escape into the PMN cytosol and was primarily targeted by phagolysosomal mechanisms. However, PMNs enabled prolonged intravacuolar survival of a resilient Lm subpopulation, largely as viable but non-culturable (VBNC) bacteria. This resilient Lm population could spread from PMNs to a cell line, resuscitate, and complete its canonical life cycle, thereby perpetuating the infection. Therefore, we identify PMNs as a mobile niche for Lm survival and provide evidence that PMNs harbor VBNC bacteria, potentially facilitating Lm dissemination within the host.

IMPORTANCE

Listeria monocytogenes (Lm) is a significant foodborne pathogen responsible for high hospitalization rates in humans, especially vulnerable groups such as the elderly, pregnant women, and immunocompromised individuals. In animals like ruminants, Lm infection leads to severe disease manifestations, notably brainstem encephalitis. This study uncovers a novel mechanism by which bovine neutrophils (PMNs) harbor Lm in a viable but non-culturable (VBNC) state, enabling the bacteria to hide in the host. PMNs, traditionally viewed as bacteria killers, may serve as Trojan horses, allowing Lm to persist and spread within the host. This discovery has broad implications for understanding Lm's persistence, its role in recurrent infections, and the development of new therapeutic strategies targeting VBNC forms of Lm to improve treatment outcomes and disease control.

Distinctive features and prognostic utility of neutrophil in severe patients with Klebsiella pneumoniae infection

Background

Neutrophil plays a pivotal role in the management of Klebsiella pneumoniae infection. Delineate the clinical characteristics and prognostic utility of neutrophil in severe patients with K. pneumoniae infection are crucial for clinical management and prognostic assessment.

Methods

K. pneumoniae patients with different infection sites were enrolled from Medical Information Mart for Intensive Care IV and eICU Collaborative Research Database. Temporal variations of neutrophil counts within 30 days of clinical onset were examined using locally weighted scatterplot smoothing curves. Logistic regression analysis was performed to assess the relationship between neutrophil counts and hospital mortality.

Results

A total of 1,705 patients caused by K. pneumonia were included in the study. The non-survivor group exhibited a comparatively older age and a higher proportion of K. pneumoniae infections originating from respiratory and bloodstream sources compared to the survivor group (38.4% vs 21.1%, p<0.0001, and 15.1% vs 10.3%, p=0.021). Patients combined with multiple drug resistance strains, respiratory infection, liver disease, and above 60 years exhibited a specific dynamic process of neutrophil levels. Neutrophils counts peaked at admission and 1-2 weeks later. There was a 'U'-shaped relationship between neutrophil counts and hospital mortality.

Conclusions

Neutrophils in K. pneumoniae infected patients have distinctive features and dynamic clinical trajectories. Close monitoring of severe patients infected with K. pneumoniae upon admission and during the first 1-2 weeks after admission is of utmost importance, particularly for patients with a neutrophil count exceeding 8.0×109/L.

Sided Stimulation of Endothelial Cells Modulates Neutrophil Trafficking in an In Vitro Sepsis Model

While the role of dysregulated polymorphonuclear leukocyte (PMN) transmigration in septic mediated tissue damage is well documented, strategies to mitigate aberrant transmigration across endothelium have yet to yield viable therapeutics. Recently, microphysiological systems (MPS) have emerged as novel in vitro mimetics that facilitate the development of human models of disease. With this advancement, aspects of endothelial physiology that are difficult to assess with other models can be directly probed. In this study, the role of endothelial cell (EC) apicobasal polarity on leukocyte trafficking response is evaluated with the µSiM-MVM (microphysiological system enabled by a silicon membrane - microvascular mimetic). Here, ECs are stimulated either apically or basally with a cytokine cocktail to model a septic-like challenge before introducing healthy donor PMNs into the device. Basally oriented stimulation generated a stronger PMN transmigratory response versus apical stimulation. Importantly, healthy PMNs are unable to migrate towards a bacterial peptide chemoattractant when ECs are apically stimulated, which mimics the attenuated PMN chemotaxis seen in sepsis. Escalating the apical inflammatory stimulus by a factor of five is necessary to elicit high PMN transmigration levels across endothelium. These results demonstrate that EC apicobasal polarity modulates PMN transmigratory behavior and provides insight into the mechanisms underlying sepsis.

Chemerin attracts neutrophil reverse migration by interacting with C-C motif chemokine receptor-like 2

Neutrophil reverse migration (rM) is a recently identified phenomenon in which neutrophils migrate away from the inflammatory site back into the vasculature following initial infiltration, which involved in the resolution of loci inflammatory response or dissemination of inflammation. Present study was aimed to explore the mechanisms in neutrophil rM. By scRNA-seq on the white blood cells in acute lung injury model, we found rM-ed neutrophils exhibited increased gene expression of C-C motif chemokine receptor-like 2 (Ccrl2), an atypical chemokine receptor. Furthermore, an air pouch model was established to directly track rM-ed neutrophils in vivo. Air pouches were generated by 3 ml filtered sterile air injected subcutaneously for 3 days, and then LPS (2 mg/kg) was injected into the pouches to mimic the inflammatory state. For the rM-ed neutrophil tracking system, cell tracker CMFDA were injected into the air pouch to stain the inflammatory loci cells, and after 6 h, stained cells in blood were regarded as the rM-ed neutrophil. Based on this tracking system, we confirmed that rM-ed neutrophils showed increased CCRL2. We also found that the concentrations of the CCRL2 ligand chemerin in plasma was increased in the late stage. Neutralizing chemerin decreased the rM-ed neutrophil ratio in the blood. These results suggest that circulating chemerin attracts neutrophils to leave inflammatory sites by interacting with CCRL2, which might involve in the dissemination of inflammation.

Detailed phenotyping reveals diverse and highly skewed neutrophil subsets in both the blood and airways during active tuberculosis infection

Introduction

Neutrophils play a complex and important role in the immunopathology of TB. Data suggest they are protective during early infection but become a main driver of immunopathology if infection progresses to active disease. Neutrophils are now recognized to exist in functionally diverse states, but little work has been done on how neutrophil states or subsets are skewed in TB disease.

Methods

To address this, we carried out comprehensive phenotyping by flow cytometry of neutrophils in the blood and airways of individuals with active pulmonary TB with and without HIV co-infection recruited in Durban, South Africa.

Results

Active TB was associated with a profound skewing of neutrophils in the blood toward phenotypes associated with activation and apoptosis, reduced phagocytosis, reverse transmigration, and immune regulation. This skewing was also apparently in airway neutrophils, particularly the regulatory subsets expressing PDL-1 and LOX-1. HIV co-infection did not impact neutrophil subsets in the blood but was associated with a phenotypic change in the airways and a reduction in key neutrophil functional proteins cathelicidin and arginase 1.

Discussion

Active TB is associated with profound skewing of blood and airway neutrophils and suggests multiple mechanisms by which neutrophils may exacerbate the immunopathology of TB. These data indicate potential avenues for reducing neutrophil-mediated lung pathology at the point of diagnosis.

The early predictive roles of NLR and NE% in in-hospital mortality of septic patients

Background

This study aimed to retrospectively investigate the early predictive value of inflammation-related parameters in-hospital mortality of septic patients.

Methods

We retrospectively recruited 606 patients from Wuhan Union Hospital from January 2009 to October 2022. The inflammation-related parameters including neutrophil-to-lymphocyte ratio (NLR), neutrophil percentage (NE%), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR) in survivals and non-survivals on day 1, 2, 3 and 7 after hospitalization were collected and analyzed.

Results

NLR and NE% in non-survivals (n = 185) were significantly higher than those in survivals (n = 421). The area under the receiver operating characteristic curve (AUC) of NLR or NE% was 0.880 or 0.852 on day 1, 0.770 or 0.790 on day 2, 0.784 or 0.777 on day 3, and 0.732 or 0.741 on day 7. The optimal cut-off values of NLR or NE% for predicting in-hospital mortality were 10.769 or 87.70% on day 1, 17.544 or 90.69% on day 2, 14.395 or 85.00% on day 3, and 9.105 or 83.93% on day 7. The day 1, 2 and 3 NLR and NE% were significant predictors of in-hospital mortality in the Cox proportional hazards models.

Conclusions

NLR ≥10.769 and NE% ≥ 87.70% could be used early biomarkers for predicting in-hospital mortality of septic patients.

MCC950 improves lipopolysaccharide‑induced systemic inflammation in mice by relieving pyroptosis in blood neutrophils

Sepsis is an infection-induced systemic inflammatory response syndrome accompanied by multiple organ injury and failure. MCC950, an inhibitor of NLR family pyrin domain containing 3 (NLRP3), can alleviate the inflammatory response and relieve inflammation-induced injury. The aim of the present study was to explore the efficacy of MCC950 in lipopolysaccharide (LPS)-induced inflammation and elucidate the underlying mechanisms. Based on a prior study, C57BL/6 mice were divided into three groups: Control, LPS, and LPS + MCC950. The mice were administered 10 mg/kg LPS to induce sepsis and 10 mg/kg MCC950 to treat sepsis 6 h before and after LPS injection. Histopathological imaging revealed organ morphology and damage during inflammation, and MCC950 alleviated organ damage and dysfunction. MCC950 prevented LPS-induced inflammatory responses by reducing inflammatory cytokine levels in the blood. To explore the mechanism by which MCC950 functions, blood neutrophils were isolated and a series of tests were performed. As revealed by measuring reactive oxygen species levels and Annexin V/PI staining of neutrophils, MCC950 reduced oxidative stress and programmed death induced by LPS. Western blotting was used to assess the protein levels of pyroptosis-related markers, including GSDMD, NLRP3, and caspase-1, in neutrophils to further explore the form of death. MCC950 reduced LPS-induced pyroptosis in neutrophils. The results of the survival analysis revealed that MCC950 increased the survival rates of mice within 72 h of LPS injection. MCC950 may be an effective treatment for sepsis that targets neutrophil pyroptosis.

The acute inflammatory response of teleost fish

Acute inflammation is crucial to the immune responses of fish. The process protects the host from infection and is central to induction of subsequent tissue repair programs. Activation of proinflammatory signals reshapes the microenvironment within an injury/infection site, initiates leukocyte recruitment, promotes antimicrobial mechanisms and contributes to the resolution of inflammation. Inflammatory cytokines and lipid mediators are primary contributors to these processes. Uncontrolled or persistent induction results in delayed tissue healing. The kinetics by which inducers and regulators of acute inflammation exert their actions is essential for understanding the pathogenesis of fish diseases and identifying potential treatments. Although, a number of these are well-conserved across, others are not, reflecting the unique physiologies and life histories of members of this unique animal group.

The Role of Cytokines in Neutrophil Development, Tissue Homing, Function and Plasticity in Health and Disease

Neutrophils are crucial innate immune cells and comprise 50-70% of the white blood cell population under homeostatic conditions. Upon infection and in cancer, blood neutrophil numbers significantly increase because of the secretion of various chemo- and cytokines by, e.g., leukocytes, pericytes, fibroblasts and endothelial cells present in the inflamed tissue or in the tumor microenvironment (TME). The function of neutrophils in cancer has recently gained considerable attention, as they can exert both pro- and anti-tumorigenic functions, dependent on the cytokine milieu present in the TME. Here, we review the effect of cytokines on neutrophil development, tissue homing, function and plasticity in cancer and autoimmune diseases as well as under physiological conditions in the bone marrow, bloodstream and various organs like the spleen, kidney, liver, lung and lymph nodes. In addition, we address several promising therapeutic options, such as cytokine therapy, immunocytokines and immunotherapy, which aim to exploit the anti-tumorigenic potential of neutrophils in cancer treatment or block excessive neutrophil-mediated inflammation in autoimmune diseases.

New genetic and epigenetic insights into the chemokine system: the latest discoveries aiding progression toward precision medicine

Over the past thirty years, the importance of chemokines and their seven-transmembrane G protein-coupled receptors (GPCRs) has been increasingly recognized. Chemokine interactions with receptors trigger signaling pathway activity to form a network fundamental to diverse immune processes, including host homeostasis and responses to disease. Genetic and nongenetic regulation of both the expression and structure of chemokines and receptors conveys chemokine functional heterogeneity. Imbalances and defects in the system contribute to the pathogenesis of a variety of diseases, including cancer, immune and inflammatory diseases, and metabolic and neurological disorders, which render the system a focus of studies aiming to discover therapies and important biomarkers. The integrated view of chemokine biology underpinning divergence and plasticity has provided insights into immune dysfunction in disease states, including, among others, coronavirus disease 2019 (COVID-19). In this review, by reporting the latest advances in chemokine biology and results from analyses of a plethora of sequencing-based datasets, we outline recent advances in the understanding of the genetic variations and nongenetic heterogeneity of chemokines and receptors and provide an updated view of their contribution to the pathophysiological network, focusing on chemokine-mediated inflammation and cancer. Clarification of the molecular basis of dynamic chemokine-receptor interactions will help advance the understanding of chemokine biology to achieve precision medicine application in the clinic.

The Regulation of Neutrophil Migration in Patients with Sepsis: The Complexity of the Molecular Mechanisms and Their Modulation in Sepsis and the Heterogeneity of Sepsis Patients

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Common causes include gram-negative and gram-positive bacteria as well as fungi. Neutrophils are among the first cells to arrive at an infection site where they function as important effector cells of the innate immune system and as regulators of the host immune response. The regulation of neutrophil migration is therefore important both for the infection-directed host response and for the development of organ dysfunctions in sepsis. Downregulation of CXCR4/CXCL12 stimulates neutrophil migration from the bone marrow. This is followed by transmigration/extravasation across the endothelial cell barrier at the infection site; this process is directed by adhesion molecules and various chemotactic gradients created by chemotactic cytokines, lipid mediators, bacterial peptides, and peptides from damaged cells. These mechanisms of neutrophil migration are modulated by sepsis, leading to reduced neutrophil migration and even reversed migration that contributes to distant organ failure. The sepsis-induced modulation seems to differ between neutrophil subsets. Furthermore, sepsis patients should be regarded as heterogeneous because neutrophil migration will possibly be further modulated by the infecting microorganisms, antimicrobial treatment, patient age/frailty/sex, other diseases (e.g., hematological malignancies and stem cell transplantation), and the metabolic status. The present review describes molecular mechanisms involved in the regulation of neutrophil migration; how these mechanisms are altered during sepsis; and how bacteria/fungi, antimicrobial treatment, and aging/frailty/comorbidity influence the regulation of neutrophil migration.

A computer vision approach for analyzing label free leukocyte trafficking dynamics on a microvascular mimetic

High-content imaging techniques in conjunction with in vitro microphysiological systems (MPS) allow for novel explorations of physiological phenomena with a high degree of translational relevance due to the usage of human cell lines. MPS featuring ultrathin and nanoporous silicon nitride membranes (µSiM) have been utilized in the past to facilitate high magnification phase contrast microscopy recordings of leukocyte trafficking events in a living mimetic of the human vascular microenvironment. Notably, the imaging plane can be set directly at the endothelial interface in a µSiM device, resulting in a high-resolution capture of an endothelial cell (EC) and leukocyte coculture reacting to different stimulatory conditions. The abundance of data generated from recording observations at this interface can be used to elucidate disease mechanisms related to vascular barrier dysfunction, such as sepsis. The appearance of leukocytes in these recordings is dynamic, changing in character, location and time. Consequently, conventional image processing techniques are incapable of extracting the spatiotemporal profiles and bulk statistics of numerous leukocytes responding to a disease state, necessitating labor-intensive manual processing, a significant limitation of this approach. Here we describe a machine learning pipeline that uses a semantic segmentation algorithm and classification script that, in combination, is capable of automated and label-free leukocyte trafficking analysis in a coculture mimetic. The developed computational toolset has demonstrable parity with manually tabulated datasets when characterizing leukocyte spatiotemporal behavior, is computationally efficient and capable of managing large imaging datasets in a semi-automated manner.

Epigenetic mechanisms of Immune remodeling in sepsis: targeting histone modification

Sepsis is a life-threatening disorder disease defined as infection-induced dysregulated immune responses and multiple organ dysfunction. The imbalance between hyperinflammation and immunosuppression is a crucial feature of sepsis immunity. Epigenetic modifications, including histone modifications, DNA methylation, chromatin remodeling, and non-coding RNA, play essential roles in regulating sepsis immunity through epi-information independent of the DNA sequence. In recent years, the mechanisms of histone modification in sepsis have received increasing attention, with ongoing discoveries of novel types of histone modifications. Due to the capacity for prolonged effects on immune cells, histone modifications can induce immune cell reprogramming and participate in the long-term immunosuppressed state of sepsis. Herein, we systematically review current mechanisms of histone modifications involved in the regulation of sepsis, summarize their role in sepsis from an immune perspective and provide potential therapeutic opportunities targeting histone modifications in sepsis treatment.

LncRNA HCG18 loaded by polymorphonuclear neutrophil-secreted exosomes aggravates sepsis acute lung injury by regulating macrophage polarization

Polymorphonuclear neutrophils (PMNs) exert significant roles in septic acute lung injury (ALI). Accumulating evidence suggests that PMN-derived exosomes (PMN-exo) are a novel subcellular entity that is the fundamental link between PMN-driven inflammation and tissue damage. However, the role of PMN-exo in septic ALI and the underlying mechanisms remain unclear. Tumor necrosis factor-α (TNF-α), a key regulator of innate immunity in septic ALI, was used to induce PMN activation in vitro. Using an in vitro co-culture system, the rat alveolar macrophage cell line NR8383 was co-cultured with TNF-α-stimulated PMN-released exosomes (TNF-α-exo) to further confirm the results of the in vitro studies and explore the underlying mechanisms involved. A septic lung injury model was established by cecal ligation and puncture surgery, and PMN-exo were injected into septic mice through the tail vein, and then lung injury, inflammatory release, macrophage polarization, and apoptosis were examined. The results reported that TNF-α-exo promoted the activation of M1 macrophages after i.p. injection in vivo or co-culture in vitro. Furthermore, TNF-α-exo affected alveolar macrophage polarization by delivering HCG18. Mechanistic studies indicated that HCG18 mediated the function of TNF-α-exo by targeting IL-32 in macrophages. In addition, tail vein injection of si-HCG18 in septic mice significantly reduced TNF-α-exo-induced M1 macrophage activation and lung macrophage death, as well as histological lesions. In conclusion, TNF-α-exo-loaded HCG18 contributes to septic ALI by regulating macrophage polarization. These findings may provide new insights into novel mechanisms of PMN-macrophage polarization interactions in septic ALI and may provide new therapeutic strategies for patients with sepsis.

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.

Leukocyte metabolism in obese type 2 diabetic individuals associated with COVID-19 severity

Recent studies show that the metabolic characteristics of different leukocytes, such as, lymphocytes, neutrophils, and macrophages, undergo changes both in the face of infection with SARS-CoV-2 and in obesity and type 2 diabetes mellitus (DM2) condition. Thus, the objective of this review is to establish a correlation between the metabolic changes caused in leukocytes in DM2 and obesity that may favor a worse prognosis during SARS-Cov-2 infection. Chronic inflammation and hyperglycemia, specific and usual characteristics of obesity and DM2, contributes for the SARS-CoV-2 replication and metabolic disturbances in different leukocytes, favoring the proinflammatory response of these cells. Thus, obesity and DM2 are important risk factors for pro-inflammatory response and metabolic dysregulation that can favor the occurrence of the cytokine storm, implicated in the severity and high mortality risk of the COVID-19 in these patients.

Identification of immune-related hub genes and miRNA-mRNA pairs involved in immune infiltration in human septic cardiomyopathy by bioinformatics analysis

Abstract

Septic cardiomyopathy (SCM) is a serious complication caused by sepsis that will further exacerbate the patient's prognosis. However, immune-related genes (IRGs) and their molecular mechanism during septic cardiomyopathy are largely unknown. Therefore, our study aims to explore the immune-related hub genes (IRHGs) and immune-related miRNA-mRNA pairs with potential biological regulation in SCM by means of bioinformatics analysis and experimental validation.

Method

Firstly, screen differentially expressed mRNAs (DE-mRNAs) from the dataset GSE79962, and construct a PPI network of DE-mRNAs. Secondly, the hub genes of SCM were identified from the PPI network and the hub genes were overlapped with immune cell marker genes (ICMGs) to further obtain IRHGs in SCM. In addition, receiver operating characteristic (ROC) curve analysis was also performed in this process to determine the disease diagnostic capability of IRHGs. Finally, the crucial miRNA-IRHG regulatory network of IRHGs was predicted and constructed by bioinformatic methods. Real-time quantitative reverse transcription-PCR (qRT-PCR) and dataset GSE72380 were used to validate the expression of the key miRNA-IRHG axis.

Result

The results of immune infiltration showed that neutrophils, Th17 cells, Tfh cells, and central memory cells in SCM had more infiltration than the control group; A total of 2 IRHGs were obtained by crossing the hub gene with the ICMGs, and the IRHGs were validated by dataset and qRT-PCR. Ultimately, we obtained the IRHG in SCM: THBS1. The ROC curve results of THBS1 showed that the area under the curve (AUC) was 0.909. Finally, the miR-222-3p/THBS1 axis regulatory network was constructed.

Conclusion

In summary, we propose that THBS1 may be a key IRHG, and can serve as a biomarker for the diagnosis of SCM; in addition, the immune-related regulatory network miR-222-3p/THBS1 may be involved in the regulation of the pathogenesis of SCM and may serve as a promising candidate for SCM therapy.

Distinct post-sepsis induced neurochemical alterations in two mouse strains

Sepsis associated encephalopathy, occurs in 70% of severe septic cases, following which survivors exhibit long-term cognitive impairment or global loss of cognitive function. Currently there is no clearly defined neurochemical basis of septic encephalopathy. Moreover, the lingering neurological complications associated with the severe acute respiratory syndrome CoV 2 (SARS-CoV-2) and the significant worsening in outcomes for those individuals with SARS-Cov-2 following sepsis underscore the need to define factors underlying the susceptibility to acute toxic encephalitis. In this study, differential neurochemical sequelae in response to sepsis (lipopolysaccharide (LPS)-induced endotoxemia and caecal ligation and puncture (CLP)), were evaluated in two inbred mouse strains, known to differ in behaviour, immune profile, and neurotransmitter levels, namely BALB/c and C57BL/6J. It was hypothesized that these strains would differ in sepsis severity, cytokine profile, peripheral tryptophan metabolism and central monoamine turnover. BALB/c mice exhibited more pronounced sickness behavioural scores, hypothermia, and significant upregulation of cytokines in the LPS model relative to C57BL/6J mice. Increased plasma kynurenine/tryptophan ratio, hippocampal serotonin and brainstem dopamine turnover were evident in both strains, but the magnitude was greater in BALB/c mice. In addition, CLP significantly enhanced kynurenine levels and hippocampal serotonergic and dopaminergic neurotransmission in C57BL/6J mice. Overall, these studies depict consistent changes in kynurenine, serotonin, and dopamine post sepsis. Further evaluation of these monoamines in the context of septic encephalopathy and cognitive decline is warranted. Moreover, these data suggest the continued evaluation of altered peripheral kynurenine metabolism as a potential blood-based biomarker of sepsis.

Immune Cell Plasticity in Inflammation: Insights into Description and Regulation of Immune Cell Phenotypes

Inflammation is a life-saving immune reaction occurring in response to invading pathogens. Nonetheless, inflammation can also occur in an uncontrolled, unrestricted manner, leading to chronic disease and organ damage. Mechanisms triggering an inflammatory response, hindering such a response, or leading to its resolution are well-studied but so far insufficiently elucidated with regard to precise therapeutic interventions. Notably, as an immune reaction evolves, requirements and environments for immune cells change, and thus cellular phenotypes adapt and shift, leading to the appearance of distinct cellular subpopulations with new functional features. In this article, we aim to highlight properties of, and overarching regulatory factors involved in, the occurrence of immune cell phenotypes with a special focus on neutrophils, macrophages and platelets. Additionally, we point out implications for both diagnostics and therapeutics in inflammation research.

The metamorphosis of neutrophil transcriptional program during Leishmania infection

The role of neutrophils in the course of Leishmania infection remains controversial, displaying tremendous variability depending on the species of parasite, stage of infection, host genetic background, and methodological discrepancies among studies. Although neutrophils have long been categorized as short-lived cells with limited capacity to express proteins de novo, recent advances have revealed significant plasticity in neutrophil transcriptional programs and intrapopulation heterogeneity, which can be regulated by both intrinsic and extrinsic factors that together determine the profile of neutrophil effector response. In this review, we focus on the current understanding of neutrophil transcriptional plasticity, neutrotime, evidence of Leishmania-mediated alterations in neutrophil transcriptome leading to the rise of subpopulations, and finally, functional implications of those findings to the course of Leishmania infection.

Neutrophil Migratory Patterns: Implications for Cardiovascular Disease

The body's inflammatory response involves a series of processes that are necessary for the immune system to mitigate threats from invading pathogens. Leukocyte migration is a crucial process in both homeostatic and inflammatory states. The mechanisms involved in immune cell recruitment to the site of inflammation are numerous and require several cascades and cues of activation. Immune cells have multiple origins and can be recruited from primary and secondary lymphoid, as well as reservoir organs within the body to generate an immune response to certain stimuli. However, no matter the origin, an important aspect of any inflammatory response is the web of networks that facilitates immune cell trafficking. The vasculature is an important organ for this trafficking, especially during an inflammatory response, mainly because it allows cells to migrate towards the source of insult/injury and serves as a reservoir for leukocytes and granulocytes under steady state conditions. One of the most active and vital leukocytes in the immune system's arsenal are neutrophils. Neutrophils exist under two forms in the vasculature: a marginated pool that is attached to the vessel walls, and a demarginated pool that freely circulates within the blood stream. In this review, we seek to present the current consensus on the mechanisms involved in leukocyte margination and demargination, with a focus on the role of neutrophil migration patterns during physio-pathological conditions, in particular diabetes and cardiovascular disease.

High-Dose Vitamin C Supplementation as a Legitimate Anti-SARS-CoV-2 Prophylaxis in Healthy Subjects—Yes or No?

Vitamin C has a number of acitvities that could contribute to its immune-modulating effects. The only question is whether we should provide ourselves with only the right level of it, or do we need much more during a pandemic? The possibility of reducing the incidence of viral diseases in a well-nourished population through the use of dietary supplements based on vitamin C is not supported in the literature. Despite this, the belief that an extra intake of vitamin C can increase the efficacy of the immune system is still popular and vitamin C is advertised as a remedy to prevent infectious disease. This article refers to the justification of the use of vitamin C in high doses as an anti-SARS-CoV-2 prophylaxis in healthy subjects. Does it make sense or not? As it turns out, any effects of vitamin C supplementation may be more prominent when the baseline vitamin C level is low, for example in physically active persons. People with hypovitaminosis C are more likely to respond to vitamin C administration. No studies regarding prevention of COVID-19 with high-dose vitamin C supplementation in healthy subjects were found.

Neutrophils at the crossroads of acute viral infections and severity

Neutrophils are versatile immune effector cells essential for mounting a first-line defense against invading pathogens. However, uncontrolled activation can lead to severe life-threatening complications. Neutrophils exist as a heterogeneous population, and their interaction with pathogens and other immune cells may shape the outcome of the host immune response. Diverse classes of viruses, including the recently identified novel SARS-CoV-2, have shown to alter the various aspects of neutrophil biology, offering possibilities for selective intervention. Here, we review heterogeneity within the neutrophil population, highlighting the functional consequences of circulating phenotypes and their critical involvement in exaggerating protective and pathological immune responses against the viruses. We discuss the recent findings of neutrophil extracellular traps (NETs) in COVID-19 pathology and cover other viruses, where neutrophil biology and NETs are crucial for developing disease severity. In the end, we have also pointed out the areas where neutrophil-mediated responses can be finely tuned to outline opportunities for therapeutic manipulation in controlling inflammation against viral infection.