Peripheral priming induces plastic transcriptomic and proteomic responses in circulating neutrophils required for pathogen containment

Targeting mitochondrial complex I of CD177+ neutrophils alleviates lung ischemia-reperfusion injury

Primary graft dysfunction (PGD) is the leading cause of early morbidity and mortality following lung transplantation, with neutrophils playing a central role in its inflammatory pathology. Here, we employ single-cell RNA sequencing and spatial transcriptomics to investigate neutrophil subtypes in the lung ischemia-reperfusion injury (IRI) model. We identify CD177+ neutrophils as an activated subpopulation that significantly contributes to lung injury and serves as an early biomarker for predicting severe PGD in human lung transplant recipients (area under the curve [AUC] = 0.871). CD177+ neutrophils exhibit elevated oxidative phosphorylation and increased mitochondrial complex I activity, driving inflammation and the formation of neutrophil extracellular traps. Targeting mitochondrial function with the complex I inhibitor IACS-010759 reduces CD177+ neutrophil activation and alleviates lung injury in both mouse IRI and rat left lung transplant models. These findings provide a comprehensive landscape of CD177+ neutrophil-driven inflammation in lung IRI and highlight its potential value for future early diagnosis and therapeutic interventions.

Immunothrombolytic monocyte-neutrophil axes dominate the single-cell landscape of human thrombosis and correlate with thrombus resolution

Thrombotic diseases remain the major cause of death and disability worldwide, and the contribution of inflammation is increasingly recognized. Thromboinflammation has been identified as a key pathomechanism, but an unsupervised map of immune-cell states, trajectories, and intercommunication at a single-cell level has been lacking. Here, we reveal innate leukocyte substates with prominent thrombolytic properties by employing single-cell omics measures on human stroke thrombi. Using in vivo and in vitro thrombosis models, we propose a pro-resolving monocyte-neutrophil axis, combining two properties: (1) NR4A1hi non-classical monocytes acquire a thrombolytic and neutrophil-chemoattractive phenotype, and (2) blood neutrophils are thereby continuously recruited to established thrombi through CXCL8-CXCR1 and CXCR2 and adopt a hypoxia-induced thrombus-resolving urokinase receptor (PLAUR)+ phenotype. This immunothrombolytic axis results in thrombus resolution. Together, with this immune landscape of thrombosis, we provide a valuable resource and introduce the concept of "immunothrombolysis" with broad mechanistic and translational implications at the crossroad of inflammation and thrombosis.

Deep phenotyping of human neutrophils in whole blood using a 33-color spectral flow cytometry panel

Neutrophils are the most abundant leukocytes in the circulation and critical players in host defense and inflammation. They respond rapidly to numerous biological, chemical, and physical stimuli, making it challenging to characterize their steady-state phenotypes, activation states, and subsets in an unbiased and precise manner. To address this problem, we designed a 33-color spectral flow cytometry panel for the deep profiling of unprocessed neutrophils in human blood. This panel allows the profiling of neutrophil phenotypes related to activation, immune modulation, granule release, ontogeny, phagocytic capacity, and migration, in addition to monitoring all major human leukocyte populations. We validated the panel using whole blood stimulations that induce distinct phenotypic shifts in the neutrophil population. This optimized spectral flow cytometry panel allows comprehensive immune profiling of the functional heterogeneity of human blood neutrophils and is suitable for longitudinal or exploratory analysis of neutrophil dynamics and activation states in clinical cohorts.

Recent Advances in Immunothrombosis and Thromboinflammation

Inflammation and thrombosis are traditionally considered two separate entities of acute host responses to barrier breaks. While inciting inflammatory responses is a prerequisite to fighting invading pathogens and subsequent restoration of tissue homeostasis, thrombus formation is a crucial step of the hemostatic response to prevent blood loss following vascular injury. Though originally designed to protect the host, excessive induction of either inflammatory signaling or thrombus formation and their reciprocal activation contribute to a plethora of disorders, including cardiovascular, autoimmune, and malignant diseases. In this state-of-the-art review, we summarize recent insights into the intricate interplay of inflammation and thrombosis. We focus on the protective aspects of immunothrombosis as well as evidence of detrimental sequelae of thromboinflammation, specifically regarding recent studies that elucidate its pathophysiology beyond coronavirus disease 2019 (COVID-19). We introduce recently identified molecular aspects of key cellular players like neutrophils, monocytes, and platelets that contribute to both immunothrombosis and thromboinflammation. Further, we describe the underlying mechanisms of activation involving circulating plasma proteins and immune complexes. We then illustrate how these factors skew the inflammatory state toward detrimental thromboinflammation across cardiovascular as well as septic and autoimmune inflammatory diseases. Finally, we discuss how the advent of new technologies and the integration with clinical data have been used to investigate the mechanisms and signaling cascades underlying immunothrombosis and thromboinflammation. This review highlights open questions that will need to be addressed by the field to translate our mechanistic understanding into clinically meaningful therapeutic targeting.

Characterizing a low-density neutrophil gene signature in acute and chronic infections and its impact on disease severity

Low-density neutrophils (LDNs) or polymorphonuclear myeloid-derived suppressor cells are involved in the pathogenesis of cancer, autoimmune, and infectious diseases. They are crucial in the host response to invading pathogens, especially during acute illness, and are associated with poor prognosis in many infectious diseases. However, their gene expression profile and contribution to disease outcomes are not well described. We conducted a meta-analysis of gene expression datasets from peripheral blood mononuclear cells (PBMCs), focusing on patients with viral and bacterial infections. We identified a consensus set of 2,798 differentially expressed genes. Among these, 49 genes were commonly found in both the neutrophil degranulation pathway and the granule lumen-specific community. To validate this signature, we evaluated its expression in RNA-seq datasets, finding consistent upregulation of 24 genes in severe infections, 17 of them overlapped with genes overexpressed in CD16int cells. We also investigated the abundance of LDN-related proteins in a PBMC proteomics dataset from a cohort of sepsis and septic shock patients. Out of the 17 genes analyzed, 13 corresponding proteins were identified, 10 of which demonstrated significantly higher abundance in sepsis and septic shock patients compared with healthy controls. In conclusion, our study identified a pattern of 17 upregulated LDN genes, common to PBMC transcriptome and RNA-seq, and upregulated in CD16int, associated with acute infections and severe clinical outcomes, marking the first time these genes have been collectively presented as a potential signature of LDNs in relation to disease severity. Further research with prospective cohorts is needed to validate this LDN signature and explore its clinical implications.

Association between neutrophil to high-density lipoprotein cholesterol ratio and hearing loss: a cross-sectional study from NHANES

BACKGROUND

This study aimed to investigate the relationship between the neutrophil-to-HDL cholesterol ratio (NHR) and the risk of hearing loss, as well as to evaluate the potential of the NHR as a biomarker for hearing loss.

METHODS

The U.S. National Health and Nutrition Examination Survey (NHANES) data covering 2005-2012 and 2015-2020 were analyzed. A weighted multivariate logistic regression model assessed the correlation between NHR and speech-frequency hearing loss (SFHL) and high-frequency hearing loss (HFHL). Restricted cubic spline (RCS) regression analysis was utilized to investigate the nonlinear correlation. Additionally, subgroup analysis was performed to identify differences among subgroups. A receiver operating characteristic (ROC) analysis was conducted to evaluate the efficacy of NHR in predicting hearing loss.

RESULTS

A total of 10,436 participants were involved. After comprehensive adjustments for confounding factors, NHR was linearly correlated with SFHL and HFHL. Subgroup analysis revealed that race and the poverty index ratio (PIR) significantly modified the association between NHR and hearing loss. ROC analysis demonstrated the predictive capability of NHR for hearing loss.

CONCLUSION

NHR is positively correlated with the risk of hearing loss. This study suggests that NHR may serve as a potential biomarker for predicting and assessing hearing loss, demonstrating significant clinical application value. However, this cross-sectional study limits the ability to establish causality. Future longitudinal studies are needed to confirm these findings and explore potential mechanisms.

Aging platelets shift their hemostatic properties to inflammatory functions

ABSTRACT

Platelets are crucial players in hemostasis and thrombosis but also contribute to immune regulation and host defense, using different receptors, signaling pathways, and effector functions, respectively. Whether distinct subsets of platelets specialize in these diverse tasks is insufficiently understood. Here, we used a pulse-labeling method in Mus musculus models for tracking in vivo platelet aging and its functional implications. Using in vitro and in vivo assays, we reveal that young, reticulated platelets show heightened responses in the setting of clot formation, with corresponding, increased responses to agonists, adhesion, and retractile function. Unexpectedly, aged platelets lose their hemostatic proficiency but are more prone to react to inflammatory challenge: compared with reticulated platelets, this cohort was more likely to form platelet-leukocyte aggregates and showed increased adhesion to neutrophils in vitro, as well as enhanced bactericidal function. In vivo, this was reflected in increased pulmonary recruitment of aged platelets in an acute lung injury model. Proteomic analyses confirmed the upregulation of immune pathways in this cohort, including enhanced procoagulant function. In mouse models of prolonged platelet half-life, this resulted in increased pulmonary leukocyte infiltration and inflammation upon acute lung injury. Similarly, human platelet concentrates decreased their hemostatic function and elevated their putative immunomodulatory potential in vitro over time, and in a mouse model of platelet transfusion, aged platelet concentrates resulted in augmented inflammation. In summary, we show that platelets exhibit age-dependent phenotypic shifts, allowing them to fulfill their diverse tasks in the vasculature. Because functional alterations of aging platelets extend to platelet concentrates, this may hold important implications for transfusion medicine.

Meningeal neutrophil immune signaling influences behavioral adaptation following threat

Social creatures must attend to threat signals from conspecifics and respond appropriately, both behaviorally and physiologically. In this work, we show in mice a threat-sensitive immune mechanism that orchestrates psychological processes and is amenable to social modulation. Repeated encounters with socially cued threats triggered meningeal neutrophil (MN) priming preferentially in males. MN activity was correlated with attenuated defensive responses to cues. Canonical neutrophil-specific activation marker CD177 was upregulated after social threat cueing, and its genetic ablation abrogated male behavioral phenotypes. CD177 signals favored meningeal T helper (Th)1-like immune bias, which blunted neural response to threatening stimuli by enhancing intrinsic GABAergic inhibition within the prelimbic cortex via interferon-gamma (IFN-γ). MN signaling was sensitized by negative emotional states and governed by socially dependent androgen release. This male-biased hormone/neutrophil regulatory axis is seemingly conserved in humans. Our findings provide insights into how immune responses influence behavioral threat responses, suggesting a possible neuroimmune basis of emotional regulation.

Comprehensive macro and micro views on immune cells in ischemic heart disease

Ischemic heart disease (IHD) is a prevalent cardiovascular condition that remains the primary cause of death due to its adverse ventricular remodelling and pathological changes in end-stage heart failure. As a complex pathologic condition, it involves intricate regulatory processes at the cellular and molecular levels. The immune system and cardiovascular system are closely interconnected, with immune cells playing a crucial role in maintaining cardiac health and influencing disease progression. Consequently, alterations in the cardiac microenvironment are influenced and controlled by various immune cells, such as macrophages, neutrophils, dendritic cells, eosinophils, and T-lymphocytes, along with the cytokines they produce. Furthermore, studies have revealed that Gata6+ pericardial cavity macrophages play a key role in regulating immune cell migration and subsequent myocardial tissue repair post IHD onset. This review outlines the role of immune cells in orchestrating inflammatory responses and facilitating myocardial repair following IHD, considering both macro and micro views. It also discusses innovative immune cell-based therapeutic strategies, offering new insights for further research on the pathophysiology of ischemic heart disease and immune cell-targeted therapy for IHD.

Comprehensive macro and micro views on immune cells in ischemic heart disease

Ischemic heart disease (IHD) is a prevalent cardiovascular condition that remains the primary cause of death due to its adverse ventricular remodelling and pathological changes in end‐stage heart failure. As a complex pathologic condition, it involves intricate regulatory processes at the cellular and molecular levels. The immune system and cardiovascular system are closely interconnected, with immune cells playing a crucial role in maintaining cardiac health and influencing disease progression. Consequently, alterations in the cardiac microenvironment are influenced and controlled by various immune cells, such as macrophages, neutrophils, dendritic cells, eosinophils, and T‐lymphocytes, along with the cytokines they produce. Furthermore, studies have revealed that Gata6+ pericardial cavity macrophages play a key role in regulating immune cell migration and subsequent myocardial tissue repair post IHD onset. This review outlines the role of immune cells in orchestrating inflammatory responses and facilitating myocardial repair following IHD, considering both macro and micro views. It also discusses innovative immune cell‐based therapeutic strategies, offering new insights for further research on the pathophysiology of ischemic heart disease and immune cell‐targeted therapy for IHD.

Proteomic profiling of neutrophils and plasma in community-acquired pneumonia reveals crucial proteins in diverse biological pathways linked to clinical outcome

Introduction

Neutrophils play a dichotomous role in community-acquired pneumonia (CAP), providing protection and potentially causing damage. Existing research on neutrophil function in CAP relies on animal studies, leaving a gap in patient-centered investigations.

Methods

We used mass spectrometry to characterize the neutrophil proteome of moderately ill CAP patients at general ward admission and related the proteome to controls and clinical outcomes.

Results

We prospectively included 57 CAP patients and 26 controls and quantified 3482 proteins in neutrophil lysates and 386 proteins in concurrently collected plasma. The extensively studied granule-related proteins in animal models did not drive the neutrophil proteome changes associated with human CAP. Proteome alterations were primarily characterized by an increased abundance of proteins related to (aerobic) metabolic activity and (m)RNA translation/processing, concurrent with a diminished presence of cytoskeletal organization-related proteins (all pathways p<0.001). Higher and lower abundances of specific proteins, primarily constituents of these pathways, were associated with prolonged time to clinical stability in CAP. Moreover, we identified a pronounced presence of platelet-related proteins in neutrophil lysates of particularly viral CAP patients, suggesting the existence of neutrophil-platelet complexes in non-critically ill CAP patients. Of the proteins measured in neutrophils, 4.3% were detected in plasma.

Discussion

Our study presents new perspectives on the neutrophil proteome associated with CAP, laying the groundwork for forthcoming patient-centred investigations. Our results could pave the way for targeted strategies to fine-tune neutrophil responses, potentially improving CAP outcomes.

Complex role of neutrophils in the tumor microenvironment: an avenue for novel immunotherapies

Neutrophils, which originate from the bone marrow and are characterized by a segmented nucleus and a brief lifespan, have a crucial role in the body's defense against infections and acute inflammation. Recent research has uncovered the complex roles of neutrophils as regulators in tumorigenesis, during which neutrophils exhibit a dualistic nature that promotes or inhibits tumor progression. This adaptability is pivotal within the tumor microenvironment (TME). In this review, we provide a comprehensive characterization of neutrophil plasticity and heterogeneity, aiming to illuminate current research findings and discuss potential therapeutic avenues. By delineating the intricate interplay of neutrophils in the TME, this review further underscores the urgent need to understand the dual functions of neutrophils with particular emphasis on the anti-tumor effects to facilitate the development of effective therapeutic strategies against cancer.