Neutrophil Heterogeneity Research Articles

Relationship between neutrophil phenotypic and functional heterogeneity and diseases

Neutrophils are the most abundant circulating leukocyte type in humans and comprise the host's first line of cellular defense against foreign pathogens invasion. On the other hand, neutrophils are the main mediators of tissue damage induced by acute and chronic inflammation. They were once considered to be short-lived, low transcriptional activity, and terminally differentiated homogeneous leucocytes that failed to return to circulation from tissue. However, more evidence has demonstrated that neutrophils can develop into different sub-populations with phenotypic heterogeneity and functional versatility under physiology and pathological conditions. This review summarizes the phenotypic and functional heterogeneity of neutrophils in sepsis and tumor genesis.

Analysis of classical neutrophils and polymorphonuclear myeloid-derived suppressor cells in cancer patients and tumor-bearing mice.

In this study, using single-cell RNA-seq, cell mass spectrometry, flow cytometry, and functional analysis, we characterized the heterogeneity of polymorphonuclear neutrophils (PMNs) in cancer. We describe three populations of PMNs in tumor-bearing mice: classical PMNs, polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), and activated PMN-MDSCs with potent immune suppressive activity. In spleens of mice, PMN-MDSCs gradually replaced PMNs during tumor progression. Activated PMN-MDSCs were found only in tumors, where they were present at the very early stages of the disease. These populations of PMNs in mice could be separated based on the expression of CD14. In peripheral blood of cancer patients, we identified two distinct populations of PMNs with characteristics of classical PMNs and PMN-MDSCs. The gene signature of tumor PMN-MDSCs was similar to that in mouse activated PMN-MDSCs and was closely associated with negative clinical outcome in cancer patients. Thus, we provide evidence that PMN-MDSCs are a distinct population of PMNs with unique features and potential for selective targeting opportunities.

Identification and characterization of neutrophil heterogeneity in sepsis

BackgroundAlthough the immune function of neutrophils in sepsis has been well described, the heterogeneity of neutrophils remains unclear during the process of sepsis.MethodsIn this study, we used a mouse CLP model to simulate the clinical scenario of patients with sepsis, neutrophil infiltration, abnormal distribution and dysfunction was analyzed. LPS was used to stimulate neutrophils in vitro to simulate sepsis; single-cell gene sequencing technology was used to explore the immunological typing. To explore the immunological function of immunosuppressive neutrophils, PD-L1 knockout neutrophils were cocultured with lymphocytes from wild-type mice.ResultsWe found that neutrophils presented variant dysfunction at the late stage of sepsis, including inhibition of apoptosis, seriously damaged chemotaxis and extensive infiltration into the tissues. Single-cell RNA sequencing revealed that multiple subclusters of neutrophils were differentiated after LPS stimulation. The two-dimensional spatial distribution analysis showed that Foxp3+ T cells were much closer to Ly-6G than the CD4+ and CD8+ cells, indicating that infiltrated neutrophils may play immunomodulatory effect on surrounding T-regs. Further observations showed that LPS mediates PD-L1 over expression through p38α-MSK1/-MK2 pathway in neutrophils. The subsets of highly expressed PD-L1 exert immunosuppressive effect under direct contact mode, including inhibition of T cell activation and induction of T cell apoptosis and trans-differentiation.ConclusionsTaken together, our data identify a previously unknown immunosuppressive subset of neutrophils as inhibitory neutrophil in order to more accurately describe the phenotype and characteristics of these cells in sepsis.

Neutrophil-derived granule cargoes: paving the way for tumor growth and progression.

Neutrophils are the key cells of our innate immune system mediating host defense via a range of effector functions including phagocytosis, degranulation, and NETosis. For this, they employ an arsenal of anti-microbial cargoes packed in their readily mobilizable granule subsets. Notably, the release of granule content is tightly regulated; however, under certain circumstances, their unregulated release can aggravate tissue damage and could be detrimental to the host. Several constituents of neutrophil granules have also been associated with various inflammatory diseases including cancer. In cancer setting, their excessive release may modulate tissue microenvironment which ultimately leads the way for tumor initiation, growth and metastasis. Neutrophils actively infiltrate within tumor tissues, wherein they show diverse phenotypic and functional heterogeneity. While most studies are focused at understanding the phenotypic heterogeneity of neutrophils, their functional heterogeneity, much of which is likely orchestrated by their granule cargoes, is beginning to emerge. Therefore, a better understanding of neutrophil granules and their cargoes will not only shed light on their diverse role in cancer but will also reveal them as novel therapeutic targets. This review provides an overview on existing knowledge of neutrophil granules and detailed insight into the pathological relevance of their cargoes in cancer. In addition, we also discuss the therapeutic approach for targeting neutrophils or their microenvironment in disease setting that will pave the way forward for future research.

Proteomic, biomechanical and functional analyses define neutrophil heterogeneity in systemic lupus erythematosus

ObjectivesLow-density granulocytes (LDGs) are a distinct subset of proinflammatory and vasculopathic neutrophils expanded in systemic lupus erythematosus (SLE). Neutrophil trafficking and immune function are intimately linked to cellular biophysical properties....

Olfactomedin 4–Positive Neutrophils Are Upregulated after Hemorrhagic Shock

Neutrophils are vital to both the inflammatory cascade and tissue repair after an injury. Neutrophil heterogeneity is well established but there is less evidence for significant, different functional roles for neutrophil subsets. OLFM4 (Olfactomedin-4) is expressed by a subset of neutrophils, and high expression of OLFM4 is associated with worse outcomes in patients with sepsis and acute respiratory distress syndrome. We hypothesized that an increased number of OLFM4+ neutrophils would occur in trauma patients with worse clinical outcomes. To test this, we prospectively enrolled patients who suffered a blunt traumatic injury. Blood was collected at the time of admission, Day 3, and Day 7 and analyzed for the percentage of neutrophils expressing OLFM4. We found that a subset of patients who suffered blunt traumatic injury upregulated their percentage of OLFM4+ neutrophils. Those who upregulated their OLFM4 had an increased length of stay, days in the ICU, and ventilator days. A majority of these patients also suffered from hemorrhagic shock. To establish a potential role for OLFM4+ neutrophils, we used a murine model of hemorrhagic shock because mice also express OLFM4 in a subset of neutrophils. These studies demonstrated that wild type mice had higher concentrations of cytokines in the plasma and myeloperoxidase in the lungs compared with OLFM4-null mice. In addition, we used an anti-OLFM4 antibody, which when given to wild type mice led to the reduction of myeloperoxidase in the lungs of mice. These findings suggest that OLFM4+ neutrophils are a unique subset of neutrophils that affect the inflammatory response after tissue injury.

Transfer Learning for Identifying Morphological Heterogeneity of Neutrophils Nuclei in Hematological Diseases Based on Nuclei Semantic Segmentations of Bone Marrow Smear

It has been known that neutrophils are also very important in hematological diseases, such as dysplasia of neutrophils in myelodysplastic syndromes (MDS). But we pay more attention to immature blood cells (blasts) on bone marrow smear, because their proportion and morphology are key indicators for diagnosing malignant hematological diseases. We seem to pay less attention to neutrophils' roles in the diagnosis and the pathogenesis of hematological diseases. As we know, the survival period of neutrophils is relatively short and the neutrophils nuclei are rich in genetic information. Therefore, we assumed that the changes of neutrophils, especially the changes of neutrophils nuclei may be a mirror that reflects different hematological diseases. Here we will explore the differences among the morphology of neutrophils nuclei in hematological diseases, and try to find the bases of these differences. We selected neutrophils from 4 types of malignant hematological diseases, which is chronic myelogenous leukemia (CML), multiple myeloma (MM), acute myeloblastic leukemia with maturation (AML-M2), acute monocytic leukemia (AML-M5) and normal bone marrow. Neutrophils were identified by two senior diagnosticians (diagnostic experience longer than 10 years). In this study, we first segmented the neutrophils image by hand, and then use ilastik, an interactive semantic segmentations tool, to perform the nucleus segmentation. We applied transfer learning to training classification model of the segmented nuclei. We found that the neutrophils nuclei from different hematological diseases can be distinguished by the model. That is, we can preliminarily judge which kind of disease based on the neutrophils nuclei. These findings suggest that it is possible to have specific neutrophils nuclei features among different hematological diseases. However, due to the black box effect of the deep learning model, we still do not know what these features are. In order to clarify these potential features of neutrophils, we performed feature extraction (including texture analysis) on the segmented nuclei, and applied Fiji or imagej to obtain the feature parameters of the nuclei. At last using R language packages rattle (version 5.3.0) for features comparison and analysis. We found that there are differences in some feature parameters of the neutrophils nuclei among them. Maybe these are the basis for the heterogeneity of neutrophils in different hematological diseases. Here we provide a preliminary study for the neutrophils phenotype heterogeneity in different hematological diseases by deep learning. Differences in morphology of neutrophils nuclei may be the base of the heterogeneity. The features analysis of the neutrophils nuclei based on machine learning pixel classification further explains the basis of image specific difference discovered by transfer learning. In the future, the morphology of the neutrophils nuclei probably play an important role on distinguishing different hematological diseases. Disclosures No relevant conflicts of interest to declare.

Deep Learning for Discovering and Identifying Morphological Heterogeneity of Neutrophils in Primary Hematological Diseases Based on Bone Marrow Neutrophils Analysis

It has been known that neutrophils play an important role in regulating homeostasis and disease. Tumor-associated neutrophils (TANs), as an important member of the tumor microenvironment, have gradually been proved their roles in a variety of solid tumors. It is generally believed that the changes in blood cell morphology (including neutrophils) are the phenotype of hematological diseases (such as in myelodysplastic syndromes) or tumor cells themselves. However, whether there is a possibility that the accumulation of abnormal neutrophils function leads to the change of hematopoietic stem cells and this is just the reason of hematological diseases? Do neutrophils play a key role in the pathogenesis and development of hematological tumors, especially acquired or age-related blood diseases, such as most acute and chronic leukemia, multiple myeloma and other diseases? TAN also has polarization, which is similar to tumor-associated macrophages (TAM), suggesting that the function and morphology of neutrophils are closely associated. Therefore, we assumed that there are function-related morphological differences in neutrophils in different hematological diseases. Finding these differences may provide clues for the functional research of neutrophils in hematological diseases. Artificial intelligence represented by deep learning can distinguish images efficiently and accurately (such as face recognition). Here we try to apply deep learning to discovery and recognize the morphological difference among neutrophils in different hematological diseases. We obtained whole slide images (WSI) from 4 types of malignant hematological diseases, which is chronic myelogenous leukemia (CML), multiple myeloma (MM), acute myeloblastic leukemia with maturation (AML-M2), acute monocytic leukemia (AML-M5) and normal bone marrow. Neutrophils were segmented from WSI by two diagnostic physicians (one with more than 40 years of diagnostic experience and the other with 13 years of diagnostic experience) There are 6115 neutrophils, and the number of cells in each disease and normal bone marrow is 593, 1404, 2509, 850, and 759, respectively. We trained these neutrophils using the transfer learning algorithm and the ratio of training and verification groups is 80:20. We established a convolutional neural network (CNN) model based on the morphological phenotype of neutrophils to judge their disease classification and used confusion matrix and receiver operator characteristic (ROC) curve for model evaluation. We found that neutrophils from different diseases can be classified into different categories, and the deep learning model has a high accuracy rate for judging the neutrophils from different diseases. Moreover, according to the obtained mixed matrix results, it is found that some M2 and M5 neutrophils are prone to misjudgment, while M2 and M5 is rarely confused with other diseases. The reason for this may be that M2 and M5 are both acute myeloid leukemia. Neutrophils from MM and normal bone marrow are prone to misjudge each other or judged as CML neutrophils, and MM often involves the plasma cell system, so some neutrophils of MM may be similar to normal bone marrow. Compared with acute leukemia, some chronic leukemia neutrophils are close to MM or normal bone marrow. Based on these results, we can further confirm that there are morphological and phenotypic differences between different types of hematological diseases. According to the ROC curve results, it is suggested that the deep learning model constructed based on the feature extraction of the CNN model can more accurately determine different hematological diseases according to morphological phenotypes of neutrophils. These findings suggest that neutrophils in different hematological diseases have their own features. These features may provide more evidence for the diagnosis of the disease and also provide clues for further research on the function of TAN in primary hematological diseases. Disclosures No relevant conflicts of interest to declare.

Harnessing lipid signaling pathways to target specialized pro-angiogenic neutrophil subsets for regenerative immunotherapy.

To gain insights into neutrophil heterogeneity dynamics in the context of sterile inflammation and wound healing, we performed a pseudotime analysis of single-cell flow cytometry data using the spanning-tree progression analysis of density-normalized events algorithm. This enables us to view neutrophil transitional subsets along a pseudotime trajectory and identify distinct VEGFR1, VEGFR2, and CXCR4 high-expressing pro-angiogenic neutrophils. While the proresolving lipid mediator aspirin-triggered resolvin D1 (AT-RvD1) has a known ability to limit neutrophil infiltration, our analysis uncovers a mode of action in which AT-RvD1 leads to inflammation resolution through the selective reprogramming toward a therapeutic neutrophil subset. This accumulation leads to enhanced vascular remodeling in the skinfold window chamber and a proregenerative shift in macrophage and dendritic cell phenotype, resulting in improved wound closure after skin transplantation. As the targeting of functional immune subsets becomes the key to regenerative immunotherapies, single-cell pseudotime analysis tools will be vital in this field.

Live Imaging of Heart Injury in Larval Zebrafish Reveals a Multi-Stage Model of Neutrophil and Macrophage Migration.

Neutrophils and macrophages are crucial effectors and modulators of repair and regeneration following myocardial infarction, but they cannot be easily observed in vivo in mammalian models. Hence many studies have utilized larval zebrafish injury models to examine neutrophils and macrophages in their tissue of interest. However, to date the migratory patterns and ontogeny of these recruited cells is unknown. In this study, we address this need by comparing our larval zebrafish model of cardiac injury to the archetypal tail fin injury model. Our in vivo imaging allowed comprehensive mapping of neutrophil and macrophage migration from primary hematopoietic sites, to the wound. Early following injury there is an acute phase of neutrophil recruitment that is followed by sustained macrophage recruitment. Both cell types are initially recruited locally and subsequently from distal sites, primarily the caudal hematopoietic tissue (CHT). Once liberated from the CHT, some neutrophils and macrophages enter circulation, but most use abluminal vascular endothelium to crawl through the larva. In both injury models the innate immune response resolves by reverse migration, with very little apoptosis or efferocytosis of neutrophils. Furthermore, our in vivo imaging led to the finding of a novel wound responsive mpeg1+ neutrophil subset, highlighting previously unrecognized heterogeneity in neutrophils. Our study provides a detailed analysis of the modes of immune cell migration in larval zebrafish, paving the way for future studies examining tissue injury and inflammation.

How to bridle a neutrophil.

Recent high-dimensional technologies have enabled the characterization of heterogeneity in the neutrophil compartment at an unprecedented resolution. In this review, we discuss the emerging notion of heterogeneity within the neutrophil pool, and provide a detailed account of evolving concepts in the field. We place special focus on neutrophil differentiation in the bone marrow and plasticity in tissues, describe the limitations that arise when exploring neutrophil heterogeneity using single-cell analyses, and suggest state-of-the-art alternatives to improve their characterization. Finally, we propose strategies arising from these new concepts that may allow us to bridle neutrophil plasticity towards therapeutic benefit.

Conundrums in leishmaniasis

Parasites of the genus Leishmania cause the disease leishmaniasis. As the sandfly vector transfers the promastigotes into the skin of the human host, the infection is either cured or exacerbated. In the process, there emerge several unsolved paradoxes of leishmaniasis. Chronologically, as the infections starts in skin, the role of the salivary proteins in supporting the infection or the host response to these proteins influencing the induction of immunological memory becomes a conundrum. As the parasite invokes inflammation, the infiltrating neutrophils may act as “Trojan Horse” to transfer parasites to macrophages that, along with dendritic cells, carry the parasite to lymphoid organs to start visceralization. As the visceralized infection becomes chronic, the acutely enhanced monocytopoiesis takes a downturn while neutropenia and thrombocytopenia ensue with concomitant rise in splenic colony-forming-units. These responses are accompanied by splenic and hepatic granulomas, polyclonal activation of B cells and deviation of T cell responses. The granuloma formation is both a containment process and a form of immunopathogenesis. The heterogeneity in neutrophils and macrophages contribute to both cure and progression of the disease. The differentiation of T-helper subsets presents another paradox of visceral leishmaniasis, as the counteractive T cell subsets influence the curing or non-curing outcome. Once the parasites are killed by chemotherapy, in some patients the cured visceral disease recurs as a cutaneous manifestation post-kala azar dermal leishmaniasis (PKDL). As no experimental model exists, the natural history of PKDL remains almost a black box at the end of the visceral disease.

CyTOF mass cytometry reveals phenotypically distinct human blood neutrophil populations differentially correlated with melanoma stage

BackgroundUnderstanding neutrophil heterogeneity and its relationship to disease progression has become a recent focus of cancer research. Indeed, several studies have identified neutrophil subpopulations associated with protumoral or antitumoral functions....

Abstract 3311: B cell like neutrophil found in peripheral blood of melanoma patients

Abstract An expansion of neutrophils often marks cancer. To date, neutrophils are assumed to be a relatively homogenous population, but recent studies describe both pro- and anti-tumor functions in neutrophils. This suggests there is more heterogeneity in neutrophils than previously appreciated. To better understand and target neutrophil functions in cancer, we must dissect neutrophil heterogeneity and how it changes from health to disease. To this end, we employed single-cell transcriptome technology to profile immature neutrophils from bone marrow of healthy individuals. Intriguingly, we identified a new neutrophil subset that expresses several B cell markers, including CD79a/b, components of the B cell receptors and PAX5, a lineage-specific transcriptional factor. We termed this population the BNeut. Using flow cytometry, we found that BNeuts are confined to the bone marrow of healthy individuals but expand into the blood of melanoma patients at an early stage, suggesting BNeuts might be a biomarker for disease. Additionally, we find BNeuts in the mouse models of different cancer types, including breast and lung carcinoma. The BNeut appears and functions more similar to a neutrophil than a B cell. BNeuts possess a neutrophil-like transcriptional profile, large cytoplasm with segmented nucleus, and produce ROS and NETs. Using imaging, we show that the BNeuts are single cells co-expressing both CD66b and CD79b, and lack the B cell surface marker CD19. To understand why neutrophils might use a B cell program, we explored different B cell functions including antigen presentation, a function that is usually absent from neutrophils. We show BNeuts are excellent at phagocytosis, including uptake of tumor cells. Further, BNeuts have increased expression of antigen presentation-related genes compared to other neutrophils and can modulate CD4+ T cell responses. Together, we have identified a novel neutrophil subset expressing B cell markers that is preferentially expanded in the blood of melanoma patients and poised to control T cell responses during disease. Citation Format: Melissa A. Meyer, Huy Q. Dinh, Yanfang Zhu, Shu Liang, Gregory Seumois, Pandurangan Vijayanand, Sergio D. Catz, Catherine C. Hedrick. B cell like neutrophil found in peripheral blood of melanoma patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3311.

Single-cell transcriptome profiling reveals neutrophil heterogeneity in homeostasis and infection.

The full neutrophil heterogeneity and differentiation landscape remains incompletely characterized. Here we profiled >25,000 differentiating and mature mouse neutrophils using single-cell RNA sequencing to provide a comprehensive transcriptional landscape of neutrophil maturation, function, and fate decision in their steady state and during bacterial infection. Eight neutrophil populations were defined by distinct molecular signatures. The three mature peripheral blood neutrophil subsets arise from distinct maturing bone marrow neutrophil subsets. Driven by both known and uncharacterized transcription factors, neutrophils gradually acquire microbicidal capability as they traverse the transcriptional landscape, representing an evolved mechanism for fine-tuned regulation of an effective but balanced neutrophil response. Bacterial infection reprograms the genetic architecture of neutrophil populations, alters dynamic transition between each subpopulation, and primes neutrophils for augmented functionality without affecting overall heterogeneity. In summary, these data establish a reference model and general framework for studying neutrophil-related disease mechanisms, biomarkers, and therapeutic targets at single-cell resolution.

Neutrophil heterogeneity and fate in inflamed tissues: implications for the resolution of inflammation.

Neutrophils are polymorphonuclear leukocytes that play a central role in host defense against infection and tissue injury. They are rapidly recruited to the inflamed site and execute a variety of functions to clear invading pathogens and damaged cells. However, many of their defense mechanisms are capable of inflicting collateral tissue damage. Neutrophil-driven inflammation is a unifying mechanism underlying many common diseases. Efficient removal of neutrophils from inflammatory loci is critical for timely resolution of inflammation and return to homeostasis. Accumulating evidence challenges the classical view that neutrophils represent a homogeneous population and that halting neutrophil influx is sufficient to explain their rapid decline within inflamed loci during the resolution of protective inflammation. Hence, understanding the mechanisms that govern neutrophil functions and their removal from the inflammatory locus is critical for minimizing damage to the surrounding tissue and for return to homeostasis. In this review, we briefly address recent advances in characterizing neutrophil phenotypic and functional heterogeneity and the molecular mechanisms that determine the fate of neutrophils within inflammatory loci and the outcome of the inflammatory response. We also discuss how these mechanisms may be harnessed as potential therapeutic targets to facilitate resolution of inflammation.

Importance of validating antibody panels: Anti-PD-L1 clone binds AF700 fluorophore

Researchers routinely use antibodies to assess the expression levels of proteins on the surface or intracellularly in a variety of different cell types. In this current study we highlight the importance of careful validation of antibodies for analysis of protein expression by flow cytometry and how failure to do so can significantly impact the interpretation of the data generated leading to false-positive results. There has been increasing awareness of the role the programmed death receptor 1 (PD-1) pathway plays in health and disease and a potential that programme death ligand 1 (PD-L1) may play a role in inflammatory disease. We aimed to investigate PD-L1 expression on human neutrophils isolated from healthy individuals and patients diagnosed with chronic obstructive pulmonary disease (COPD). We observed an increase in surface expression of PD-L1 by human neutrophils when incubated with AlexaFluor™700-conjugated anti-CD16. Through careful interrogation and antibody validation, we found a novel interaction between a commercially available anti-PD-L1 antibody and the AlexaFluor™700 fluorophore, resulting in this observed increase in PD-L1 signal. Surface expression of PD-L1 was not observed on neutrophils from healthy volunteers or patients with COPD when clone 29E.2A3 of anti-PD-L1 was not used with AlexaFluor™700-conjugated anti-CD16. This highlights the importance of robust antibody validation to ensure antibody compatibility in the context of multi-parametric flow cytometry panels. We also show that, without these validation experiments, novel neutrophil phenotypes could be falsely reported – an important consideration when there is increasing interest in neutrophil heterogeneity.

ANCA autoantigen gene expression highlights neutrophil heterogeneity where expression in normal-density neutrophils correlates with ANCA-induced activation

ANCA vasculitis is an autoimmune disease with increased expression of the autoantigen genes, myeloperoxidase (MPO) and proteinase 3 (PRTN3), but the origin and significance of expression is less distinct. To clarify this, we measured MPO and PRTN3 messenger RNA in monocytes, normal-density neutrophils, and in enriched leukocytes from peripheral blood mononuclear cells. Increased autoantigen gene expression was detected in normal-density neutrophils and enriched leukocytes from patients during active disease compared to healthy individuals, with the largest difference in enriched leukocytes. RNA-seq of enriched leukocytes comparing active-remission pairs identified a gene signature for low-density neutrophils. Cell sorting revealed low-density neutrophils contained mature and immature neutrophils depending on the presence or absence of CD10. Both populations contributed to autoantigen expression but the frequency of immature cells in low-density neutrophils did not correlate with low-density neutrophil MPO or PRTN3 expression. Low-density neutrophils were refractory to MPO-ANCA induced oxidative burst, suggesting an alternative role for low-density neutrophils in ANCA vasculitis pathogenesis. In contrast, normal-density neutrophils were activated by MPO-ANCA and monoclonal anti-PR3 antibody. Normal-density neutrophil activation correlated with MPO and PRTN3 mRNA. Increased autoantigen gene expression originating from the mature low-density and normal-density neutrophils suggests transcriptional dysregulation is a hallmark of ANCA vasculitis. Thus, the correlation between autoantigen gene expression and antibody-mediated normal-density neutrophil activation connects autoantigen gene expression with disease pathogenesis.

Neutrophils at the crossroads of innate and adaptive immunity.

Neutrophils are the most abundant leukocytes in blood. From the circulation, they are quickly mobilized to sites of inflammation and/or infection. At the affected tissues, neutrophils display an impressive array of antimicrobial functions, including degranulation, production of reactive oxygen species (ROS), phagocytosis, and formation of neutrophil extracellular traps (NET). Because neutrophils are the first type of leukocytes to arrive at affected tissues and display potent microbicidal functions, they have been classically viewed as the first line of defense. In this view, neutrophils only destroy invading pathogens and then quietly die at the site of infection. However, in the last decade it has become increasingly evident that neutrophils are much more complex cells having not only effector functions in the innate immune response, but also the capacity of modulating the adaptive immune response, via direct interaction with, or by producing cytokines that affect dendritic cells and lymphocytes. In addition, neutrophil heterogeneity with clear different functional phenotypes has been recently described particularly in cancer and inflammation. This review provides an overview on the life of a neutrophil describing its beginnings, lifespan, and their principal functions in innate and adaptive immunity. Also, neutrophil heterogeneity and our current understanding of neutrophil contributions to health and disease are discussed.

Transcriptomic, epigenetic, and functional analyses implicate neutrophil diversity in the pathogenesis of systemic lupus erythematosus

Neutrophil dysregulation is implicated in the pathogenesis of systemic lupus erythematosus (SLE). SLE is characterized by elevated levels of a pathogenic neutrophil subset known as low-density granulocytes (LDGs). The origin and phenotypic, functional, and pathogenic heterogeneity of LDGs remain to be systematically determined. Transcriptomics and epigenetic assessment of lupus LDGs, autologous normal-density neutrophils, and healthy control neutrophils was performed by bulk and single-cell RNA sequencing and assay for transposase-accessible chromatin sequencing. Functional readouts were compared among neutrophil subsets. SLE LDGs display significant transcriptional and epigenetic heterogeneity and comprise 2 subpopulations of intermediate-mature and immature neutrophils, with different degrees of chromatin accessibility and differences in transcription factor motif analysis. Differences in neutrophil extracellular trap (NET) formation, oxidized mitochondrial DNA release, chemotaxis, phagocytosis, degranulation, ability to harm the endothelium, and responses to type I interferon (IFN) stimulation are evident among LDG subsets. Compared with other immune cell subsets, LDGs display the highest expression of IFN-inducible genes. Distinct LDG subsets correlate with specific clinical features of lupus and with the presence and severity of coronary artery disease. Phenotypic, functional, and pathogenic neutrophil heterogeneity are prevalent in SLE and may promote immune dysregulation and prominent vascular damage characteristic of this disease.