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International audience; High-throughput single-cell methods have uncovered substantial heterogeneity in the pool of hematopoietic stem and progenitor cells (HSPCs), but how much instruction is inherited by offspring from their heterogeneous ancestors remains unanswered. Using a method that enables simultaneous determination of common ancestor, division number, and differentiation status of a large collection of single cells, our data revealed that murine cells that derived from a common ancestor had significant similarities in their division progression and differentiation outcomes. Although each family diversifies, the overall collection of cell types observed is composed of homogeneous families. Heterogeneity between families could be explained, in part, by differences in ancestral expression of cell surface markers. Our analyses demonstrate that fate decisions of cells are largely inherited from ancestor cells, indicating the importance of common ancestor effects. These results may have ramifications for bone marrow transplantation and leukemia, where substantial heterogeneity in HSPC behavior is observed.

Cellular barcoding is a powerful technique that allows for high-throughput mapping of the fate of single cells, notably hematopoietic stem and progenitor cells (HSPCs) after transplantation. Unique artificial DNA fragments, termed barcodes, are stably inserted into HSPCs using lentiviral transduction, making sure that each individual cell receives a single unique barcode. Barcoded HSPCs are transplanted into sublethally irradiated mice where they reconstitute the hematopoietic system through proliferation and differentiation. During this process, the barcode of each HSPC is inherited by all of its daughter cells and their subsequent mature hematopoietic cell progeny. After sorting mature hematopoietic cell subsets, their barcodes can be retrieved from genomic DNA through nested PCR and sequencing. Analysis of barcode sequencing results allows for determination of clonal relationships between the mature cells, that is, which cell types were produced by a single barcoded HSPC, as well as the heterogeneity of the initial HSPC population. Here, we give a detailed protocol of a complete HSPC cellular barcoding experiment, starting with barcode lentivirus production, isolation, transduction, and transplantation of HSPCs, isolation of target cells followed by PCR amplification and sequencing of DNA barcodes. Finally, we describe the basic filtering and analysis steps of barcode sequencing data to ensure high-quality results.

The advent of high throughput single cell methods such as scRNA-seq has uncovered substantial heterogeneity in the pool of hematopoietic stem and progenitor cells (HSPCs). A significant issue is how to reconcile those findings with the standard model of hematopoietic development, and a fundamental question is how much instruction is inherited by offspring from their ancestors. To address this, we further developed a high-throughput method that enables simultaneously determination of common ancestor, generation, and differentiation status of a large collection of single cells. Data from it revealed that while there is substantial population-level heterogeneity, cells that derived from a common ancestor were highly concordant in their division progression and share similar differentiation outcomes, revealing significant familial effects on both division and differentiation. Although each family diversifies to some extent, the overall collection of cell types observed in a population is largely composed of homogeneous families from heterogeneous ancestors. Heterogeneity between families could be explained, in part, by differences in ancestral expression of cell-surface markers that are used for phenotypic HSPC identification: CD48, SCA-1, c-kit and Flt3. These data call for a revision of the fundamental model of haematopoiesis from a single tree to an ensemble of trees from distinct ancestors where common ancestor effect must be considered. As HSPCs are cultured in the clinic before bone marrow transplantation, our results suggest that the broad range of engraftment and proliferation capacities of HSPCs could be consequences of the heterogeneity in their engrafted families, and altered culture conditions might reduce heterogeneity between families, possibly improving transplantation outcomes.

Severe influenza virus infection can lead to life-threatening pathology through immune-mediated tissue damage. In various experimental models, this damage is dependent on T cells. There is conflicting evidence regarding the role of neutrophils in influenza-mediated pathology. Neutrophils are often regarded as cells causing tissue damage, but, in recent years, it has become clear that a subset of human neutrophils is capable of suppressing T cells, which is dependent on macrophage-1 antigen (CD11b/CD18). Therefore, we tested the hypothesis that immune suppression by neutrophils can reduce T cell-mediated pathology after influenza infection. Wild-type (WT) and CD11b-/- mice were infected with A/HK/2/68 (H3N2) influenza virus. Disease severity was monitored by weight loss, leukocyte infiltration, and immunohistochemistry. We demonstrated that CD11b-/- mice suffered increased weight loss compared with WT animals upon infection with influenza virus. This was accompanied by increased pulmonary leukocyte infiltration and lung damage. The exaggerated pathology in CD11b-/- mice was dependent on T cells, as it was reduced by T cell depletion. In addition, pathology in CD11b-/- mice was accompanied by higher numbers of T cells in the lungs early during infection compared with WT mice. Importantly, these differences in pathology were not associated with an increased viral load, suggesting that pathology was immune-mediated rather than caused by virus-induced damage. In contrast to adoptive transfer of CD11b-/- neutrophils, a single adoptive transfer of WT neutrophils partly restored protection against influenza-induced pathology, demonstrating the importance of neutrophil CD11b/CD18. Our data show that neutrophil CD11b/CD18 limits pathology in influenza-induced, T cell-mediated disease.

To the editor: Monocytes originate from the bone marrow (BM), are distributed in the bloodstream, and can differentiate in the tissue into skin macrophages or intestinal dendritic cells (DCs).[1][1] They play an essential role in the defense against pathogens[2][2] and are implicated in a range of

Bloodstream infection is a hallmark of sepsis, a medically emergent condition requiring rapid treatment. However, up-regulation of host defense proteins through Toll-like receptors (TLRs) and nuclear factor B requires hours after endotoxin detection. Using confocal pulmonary intravital microscopy, we identified that the lung provides a TLR4–Myd88 (myeloid differentiation primary response gene 88)–dependent and abl tyrosine kinase–dependent niche for immediate CD11b-dependent neutrophil responses to endotoxin and Gram-negative bloodstream pathogens. In an in vivo model of bacteremia, neutrophils crawled to and rapidly phagocytosed Escherichia coli sequestered to the lung endothelium. Therefore, the lung capillaries provide a vascular defensive niche whereby endothelium and neutrophils cooperate for immediate detection and capture of disseminating pathogens.

Neutrophils are the most abundant white blood cells and are indispensable for host defense. Recently, they have also been implicated in immune regulation and suppression. The latter functions seem hard to reconcile with the widely held view that neutrophils are very short-lived, with a circulatory half-life of

Neutrophils are essential effector cells in the host defense against invading pathogens. Recently, novel neutrophil functions have emerged in addition to their classical anti-microbial role. One of these functions is the suppression of T cell responses. In this respect, neutrophils share similarities with granulocytic myeloid-derived suppressor cells (G-MDSCs). In this review, we will discuss the similarities and differences between neutrophils and G-MDSCs. Various types of G-MDSCs have been described, ranging from immature to mature cells shaping the immune response by different immune suppressive mechanisms. However, all types of G-MDSCs share distinct features of neutrophils, such as surface markers and morphology. We propose that G-MDSCs are heterogeneous and represent novel phenotypes of neutrophils, capable of suppressing the immune response. In this review, we will attempt to clarify the differences and similarities between neutrophils and G-MDSCs and attempt to facilitate further research.

Summary Inflammatory phenotypes of asthma are associated with differences in disease characteristics. It is unknown whether these inflammatory phenotypes are reflected by the activation status of neutrophils in blood and sputum. We obtained peripheral blood and induced sputum from 21 asthma patients and stratified our samples based on sputum eosinophilia resulting in two groups (>3% eosinophils: n = 13

Three human monocyte subsets are recognized with different functions in the immune system: CD14++/CD16- classical monocytes (CM), CD14++/CD16+ intermediate monocytes (IM) and CD14+/CD16++ non-classical monocytes (NCM). Increased IM and NCM percentages have been reported under inflammatory conditions, yet little is known about monocyte subsets at the onset of inflammation. The human endotoxemia model is uniquely capable of studying the first phases of acute inflammation induced by intravenous injection of 2 ng/kg bodyweight lipopolysaccharide (LPS) into healthy volunteers. After that, monocyte subset counts, activation/differentiation status and chemokine levels were studied over 24 h. The numbers of all subsets were decreased by >95% after LPS injection. CM numbers recovered first (3- 6 h), followed by IM (6-8 h) and NCM numbers (8-24 h). Similarly, increased monocyte counts were observed first in CM (8 h), followed by IM and NCM (24 h). Monocytes did not display a clear activated phenotype (minor increase in CD11b and CD38 expression). Plasma levels of CCL2, CCL4 and CX3CL1 closely resembled the cell numbers of CM, IM and NCM, respectively. Our study provides critical insights into the earliest stages of acute inflammation and emphasizes the necessity to stain for different monocyte subsets when studying the role of monocytes in disease, as neither function nor kinetics of the subsets overlap.

Background Systemic onset Juvenile Idiopathic Artritis (sJIA) is a systemic autoinflammatory disease, characterised by arthritis, spiking fever and rash and elevation of serum S100-proteins and interleukin (IL)-18. The role of monocytes and neutrophils in the inflammatory cascade of sJIA is still unclear. Objective To study the role of monocytes and neutrophils in the inflammatory cascade of sJIA. Methods We determined neutrophil activation ex vivo (phenotype and cell membrane markers) and after stimulation (ROS-production and degranulation) of cells derived from sJIA with disease onset or in remission, compared to healthy donors (HDs). To investigate the role of monocytes, we assessed cytokine production of PBMCs from sJIA patients and HDs after stimulation with TLR-4 activating S100-proteins (+/- ATP) or other TLR-ligands. In a cohort of sJIA patients at onset and during inactive disease, we evaluated cell counts and serum levels of cytokines, chemokines and other analytes. Cytokine concentrations in supernatant and serum were determined by multiplex immunoassay. Results Twenty-one of 23 patients with onset sJIA had elevated neutrophil counts, while monocyte counts were elevated in only 5/23 patients. Many inflammatory markers were significantly elevated in serum of onset sJIA patients, among which several neutrophil specific proteins indicating the importance of this cell type. Neutrophils from onset sJIA patients showed an activated phenotype, reflected by higherex vivocell membraneexpression of FC-gamma receptors (CD32 and CD64), markers of secretory vesicles (CD35) and specific granules (CD66b). ROS production and degranulation were also enhanced in onset sJIA. Neutrophil phenotypenormalized when patients were in remission. In contrast to the hyperactivated status of neutrophils in active sJIA, PBMCs from these patients produced less Il-1b, IL-18, IL-6 and TNF-a upon TLR-stimulation compared to PBMCs from remission patients or HDs, suggesting tolerance after exposure to high TLR4 stimulating S100-levels in vivo. Conclusions We show here that monocytes from onset sJIA patients produce less cytokines upon stimulation, while the neutrophils are hyperactivated, reflected by increased cell membrane activation markers, ROS production and degranulation. The exact role of each cell type and activity and their interaction in sJIA pathology is currently under investigation.

Contains fulltext : 108037.pdf (Publisher’s version ) (Open Access) Suppression of immune responses is necessary to limit damage to host tissue during inflammation, but it can be detrimental in specific immune responses, such as sepsis and antitumor immunity. Recently, immature myeloid cells have been implicated in the suppression of immune responses in mouse models of cancer, infectious disease, bone marrow transplantation, and autoimmune disease. Here, we report the identification of a subset of mature human neutrophils (CD11cbright/CD62Ldim/CD11bbright/CD16bright) as what we believe to be a unique circulating population of myeloid cells, capable of suppressing human T cell proliferation. These cells were observed in humans in vivo during acute systemic inflammation induced by endotoxin challenge or by severe injury. Local release of hydrogen peroxide from the neutrophils into the immunological synapse between the neutrophils and T cells mediated the suppression of T cell proliferation and required neutrophil expression of the integrin Mac-1 (alphaMbeta2). Our data demonstrate that suppression of T cell function can be accomplished by a subset of human neutrophils that can be systemically induced in response to acute inflammation. Identification of the pivotal role of neutrophil Mac-1 and ROS in this process provides a potential target for modulating immune responses in humans.

The cytokine erythropoietin (EPO) is a potent inducer of erythrocyte development and one of the most prescribed biopharmaceuticals. The action of EPO on erythroid progenitor cells is well established, but its direct action on hematopoietic stem and progenitor cells (HSPCs) is still debated. Here, using cellular barcoding, we traced the differentiation of hundreds of single murine HSPCs, after ex vivo EPO-exposure and transplantation, in five different hematopoietic cell lineages, and observed the transient occurrence of high-output Myeloid-Erythroid-megaKaryocyte (MEK)-biased and Myeloid-B-cell-Dendritic cell (MBDC)-biased clones. Single-cell RNA sequencing (ScRNAseq) analysis of ex vivo EPO-exposed HSPCs revealed that EPO induced the upregulation of erythroid associated genes in a subset of HSPCs, overlapping with multipotent progenitor (MPP) 1 and MPP2. Transplantation of Barcoded EPO-exposed-MPP2 confirmed their enrichment in Myeloid-Erythroid-biased clones. Collectively, our data show that EPO does act directly on MPP independent of the niche, and modulates fate by remodeling the clonal composition of the MPP pool.