-
Cell Apr 2021A dysfunctional immune response in coronavirus disease 2019 (COVID-19) patients is a recurrent theme impacting symptoms and mortality, yet a detailed understanding of...
A dysfunctional immune response in coronavirus disease 2019 (COVID-19) patients is a recurrent theme impacting symptoms and mortality, yet a detailed understanding of pertinent immune cells is not complete. We applied single-cell RNA sequencing to 284 samples from 196 COVID-19 patients and controls and created a comprehensive immune landscape with 1.46 million cells. The large dataset enabled us to identify that different peripheral immune subtype changes are associated with distinct clinical features, including age, sex, severity, and disease stages of COVID-19. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA was found in diverse epithelial and immune cell types, accompanied by dramatic transcriptomic changes within virus-positive cells. Systemic upregulation of S100A8/A9, mainly by megakaryocytes and monocytes in the peripheral blood, may contribute to the cytokine storms frequently observed in severe patients. Our data provide a rich resource for understanding the pathogenesis of and developing effective therapeutic strategies for COVID-19.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; COVID-19; Child; China; Cohort Studies; Cytokines; Female; Humans; Male; Megakaryocytes; Middle Aged; Monocytes; RNA, Viral; SARS-CoV-2; Single-Cell Analysis; Transcriptome; Young Adult
PubMed: 33657410
DOI: 10.1016/j.cell.2021.01.053 -
Circulation Research Jan 2022Classically, platelets have been described as the cellular blood component that mediates hemostasis and thrombosis. This important platelet function has received... (Review)
Review
Classically, platelets have been described as the cellular blood component that mediates hemostasis and thrombosis. This important platelet function has received significant research attention for >150 years. The immune cell functions of platelets are much less appreciated. Platelets interact with and activate cells of all branches of immunity in response to pathogen exposures and infection, as well as in response to sterile tissue injury. In this review, we focus on innate immune mechanisms of platelet activation, platelet interactions with innate immune cells, as well as the intersection of platelets and adaptive immunity. The immune potential of platelets is dependent in part on their megakaryocyte precursor providing them with the molecular composition to be first responders and immune sentinels in initiating and orchestrating coordinated pathogen immune responses. There is emerging evidence that extramedullary megakaryocytes may be immune differentiated compared with bone marrow megakaryocytes, but the physiological relevance of immunophenotypic differences are just beginning to be explored. These concepts are also discussed in this review. The immune functions of the megakaryocyte/platelet lineage have likely evolved to coordinate the need to repair a vascular breach with the simultaneous need to induce an immune response that may limit pathogen invasion once the blood is exposed to an external environment.
Topics: Adaptive Immunity; Animals; Blood Platelets; Humans; Immunity, Innate; Megakaryocytes
PubMed: 35050690
DOI: 10.1161/CIRCRESAHA.121.319821 -
Arteriosclerosis, Thrombosis, and... Jul 2019Megakaryocytes are hematopoietic cells, which are responsible for the production of blood platelets. The traditional view of megakaryopoiesis describes the cellular... (Review)
Review
Megakaryocytes are hematopoietic cells, which are responsible for the production of blood platelets. The traditional view of megakaryopoiesis describes the cellular journey from hematopoietic stem cells, through a hierarchical series of progenitor cells, ultimately to a mature megakaryocyte. Once mature, the megakaryocyte then undergoes a terminal maturation process involving multiple rounds of endomitosis and cytoplasmic restructuring to allow platelet formation. However, recent studies have begun to redefine this hierarchy and shed new light on alternative routes by which hematopoietic stem cells are differentiated into megakaryocytes. In particular, the origin of megakaryocytes, including the existence and hierarchy of megakaryocyte progenitors, has been redefined, as new studies are suggesting that hematopoietic stem cells originate as megakaryocyte-primed and can bypass traditional lineage checkpoints. Overall, it is becoming evident that megakaryopoiesis does not only occur as a stepwise process, but is dynamic and adaptive to biological needs. In this review, we will reexamine the canonical dogmas of megakaryopoiesis and provide an updated framework for interpreting the roles of traditional pathways in the context of new megakaryocyte biology. Visual Overview- An online visual overview is available for this article.
Topics: Bone Marrow Cells; Cell Communication; Cell Cycle; Cell Differentiation; Cell Lineage; Hematopoietic Stem Cells; Humans; Inflammation; Megakaryocytes; Signal Transduction; Thrombopoiesis; Thrombopoietin; Transcription Factors
PubMed: 31043076
DOI: 10.1161/ATVBAHA.119.312129 -
Cells Mar 2023The haematopoietic system plays an essential role in our health and survival. It is comprised of a range of mature blood and immune cell types, including oxygen-carrying... (Review)
Review
The haematopoietic system plays an essential role in our health and survival. It is comprised of a range of mature blood and immune cell types, including oxygen-carrying erythrocytes, platelet-producing megakaryocytes and infection-fighting myeloid and lymphoid cells. Self-renewing multipotent haematopoietic stem cells (HSCs) and a range of intermediate haematopoietic progenitor cell types differentiate into these mature cell types to continuously support haematopoietic system homeostasis throughout life. This process of haematopoiesis is tightly regulated in vivo and primarily takes place in the bone marrow. Over the years, a range of in vitro culture systems have been developed, either to expand haematopoietic stem and progenitor cells or to differentiate them into the various haematopoietic lineages, based on the use of recombinant cytokines, co-culture systems and/or small molecules. These approaches provide important tractable models to study human haematopoiesis in vitro. Additionally, haematopoietic cell culture systems are being developed and clinical tested as a source of cell products for transplantation and transfusion medicine. This review discusses the in vitro culture protocols for human HSC expansion and differentiation, and summarises the key factors involved in these biological processes.
Topics: Humans; Hematopoietic Stem Cells; Cell Differentiation; Megakaryocytes; Hematopoiesis; Bone Marrow
PubMed: 36980237
DOI: 10.3390/cells12060896 -
Cell Stem Cell Mar 2021Despite our growing understanding of embryonic immune development, rare early megakaryocytes (MKs) remain relatively understudied. Here we used single-cell RNA...
Despite our growing understanding of embryonic immune development, rare early megakaryocytes (MKs) remain relatively understudied. Here we used single-cell RNA sequencing of human MKs from embryonic yolk sac (YS) and fetal liver (FL) to characterize the transcriptome, cellular heterogeneity, and developmental trajectories of early megakaryopoiesis. In the YS and FL, we found heterogeneous MK subpopulations with distinct developmental routes and patterns of gene expression that could reflect early functional specialization. Intriguingly, we identified a subpopulation of CD42bCD14 MKs in vivo that exhibit high expression of genes associated with immune responses and can also be derived from human embryonic stem cells (hESCs) in vitro. Furthermore, we identified THBS1 as an early marker for MK-biased embryonic endothelial cells. Overall, we provide important insights and invaluable resources for dissection of the molecular and cellular programs underlying early human megakaryopoiesis.
Topics: Cell Differentiation; Endothelial Cells; Human Embryonic Stem Cells; Humans; Megakaryocytes; Thrombopoiesis
PubMed: 33340451
DOI: 10.1016/j.stem.2020.11.006 -
Blood Jun 2021Platelets have long been known to play important roles beyond hemostasis and thrombosis. Now recognized as a bona fide mediator of malignant disease, platelets influence... (Review)
Review
Platelets have long been known to play important roles beyond hemostasis and thrombosis. Now recognized as a bona fide mediator of malignant disease, platelets influence various aspects of cancer progression, most notably tumor cell metastasis. Interestingly, platelets isolated from cancer patients often display distinct RNA and protein profiles, with no clear alterations in hemostatic activity. This phenotypically distinct population, termed tumor-educated platelets, now receive significant attention for their potential use as a readily available liquid biopsy for early cancer detection. Although the mechanisms underpinning platelet education are still being defined, direct uptake and storage of tumor-derived factors, signal-dependent changes in platelet RNA processing, and differential platelet production by tumor-educated megakaryocytes are the most prominent scenarios. This article aims to cover the various modalities of platelet education by tumors, in addition to assessing their diagnostic potential.
Topics: Animals; Blood Platelets; Humans; Liquid Biopsy; Megakaryocytes; Neoplasm Metastasis; Neoplasm Proteins; Neoplasms; RNA, Neoplasm
PubMed: 33940594
DOI: 10.1182/blood.2019003976 -
Transfusion Medicine Reviews Oct 2020Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can... (Review)
Review
Platelets are the primary cellular mediators of hemostasis and this function firmly acquaints them with a variety of inflammatory processes. For example, platelets can act as circulating sentinels by expressing Toll-like receptors (TLR) that bind pathogens and this allows platelets to effectively kill them or present them to cells of the immune system. Furthermore, activated platelets secrete and express many pro- and anti-inflammatory molecules that attract and capture circulating leukocytes and direct them to inflamed tissues. In addition, platelets can directly influence adaptive immune responses via secretion of, for example, CD40 and CD40L molecules. Platelets are also the source of most of the microvesicles in the circulation and these miniscule elements further enhance the platelet's ability to communicate with the immune system. More recently, it has been demonstrated that platelets and their parent cells, the megakaryocytes (MK), can also uptake, process and present both foreign and self-antigens to CD8+ T-cells conferring on them the ability to directly alter adaptive immune responses. This review will highlight several of the non-hemostatic attributes of platelets that clearly and rightfully place them as integral players in immune reactions.
Topics: Adaptive Immunity; Biomarkers; Blood Platelets; Humans; Immunity, Innate; Immunomodulation; Inflammation; Megakaryocytes; Platelet Transfusion
PubMed: 33051111
DOI: 10.1016/j.tmrv.2020.09.005 -
Immunity Dec 2022Intravascular neutrophils and platelets collaborate in maintaining host integrity, but their interaction can also trigger thrombotic complications. We report here that...
Intravascular neutrophils and platelets collaborate in maintaining host integrity, but their interaction can also trigger thrombotic complications. We report here that cooperation between neutrophil and platelet lineages extends to the earliest stages of platelet formation by megakaryocytes in the bone marrow. Using intravital microscopy, we show that neutrophils "plucked" intravascular megakaryocyte extensions, termed proplatelets, to control platelet production. Following CXCR4-CXCL12-dependent migration towards perisinusoidal megakaryocytes, plucking neutrophils actively pulled on proplatelets and triggered myosin light chain and extracellular-signal-regulated kinase activation through reactive oxygen species. By these mechanisms, neutrophils accelerate proplatelet growth and facilitate continuous release of platelets in steady state. Following myocardial infarction, plucking neutrophils drove excessive release of young, reticulated platelets and boosted the risk of recurrent ischemia. Ablation of neutrophil plucking normalized thrombopoiesis and reduced recurrent thrombosis after myocardial infarction and thrombus burden in venous thrombosis. We establish neutrophil plucking as a target to reduce thromboischemic events.
Topics: Humans; Megakaryocytes; Thrombopoiesis; Neutrophils; Cardiovascular Diseases; Blood Platelets; Thrombosis; Myocardial Infarction
PubMed: 36272416
DOI: 10.1016/j.immuni.2022.10.001 -
The Journal of Clinical Investigation Jan 2021Although platelets are the cellular mediators of thrombosis, they are also immune cells. Platelets interact both directly and indirectly with immune cells, impacting...
Although platelets are the cellular mediators of thrombosis, they are also immune cells. Platelets interact both directly and indirectly with immune cells, impacting their activation and differentiation, as well as all phases of the immune response. Megakaryocytes (Mks) are the cell source of circulating platelets, and until recently Mks were typically only considered bone marrow-resident (BM-resident) cells. However, platelet-producing Mks also reside in the lung, and lung Mks express greater levels of immune molecules compared with BM Mks. We therefore sought to define the immune functions of lung Mks. Using single-cell RNA sequencing of BM and lung myeloid-enriched cells, we found that lung Mks, which we term MkL, had gene expression patterns that are similar to antigen-presenting cells. This was confirmed using imaging and conventional flow cytometry. The immune phenotype of Mks was plastic and driven by the tissue immune environment, as evidenced by BM Mks having an MkL-like phenotype under the influence of pathogen receptor challenge and lung-associated immune molecules, such as IL-33. Our in vitro and in vivo assays demonstrated that MkL internalized and processed both antigenic proteins and bacterial pathogens. Furthermore, MkL induced CD4+ T cell activation in an MHC II-dependent manner both in vitro and in vivo. These data indicated that MkL had key immune regulatory roles dictated in part by the tissue environment.
Topics: Animals; Antigen-Presenting Cells; CD4-Positive T-Lymphocytes; Histocompatibility Antigens Class II; Lung; Lymphocyte Activation; Megakaryocytes; Mice; Mice, Knockout; RNA-Seq; Single-Cell Analysis
PubMed: 33079726
DOI: 10.1172/JCI137377 -
Annals of the Rheumatic Diseases Mar 2022Rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) share many clinical manifestations and serological features. The aim...
OBJECTIVES
Rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) share many clinical manifestations and serological features. The aim of this study was to identify the common transcriptional profiling and composition of immune cells in peripheral blood in these autoimmune diseases (ADs).
METHODS
We analysed bulk RNA-seq data for enrichment of biological processes, transcription factors (TFs) and deconvolution-based immune cell types from peripheral blood mononuclear cells (PBMCs) in 119 treatment-naive patients (41 RA, 38 pSS, 28 SLE and 12 polyautoimmunity) and 20 healthy controls. The single-cell RNA-seq (scRNA-seq) and flow cytometry had been performed to further define the immune cell subsets on PBMCs.
RESULTS
Similar transcriptional profiles and common gene expression signatures associated with nucleosome assembly and haemostasis were identified across RA, SLE, pSS and polyautoimmunity. Distinct TF ensembles and gene regulatory network were mainly enriched in haematopoiesis. The upregulated cell-lineage-specific TFs , , and demonstrated a strong gene expression signature of megakaryocyte (MK) expansion. Gene expression-based cell type enrichment revealed elevated MK composition, specifically, CD41bCD42b and CD41bCD61 MKs were expanded, further confirmed by flow cytometry in these ADs. In scRNA-seq data, MKs were defined by TFs and pre-T-cell antigen receptor gene, . Cellular heterogeneity and a distinct immune subpopulation with functional enrichment of antigen presentation were observed in MKs.
CONCLUSIONS
The identification of MK expansion provided new insights into the peripheral immune cell atlas across RA, SLE, pSS and polyautoimmunity. Aberrant regulation of the MK expansion might contribute to the pathogenesis of these ADs.
Topics: Adult; Arthritis, Rheumatoid; Autoimmunity; Case-Control Studies; Female; Flow Cytometry; Gene Expression Profiling; Humans; Leukocytes, Mononuclear; Lupus Erythematosus, Systemic; Male; Megakaryocytes; Middle Aged; RNA-Seq; Sjogren's Syndrome; Transcriptome
PubMed: 34462261
DOI: 10.1136/annrheumdis-2021-220066