The Ways of the Virus: Interactions of Platelets and Red Blood Cells with SARS-CoV-2, and Their Potential Pathophysiological Significance in COVID-19

The hematological effects of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are important in COVID-19 pathophysiology. However, the interactions of SARS-CoV-2 with platelets and red blood cells are still poorly understood. There are conflicting data regarding the mechanisms and significance of these interactions. The aim of this review is to put together available data and discuss hypotheses, the known and suspected effects of the virus on these blood cells, their pathophysiological and diagnostic significance, and the potential role of platelets and red blood cells in the virus's transport, propagation, and clearance by the immune system. We pay particular attention to the mutual activation of platelets, the immune system, the endothelium, and blood coagulation and how this changes with the evolution of SARS-CoV-2. There is now convincing evidence that platelets, along with platelet and erythroid precursors (but not mature erythrocytes), are frequently infected by SARS-CoV-2 and functionally changed. The mechanisms of infection of these cells and their role are not yet entirely clear. Still, the changes in platelets and red blood cells in COVID-19 are significantly associated with disease severity and are likely to have prognostic and pathophysiological significance in the development of thrombotic and pulmonary complications.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

Refractory kaposiform lymphangiomatosis relieved by splenectomy

Introduction

Kaposiform lymphangiomatosis (KLA) is a rare and complex lymphatic anomaly with a poor prognosis. There is no standard treatment, and drug therapies are the most common therapeutic method. However, some patients' symptoms become gradually aggravated despite medical treatment. Splenectomy may be an alternative option when pharmacological therapies are ineffective.

Materials and Methods

We reviewed and evaluated the cases of 3 patients with KLA who ultimately underwent splenectomy. Results: The lesions were diffusely distributed and involved the lungs and spleens of the 3 patients. Laboratory examinations revealed that all three patients had thrombocytopenia and reduced fibrinogen levels. All patients underwent symptomatic splenectomy after the medication failed. Surprisingly, their symptoms greatly improved. Histopathological investigation of the splenic lesions of the three patients confirmed the diagnosis of KLA. Immunohistochemical staining showed positivity for CD31, CD34, podoplanin, Prox-1 and angiopoietin 2 (Ang-2).

Discussion

This study aimed to review the features of KLA patients treated by splenectomy and explore the underlying link between splenectomy and prognosis. The reason for the improvement after splenectomy may be related to increased Ang-2 levels and platelet activation in patients with KLA. Future research should seek to develop more targeted drugs based on molecular findings, which may give new hope for the treatment of KLA.

Cell-Specific Mechanisms in the Heart of COVID-19 Patients

From the onset of the pandemic, evidence of cardiac involvement in acute COVID-19 abounded. Cardiac presentations ranged from arrhythmias to ischemia, myopericarditis/myocarditis, ventricular dysfunction to acute heart failure, and even cardiogenic shock. Elevated serum cardiac troponin levels were prevalent among hospitalized patients with COVID-19; the higher the magnitude of troponin elevation, the greater the COVID-19 illness severity and in-hospital death risk. Whether these consequences were due to direct SARS-CoV-2 infection of cardiac cells or secondary to inflammatory responses steered early cardiac autopsy studies. SARS-CoV-2 was reportedly detected in endothelial cells, cardiac myocytes, and within the extracellular space. However, findings were inconsistent and different methodologies had their limitations. Initial autopsy reports suggested that SARS-CoV-2 myocarditis was common, setting off studies to find and phenotype inflammatory infiltrates in the heart. Nonetheless, subsequent studies rarely detected myocarditis. Microthrombi, cardiomyocyte necrosis, and inflammatory infiltrates without cardiomyocyte damage were much more common. In vitro and ex vivo experimental platforms have assessed the cellular tropism of SARS-CoV-2 and elucidated mechanisms of viral entry into and replication within cardiac cells. Data point to pericytes as the primary target of SARS-CoV-2 in the heart. Infection of pericytes can account for the observed pericyte and endothelial cell death, innate immune response, and immunothrombosis commonly observed in COVID-19 hearts. These processes are bidirectional and synergistic, rendering a definitive order of events elusive. Single-cell/nucleus analyses of COVID-19 myocardial tissue and isolated cardiac cells have provided granular data about the cellular composition and cell type-specific transcriptomic signatures of COVID-19 and microthrombi-positive COVID-19 hearts. Still, much remains unknown and more in vivo studies are needed. This review seeks to provide an overview of the current understanding of COVID-19 cardiac pathophysiology. Cell type-specific mechanisms and the studies that provided such insights will be highlighted. Given the unprecedented pace of COVID-19 research, more mechanistic details are sure to emerge since the writing of this review. Importantly, our current knowledge offers significant clues about the cardiac pathophysiology of long COVID-19, the increased postrecovery risk of cardiac events, and thus, the future landscape of cardiovascular disease.

Toll-Like Receptor 3 in Cardiovascular Diseases

Toll-like receptor 3 (TLR3) is an important member of the innate immune response receptor toll-like receptors (TLRs) family, which plays a vital role in regulating immune response, promoting the maturation and differentiation of immune cells, and participating in the response of pro-inflammatory factors. TLR3 is activated by pathogen-associated molecular patterns and damage-associated molecular patterns, which support the pathophysiology of many diseases related to inflammation. An increasing number of studies have confirmed that TLR3, as a crucial medium of innate immunity, participates in the occurrence and development of cardiovascular diseases (CVDs) by regulating the transcription and translation of various cytokines, thus affecting the structure and physiological function of resident cells in the cardiovascular system, including vascular endothelial cells, vascular smooth muscle cells, cardiomyocytes, fibroblasts and macrophages. The dysfunction and structural damage of vascular endothelial cells and proliferation of vascular smooth muscle cells are the key factors in the occurrence of vascular diseases such as pulmonary arterial hypertension, atherosclerosis, myocardial hypertrophy, myocardial infarction, ischaemia/reperfusion injury, and heart failure. Meanwhile, cardiomyocytes, fibroblasts, and macrophages are involved in the development of CVDs. Therefore, the purpose of this review was to explore the latest research published on TLR3 in CVDs and discuss current understanding of potential mechanisms by which TLR3 contributes to CVDs. Even though TLR3 is a developing area, it has strong treatment potential as an immunomodulator and deserves further study for clinical translation.

Targeting vascular inflammation through emerging methods and drug carriers

Acute inflammation is a common dangerous component of pathogenesis of many prevalent conditions with high morbidity and mortality including sepsis, thrombosis, acute respiratory distress syndrome (ARDS), COVID-19, myocardial and cerebral ischemia-reperfusion, infection, and trauma. Inflammatory changes of the vasculature and blood mediate the course and outcome of the pathology in the tissue site of insult, remote organs and systemically. Endothelial cells lining the luminal surface of the vasculature play the key regulatory functions in the body, distinct under normal vs. pathological conditions. In theory, pharmacological interventions in the endothelial cells might enable therapeutic correction of the overzealous damaging pro-inflammatory and pro-thrombotic changes in the vasculature. However, current agents and drug delivery systems (DDS) have inadequate pharmacokinetics and lack the spatiotemporal precision of vascular delivery in the context of acute inflammation. To attain this level of precision, many groups design DDS targeted to specific endothelial surface determinants. These DDS are able to provide specificity for desired tissues, organs, cells, and sub-cellular compartments needed for a particular intervention. We provide a brief overview of endothelial determinants, design of DDS targeted to these molecules, their performance in experimental models with focus on animal studies and appraisal of emerging new approaches. Particular attention is paid to challenges and perspectives of targeted therapeutics and nanomedicine for advanced management of acute inflammation.

Platelet-Derived Exosomes and Atherothrombosis

Platelet-derived exosomes (PLT-Exos) are the main subtype of extracellular vesicles secreted by platelets, which carry proteins, nucleotides, lipids, and other substances to acceptor cells, playing an important role in intercellular communication. PLT-Exos increase with platelet activation and are involved in the process of atherothrombosis by delivering cargo to acceptor cells. Atherosclerotic plaque rupture, causing thrombosis and arterial occlusion, is the basic pathological change leading to cardiovascular events. PLT-Exos from different donors have different functions. PLT-Exos secreted by healthy volunteer or mice can inhibit platelet activation and inflammation of endothelial cells, thus exerting an antithrombotic effect, while PLT-Exos derived from some patients induce endothelial apoptosis and an inflammatory response to promote atherothrombosis. Furthermore, increased PLT-Exos reflect platelet activation and their cargoes also are derived from platelets; therefore, PLT-Exos can also be used as a biomarkers for the diagnosis and prognosis of cardiovascular disease. This article reviews the characteristics of PLT-Exos and discusses their role in cell-to-cell communication and atherothrombosis.

Emerging Role of Platelet-Endothelium Interactions in the Pathogenesis of Severe SARS-CoV-2 Infection-Associated Myocardial Injury

Cardiovascular dysfunction and disease are common and frequently fatal complications of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Indeed, from early on during the SARS-CoV-2 virus pandemic it was recognized that cardiac complications may occur, even in patients with no underlying cardiac disorders, as part of the acute infection, and that these were associated with more severe disease and increased morbidity and mortality. The most common cardiac complication is acute cardiac injury, defined by significant elevation of cardiac troponins. The potential mechanisms of cardiovascular complications include direct viral myocardial injury, systemic inflammation induced by the virus, sepsis, arrhythmia, myocardial oxygen supply-demand mismatch, electrolyte abnormalities, and hypercoagulability. This review is focused on the prevalence, risk factors and clinical course of COVID-19-related myocardial injury, as well as on current data with regard to disease pathogenesis, specifically the interaction of platelets with the vascular endothelium. The latter section includes consideration of the role of SARS-CoV-2 proteins in triggering development of a generalized endotheliitis that, in turn, drives intense activation of platelets. Most prominently, SARS-CoV-2–induced endotheliitis involves interaction of the viral spike protein with endothelial angiotensin-converting enzyme 2 (ACE2) together with alternative mechanisms that involve the nucleocapsid and viroporin. In addition, the mechanisms by which activated platelets intensify endothelial activation and dysfunction, seemingly driven by release of the platelet-derived calcium-binding proteins, SA100A8 and SA100A9, are described. These events create a SARS-CoV-2–driven cycle of intravascular inflammation and coagulation, which contributes significantly to a poor clinical outcome in patients with severe disease.

Ultrastructural Study of Platelet Behavior and Interrelationship in Sprouting and Intussusceptive Angiogenesis during Arterial Intimal Thickening Formation

Platelets in atherosclerosis, bypass stenosis, and restenosis have been extensively assessed. However, a sequential ultrastructural study of platelets in angiogenesis during the early phases of these lesions has received less attention. Our objective was the study of platelets in angiogenesis and vessel regression during intimal thickening (IT) formation, a precursor process of these occlusive vascular diseases. For this purpose, we used an experimental model of rat occluded arteries and procedures for ultrastructural observation. The results show (a) the absence of platelet adhesion in the de-endothelialized occluded arterial segment isolated from the circulation, (b) that intraarterial myriad platelets contributed from neovessels originated by sprouting angiogenesis from the periarterial microvasculature, (c) the association of platelets with blood components (fibrin, neutrophils, macrophages, and eosinophils) and non-polarized endothelial cells (ECs) forming aggregates (spheroids) in the arterial lumen, (d) the establishment of peg-and-socket junctions between platelets and polarized Ecs during intussusceptive angiogenesis originated from the EC aggregates, with the initial formation of IT, and (e) the aggregation of platelets in regressing neovessels (‘transitory paracrine organoid’) and IT increases. In conclusion, in sprouting and intussusceptive angiogenesis and vessel regression during IT formation, we contribute sequential ultrastructural findings on platelet behavior and relationships, which can be the basis for further studies using other procedures.

Vitamin D and Platelets: A Menacing Duo in COVID-19 and Potential Relation to Bone Remodeling

Global data correlate severe vitamin D deficiency with COVID-19-associated coagulopathy, further suggesting the presence of a hypercoagulable state in severe COVID-19 patients, which could promote thrombosis in the lungs and in other organs. The feedback loop between COVID-19-associated coagulopathy and vitamin D also involves platelets (PLTs), since vitamin D deficiency stimulates PLT activation and aggregation and increases fibrinolysis and thrombosis. Vitamin D and PLTs share and play specific roles not only in coagulation and thrombosis but also during inflammation, endothelial dysfunction, and immune response. Additionally, another ‘fil rouge’ between vitamin D and PLTs is represented by their role in mineral metabolism and bone health, since vitamin D deficiency, low PLT count, and altered PLT-related parameters are linked to abnormal bone remodeling in certain pathological conditions, such as osteoporosis (OP). Hence, it is possible to speculate that severe COVID-19 patients are characterized by the presence of several predisposing factors to bone fragility and OP that may be monitored to avoid potential complications. Here, we hypothesize different pervasive actions of vitamin D and PLT association in COVID-19, also allowing for potential preliminary information on bone health status during COVID-19 infection.

Interactions of HIV and Antiretroviral Therapy With Neutrophils and Platelets

Neutrophils are important components of the innate immune system that mediate pathogen defense by multiple processes including phagocytosis, release of proteolytic enzymes, production of reactive oxygen species, and neutrophil extracellular trap formation. Abnormalities of neutrophil count and function have been described in the setting of HIV infection, with the majority of antiretroviral agents (ARVs), excluding zidovudine, having been reported to correct neutropenia. Questions still remain, however, about their impact on neutrophil function, particularly the possibility of persistent neutrophil activation, which could predispose people living with HIV to chronic inflammatory disorders, even in the presence of virally-suppressive treatment. In this context, the effects of protease inhibitors and integrase strand transfer inhibitors, in particular, on neutrophil function remain poorly understood and deserve further study. Besides mediating hemostatic functions, platelets are increasingly recognized as critical role players in the immune response against infection. In the setting of HIV, these cells have been found to harbor the virus, even in the presence of antiretroviral therapy (ART) potentially promoting viral dissemination. While HIV-infected individuals often present with thrombocytopenia, they have also been reported to have increased platelet activation, as measured by an upregulation of expression of CD62P (P-selectin), CD40 ligand, glycoprotein IV, and RANTES. Despite ART-mediated viral suppression, HIV-infected individuals reportedly have sustained platelet activation and dysfunction. This, in turn, contributes to persistent immune activation and an inflammatory vascular environment, seemingly involving neutrophil-platelet-endothelium interactions that increase the risk for development of comorbidities such as cardiovascular disease (CVD) that has become the leading cause of morbidity and mortality in HIV-infected individuals on treatment, clearly underscoring the importance of unraveling the possible etiologic roles of ARVs. In this context, abacavir and ritonavir-boosted lopinavir and darunavir have all been linked to an increased risk of CVD. This narrative review is therefore focused primarily on the role of neutrophils and platelets in HIV transmission and disease, as well as on the effect of HIV and the most common ARVs on the numbers and functions of these cells, including neutrophil-platelet-endothelial interactions.

Lactobacillus casei CRL431 modulates hemostatic activation induced by protein malnourishment and pneumococcal respiratory infection

Previously, we demonstrated that Lactobacillus casei CRL431, a well-known immunomodulatory bacterium, beneficially regulates coagulation activation, fibrin formation in lung, and the pro-inflammatory state induced by protein malnourishment and pneumococcal infection. In this study, we deepen in the understanding of the mechanisms involved in the immunoregulatory activity of L. casei CRL431 during a nutritional repletion process by evaluating (a) platelet and endothelial activation, (b) tissue factor (TF) expression, and (c) protease-activated receptor (PAR) activation in an experimental bacterial respiratory infection model in malnourished mice. Our findings demonstrate for the first time that the repletion diet supplemented with L. casei CRL431 was effective to normalize platelet counts in blood, modulate platelet activation and their recruitment into the lung, and regulate local and systemic TF expression and endothelial activation, which were affected by malnourishment. Streptococcus pneumoniae challenge induced local and systemic increase of platelet counts, PARs activation, P-selectin and TF expression, as well as endothelial activation in both well-nourished and malnourished mice. Malnourished animals evidenced the highest alterations of the parameters evaluated while the mice fed with the probiotic bacterium had similar behavior to normal controls but with lower PAR activation in lung. These results demonstrate that supplementation of repletion diet with L. casei CRL431 is effective to modulate alterations induced by malnourishment and pneumococcal infection, restraining coagulation activation, the inflammatory process, and lung damage. These observations contribute to set the basis for the application of probiotic functional foods to modulate the inflammation-hemostasis interactions altered by malnourishment or bacterial respiratory infections. KEY POINTS: • Pneumococcal infection increases pro-coagulant state induced by protein malnourishment. • Repletion with L. casei CRL431 modulates platelet, TF, and endothelial activation. • L. casei CRL431 improves immune-coagulative response in protein malnourishment.

Circulating Platelets as Mediators of Immunity, Inflammation, and Thrombosis

Platelets, non-nucleated blood components first described over 130 years ago, are recognized as the primary cell regulating hemostasis and thrombosis. The vascular importance of platelets has been attributed to their essential role in thrombosis, mediating myocardial infarction, stroke, and venous thromboembolism. Increasing knowledge on the platelets' role in the vasculature has led to many advances in understanding not only how platelets interact with the vessel wall but also how they convey changes in the environment to other circulating cells. In addition to their well-described hemostatic function, platelets are active participants in the immune response to microbial organisms and foreign substances. Although incompletely understood, the immune role of platelets is a delicate balance between its pathogenic response and its regulation of thrombotic and hemostatic functions. Platelets mediate complex vascular homeostasis via specific receptors and granule release, RNA transfer, and mitochondrial secretion that subsequently regulates hemostasis and thrombosis, infection, and innate and adaptive immunity.

Gustav Born: pioneer in imaging platelet and leukocyte biology

Gustav Born achieved scientific fame for his application of light transmission aggregometry to the study of platelet function, but also led interdisciplinary research teams in pioneering quantitative in vivo imaging studies of platelet aggregation and leukocyte adhesion, and in conducting the first research into the biomechanical factors underlying atherosclerotic plaque rupture. Gus Born also communicated both current research findings and an integrated understanding of cardiovascular biology to a wide audience through acting as scientific advisor on several television productions. Using footage from two of these films, we discuss Gustav Born's scientific achievements and legacy.

Nitric oxide deficiency and endothelial-mesenchymal transition of pulmonary endothelium in the progression of 4T1 metastatic breast cancer in mice

Background

Mesenchymal transformation of pulmonary endothelial cells contributes to the formation of a metastatic microenvironment, but it is not known whether this precedes or follows early metastasis formation. In the present work, we characterize the development of nitric oxide (NO) deficiency and markers of endothelial–mesenchymal transition (EndMT) in the lung in relation to the progression of 4T1 metastatic breast cancer injected orthotopically in mice.

Methods

NO production, endothelial nitric oxide synthase (eNOS) phosphorylation status, markers of EndMT in the lung, pulmonary endothelium permeability, and platelet activation/reactivity were analyzed in relation to the progression of 4T1 breast cancer metastasis to the lung, as well as to lung tissue remodeling, 1–5 weeks after 4T1 cancer cell inoculation in Balb/c mice.

Results

Phosphorylation of eNOS and NO production in the lungs of 4T1 breast cancer-bearing mice was compromised prior to the development of pulmonary metastasis, and was associated with overexpression of Snail transcription factor in the pulmonary endothelium. These changes developed prior to the mesenchymal phenotypic switch in the lungs evidenced by a decrease in vascular endothelial-cadherin (VE-CAD) and CD31 expression, and the increase in pulmonary endothelial permeability, phenomena which coincided with early pulmonary metastasis. Increased activation of platelets was also detected prior to the early phase of metastasis and persisted to the late phase of metastasis, as evidenced by the higher percentage of unstimulated platelets binding fibrinogen without changes in von Willebrand factor and fibrinogen binding in response to ADP stimulation.

Conclusions

Decreased eNOS activity and phosphorylation resulting in a low NO production state featuring pulmonary endothelial dysfunction was an early event in breast cancer pulmonary metastasis, preceding the onset of its phenotypic switch toward a mesenchymal phenotype (EndMT) evidenced by a decrease in VE-CAD and CD31 expression. The latter coincided with development of the first metastatic nodules in the lungs. These findings suggest that early endothelial dysfunction featured by NO deficiency rather than EndMT, might represent a primary regulatory target to prevent early pulmonary metastasis.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1013-z) contains supplementary material, which is available to authorized users.

Blood platelets and sepsis pathophysiology: A new therapeutic prospect in critically [corrected] ill patients?

Beyond haemostasis, platelets have emerged as versatile effectors of the immune response. The contribution of platelets in inflammation, tissue integrity and defence against infections has considerably widened the spectrum of their role in health and disease. Here, we propose a narrative review that first describes these new platelet attributes. We then examine their relevance to microcirculatory alterations in multi-organ dysfunction, a major sepsis complication. Rapid progresses that are made on the knowledge of novel platelet functions should improve the understanding of thrombocytopenia, a common condition and a predictor of adverse outcome in sepsis, and may provide potential avenues for management and therapy.

Determination of predictors of severity for recipient adverse reactions during platelet product transfusions

The introduction of allogeneic cells is not a natural process, even if the transfusion is therapeutic and - when no alternative exists, as is often the case - essential. Transfusion of cellular products creates some level of danger sensed by recipients. Danger may manifest itself clinically or biologically, in which case we are dealing with recipient adverse reactions. Platelet concentrate transfusion in particular may be responsible for notable adverse reactions. Some appear to be inevitable, while others are tied to recipient factors: either health or genetic characteristics. The authors' research is specifically focused on platelet storage lesion and stress factors, and the means of controlling them to ensure greater recipient tolerance.

Stimulation of PAR-1 or PAR-4 promotes similar pattern of VEGF and endostatin release and pro-angiogenic responses mediated by human platelets

BACKGROUND

Platelets mediate angiogenesis through the secretion of several factors, including the pro-angiogenic vascular endothelial growth factor (VEGF) and the anti-angiogenic endostatin. Although previous findings indicated that these molecules are packed into different alpha-granules and selectively released by specific stimulation of protease-activated receptor (PAR)-1 or PAR-4, recent evidences are against this hypothesis.

OBJECTIVES

To elucidate the controversies about the VEGF and endostatin release and the overall angiogenic effect of PARs-stimulated platelets.

METHODS

VEGF and endostatin were quantified by enzyme linked-immunosorbent assay (ELISA). Endothelial proliferation (pNPP assay), wound healing (scratch assay) and tubule formation (matrigel) of human microvascular endothelial cells (HMEC-1) and endothelial progenitor cells (EPC) were determined using supernatants from PAR-1- or PAR-4-stimulated platelets.

RESULTS

Activation of washed platelets (WPs) by PAR-1- or PAR-4-activating peptide (AP) promoted the VEGF and endostatin secretion in a concentration-dependent manner, being PAR-1-AP more potent than PAR-4-AP. The release of both molecules was abrogated by pre-incubation of platelets with PAR antagonists. Activation of platelet-rich plasma (PRP) with either PAR-1-AP or PAR-4-AP induced a significant VEGF secretion. Quantification of platelet-endostatin secretion was not possible in PRP due to the high levels of plasmatic endostatin vs. platelet content. Releasates from PAR-1- or PAR-4-activated WPs promoted similar pattern of angiogenic responses of HMEC-1 or EPC. Moreover, proliferation of HMEC-1 mediated by PAR-stimulated PRP releasates was delayed and significantly lower compared with that induced by PAR-stimulated WPs.

CONCLUSIONS

Our results are in contrast with the previously described differential release of VEGF and endostatin induced by the selective PAR-1 or PAR-4 stimulation, and support the notion that while circulating endostatin accounts for the maintenance of a systemic anti-angiogenic state, locally, the release of platelet alpha-granule content promotes angiogenesis.

Platelets in inflammation and atherogenesis

Platelets contribute to processes beyond thrombus formation and may play a so far underestimated role as an immune cell in various circumstances. This review outlines immune functions of platelets in host defense, but also how they may contribute to mechanisms of infectious diseases. A particular emphasis is placed on the interaction of platelets with other immune cells. Furthermore, this article outlines the features of atherosclerosis as an inflammatory vascular disease highlighting the role of platelet crosstalk with cellular and soluble factors involved in atheroprogression. Understanding, how platelets influence these processes of vascular remodeling will shed light on their role for tissue homeostasis beyond intravascular thrombosis. Finally, translational implications of platelet-mediated inflammation in atherosclerosis are discussed.