Platelet-leukocyte interactions in the pathogenesis of viral infections

Viruses and thrombocytopenia

Thrombocytopenia, characterized by a decrease in platelet count, is a multifaceted clinical manifestation that can arise from various underlying causes. This review delves into the intriguing nexus between viruses and thrombocytopenia, shedding light on intricate pathophysiological mechanisms and highlighting the pivotal role of platelets in viral infections. The review further navigates the landscape of thrombocytopenia in relation to specific viruses, and sheds light on the diverse mechanisms through which hepatitis C virus (HCV), measles virus, parvovirus B19, and other viral agents contribute to platelet depletion. As we gain deeper insights into these interactions, we move closer to elucidating potential therapeutic avenues and preventive strategies for managing thrombocytopenia in the context of viral infections.

Expression of Tissue Factor and Platelet/Leukocyte Markers on Extracellular Vesicles Reflect Platelet-Leukocyte Interaction in Severe COVID-19

Severe COVID-19 is frequently associated with thromboembolic complications. Increased platelet activation and platelet-leukocyte aggregate formation can amplify thrombotic responses by inducing tissue factor (TF) expression on leukocytes. Here, we characterized TF-positive extracellular vesicles (EVs) and their cellular origin in 12 patients suffering from severe COVID-19 (time course, 134 samples overall) and 25 healthy controls. EVs exposing phosphatidylserine (PS) were characterized by flow cytometry. Their cellular origin was determined by staining with anti-CD41, anti-CD45, anti-CD235a, and anti-CD105 as platelet, leukocyte, red blood cell, and endothelial markers. We further investigated the association of EVs with TF, platelet factor 4 (PF4), C-reactive protein (CRP), and high mobility group box-1 protein (HMGB-1). COVID-19 patients showed higher levels of PS-exposing EVs compared to controls. The majority of these EVs originated from platelets. A higher amount of EVs in patient samples was associated with CRP, HMGB-1, PF4, and TF as compared to EVs from healthy donors. In COVID-19 samples, 16.5% of all CD41+ EVs displayed the leukocyte marker CD45, and 55.5% of all EV aggregates (CD41+CD45+) co-expressed TF, which reflects the interaction of platelets and leukocytes in COVID-19 on an EV level.

The safety and effectiveness of clopidogrel versus aspirin in Kawasaki disease with mild-to-moderate liver injury

Kawasaki disease can be combined with liver injury. As a mainstay treatment for Kawasaki disease, aspirin may cause liver injury. This study aimed to compare the safety and effectiveness of clopidogrel versus aspirin in Kawasaki disease with mild-to-moderate liver injury. This study retrospectively analysed 166 children with Kawasaki disease combined with mild-to-moderate liver injury. The children treated with clopidogrel were less likely to have aggravated liver injury than those treated with aspirin (n = 2/100 vs. n = 13/66, P < 0.001). The initial alanine aminotransferase value of the clopidogrel group was higher (131.5 [98.5, 167.5] vs. 96 [72, 133], P < 0.001), while the time of alanine aminotransferase recovery to normal was similar (5 [4, 7] vs. 4 [3, 7], P = 0.179). No significant fever differences observed between groups: 7.5 [6, 9] for aspirin vs. 7 [6, 8] for clopidogrel group, P = 0.064. The probability of nonresponse to intravenous immunoglobulin (n = 29/100 vs. n = 30/66, P = 0.030) and the days of hospitalization (n = 6 [4, 9] vs. n = 7 [5, 10], P = 0.007) in the clopidogrel group were less than those in the aspirin group. In conclusion, the application of clopidogrel is potentially superior to aspirin in Kawasaki disease combined with mild-to-moderate liver injury.

[Recent research on platelet-leukocyte aggregates and their role in the pathogenesis of Kawasaki disease]

Activated platelets may interact with various types of leukocytes such as monocytes, neutrophils, dendritic cells, and lymphocytes, trigger intercellular signal transduction, and thus lead to thrombosis and synthesis of massive inflammatory mediators. Elevated levels of circulating platelet-leukocyte aggregates have been found in patients with thrombotic or inflammatory diseases. This article reviews the latest research on the formation, function, and detection methods of platelet-leukocyte aggregates and their role in the onset of Kawasaki disease, so as to provide new ideas for studying the pathogenesis of Kawasaki disease.

Blood Platelets in Infection: The Multiple Roles of the Platelet Signalling Machinery

Platelets are classically recognized for their important role in hemostasis and thrombosis but they are also involved in many other physiological and pathophysiological processes, including infection. Platelets are among the first cells recruited to sites of inflammation and infection and they exert their antimicrobial response actively cooperating with the immune system. This review aims to summarize the current knowledge on platelet receptor interaction with different types of pathogens and the consequent modulations of innate and adaptive immune responses.

Influence of confirmed viral infection on adult acute fulminant myocarditis supported with extracorporeal membrane oxygenation

BACKGROUND

The impact of etiologies of acute fulminant myocarditis (AFM), which requires extracorporeal membrane oxygenation (ECMO), on clinical outcomes remains unknown. This study aimed to investigate the risk factors for ECMO weaning and mortality among patients with AFM due to viral etiologies in a tertiary referral medical center.

METHODS

We included 33 adults with AFM who received ECMO and were admitted between January 2002 and January 2021. General demographics, laboratory data, echocardiography findings, and long-term outcomes were analyzed for confirmed viral etiology and unconfirmed etiology groups.

RESULTS

The overall hospital survival rate was 54.5%. The age, sex, severity of the hemodynamic condition, and cardiac rhythm were similar between the two groups. Multivariate Cox regression analysis revealed that a confirmed viral etiology (HR 4.201, 95% CI 1.061-16.666), peri-ECMO renal replacement therapy (RRT) (HR 9.804, 1.140-83.333) and a high positive end-expiratory pressure (PEEP) in the ventilator settings at 24 h after ECMO (HR 1.479, 1.020-2.143) were significant prognostic factors for in-hospital mortality. Peri-ECMO RRT was also a significant negative prognostic factor for successful ECMO weaning (OR 0.061, 0.006-0.600) in the multivariate logistic model.

CONCLUSIONS

Among AFM patients receiving ECMO support, RRT use was associated with a decreased chance of survival to ECMO weaning. Multiple organ dysfunction and a high PEEP were also predictive of a lower chance of hospital survival. Those with a confirmed diagnosis of viral myocarditis may require more medical attention due to the higher risk of hospital mortality than those without a definite diagnosis.

P2Y12 Inhibition Suppresses Proinflammatory Platelet-Monocyte Interactions

BACKGROUND

 Monocyte-platelet aggregates (MPAs) represent the crossroads between thrombosis and inflammation, and targeting this axis may suppress thromboinflammation. While antiplatelet therapy (APT) reduces platelet-platelet aggregation and thrombosis, its effects on MPA and platelet effector properties on monocytes are uncertain.

OBJECTIVES

 To analyze the effect of platelets on monocyte activation and APT on MPA and platelet-induced monocyte activation.

METHODS

 Agonist-stimulated whole blood was incubated in the presence of P-selectin, PSGL1, PAR1, P2Y12, GP IIb/IIIa, and COX-1 inhibitors and assessed for platelet and monocyte activity via flow cytometry. RNA-Seq of monocytes incubated with platelets was used to identify platelet-induced monocyte transcripts and was validated by RT-qPCR in monocyte-PR co-incubation ± APT.

RESULTS

 Consistent with a proinflammatory platelet effector role, MPAs were increased in patients with COVID-19. RNA-Seq revealed a thromboinflammatory monocyte transcriptome upon incubation with platelets. Monocytes aggregated to platelets expressed higher CD40 and tissue factor than monocytes without platelets (p < 0.05 for each). Inhibition with P-selectin (85% reduction) and PSGL1 (87% reduction) led to a robust decrease in MPA. P2Y12 and PAR1 inhibition lowered MPA formation (30 and 21% reduction, p < 0.05, respectively) and decreased monocyte CD40 and TF expression, while GP IIb/IIIa and COX1 inhibition had no effect. Pretreatment of platelets with P2Y12 inhibitors reduced the expression of platelet-mediated monocyte transcription of proinflammatory SOCS3 and OSM. CONCLUSIONS:  Platelets skew monocytes toward a proinflammatory phenotype. Among traditional APTs, P2Y12 inhibition attenuates platelet-induced monocyte activation.

Dengue induces iNOS expression and nitric oxide synthesis in platelets through IL-1R

Introduction

Dengue is an arthropod-born disease caused by dengue virus (DENV), that may manifest as a mild illness or severe form, characterized by hemorrhagic fever and shock. Nitric oxide (NO) is a vasodilator signaling molecule and an inhibitor of platelet aggregation known to be increased in platelets from dengue patients. However, the mechanisms underlying NO synthesis by platelets during dengue are not yet elucidated. IL-1β is a pro-inflammatory cytokine able to induce iNOS expression in leukocytes and present in dengue patients at high levels. Nevertheless, the role of IL-1β in platelet activation, especially regarding iNOS expression, are not clear.

Methods

We prospectively followed a cohort of 28 dengue-infected patients to study NO synthesis in platelets and its relationship with disease outcomes. We used in vitro infection and stimulation models to gain insights on the mechanisms.

Results and Discussion

We confirmed that platelets from dengue patients express iNOS and produce higher levels of NO during the acute phase compared to healthy volunteers, returning to normal levels after recovery. Platelet NO production during acute dengue infection was associated with the presence of warning signs, hypoalbuminemia and hemorrhagic manifestations, suggesting a role in dengue pathophysiology. By investigating the mechanisms, we evidenced increased iNOS expression in platelets stimulated with dengue patients´ plasma, indicating induction by circulating inflammatory mediators. We then investigated possible factors able to induce platelet iNOS expression and observed higher levels of IL-1β in plasma from patients with dengue, which were correlated with NO production by platelets. Since platelets can synthesize and respond to IL-1β, we investigated whether IL-1β induces iNOS expression and NO synthesis in platelets. We observed that recombinant human IL-1β enhanced iNOS expression and dose-dependently increased NO synthesis by platelets. Finally, platelet infection with DENV in vitro induced iNOS expression and NO production, besides the secretion of both IL-1α and IL-1β. Importantly, treatment with IL-1 receptor antagonist or a combination of anti-IL-1α and anti-IL-1β antibodies prevented DENV-induced iNOS expression and NO synthesis. Our data show that DENV induces iNOS expression and NO production in platelets through mechanisms depending on IL-1 receptor signaling.

A distinct four-value blood signature of pyrexia under combination therapy of malignant melanoma with dabrafenib and trametinib evidenced by an algorithm-defined pyrexia score

Pyrexia is a frequent adverse event of BRAF/MEK-inhibitor combination therapy in patients with metastasized malignant melanoma (MM). The study’s objective was to identify laboratory changes which might correlate with the appearance of pyrexia. Initially, data of 38 MM patients treated with dabrafenib plus trametinib, of which 14 patients developed pyrexia, were analysed retrospectively. Graphical visualization of time series of laboratory values suggested that a rise in C-reactive-protein, in parallel with a fall of leukocytes and thrombocytes, were indicative of pyrexia. Additionally, statistical analysis showed a significant correlation between lactate dehydrogenase (LDH) and pyrexia. An algorithm based on these observations was designed using a deductive and heuristic approach in order to calculate a pyrexia score (PS) for each laboratory assessment in treated patients. A second independent data set of 28 MM patients, 8 with pyrexia, was used for the validation of the algorithm. PS based on the four parameters CRP, LDH, leukocyte and thrombocyte numbers, were statistically significantly higher in pyrexia patients, differentiated between groups (F = 20.8; p = <0.0001) and showed a significant predictive value for the diagnosis of pyrexia (F = 6.24; p = 0.013). We provide first evidence that pyrexia in patients treated with BRAF/MEK-blockade can be identified by an algorithm that calculates a score.

Platelet proteome reveals features of cell death, antiviral response and viral replication in covid-19

Coronavirus disease 2019 (COVID-19) has affected over 400 million people worldwide, leading to 6 million deaths. Among the complex symptomatology of COVID-19, hypercoagulation and thrombosis have been described to directly contribute to lethality, pointing out platelets as an important SARS-CoV-2 target. In this work, we explored the platelet proteome of COVID-19 patients through a label-free shotgun proteomics approach to identify platelet responses to infection, as well as validation experiments in a larger patient cohort. Exclusively detected proteins (EPs) and differentially expressed proteins (DEPs) were identified in the proteomic dataset and thus classified into biological processes to map pathways correlated with pathogenesis. Significant changes in the expression of proteins related to platelet activation, cell death, and antiviral response through interferon type-I were found in all patients. Since the outcome of COVID-19 varies highly among individuals, we also performed a cross-comparison of proteins found in survivors and nonsurvivors. Proteins belonging to the translation pathway were strongly highlighted in the nonsurvivor group. Moreover, the SARS-CoV-2 genome was fully sequenced in platelets from five patients, indicating viral internalization and preprocessing, with CD147 as a potential entry route. In summary, platelets play a significant role in COVID-19 pathogenesis via platelet activation, antiviral response, and disease severity.

Disease Severity in Moderate-to-Severe COVID-19 Is Associated With Platelet Hyperreactivity and Innate Immune Activation

Background

Hemostasis and inflammation are both dysregulated in patients with moderate-to-severe coronavirus disease 2019 (COVID-19). Yet, both processes can also be disturbed in patients with other respiratory diseases, and the interactions between coagulation, inflammation, and disease severity specific to COVID-19 are still vague.

Methods

Hospitalized patients with acute respiratory symptoms and with severe acute respiratory syndrome coronavirus 2 (SARS-CoV2)-positive (COVpos) and SARS-CoV2-negative (COVneg) status were included. We assessed adenosine diphosphate (ADP)-, thrombin receptor activator peptide 6 (TRAP)-, and arachidonic acid (AA)-induced platelet reactivity by impedance aggregometry, as well as leukocyte subtype spectrum and platelet-leukocyte aggregates by flow cytometry and inflammatory cytokines by cytometric bead array.

Results

ADP-, TRAP-, and AA-induced platelet reactivity was significantly higher in COVpos than in COVneg patients. Disease severity, assessed by sequential organ failure assessment (SOFA) score, was higher in COVpos than in COVneg patients and again higher in deceased COVpos patients than in surviving COVpos. The SOFA score correlated significantly with the mean platelet volume and TRAP-induced platelet aggregability. A larger percentage of classical and intermediate monocytes, and of CD4pos T cells (TH) aggregated with platelets in COVpos than in COVneg patients. Interleukin (IL)-1 receptor antagonist (RA) and IL-6 levels were higher in COVpos than in COVneg patients and again higher in deceased COVpos patients than in surviving COVpos. IL-1RA and IL-6 levels correlated with the SOFA score in COVpos but not in COVneg patients. In both respiratory disease groups, absolute levels of B-cell-platelet aggregates and NK-cell-platelet aggregates were correlated with ex vivo platelet aggegation upon stimulation with AA and ADP, respectively, indicating a universal, but not a COVID-19-specific mechanism.

Conclusion

In moderate-to-severe COVID-19, but not in other respiratory diseases, disease severity was associated with platelet hyperreactivity and a typical inflammatory signature. In addition to a severe inflammatory response, platelet hyperreactivity associated to a worse clinical outcome in patients with COVID-19, pointing to the importance of antithrombotic therapy for reducing disease severity.

Platelet-Leucocyte Aggregates as Novel Biomarkers in Cardiovascular Diseases

Simple Summary

Cardiovascular diseases are the most common cause of death worldwide. Hence, novel biomarkers are urgently needed to improve diagnosis and treatment. Platelet–leucocyte aggregates are conglomerates of platelets and leucocytes and are widely investigated as biomarkers in cardiovascular diseases. Platelet–leucocytes aggregates are present in health, but increase in patients with cardiovascular risk factors and acute or stable coronary syndromes, making them a potential diagnostic marker. Moreover, platelet–leucocyte aggregates predict outcomes after surgery or percutaneous treatment and could be used to monitor antiplatelet therapy. Emerging data about the participation of platelet–leucocyte aggregates in cardiovascular diseases pathogenesis make them an attractive target for novel therapies. Furthermore, simple detection with conventional flow cytometry provides accurate and reproducible results, although requires specific sample handling. The main task for the future is to determine the standardized protocol to measure blood concentrations of platelet–leucocyte aggregates and subsequently establish their normal range in health and disease.

Abstract

Platelet–leucocyte aggregates (PLA) are a formation of leucocytes and platelets bound by specific receptors. They arise in the condition of sheer stress, thrombosis, immune reaction, vessel injury, and the activation of leukocytes or platelets. PLA participate in cardiovascular diseases (CVD). Increased levels of PLA were revealed in acute and chronic coronary syndromes, carotid stenosis cardiovascular risk factors. Due to accessible, available, replicable, quick, and low-cost quantifying using flow cytometry, PLA constitute an ideal biomarker for clinical practice. PLA are promising in early diagnosing and estimating prognosis in patients with acute or chronic coronary syndromes treated by percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG). PLA were also a reliable marker of platelet activity for monitoring antiplatelet therapy. PLA consist also targets potential therapies in CVD. All of the above potential clinical applications require further studies to validate methods of assay and proof clinical benefits.

Prothrombotic Phenotype in COVID-19: Focus on Platelets

COVID-19 infection is associated with a broad spectrum of presentations, but alveolar capillary microthrombi have been described as a common finding in COVID-19 patients, appearing as a consequence of a severe endothelial injury with endothelial cell membrane disruption. These observations clearly point to the identification of a COVID-19-associated coagulopathy, which may contribute to thrombosis, multi-organ damage, and cause of severity and fatality. One significant finding that emerges in prothrombotic abnormalities observed in COVID-19 patients is that the coagulation alterations are mainly mediated by the activation of platelets and intrinsically related to viral-mediated endothelial inflammation. Beyond the well-known role in hemostasis, the ability of platelets to also release various potent cytokines and chemokines has elevated these small cells from simple cell fragments to crucial modulators in the blood, including their inflammatory functions, that have a large influence on the immune response during infectious disease. Indeed, platelets are involved in the pathogenesis of acute lung injury also by promoting NET formation and affecting vascular permeability. Specifically, the deposition by activated platelets of the chemokine platelet factor 4 at sites of inflammation promotes adhesion of neutrophils on endothelial cells and thrombogenesis, and it seems deeply involved in the phenomenon of vaccine-induced thrombocytopenia and thrombosis. Importantly, the hyperactivated platelet phenotype along with evidence of cytokine storm, high levels of P-selectin, D-dimer, and, on the other hand, decreased levels of fibrinogen, von Willebrand factor, and thrombocytopenia may be considered suitable biomarkers that distinguish the late stage of COVID-19 progression in critically ill patients.

Single-cell landscape of peripheral immune responses to fatal SFTS

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease with high fatality. Poor prognosis of SFTS has been associated with dysregulated host immunity; however, the immune patterns associated with pathophysiology involving SFTS exacerbation remain unclear. Here, we show that the single-cell landscape of peripheral immune responses is reprogrammed in SFTS and characterized by monocyte shift to an intermediate type along with complement activation, perturbation of plasmablast composition, and highly exhausted T cells, all correlated with lethal consequences. We identify the overexpression of interferon (IFN)-stimulated genes across most immune cell types after SFTSV infection, which are simultaneously related to older age, high viremia, and a hyperinflammatory response. A retrospective clinical study reveals no efficiency of IFN-α in treating SFTS. These data collectively support the intermediate monocytes and IFN-I-inducible plasmablasts to be major targets for SFTS virus infection, and they indicate the pivotal role of the IFN-I response in exacerbating hyperinflammation and lethal SFTS.

The roles of platelets in COVID-19-associated coagulopathy and vaccine-induced immune thrombotic thrombocytopenia

In coronavirus disease 2019 (COVID-19), multiple thromboinflammatory events contribute to the pathophysiology, including coagulation system activation, suppressed fibrinolysis, vascular endothelial cell injury, and prothrombotic alterations in immune cells such as macrophages and neutrophils. Although thrombocytopenia is not an initial presentation as an infectious coagulopathy, recent studies have demonstrated the vital role of platelets in COVID-19-associated coagulopathy SARS-CoV-2 and its spike protein have been known to directly or indirectly promote release of prothrombotic and inflammatory mediators that lead to COVID-19-associated coagulopathy. Although clinical features of vaccine-induced immune thrombotic thrombocytopenia include uncommon locations of thrombosis, including cerebral venous sinus, we speculate coronavirus spike-protein-initiated prothrombotic pathways are involved in the pathogenesis of vaccine-induced immune thrombotic thrombocytopenia, as current evidence suggests that the spike protein is the promotor and other cofactors such as perturbed immune response and inflammatory reaction enhance the production of anti-platelet factor 4 antibody.