Platelet activation and platelet-monocyte aggregate formation trigger tissue factor expression in patients with severe COVID-19

Structural and functional changes underlying activation of monocytes in heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated disorder associated with thrombosis developing in response to anticoagulation with heparin. Monocytes targeted by HIT antibodies contribute to the prothrombotic state, but structural and functional alterations of the activated monocytes have not been described.

OBJECTIVES

To study morphologic and functional changes in monocytes caused by HIT antibodies interacting with membrane-associated platelet factor 4 (PF4) in vitro.

METHODS

THP-1, isolated human, or FcγRIIA-positive and FcγRIIA-negative mouse monocytes were incubated with recombinant human PF4 and/or anti-PF4/heparin antibodies followed by scanning electron microscopy and confocal microscopy.

RESULTS

Binding of PF4 to monocytes induced formation of "knobs" ∼150 nm in size that protruded from the cell surface. Addition of pathogenic HIT-like monoclonal antibodies (KKO) caused profound remodeling of the cell membrane and time-dependent formation and clustering of KKO/PF4/glycosaminoglycan complexes into large "blebs" ranging in size from 500 to 1200 nm. Dynamic confocal microscopy revealed formation of monocyte-derived microvesicles in response to PF4 and KKO. In contrast, RTO, a monoclonal antibody that blocks PF4 oligomerization and prevents thrombocytopenia/thrombosis in an animal HIT model, inhibited PF4-induced modification of monocyte surfaces. Comparing monocytes from transgenic mice expressing hFcγRIIA to wild-type mice lacking FcγRIIA indicated that bleb formation results from clustering of knobs caused by bivalent HIT antibodies through crosslinking of FcγRIIA.

CONCLUSIONS

Binding of pathogenic HIT antibodies to PF4-containing antigenic complexes assembled on the monocyte surface promotes large-scale plasma membrane remodeling as part of cell activation through the FcγRIIA receptors, resulting in the release of procoagulant microvesicles, which together may contribute to thrombosis in HIT.

Recent Advances in Immunothrombosis and Thromboinflammation

Inflammation and thrombosis are traditionally considered two separate entities of acute host responses to barrier breaks. While inciting inflammatory responses is a prerequisite to fighting invading pathogens and subsequent restoration of tissue homeostasis, thrombus formation is a crucial step of the hemostatic response to prevent blood loss following vascular injury. Though originally designed to protect the host, excessive induction of either inflammatory signaling or thrombus formation and their reciprocal activation contribute to a plethora of disorders, including cardiovascular, autoimmune, and malignant diseases. In this state-of-the-art review, we summarize recent insights into the intricate interplay of inflammation and thrombosis. We focus on the protective aspects of immunothrombosis as well as evidence of detrimental sequelae of thromboinflammation, specifically regarding recent studies that elucidate its pathophysiology beyond coronavirus disease 2019 (COVID-19). We introduce recently identified molecular aspects of key cellular players like neutrophils, monocytes, and platelets that contribute to both immunothrombosis and thromboinflammation. Further, we describe the underlying mechanisms of activation involving circulating plasma proteins and immune complexes. We then illustrate how these factors skew the inflammatory state toward detrimental thromboinflammation across cardiovascular as well as septic and autoimmune inflammatory diseases. Finally, we discuss how the advent of new technologies and the integration with clinical data have been used to investigate the mechanisms and signaling cascades underlying immunothrombosis and thromboinflammation. This review highlights open questions that will need to be addressed by the field to translate our mechanistic understanding into clinically meaningful therapeutic targeting.

MONOCYTES AND B CELLS MEDIATE ALTERATIONS IN THE GENETIC ASSOCIATION BETWEEN PLATELETS AND SEPSIS VIA CLEC SIGNALING PATHWAY

ABSTRACT

Background: Sepsis is a life-threatening condition characterized by multiple organ dysfunction. Blood cells abnormalities play a significant role in the onset and progression of sepsis; however, the potential causal relationship between platelets and sepsis remains unclear, as does whether immune cells mediate the interaction between platelets and sepsis. This study aims to explore the potential causal relationship between platelets and sepsis and analyze the mediating effect of immune cells. In addition, cell-to-cell communication was analyzed to explore the interaction between blood cells and immune cells. Material and methods: In this study, genome-wide association study data were utilized to examine the association between blood cells and sepsis. Two-sample Mendelian randomization (MR) and reverse MR were performed to investigate the potential causal relationship between blood cells and sepsis, with a specific focus on the relationship between platelets and sepsis. Subsequently, two-step MR was employed to identify the immune cells that mediate the interaction between platelets and sepsis and to assess their potential mediating effects. Cellchat software was used to analyze cell-to-cell communication. Results: The results of two-sample MR indicated that platelets were negatively correlated with sepsis (OR = 0.976, 95% CI 0.959-0.993, P = 0.005), suggesting that platelets have a protective effect against sepsis. Additionally, reverse MR demonstrated that sepsis had no significant effect on platelets (OR = 0.909, 95% CI 0.156-5.296, P = 0.916). The mediating effect analysis revealed that monocytes and B cells were important mediators in the relationship between platelets and sepsis. Notably, the correlation between platelets and sepsis shifted from negative to positive with the involvement of monocytes and B cells. The number and strength of cell-cell interactions were decreased in sepsis. Monocytes and B cells primarily regulate platelets through the CLEC signaling pathway, contributing to the pathogenesis of sepsis. Conclusion: This study confirmed the protective role of platelets in sepsis. Monocytes and B cells mediate changes in the genetic association between platelets and sepsis. Monocytes and B cells primarily interact with platelets via the CLEC pathway, thereby modulating the genetic association between platelets and sepsis. These findings indicate that thrombocytopenia, especially when accompanied by elevated monocytes and B cells, may serve as a potential marker for sepsis.

Platelets from COVID-19 Patients Show an Altered Nitric Oxide/Reactive Oxygen Species Production Balance

Oxidative stress has been associated with COVID-19-related thrombotic complications. No investigations have explored nitric oxide (NO) and radical oxygen species (ROS) production by platelets. Indeed, activated platelets generate both NO and ROS which in turn regulate platelet function. The aim of the present study was to measure platelet NO and ROS production in COVID-19 patients, to assess whether they correlate with disease outcome and to clarify the mechanisms of platelet NO/ROS imbalance in COVID-19.Hospitalized mild and severe COVID-19 patients, age- and sex-matched healthy controls, and patients hospitalized in intensive care units for reasons different from COVID-19 were enrolled. Platelet NO and ROS production was assessed by flow cytometry. The oxidant and antioxidant capacity of COVID-19 plasma was assessed using lipid peroxidation and ORAC assays. The effect of COVID-19 plasma on platelet NO production and the impact of antioxidants on it were studied by flow cytometry.Platelets from COVID-19 patients displayed an altered NO/ROS balance, with defective NO and increased ROS production. Platelet NO production was significantly lower in patients who developed thrombotic events during hospitalization. COVID-19 patients showed significantly increased plasma lipid peroxidation and reduced antioxidant capacity compared with healthy controls. Concordantly, plasma from COVID-19 patients impaired NO production by healthy control species platelets, which was restored by the antioxidant agent Hydroxy-TEMPO.Our findings suggest that the unbalanced platelet NO/ROS production in COVID-19 plays a role in the thrombotic complications of SARS-CoV-2 infection. The restoration of platelet NO production may represent a therapeutic target for the prevention of thrombotic events in COVID-19 patients.

SARS-CoV-2 S1 protein induces IgG-mediated platelet activation and is prevented by 1.8-cineole

COVID-19 patients face an increased risk of thromboembolic complications, yet the exact pathophysiological role of platelets in the disease remains unclear. Considering the multifaceted nature of COVID-19 symptoms, including platelet hyperactivation and inflammation, the development of compounds that simultaneously target both represents a promising therapeutic strategy. The monoterpene 1.8-cineole (CNL-1976) is known for its anti-inflammatory and anti-aggregatory effects. Thus, understanding the mechanism behind platelet hyperactivation and the effect of 1.8-cineole during COVID-19 is crucial when aiming for a reduction of disease severity. In this study, we investigated the mechanism of platelet activation triggered by the SARS-CoV-2 S1 spike protein (S1). Utilizing S1-coupled beads, we discovered that platelet activation and aggregation were dependent on plasma components, particularly S1-specific IgG antibodies. The formation of immune complexes through IgG binding to S1 facilitated the crosslinking of the platelet expressed FcγRIIa receptor, initiating platelet activation and aggregation, as well as formation of platelet-leukocyte aggregates (PLAs). Importantly, treatment with 1.8-cineole significantly inhibited S1-bead-induced platelet activity and PLA formation. These findings strongly suggest that antibody-mediated platelet activation via FcγRIIa directly contributes to the well-recognized prothrombotic environment during COVID-19. Moreover, our data indicate that 1.8-cineole can serve as a potential therapeutic compound, alleviating platelet-driven thromboinflammatory complications associated with COVID-19 and post-acute sequelae of SARS-CoV-2 (PASC).

The concept of immunothrombosis in pancreas transplantation

Early failure of a pancreatic allograft due to complete thrombosis has an incidence of approximately 10% and is the main cause of comorbidity in pancreas transplantation. Although several risk factors have been identified, the exact mechanisms leading to this serious complication are still unclear. In this review, we define the roles of the individual components involved during sterile immunothrombosis-namely endothelial cells, platelets, and innate immune cells. Further, we review the published evidence linking the main risk factors for pancreatic thrombosis to cellular activation and vascular modifications. We also explore the unique features of the pancreas itself: the vessel endothelium, specific vascularization, and relationship to other organs-notably the spleen and adipose tissue. Finally, we summarize the therapeutic possibilities for the prevention of pancreatic thrombosis depending on the different mechanisms such as anticoagulation, anti-inflammatory molecules, endothelium protectors, antagonism of damage-associated molecular patterns, and use of machine perfusion.

Protocol for assessing and visualizing cell microaggregate formation in whole blood by imaging flow cytometry

Blood cell aggregates are clinically useful biomarkers in a number of medical disorders. This protocol provides accurate and quantitative analysis of cell aggregates using a small volume of whole blood and imaging flow cytometry. We describe steps for sample collection, staining, and measurement. We then detail gating procedures and analysis of cell morphology. Sample preparation artifacts, activation, and morphological changes of cells are mitigated by omitting erythrocyte lysis and leukocyte isolation while maintaining high-throughput accurate imaging of leukocytes and platelets.

Post-transfusion activation of coagulation pathways during severe COVID-19 correlates with COVID-19 convalescent plasma antibody profiles

Early antibody therapy can prevent severe SARS-CoV-2 infection (COVID-19). However, the effectiveness of COVID-19 convalescent plasma (CCP) therapy in treating severe COVID-19 remains inconclusive. To test a hypothesis that some CCP units are associated with a coagulopathy hazard in severe disease that offsets its benefits, we tracked 304 CCP units administered to 414 hospitalized COVID-19 patients to assess their association with the onset of unfavorable post-transfusion D-dimer trends. CCP recipients with increasing or persistently elevated D-dimer trajectories after transfusion experienced higher mortality than those whose D-dimer levels were persistently low or decreasing after transfusion. Within the CCP donor-recipient network, recipients with increasing or persistently high D-dimer trajectories were skewed toward association with a minority of CCP units. In in vitro assays, CCP from "higher-risk" units had higher cross-reactivity with the spike protein of human seasonal betacoronavirus OC43. "Higher-risk" CCP units also mediated greater Fcγ receptor IIa signaling against cells expressing SARS-CoV-2 spike compared with "lower-risk" units. This study finds that post-transfusion activation of coagulation pathways during severe COVID-19 is associated with specific CCP antibody profiles and supports a potential mechanism of immune complex-activated coagulopathy.

Discrete and conserved inflammatory signatures drive thrombosis in different organs after Salmonella infection

Inflammation-induced thrombosis is a common consequence of bacterial infections, such as those caused by Salmonella Typhimurium (STm). The presentation of multi-organ thrombosis post-infection that develops and resolves with organ-specific kinetics raises significant challenges for its therapeutic control. Here, we identify specific inflammatory events driving thrombosis in the spleens and livers of STm-infected mice. IFN-γ or platelet expression of C-type lectin-like receptor CLEC-2, key drivers of thrombosis in liver, are dispensable for thrombosis in the spleen. Platelets, monocytes, and neutrophils are identified as core constituents of thrombi in both organs. Depleting either neutrophils or monocytic cells abrogates thrombus formation. Neutrophils and monocytes secrete TNF and blocking TNF diminishes both thrombosis and inflammation, which correlates with reduced endothelial expression of E-selectin and leukocyte infiltration. Moreover, inhibiting tissue factor and P-selectin glycoprotein ligand-1 pathways impairs thrombosis in both spleen and liver. Therefore, we identify organ-specific, and shared mechanisms driving thrombosis within a single infection. This may inform on tailoring treatments towards infection-induced inflammation, and single- or multi-organ thrombosis, based on the clinical need.

Platelet-neutrophil aggregate formation induces NLRP3 inflammasome activation in vaccine-induced thrombotic thrombocytopenia

BACKGROUND

Although rare, vaccine-induced thrombotic thrombocytopenia (VITT) following adenoviral vector COVID-19 vaccination is a concerning and often severe adverse effect of vaccination. The generation of high antiplatelet factor 4 antibody titers promotes the formation of immune complexes capable of activating platelets and neutrophils through FcγRIIa.

OBJECTIVES

Given that platelet-leukocyte aggregate formation and inflammasome activation are common features of thromboinflammatory diseases, we aimed to evaluate if these are also features of VITT.

METHODS

Samples from a cohort of 57 postvaccination thrombosis patients and 28 age- and sex-matched unvaccinated individuals were used for ex vivo investigation of platelet-leukocyte aggregate formation and inflammasome activation.

RESULTS

Patients with clinical features of VITT presented elevated levels of activated caspase-1, interleukin-18, and interleukin-1β in the plasma. We also found that soluble factors in the plasma of VITT patients induce the formation of platelet-neutrophil aggregates but not platelet-monocyte or platelet T-cell aggregates, which are associated with increased caspase-1 activation in neutrophils ex vivo. Platelet-neutrophil aggregate formation was prevented through blockage of FcγRIIa with the neutralizing antibody IV.3 and through blockage of P-selectin or integrin αIIbβ3, also inhibiting caspase-1 activation. Additionally, MCC950, an NLRP3 inflammasome inhibitor, blocked caspase-1 activation.

CONCLUSION

Taken together, these data show that VITT plasma induces platelet-neutrophil aggregate formation in a FcγRIIa-dependent manner and that platelet-neutrophil interactions may contribute to thromboinflammation in VITT patients by supporting NLRP3 inflammasome activation. These data shed light on novel immunopathological events associated with inflammation and thrombosis in VITT patients.

Effectiveness of the Original Monovalent Messenger RNA Coronavirus Disease 2019 (COVID-19) Vaccination Series Against Hospitalization for COVID-19-Associated Venous Thromboembolism

BACKGROUND

Coronavirus disease 2019 (COVID-19) is a strong risk factor for venous thromboembolism (VTE). Few studies have evaluated the effectiveness of COVID-19 vaccination in preventing hospitalization for COVID-19 with VTE.

METHODS

Adults hospitalized at 21 sites between March 2021 and October 2022 with symptoms of acute respiratory illness were assessed for COVID-19, completion of the original monovalent messenger RNA (mRNA) COVID-19 vaccination series, and VTE. Prevalence of VTE was compared between unvaccinated and vaccinated patients with COVID-19. The vaccine effectiveness (VE) in preventing COVID-19 hospitalization with VTE was calculated using a test-negative design. The VE was also stratified by predominant circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant.

RESULTS

Among 18 811 patients (median age [interquartile range], 63 [50-73] years; 49% women; 59% non-Hispanic white, 20% non-Hispanic black, and 14% Hispanic; and median of 2 comorbid conditions [interquartile range, 1-3]), 9792 were admitted with COVID-19 (44% vaccinated), and 9019 were test-negative controls (73% vaccinated). Among patients with COVID-19, 601 had VTE diagnosed by hospital day 28, of whom 170 were vaccinated. VTE was more common among unvaccinated than vaccinated patients with COVID-19 (7.8% vs 4.0%; P = .001). The VE against COVID-19 hospitalization with VTE was 84% overall (95% confidence interval, 80%-87%), and VE stratified by predominant circulating variant was 88% (73%-95%) for Alpha, 93% (90%-95%) for Delta, and 68% (58%-76%) for Omicron variants.

CONCLUSIONS

Vaccination with the original monovalent mRNA series was associated with a decrease in COVID-19 hospitalization with VTE, though data detailing prior history of VTE and use of anticoagulation were not available. These findings will inform risk-benefit considerations for those considering vaccination.

Oxidative Score and Microvesicle Profile Suggest Cardiovascular Risk in Chronic Kidney Disease

Chronic kidney disease (CKD) is associated with a high incidence of cardiovascular disease (CVD) due to the accumulation of uremic toxins, altered redox state, and chronic systemic inflammation. This study aimed to analyze the relationship between the redox status of patients with CKD and the phenotype of microvesicles (MVs) subtypes, and cardiovascular events. The oxidative stress level of each participant was determined using an individualized OXY-SCORE. The relationship between pro-oxidant and antioxidant parameters and the expression of membrane markers in endothelial-derived microvesicles (EMVs) and platelet-derived microvesicles (PMVs) was established. Patients with advanced CKD (ACKD) and hemodialysis (HD) had a higher OXY-SCORE than healthy subjects (HS), whereas peritoneal dialysis (PD) patients had similar scores to HS. PD patients showed elevated PMVs and CD41 expression, whereas HD patients had higher EMVs and CD31 expression. Patients with ACKD had higher tissue factor (TF) expression in the PMVs and EMVs. TF expression was correlated with xanthine oxidase (XO) activity and was negatively correlated with antioxidant parameters. Patients with cardiovascular events show elevated TF. In conclusion, microvesicles and oxidative stress may serve as markers of cardiovascular risk in CKD, with TF expression in PMVs and EMVs being potential predictive and prognostic biomarkers of CVD.

Platelet-Monocyte Aggregate Instigates Inflammation and Vasculopathy in Kawasaki Disease

Kawasaki disease (KD) is a severe acute febrile illness and systemic vasculitis that causes coronary artery aneurysms in young children. Platelet hyperreactivity and an aberrant immune response are key indicators of KD; however, the mechanism by which hyperactive platelets contribute to inflammation and vasculopathy in KD remains unclear. A cytokine-mediated positive feedback loop between KD platelets and monocytes is identified. KD platelet-monocyte aggregates (MPAs) are mediated by an initial interaction of P-selectin (cluster of differentiation 62P, CD62p) and its glycoprotein ligand 1 (PSGL-1). This is followed by a coordinated interaction of platelet glycoprotein (GP)Ibα with monocyte CD11b. Monocyte-activated platelets initiate transforming growth factor (TGF)β1 release, which results in nuclear localization of nuclear factor kappaB in monocytes, therefore, driving the phenotypic conversion of classical monocytes (CD14+CD16-) into proinflammatory monocytes (CD14+CD16+). The platelet-activated monocytes release interleukin-1 and tissue necrotic factor-α, which promote further platelet activation. KD-induced inflammation and vasculopathy are prevented by inhibiting the components of this positive feedback loop. Notably, mice deficient in platelet TGFβ1 show less MPA and CD14+CD16+ monocytes, along with reduced inflammation and vasculopathy. These findings reveal that platelet-monocyte interactive proteins (CD62p/PSGL-1 and (GP)Ibα/CD11b) and cytokine mediators (platelet TGFβ1) are potential biomarkers and therapeutic targets for KD vasculopathy.

Association between platelet count and 30-day in-hospital mortality among intensive care unit patients with sepsis: a multicenter retrospective cohort study

Background

The relationship between platelet count and sepsis outcomes in intensive care units (ICUs) requires comprehensive investigation through large-scale multicenter studies.

Methods

In this multicenter retrospective cohort study, we analyzed 17,977 sepsis patients from 208 U.S. hospitals (2014-2015) using the eICU Collaborative Research Database v2.0. Analyses were adjusted for demographics, clinical parameters, comorbidities, and treatments. Generalized additive models and two-piecewise linear regression were used to assess the relationship between platelet count and mortality.

Results

A U-shaped relationship was identified with an inflection point at 176 × 10⁹/L. Below this threshold, each 10 × 10⁹/L increase in platelet count was associated with a 6% decrease in mortality risk (adjusted OR 0.94, 95% CI 0.93-0.95, p < 0.0001), while above it, each 10 × 10⁹/L increase was associated with a 1% increase in mortality risk (adjusted OR 1.01, 95% CI 1.00-1.01, p = 0.0153).

Conclusion

This large-scale, multicenter retrospective study has made a significant contribution to understanding the association between platelet count and mortality in patients with sepsis in intensive care units. We identified a critical threshold of 176 × 109/L for platelet count and demonstrated a distinct U-shaped relationship with 30-day in-hospital mortality, providing valuable reference criteria for clinical risk stratification.

COVID-19 and HIV: Clinical Outcomes and Inflammatory Markers in a Cohort from a Reference Hospital in Rio de Janeiro, Brazil

BACKGROUND

Severe COVID-19 presents a variety of clinical manifestations associated with inflammatory profiles. People living with HIV (PLWH) could face a higher risk of hospitalization and mortality from COVID-19, depending on their immunosuppression levels. This study describes inflammatory markers in COVID-19 clinical outcomes with and without HIV infection.

METHODS

We analyzed 112 inpatients of the Hospital Center for COVID-19 (INI/FIOCRUZ), including 22 cases of COVID-19 in PLWH (COVID/PLWH group). Plasma samples were tested for a panel of 15 cytokines by Luminex. Sociodemographic, clinical, and laboratory data were collected from patients' clinical records.

RESULTS

COVID-19 individuals were stratified according to the WHO clinical severity profiles at hospitalization. Significant differences in clinical scores, symptoms (coughs), and the occurrence of HIV infection were found among the groups. Clinical blood parameters and plasma cytokines were analyzed among COVID-19 groups with distinct severity profiles. Critical COVID-19 cases showed higher levels of inflammatory markers (Bilirubin, D-dimer, PCR, and urea, as well as IL-8, IL-10, TNF-α, INF-α, IL-1β, IL-17A, IL-23, IL-6) than moderate and severe groups. The COVID/PLWH group had lower CD4 counts (64 cells/mm3) and cytokine levels than other COVID-19 patients.

CONCLUSIONS

Overall, critically ill COVID-19 patients exhibited heightened inflammatory responses, while COVID/PLWH demonstrated unique immunological characteristics without increased mortality risk.

Relevance of anti-platelet factor 4/heparin antibodies and platelet activation in systemic inflammatory diseases and thrombosis disorders: insight from the COVID-19 pandemic

Background

The increased interest in anti-platelet factor 4 (PF4)-heparin complex (anti-PF4/H) antibodies following the COVID-19 pandemic has established them as crucial players in immunothrombosis.

Objectives

We aimed to investigate the involvement of anti-PF4/H antibodies during COVID-19 and after vaccination, particularly in patients with systemic inflammatory disease (SID).

Methods

This retrospective study analyzed the presence of anti-PF4/H antibodies and their ability to induce platelet activation in COVID-19 patients with and without suspected heparin-induced thrombocytopenia (HIT), vaccine-induced immune thrombotic thrombocytopenia (VITT) patients, and in controls and SID patients following COVID-19 vaccination.

Results

No significant increase in anti-PF4/H antibody levels was observed during COVID-19 regardless of disease severity. Despite a 2-fold increase in HIT suspicion observed during the pandemic, there was no corresponding increase in HIT diagnoses. Additionally, no significant increase in anti-PF4/H levels was noted after vaccination, even in SID patients. None of the positive anti-PF4/H antibodies detected in COVID-19 or vaccination cohorts induced platelet activation, measured by soluble P-selectin levels and flow cytometry-based on platelet microvesicle generation. Finally, in VITT patients, unlike in HIT patients, anti-PF4/H levels were strongly associated with platelet microvesicle assay and moderately with soluble P-selectin levels.

Conclusion

Our study found no significant increase in anti-PF4/H antibodies in COVID-19 or after vaccination, including in SID patients. However, in VITT patients, but not in HIT patients, these antibodies were correlated with platelet activation. This finding suggests that anti-PF4/H antibodies play a different role in the pathophysiology of VITT but that their interest is limited outside clear contexts of HIT/VITT suspicion.

An insight into COVID-19 host immunity at single-cell resolution

Host immunity helps the body to fight against COVID-19. Single-cell transcriptomics has provided the scope of investigating cellular and molecular underpinnings of host immune response against SARS-CoV-2 infection at high resolution. In this review, we have systematically described the virus-induced dysregulation of relative abundance as well as molecular behavior of each innate and adaptive immune cell type and cell state during COVID-19 infection and for different vaccinations, based on single-cell studies published in last three-four years. Identification and characterization of these disease-associated specific cell populations might help to design better, efficient, and targeted therapeutic avenues.

A loss of tuning of both pro-coagulant and inflammatory responses in monocytes in patients with preeclampsia

An imbalance between pro- and anti-angiogenesis is one of the leading causes of preeclampsia (PE). Monocytes, known as regulators of angiogenesis during immune responses, cooperate with platelets, but the specifics of these responses during pregnancy remain unclear. In this study, we investigated the relationship between pro-coagulant responses on monocytes [platelet activation marker CD61 as a monocyte-platelet aggregate (MPA), tissue factor (CD142), etc.], inflammatory responses [soluble CD40 ligand (sCD40L), soluble suppression of tumorigenesis-2 (sST2), etc.], and the balance of angiogenesis [soluble Fms-related receptor tyrosine kinase 1/placental growth factor (sFlt-1/PLGF) ratio]. In PE, markers of pro-coagulant and inflammatory responses were higher than those in normal pregnancy (NP). Interestingly, in NP, these markers harmonized with the sFlt-1/PLGF ratio, but not in PE. Furthermore, ex vivo examinations showed that upregulation of CD142 induced by additional platelet activation with adenosine diphosphate was diminished in PE. Conversely, low-dose aspirin, which is used as a preventive treatment for PE, could inhibit the increase of CD61 and sST2 under inflammatory stimuli and platelet activation in NP but not in PE. These results indicate that monocytes in PE upregulate basal activity and lose responsiveness to stimulation. The elevation of pro-coagulant and inflammatory responses may be mitigated by prophylaxis with low-dose aspirin. Therefore, the findings suggesting a loss of tuning of both pro-coagulant and inflammatory responses on monocytes help in understanding the pathology of PE. The harmonization between pro-coagulant responses, inflammatory responses, and angiogenesis may serve as useful indicators for the prediction and preventive treatment of PE.

Viral coagulation: pushing the envelope

Many virus types affect the blood clotting system with correlations to pathology that range widely from thrombosis to hemorrhage linking to inflammation. Here we overview the intricate crosstalk induced by infection between proteins on the virus encoded by either the host or virus genomes, coagulation proteins, platelets, leukocytes, and endothelial cells. For blood-borne viruses with an outer covering acquired from the host cell, the envelope, a key player may be the cell-derived trigger of coagulation on the virus surface, tissue factor (TF). TF is a multifunctional transmembrane cofactor that accelerates factor (F)VIIa-dependent activation of FX to FXa, leading to clot formation. However, the nascent TF/FVIIa/FXa complex also facilitates G protein-coupled modulation of cells via protease-activated receptor 2. As a viral envelope constituent, TF can bypass the physiological modes of regulation, thereby initiating the activation of neighboring platelets, leukocytes, and endothelial cells. A thromboinflammatory environment is predicted due to feedback amplification in response to cellular release of cytokines, procoagulant proteins, neutrophil extracellular traps, and stimulus-induced accessibility of adhesive receptors, resulting in cellular aggregates. The pathobiological effects of thromboinflammation ultimately contribute to innate and adaptive immunity for viral clearance. In contrast, the preceding stages of viral infection may be enhanced via the TF-protease axis.

Elevated levels of pro-thrombotic eNOS-negative platelets in COVID-19 patients

BACKGROUND

Platelet-rich microvascular thrombi are common in severe COVID-19. Endogenous nitric oxide (NO)-signaling limits thrombus formation and previously we identified platelet subpopulations with a differential ability to produce NO based on the presence or absence of endothelial nitric oxide synthase (eNOS). eNOS expression is counter-regulated by cytokines, and COVID-19-associated immune/inflammatory responses may affect the transcriptome profile of megakaryocytes and their platelet progeny.

OBJECTIVES

We investigated whether the percentage of eNOS-negative to eNOS-positive platelets increases in COVID-19 patients and whether this change may be due to the actions of pro-inflammatory cytokines on megakaryocytes.

METHODS

Platelets were isolated from hospitalized COVID-19 patients and COVID-19-negative controls. Platelet eNOS was measured by flow cytometry and plasma inflammatory cytokines by ELISA. Megakaryocytes from eNOS-GFP transgenic mice and the Meg-01 cell line were characterized to identify an appropriate model to study eNOS-based platelet subpopulation formation in response to inflammatory cytokines.

RESULTS

COVID-19 patients demonstrated a significant increase in eNOS-negative and a concomitant decrease in eNOS-positive platelets compared to controls, and this change was associated with disease severity as assessed by ICU admission. A higher eNOS-negative to -positive platelet percentage was associated with enhanced platelet activation as measured by surface CD62P. Accordingly, COVID-19 patients demonstrated higher TNF-α, IL-6, and IL-1β plasma concentrations than controls. Inflammatory cytokines associated with COVID-19 promoted eNOS-negative Meg-01 formation and enhanced subsequent eNOS-negative platelet-like particle formation.

CONCLUSIONS

COVID-19 patients have a higher percentage of eNOS-negative to -positive platelets, likely as a result of inflammatory response reducing megakaryocyte eNOS expression, which predisposes to thrombosis.

Platelet-Leukocyte Aggregate and Interleukin-6: An Emerging Perspective on a New Diagnostic and Therapeutic Clue for Acute Coronary Syndrome, A Case-Control Study

Background and Aims

Acute coronary syndrome (ACS) is one of the most important cardiovascular diseases. The rupture of atherosclerotic plaques in coronary arteries is considered the underlying pathophysiology of ACS. The interaction between cytokines and leukocytes in the presence of platelets results in platelet-leukocyte aggregate (PLA). Monocytes, neutrophils, and cytokines are prime factors that promote PLA formation, which leads to atherosclerotic plaque progression and subsequent ACS development. This study aimed to investigate PLA (PMA and PNA) formation and cytokine (IL-6 and TNF-α) levels as well as the correlation between them in ACS patient samples to identify diagnostic markers.

Methods

A total of 30 patients with ACS and 24 healthy controls participated in this study. Flow cytometry analysis was performed to evaluate PLA formation, and the serum levels of cytokines were assessed by ELISA. The Pearson's correlation coefficient and ROC curve were calculated to investigate the correlation between the parameters and their diagnostic value, respectively.

Results

The results showed that PMA, PNA, and IL-6 levels were significantly higher in ACS patients than in healthy controls. Additionally, TNF-α levels were not significantly increased in the patient group. In addition, the Pearson's correlation coefficient results revealed a direct linear and statistically significant relationship between PMA-IL-6 and PNA-IL-6 as well as a direct linear but statistically nonsignificant relationship between IL-6-TNF-α and PMA-PNA, whereas a convers linear but nonsignificant correlation was shown between PMA and TNF-α and no correlation was detected between PNA and TNF-α. Finally, ROC curve analysis revealed that the PMA, PNA, and IL-6 can have diagnostic value.

Conclusion

In conclusion, the PMA, PNA, and IL-6 can be used as powerful diagnostic markers in ACS patients. Therefore, disrupting PMA and PNA formation and inhibiting cytokine production may be new strategies for the treatment of ACS. However, further investigations are required to explore these parameters in the clinical diagnosis of ACS.

Platelet activation through CD62P and the formation of platelet-monocyte complexes are associated with the exacerbation of mucosal inflammation in patients with ulcerative colitis

Ulcerative colitis (UC) is a refractory, chronic inflammatory bowel disease of unknown etiology. Although platelets are activated in UC, their relevance in pathophysiology remains unclear. We analyzed the correlation of platelet activation and platelet-monocyte complexes (PMCs) with severity of mucosal inflammation using the Mayo endoscopic subscore (MES). Platelet activation marker, CD62P was upregulated in patients with UC compared with that in healthy controls (P < 0.05). CD62P expression was significantly higher in patients with MES3 (severe inflammation) than in those with MES ≤ 2 (endoscopic remission to moderate inflammation) (P < 0.001). The concentration of sCD62P in patients with MES0 (endoscopic remission) was significantly higher than in those with MES ≥ 1 (P < 0.01). The expression of CD40L, CD63, PAC-1, annexin V, and CD36, and the concentrations of sCD40L, PF4, and RANTES did not correlate with MES. The proportion of PMCs in patients with MES3 was higher than in those with MES ≤ 2 (P < 0.05). CD16 expression on monocytes with platelets was significantly higher than in monocytes without platelets (P < 0.001). Patients with complete remission after treatment showed significant reduction in PMCs 3 months after treatment (P < 0.05) but had no change in CD62P and sCD62P. Our data suggest that platelet activation via the CD62P-PMC axis is involved in UC pathophysiology.

Hyperexpression of PTAFR and PF4 as Possible Platelet Risk Biomarkers in Patients With COVID-19

BACKGROUND/AIM

SARS-CoV-2 infection presents different severity levels that suggest the influence of genetic factors on the clinical outcome of the disease. In cases of severe COVID-19, the presence of elevated coagulation markers, increased platelet activation and aggregation and the risk of thrombotic complications are described. Given the participation of these cells in several serious viral infections and their negative role when associated with a prothrombotic response, it is important to understand the mechanistic role of SARS-CoV-2 in platelet physiology. This study evaluated the hyperexpression of platelet-activating factor receptor (PTAFR) and platelet factor 4 (PF4) in unvaccinated and hospitalized patients with COVID-19.

PATIENTS AND METHODS

The study included 43 COVID-19 patients stratified according to WHO guidelines. Subsequently, the expression of the PTAFR and PF4 genes were evaluated using the real-time quantitative PCR and their possible correlation with the severity of the disease and clinical variables including hospitalization, outcome, sex, age and laboratory parameters (platelet count, INR and D-dimer).

RESULTS

The analysis demonstrated a significant (p<0.05) hyperexpression of these genes COVID-19 patients (n=43) compared to healthy controls. Expression of these genes in patients was not statistically significant (p>0.05) different between patients stratified according to clinical variables.

CONCLUSION

The expression of PTAFR and PF4 suggests an important molecular pathway in the pathophysiology of the disease and may be valuable platelet biomarkers to indicate increased risk in patients with COVID-19 who require hospital care, contributing to personalized intervention strategies and improving their clinical management.

Immunity and Coagulation in COVID-19

Discovered in late 2019, the SARS-CoV-2 coronavirus has caused the largest pandemic of the 21st century, claiming more than seven million lives. In most cases, the COVID-19 disease caused by the SARS-CoV-2 virus is relatively mild and affects only the upper respiratory tract; it most often manifests itself with fever, chills, cough, and sore throat, but also has less-common mild symptoms. In most cases, patients do not require hospitalization, and fully recover. However, in some cases, infection with the SARS-CoV-2 virus leads to the development of a severe form of COVID-19, which is characterized by the development of life-threatening complications affecting not only the lungs, but also other organs and systems. In particular, various forms of thrombotic complications are common among patients with a severe form of COVID-19. The mechanisms for the development of thrombotic complications in COVID-19 remain unclear. Accumulated data indicate that the pathogenesis of severe COVID-19 is based on disruptions in the functioning of various innate immune systems. The key role in the primary response to a viral infection is assigned to two systems. These are the pattern recognition receptors, primarily members of the toll-like receptor (TLR) family, and the complement system. Both systems are the first to engage in the fight against the virus and launch a whole range of mechanisms aimed at its rapid elimination. Normally, their joint activity leads to the destruction of the pathogen and recovery. However, disruptions in the functioning of these innate immune systems in COVID-19 can cause the development of an excessive inflammatory response that is dangerous for the body. In turn, excessive inflammation entails activation of and damage to the vascular endothelium, as well as the development of the hypercoagulable state observed in patients seriously ill with COVID-19. Activation of the endothelium and hypercoagulation lead to the development of thrombosis and, as a result, damage to organs and tissues. Immune-mediated thrombotic complications are termed "immunothrombosis". In this review, we discuss in detail the features of immunothrombosis associated with SARS-CoV-2 infection and its potential underlying mechanisms.

The First Comprehensive Description of the Platelet Single Cell Transcriptome

Platelets are derived from megakaryocytes, either in peripheral or pulmonic circulation. The transcriptome of megakaryocytes has been studied, while the platelet transcriptome is thought to be a reflection of their parent cells; it has not yet been investigated. Although platelets lack nuclei, they inherit RNA from their parent megakaryocytes, while only about 10% of them are believed to contain enough RNA for meaningful analysis. This study explores the potential of single-cell RNA sequencing to analyze the platelet transcriptome, aiming to expand our understanding of platelets beyond their traditional role in coagulation. Using acridine orange staining and antibody-based sequencing, we successfully sequenced RNA from seven healthy donors. Results revealed significant heterogeneity in gene expression, with common platelet markers, such as ITGA2B and GP1B, being less abundant than expected. Interestingly, immune markers associated with lung megakaryocytes were not strongly represented in peripheral platelets. Comparison with current algorithms for cell identification suggests that platelets are often misclassified as other blood cell types, highlighting limitations of existing pipelines in platelet annotation. This misclassification may have led to misrepresentation of platelet transcriptomics in previous studies. These findings underscore the need for tailored sequencing methods to accurately profile platelets and set the foundation for further exploration of platelet biology and immune function, potentially opening avenues for therapeutic interventions in immune modulation, drug delivery, and the use of platelets as disease biomarkers in cancer and other conditions.

Key Points

Platelet single cell sequencing can be implemented with appropriate technical refinements to ensure optimal isolation without exogenous activation. In comparison to bulk sequencing techniques, single cell analysis affords the ability to exclude contaminating cells enabling examination of the authentic platelet transcriptome. This is critically important as contaminating cells contain far more RNA ultimately skewing results of transcriptomic analysis.Most platelets do not contain significant levels of commonly expected transcripts such as ITGA2B, GP1B, TREML1. In the context of recent data, our single cell transcriptomic data supports the intradividual and interindividual heterogeneity of the platelet transcriptome. The lung megakaryocyte signature is not disguisable in peripheral platelets. Further studies are needed to understand sources of RNA within platelets and the impact of the platelet microenvironment.

Abstract Figure

Pink1/Parkin deficiency alters circulating lymphocyte populations and increases platelet-T cell aggregates in rats

Parkinson's disease (PD) is the most common progressive neurodegenerative movement disorder and results from the selective loss of dopaminergic neurons in the substantia nigra pars compacta. Pink1 and Parkin are proteins that function together in mitochondrial quality control, and when they carry loss-of-function mutations lead to familial forms of PD. While much research has focused on central nervous system alterations in PD, peripheral contributions to PD pathogenesis are increasingly appreciated. We report Pink1/Parkin regulate glycolytic and mitochondrial oxidative metabolism in peripheral blood mononuclear cells (PBMCs) from rats. Pink1/Parkin deficiency induces changes in the circulating lymphocyte populations, namely increased CD4 + T cells and decreased CD8 + T cells and B cells. Loss of Pink1/Parkin leads to elevated platelet counts in the blood and increased platelet-T cell aggregation. Platelet-lymphocyte aggregates are associated with increased thrombosis risk suggesting targeting the Pink1/Parkin pathway in the periphery might have therapeutic potential.

Targeting senescent cells in aging and COVID-19: from cellular mechanisms to therapeutic opportunities

The COVID-19 pandemic has caused a global health crisis and significant social economic burden. While most individuals experience mild or non-specific symptoms, elderly individuals are at a higher risk of developing severe symptoms and life-threatening complications. Exploring the key factors associated with clinical severity highlights that key characteristics of aging, such as cellular senescence, immune dysregulation, metabolic alterations, and impaired regenerative potential, contribute to disruption of tissue homeostasis of the lung and worse clinical outcome. Senolytic and senomorphic drugs, which are anti-aging treatments designed to eliminate senescent cells or decrease the associated phenotypes, have shown promise in alleviating age-related dysfunctions and offer a novel approach to treating diseases that share certain aspects of underlying mechanisms with aging, including COVID-19. This review summarizes the current understanding of aging in COVID-19 progression, and highlights recent findings on anti-aging drugs that could be repurposed for COVID-19 treatment to complement existing therapies.

Platelet dysfunction caused by differentially expressed genes as key pathogenic mechanisms in COVID-19

At the end of 2019, the novel coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) became prevalent worldwide, which brought a heavy medical burden and tremendous economic losses to the world population. In addition to the common clinical respiratory symptoms such as fever, cough and headache, patients with COVID-19 often have hematological diseases, especially platelet dysfunction. Platelet dysfunction usually leads to multiple organ dysfunction, which is closely related to patient severity or mortality. In addition, studies have confirmed significant changes in the gene expression profile of circulating platelets under SARS-CoV-2 infection, which will further lead to changes in platelet function. At the same time, studies have shown that platelets may absorb SARS-COV-2 mRNA independently of ACE2, which further emphasizes the importance of the stability of platelet function in defense against SARS-CoV-2 infection. This study reviewed the relationship between COVID-19 and platelet and SARS-CoV-2 damage to the circulatory system, and further analyzed the significantly differentially expressed mRNA in platelets after infection with SARS-CoV-2 on the basis of previous studies. The top eight hub genes were identified as NLRP3, MT-CO1, CD86, ICAM1, MT-CYB, CASP8, CXCL8 and CXCR4. Subsequently, the effects of SARS-CoV-2 infection on platelet transcript abnormalities and platelet dysfunction were further explored on the basis of 8 hub genes. Finally, the treatment measures of complications caused by platelet dysfunction in patients with COVID-19 were discussed in detail, so as to provide reference for the prevention, diagnosis and treatment of COVID-19.

BALB/c mice challenged with SARS-CoV-2 B.1.351 β variant cause pathophysiological and neurological changes within the lungs and brains

Up to one-third of individuals suffering from acute SARS-CoV-2 infection with the onset of severe-to-mild diseases could develop several symptoms of neurological disorders, which could last long after resolving the infection, known as neuro-COVID. Effective therapeutic treatments for neuro-COVID remain unavailable, in part, due to the absence of animal models for studying its underlying mechanisms and developing medical countermeasures against it. Here, we explored the impact of SARS-CoV-2 infection on the well-being of respiratory and neurological functions of BALB/c mice by using a clinical isolate of β-variant, i.e. B.1.351. We found that this β-variant of SARS-CoV-2 primarily infected the lungs, causing tissue damage, profound inflammatory responses, altered respiratory functions and transient but significant hypoxia. Although live progeny viruses could not be isolated, viral RNAs were detected across many anatomical regions of the brains in most challenged mice and triggered activation of genes encoding for NF-kB, IL-6, IP-10 and RANTES and microglial cells. We noted that the significantly activated IL-6-encoded gene persisted at 4 weeks after infection. Together, these results suggest that this B.1.351/BALB/c model of SARS-CoV-2 infection warrants further studies to establish it as a desirable model for studies of neuropathogenesis and the development of effective therapeutics of neuro-COVID.

The Role of Myeloid Cells in Thromboinflammatory Disease

Inflammation contributes to the development of thrombosis, but the mechanistic basis for this association remains poorly understood. Innate immune responses and coagulation pathways are activated in parallel following infection or injury, and represent an important host defense mechanism to limit pathogen spread in the bloodstream. However, dysregulated proinflammatory activity is implicated in the progression of venous thromboembolism and arterial thrombosis. In this review, we focus on the role of myeloid cells in propagating thromboinflammation in acute inflammatory conditions, such as sepsis and coronavirus disease 2019 (COVID-19), and chronic inflammatory conditions, such as obesity, atherosclerosis, and inflammatory bowel disease. Myeloid cells are considered key drivers of thromboinflammation via upregulated tissue factor activity, formation of neutrophil extracellular traps (NETs), contact pathway activation, and aberrant coagulation factor-mediated protease-activated receptor (PAR) signaling. We discuss how strategies to target the intersection between myeloid cell-mediated inflammation and activation of blood coagulation represent an exciting new approach to combat immunothrombosis. Specifically, repurposed anti-inflammatory drugs, immunometabolic regulators, and NETosis inhibitors present opportunities that have the potential to dampen immunothrombotic activity without interfering with hemostasis. Such therapies could have far-reaching benefits for patient care across many thromboinflammatory conditions.

One immune cell to bind them all: platelet contribution to neurodegenerative disease

Alzheimer's disease (AD) and related dementias (ADRD) collectively affect a significant portion of the aging population worldwide. The pathological progression of AD involves not only the classical hallmarks of amyloid beta (Aβ) plaque buildup and neurofibrillary tangle development but also the effects of vasculature and chronic inflammatory processes. Recently, platelets have emerged as central players in systemic and neuroinflammation. Studies have shown that patients with altered platelet receptor expression exhibit accelerated cognitive decline independent of traditional risk factors. Additionally, platelets from AD patients exhibit heightened unstimulated activation compared to control groups. Platelet granules contain crucial AD-related proteins like tau and amyloid precursor protein (APP). Dysregulation of platelet exocytosis contributes to disease phenotypes characterized by increased bleeding, stroke, and cognitive decline risk. Recent studies have indicated that these effects are not associated with the quantity of platelets present in circulation. This underscores the hypothesis that disruptions in platelet-mediated inflammation and healing processes may play a crucial role in the development of ADRD. A thorough look at platelets, encompassing their receptors, secreted molecules, and diverse roles in inflammatory interactions with other cells in the circulatory system in AD and ADRD, holds promising prospects for disease management and intervention. This review discusses the pivotal roles of platelets in ADRD.

Higher Platelet Count Mostly in the Normal Range Is Associated with the First Episode of Peritonitis Risk in Incident Peritoneal Dialysis Patients

INTRODUCTION

Platelets play parts in infection and immune processes. However, the association between platelet count and the risk of peritoneal dialysis (PD)-associated peritonitis is unclear.

METHODS

This was a retrospective, observational, single-center cohort study. A Cox regression analysis was used to evaluate the independent association of platelet count with the occurrence of first PD-associated peritonitis. Models were adjusted for gender, age, body mass index, cardiovascular disease, diabetes mellitus, white blood cell count, neutrophil-lymphocyte ratio, hemoglobin level, albumin level, potassium level, and anti-platelet medication usage.

RESULTS

A total of 2,374 patients were enrolled in this study (59% men; mean age 47.40 ± 12.12). The average platelet count was 229.30 ± 82.12 × 109/L. 467 (20%) patients suffered from PD-associated peritonitis at least once. In the multivariable model, the adjusted hazard ratios (HRs) for quartiles 2, 3 and 4 versus quartile 1 were 1.428 (95% CI 1.060-1.924, p = 0.019), 1.663 (95% CI 1.240-2.229, p < 0.001) and 1.843 (95% CI 1.363-2.492, p < 0.001) with baseline data. A nonlinear relationship between platelet count and first PD-associated peritonitis was observed. Further, the association between platelet and first PD-associated peritonitis was significant in the patients with hypokalemia (P for interaction = 0.040).

CONCLUSION

In PD patients, elevated platelet counts were significantly associated with an increased risk of the first onset of PD-associated peritonitis.

Anticoagulant use before COVID-19 diagnosis prevent COVID-19 associated acute venous thromboembolism or not: A systematic review and meta-analysis

BACKGROUND

Coagulopathy and thromboembolic events are associated with poor outcomes in coronavirus disease 2019 (COVID-19) patients. There is conflicting evidence on the effects of chronic anticoagulation on mortality and severity of COVID-19 disease.

AIM

To summarize the body of evidence on the effects of pre-hospital anticoagulation on outcomes in COVID-19 patients.

METHODS

A Literature search was performed on LitCovid PubMed, WHO, and Scopus databases from inception (December 2019) till June 2023 for original studies reporting an association between prior use of anticoagulants and patient outcomes in adults with COVID-19. The primary outcome was the risk of thromboembolic events in COVID-19 patients taking anticoagulants. Secondary outcomes included COVID-19 disease severity, in terms of intensive care unit admission or invasive mechanical ventilation/intubation requirement in patients hospitalized with COVID-19 infection, and mortality. The random effects models were used to calculate crude and adjusted odds ratios (aORs) with 95% confidence intervals (95%CIs).

RESULTS

Forty-six observational studies met our inclusion criteria. The unadjusted analysis found no association between prior anticoagulation and thromboembolic event risk [n = 43851, 9 studies, odds ratio (OR)= 0.67 (0.22, 2.07); P = 0.49; I 2 = 95%]. The association between prior anticoagulation and disease severity was non-significant [n = 186782; 22 studies, OR = 1.08 (0.78, 1.49); P = 0.64; I 2 = 89%]. However, pre-hospital anticoagulation significantly increased all-cause mortality risk [n = 207292; 35 studies, OR = 1.72 (1.37, 2.17); P < 0.00001; I 2 = 93%]. Pooling adjusted estimates revealed a statistically non-significant association between pre-hospital anticoagulation and thromboembolic event risk [aOR = 0.87 (0.42, 1.80); P = 0.71], mortality [aOR = 0.94 (0.84, 1.05); P = 0.31], and disease severity [aOR = 0.96 (0.72, 1.26); P = 0.76].

CONCLUSION

Prehospital anticoagulation was not significantly associated with reduced risk of thromboembolic events, improved survival, and lower disease severity in COVID-19 patients.

Sulfated Bile Acids in Serum as Potential Biomarkers of Disease Severity and Mortality in COVID-19

The fight against coronavirus disease 2019 (COVID-19) continues. Since the pandemic's onset, several biomarkers have been proposed to assess the diagnosis and prognosis of this disease. This research aimed to identify potential disease severity biomarkers in serum samples of patients with COVID-19 during the disease course. Data were collected using untargeted and targeted mass spectrometry methods. The results were interpreted by performing univariate and multivariate analyses. Important metabolite classes were identified by qualitative untargeted metabolomics in 15 serum samples from survivors of COVID-19. Quantitative targeted metabolomics on a larger patient cohort including 15 non-survivors confirmed serum 3-sulfate bile acids (i.e. GLCA-3S) were significantly increased in non-survivors compared to survivors during the early disease stage (p-value < 0.0001). Notably, it was associated with a higher risk of mortality (odds ratio of 26). A principal component analysis showed the ability to discriminate between survivors and non-survivors using the BA concentrations. Furthermore, increased BA-S is highly correlated with known parameters altered in severe clinical conditions.

Adequate serum 25-hydroxy-vitamin D levels are correlated with low anti-PF4 levels in mild COVID-19 Patients: An observational study

The worldwide spread of coronavirus disease 2019 (COVID-19) has resulted in an unparalleled health emergency of global proportions. Around 31% of individuals with COVID-19 experience thrombosis associated with hypercoagulation. COVID-19 patients have shown an increase in platelet activation, but the mechanism has not been fully understood yet. One theory suggests that this could be related to the heparin-induced thrombocytopenia phenomenon, where platelet activation involves anti-PF4 antibodies that are associated with thrombosis. Vitamin D has been established to exert an influence on immunological responses and inflammation. The aim of this study is to analyze the correlation between serum 25-hydroxy-cholecalciferol [25(OH)D] levels and anti-PF4 antibodies among COVID-19 patients. A cross-sectional study was conducted among 160 COVID-19 patients at Cipto Mangunkusumo General Hospital and Wisma Atlit Hospital Jakarta from October 2021 to January 2022. The mean serum 25(OH)D level was 15.1 ng/mL. A significant negative correlation was found between serum 25(OH)D and anti-PF4 levels in mild COVID-19 patients (P = .035; R = -0.236). Remarkably, P-selectin levels were significantly higher in the moderate COVID-19 group compared to the severe group (P = .031). Serum 25(OH)D level had a significant negative correlation with anti-PF4 level in mild COVID-19 patients. Thus, it is highly recommended to ensure that serum 25(OH)D levels are maintained above 30 ng/mL. Remarkably, the P-selectin level was significantly higher in the moderate COVID-19 group compared to the severe group.

Bioinformatics analysis of potential common pathogenic mechanisms for COVID-19 and venous thromboembolism

BACKGROUND

A growing body of research has shown that patients with coronavirus disease 2019 (COVID-19) have significantly higher rates of venous thromboembolism (VTE) than healthy. However, the mechanism remains incompletely elucidated. This study aimed to further investigate the molecular mechanisms underlying the development of this complication.

METHODS

The gene expression profiles of COVID-19 and VTE were downloaded from the Gene Expression Omnibus (GEO) database. After identifying the common differentially expressed genes (DEGs) for COVID-19 and VTE, functional annotation, a protein-protein interactions (PPI) network, module construction, and hub gene identification were performed. Finally, we constructed a transcription factor (TF)-gene regulatory network and a TF-miRNA regulatory network for hub genes.

RESULTS

A total of 42 common DEGs were selected for subsequent analyses. Functional analyses showed that biological function and signaling pathways collectively participated in the development and progression of VTE and COVID-19. Finally, 8 significant hub genes were identified using the cytoHubba plugin, including RSL24D1, RPS17, RPS27, HINT1, COX7C, RPL35, RPL34, and NDUFA4, which had preferable values as diagnostic markers for COVID-19 and VTE.

CONCLUSIONS

Our study revealed the common pathogenesis of COVID-19 and VTE. These common pathways and pivotal genes may provide new ideas for further mechanistic studies.

Extracellular histones: a unifying mechanism driving platelet-dependent extracellular vesicle release and thrombus formation in COVID-19

BACKGROUND

COVID-19 can cause profound inflammation and coagulopathy, and while many mechanisms have been proposed, there is no known common pathway leading to a prothrombotic state.

OBJECTIVES

From the beginning of the COVID-19 pandemic, elevated levels of extracellular histones have been found in plasma of patients infected with SARS-CoV-2. We hypothesized that platelet activation triggered by extracellular histones might represent a unifying mechanism leading to increased thrombin generation and thrombosis.

METHODS

We utilized blood samples collected from an early clinical trial of hospitalized COVID-19 patients (NCT04360824) and recruited healthy subjects as controls. Using plasma samples, we measured the procoagulant and prothrombotic potential of circulating extracellular histones and extracellular vesicles (EVs). Platelet prothrombotic activity was assessed via thrombin generation potential and platelet thrombus growth. Circulating EVs were assessed for thrombin generation potential in vitro in plasma and enhancement of thrombotic susceptibility in vivo in mice.

RESULTS

Compared with controls, COVID-19 patients had elevated plasma levels of citrullinated histone H3, cell-free DNA, nucleosomes, and EVs. Plasma from COVID-19 patients promoted platelet activation, platelet-dependent thrombin generation, thrombus growth under venous shear stress, and release of platelet-derived EVs. These prothrombotic effects of COVID-19 plasma were inhibited by an RNA aptamer that neutralizes both free and DNA-bound histones. EVs isolated from COVID-19 plasma enhanced thrombin generation in vitro and potentiated venous thrombosis in mice in vivo.

CONCLUSION

We conclude that extracellular histones and procoagulant EVs drive the prothrombotic state in COVID-19 and that histone-targeted therapy may prove beneficial.

P-selectin Facilitates SARS-CoV-2 Spike 1 Subunit Attachment to Vesicular Endothelium and Platelets

SARS-CoV-2 infection starts from the association of its spike 1 (S1) subunit with sensitive cells. Vesicular endothelial cells and platelets are among the cell types that bind SARS-CoV-2, but the effectors that mediate viral attachment on the cell membrane have not been fully elucidated. Herein, we show that P-selectin (SELP), a biomarker for endothelial dysfunction and platelet activation, can facilitate the attachment of SARS-CoV-2 S1. Since we observe colocalization of SELP with S1 in the lung tissues of COVID-19 patients, we perform molecular biology experiments on human umbilical vein endothelial cells (HUVECs) to confirm the intermolecular interaction between SELP and S1. SELP overexpression increases S1 recruitment to HUVECs and enhances SARS-CoV-2 spike pseudovirion infection. The opposite results are determined after SELP downregulation. As S1 causes endothelial inflammatory responses in a dose-dependent manner, by activating the interleukin (IL)-17 signaling pathway, SELP-induced S1 recruitment may contribute to the development of a "cytokine storm" after viral infection. Furthermore, SELP also promotes the attachment of S1 to the platelet membrane. Employment of PSI-697, a small inhibitor of SELP, markedly decreases S1 adhesion to both HUVECs and platelets. In addition to the role of membrane SELP in facilitating S1 attachment, we also discover that soluble SELP is a prognostic factor for severe COVID-19 through a meta-analysis. In this study, we identify SELP as an adhesive site for the SARS-CoV-2 S1, thus providing a potential drug target for COVID-19 treatment.

COVID-19 in the Initiation and Progression of Atherosclerosis: Pathophysiology During and Beyond the Acute Phase

The incidence of atherosclerotic cardiovascular disease is increasing globally, especially in low- and middle-income countries, despite significant efforts to reduce traditional risk factors. Premature subclinical atherosclerosis has been documented in association with several viral infections. The magnitude of the recent COVID-19 pandemic has highlighted the need to understand the association between SARS-CoV-2 and atherosclerosis. This review examines various pathophysiological mechanisms, including endothelial dysfunction, platelet activation, and inflammatory and immune hyperactivation triggered by SARS-CoV-2 infection, with specific attention on their roles in initiating and promoting the progression of atherosclerotic lesions. Additionally, it addresses the various pathogenic mechanisms by which COVID-19 in the post-acute phase may contribute to the development of vascular disease. Understanding the overlap of these syndromes may enable novel therapeutic strategies. We further explore the need for guidelines for closer follow-up for the often-overlooked evidence of atherosclerotic cardiovascular disease among patients with recent COVID-19, particularly those with cardiometabolic risk factors.

Causal Effects of COVID-19 on the Risk of Thrombosis: A Two-Sample Mendel Randomization Study

BACKGROUND

 Coronavirus disease 2019 (COVID-19) and thrombosis are linked, but the biomolecular mechanism is unclear. We aimed to investigate the causal relationship between COVID-19 and thrombotic biomarkers.

METHODS

 We used two-sample Mendelian randomization (MR) to assess the effect of COVID-19 on 20 thrombotic biomarkers. We estimated causality using inverse variance weighting with multiplicative random effect, and performed sensitivity analysis using weighted median, MR-Egger regression and MR Pleiotropy Residual Sum and Outlier (MR-PRESSO) methods. All the results were examined by false discovery rate (FDR) with the Benjamin and Hochberg method for this correction to minimize false positives. We used R language for the analysis.

RESULTS

 All COVID-19 classes showed lower levels of tissue factor pathway inhibitor (TFPI) and interleukin-1 receptor type 1 (IL-1R1). COVID-19 significantly reduced TFPI (odds ratio [OR] = 0.639, 95% confidence interval [CI]: 0.435-0.938) and IL-1R1 (OR = 0.603, 95% CI = 0.417-0.872), nearly doubling the odds. We also found that COVID-19 lowered multiple coagulation factor deficiency protein 2 and increased C-C motif chemokine 3. Hospitalized COVID-19 cases had less plasminogen activator, tissue type (tPA) and P-selectin glycoprotein ligand 1 (PSGL-1), while severe cases had higher mean platelet volume (MPV) and lower platelet count. These changes in TFPI, tPA, IL-1R1, MPV, and platelet count suggested a higher risk of thrombosis. Decreased PSGL-1 indicated a lower risk of thrombosis.

CONCLUSION

 TFPI, IL-1R, and seven other indicators provide causal clues of the pathogenesis of COVID-19 and thrombosis. This study demonstrated that COVID-19 causally influences thrombosis at the biomolecular level.

Platelet Activation is Upregulated in Cirrhotic Patients with Portal Vein Thrombosis

OBJECTIVE

 Platelet plays a key role in thrombosis formation, especially that the alteration of platelet function may influence the thrombosis development. This study aimed to investigate platelet function alterations in the formation of portal vein thrombosis (PVT) in cirrhosis.

METHODS

 Cirrhotic patients admitted to The First Affiliated Hospital of Soochow University between October 2021 and April 2023 were recruited and divided into PVT and non-PVT groups according to radiological results. Clinical parameters and prognosis were also collected and assessed to identify potential risk factors. Flow cytometry was used to detect the expression of CD62p, CD63, monocyte-platelet aggregates (MPAs), neutrophil-platelet aggregates (NPAs), and von Willebrand factor antigen (vWF-Ag) to evaluate platelet activation and adhesion function.

RESULTS

 A total of 145 subjects were enrolled in our study including 60 cirrhotic PVT patients, 60 cirrhotic non-PVT patients, and 25 healthy volunteers. Multivariate analysis suggested that esophageal gastric varices, splenectomy, and D-dimer were independent risk factors for PVT pathogenesis in cirrhosis. The vWF-Ag expression level was reduced in the PVT group compared with the non-PVT group (p = 0.046) but was not an independent risk factor for PVT formation pathogenesis. The expression of CD41+CD62p+ and CD41+CD63+ platelets in the PVT group was significantly elevated compared with that in the non-PVT group (p < 0.05). There were no significant differences in MPAs and NPAs between the two cirrhotic groups. Subgroup analysis showed that the mean fluorescence intensity (MFI) of CD62p and CD63 was associated with portal hypertension-related complications (p = 0.008, p < 0.001), and CD63 MFI was significantly associated with thrombosis burden (p = 0.019). CD41+CD62p+ and CD41+CD63+ platelets as well as MPAs and NPAs were highly expressed in the splenectomy group compared with those in the nonsplenectomy group in cirrhotic patients (p < 0.05). Positive correlations were found between CD62p MFI and CD63 MFI, MPAs and NPAs (r = 0.642, p < 0.001; r = 0.378, p = 0.003; r = 0.430, p < 0.001). In addition, platelet counts were also correlated with MPAs (r = 0.556, p < 0.001) and NPAs (r = 0.467, p < 0.001). Cirrhotic patients with PVT had higher mortality and were more likely to experience portal hypertension-related complications in the prognostic analysis (p < 0.05).

CONCLUSION

 Highly activated platelet function exists in patients with cirrhosis, and platelet activation was elevated during PVT formation, suggesting that activated platelets may participate in the formation of PVT in patients with cirrhosis.

Persistently High Platelet Factor 4 Levels in an Adolescent with Recurrent Late Thrombotic Complications after SARS-CoV-2 mRNA Vaccination

Thrombosis after severe acute respiratory syndrome coronavirus 2 vaccination is a serious complication in patients with a thrombophilic predisposition. Herein, we present a 17-year-old female who had underlying antiphospholipid syndrome (APS) and developed deep vein thrombosis (DVT) 6 months after her second BNT162b2 vaccine dose. Although she had no family history of thrombosis, she had previously developed DVT at 6 years of age, with thrombus formation in the right common iliac vein and the inferior vena cava, along with concomitant left pulmonary infarction. The patient had received anticoagulant therapy for 6 years after DVT onset, with subsequent treatment cessation for 5 years without recurrence. She received the BNT162b2 vaccine at 17 years of age, 1 week before a routine outpatient visit. Platelet factor 4 elevation was detected 14 days after the first vaccination, persisting for 5 months without thrombotic symptoms. Six months after the second vaccine dose, the DVT recurred and was treated with a direct oral anticoagulant. The vaccine was hypothesized to exacerbate the patient's APS by activating coagulation. Platelet factor 4 levels may indicate coagulation status. When patients predisposed to thrombosis are vaccinated, coagulation status and platelet activation markers should be monitored to prevent DVT development.

Cytokine Storm in COVID-19: Insight into Pathological Mechanisms and Therapeutic Benefits of Chinese Herbal Medicines

Cytokine storm (CS) is the main driver of SARS-CoV-2-induced acute respiratory distress syndrome (ARDS) in severe coronavirus disease-19 (COVID-19). The pathological mechanisms of CS are quite complex and involve multiple critical molecular targets that turn self-limited and mild COVID-19 into a severe and life-threatening concern. At present, vaccines are strongly recommended as safe and effective treatments for preventing serious illness or death from COVID-19. However, effective treatment options are still lacking for people who are at the most risk or hospitalized with severe disease. Chinese herbal medicines have been shown to improve the clinical outcomes of mild to severe COVID-19 as an adjunct therapy, particular preventing the development of mild to severe ARDS. This review illustrates in detail the pathogenesis of CS-involved ARDS and its associated key molecular targets, cytokines and signalling pathways. The therapeutic targets were identified particularly in relation to the turning points of the development of COVID-19, from mild symptoms to severe ARDS. Preclinical and clinical studies were reviewed for the effects of Chinese herbal medicines together with conventional therapies in reducing ARDS symptoms and addressing critical therapeutic targets associated with CS. Multiple herbal formulations, herbal extracts and single bioactive phytochemicals with or without conventional therapies demonstrated strong anti-CS effects through multiple mechanisms. However, evidence from larger, well-designed clinical trials is lacking and their detailed mechanisms of action are yet to be well elucidated. More research is warranted to further evaluate the therapeutic value of Chinese herbal medicine for CS in COVID-19-induced ARDS.

Preferential and sustained platelet activation in COVID-19 survivors with mental disorders

Pre-existing mental disorders are considered a risk factor for severe COVID-19 outcomes, possibly because of higher vascular burden. Moreover, an unconventional platelet activation characterizes COVID-19 and contributes to inflammatory and thrombotic manifestations. In the light of the inflammation theory of mental disorders, we hypothesized that patients with mental disorders could be sensitive to the SARS-CoV-2 elicited platelet activation. We investigated platelet activation in 141 COVID-19 survivors at one month after clearance of the virus, comparing subjects with or without an established pre-existing diagnosis of mental disorder according to the DSM-5. We found that platelets from patients with a positive history of psychiatric disorder underwent unconventional activation more frequently than conventional activation or no activation at all. Such preferential activation was not detected when platelets from patients without a previous psychiatric diagnosis were studied. When testing the effects of age, sex, and psychiatric history on the platelet activation, GLZM multivariate analysis confirmed the significant effect of diagnosis only. These findings suggest a preferential platelet activation during acute COVID-19 in patients with a pre-existing psychiatric disorder, mediated by mechanisms associated with thromboinflammation. This event could have contributed to the higher risk of severe outcome in the psychiatric population.

Potential Immune-Inflammatory Proteome Biomarkers for Guiding the Treatment of Patients with Primary Acute Angle-Closure Glaucoma Caused by COVID-19

Primary acute angle-closure glaucoma (PAACG) is a sight-threatening condition that can lead to blindness. With the increasing incidence of COVID-19, a multitude of people are experiencing acute vision loss and severe swelling of the eyes and head. These patients were then diagnosed with acute angle closure, with or without a history of PACG. However, the mechanism by which viral infection causes PACG has not been clarified. This is the first study to explore the specific inflammatory proteomic landscape in SARS-CoV-2-induced PAACG. The expression of 92 inflammation-related proteins in 19 aqueous humor samples from PAACGs or cataract patients was detected using the Olink Target 96 Inflammation Panel based on a highly sensitive and specific proximity extension assay technology. The results showed that 76 proteins were significantly more abundant in the PAACG group than in the cataract group. Notably, the top eight differentially expressed proteins were IL-8, MCP-1, TNFRSF9, DNER, CCL4, Flt3L, CXCL10, and CD40. Generally, immune markers are related to inflammation, macrophage activation, and viral infection, revealing the crucial role of macrophages in the occurrence of PAACGs caused by SARS-CoV-2.

Role of microbiota-derived corisin in coagulation activation during SARS-CoV-2 infection

BACKGROUND

Coagulopathy is a major cause of morbidity and mortality in COVID-19 patients. Hypercoagulability in COVID-19 results in deep vein thrombosis, thromboembolic complications, and diffuse intravascular coagulation. Microbiome dysbiosis influences the clinical course of COVID-19. However, the role of dysbiosis in COVID-19-associated coagulopathy is not fully understood.

OBJECTIVES

The present study tested the hypothesis that the microbiota-derived proapoptotic corisin is involved in the coagulation system activation during SARS-CoV-2 infection.

METHODS

This cross-sectional study included 47 consecutive patients who consulted for symptoms of COVID-19. A mouse acute lung injury model was used to recapitulate the clinical findings. A549 alveolar epithelial, THP-1, and human umbilical vein endothelial cells were used to evaluate procoagulant and anticoagulant activity of corisin.

RESULTS

COVID-19 patients showed significantly high circulating levels of corisin, thrombin-antithrombin complex, D-dimer, tumor necrosis factor-α, and monocyte-chemoattractant protein-1 with reduced levels of free protein S compared with healthy subjects. The levels of thrombin-antithrombin complex, D-dimer, and corisin were significantly correlated. A monoclonal anticorisin-neutralizing antibody significantly inhibited the inflammatory response and coagulation system activation in a SARS-CoV-2 spike protein-associated acute lung injury mouse model, and the levels of corisin and thrombin-antithrombin complex were significantly correlated. In an in vitro experiment, corisin increased the tissue factor activity and decreased the anticoagulant activity of thrombomodulin in epithelial, endothelial, and monocytic cells.

CONCLUSION

The microbiota-derived corisin is significantly increased and correlated with activation of the coagulation system during SARS-CoV-2 infection, and corisin may directly increase the procoagulant activity in epithelial, endothelial, and monocytic cells.

Red ginseng extract inhibits lipopolysaccharide-induced platelet-leukocyte aggregates in mice

Background

Platelet-leukocyte aggregates (PLAs) play important roles in cardiovascular disease and sepsis. Red ginseng extract (RGE) has been well-studied for its antiplatelet and anti-inflammatory activities. However, the potential inhibitory effects of RGE on PLA have not been investigated.

Methods

Six-week-old ICR mice were given oral gavage of RGE for 7 days, followed by an intraperitoneal injection of 15 mg/kg of lipopolysaccharide. Mice were euthanized 24 h later, and blood samples were collected for further analysis. Flow cytometry was utilized to sort populations of PLAs and platelet-neutrophil aggregates (PNAs). By using confocal microscopy, PNAs were validated. Morphological changes in platelets and leukocytes were visualized with scanning electron microscopy. Expressions of tissue factor (TF) and platelet factor 4 (PF4) were investigated using enzyme-linked immunosorbent assay.

Results

Populations of activated platelets, PLAs and PNAs, were significantly increased with LPS-induction. Treatment with 200 and 400 mg/kg of RGE decreased platelet activation. Moreover, the populations of PLAs and PNAs were reduced. PNAs were visible in the blood of septic mice, and this was attenuated by treatment with 400 mg/kg of RGE. Morphologically, sepsisinduced platelet activation and fibrin formation in the blood. This was reduced with RGE treatment. Sepsis-induced increase in the plasma levels of TF and PF4 was also reduced with RGE treatment.

Conclusion

This study shows that RGE is a potential therapeutic that reduces the activation of platelets and targets PLA and PNA formation. Detailed inhibitory mechanisms of RGE should be studied.

Increased platelet-CD8+ T-cell aggregates displaying high activation, exhaustion, and tendency to death correlate with disease progression in people with HIV-1

Platelets engage in HIV-1 infection by interacting with immune cells, which has been realized broadly. However, the potential interaction between platelets and CD8+ T cells remains unidentified. Here, treatment-naive individuals with HIV-1, complete immunological responders to antiretroviral therapy, and healthy controls were enrolled. First, we found that treatment-naive individuals with HIV-1 had low platelet numbers and high CD8+ T-cell counts when compared with complete immunological responders to antiretroviral therapy and healthy controls, leading to a low platelet/CD8+ T-cell ratio in peripheral blood, which could effectively differentiate the status of HIV-1 infection. Moreover, cytokines that may have been derived from platelets were higher in the plasma of people with HIV-1 despite viral suppression. Furthermore, we demonstrated that platelet-CD8+ T-cell aggregates were elevated in treatment-naive individuals with HIV-1, which positively correlated with HIV-1 viral load but negatively correlated with CD4+ T-cell count and CD4/CD8 ratio. Finally, we revealed that platelet-CD8+ T-cell aggregates correlate with enhanced activation/exhaustion and pyroptosis/apoptosis compared with free CD8+ T cells. Moreover, platelet-induced caspase 1 activation of CD8+ T cells correlated with IL-1β and IL-18 plasma levels. In brief, we reveal the importance of platelets in HIV-1 infection, which might secrete more cytokines and mediate CD8+ T-cell phenotypic characteristics by forming platelet-CD8+ T-cell aggregates, which are related to poor prognosis.

Physiological platelet aggregation assay to mitigate drug-induced thrombocytopenia using a microphysiological system

Developing a reliable method to predict thrombocytopenia is imperative in drug discovery. Here, we establish an assay using a microphysiological system (MPS) to recapitulate the in-vivo mechanisms of platelet aggregation and adhesion. This assay highlights the role of shear stress on platelet aggregation and their interactions with vascular endothelial cells. Platelet aggregation induced by soluble collagen was detected under agitated, but not static, conditions using a plate shaker and gravity-driven flow using MPS. Notably, aggregates adhered on vascular endothelial cells under gravity-driven flow in the MPS, and this incident increased in a concentration-dependent manner. Upon comparing the soluble collagen-induced aggregation activity in platelet-rich plasma (PRP) and whole blood, remarkable platelet aggregate formation was observed at concentrations of 30 µg/mL and 3 µg/mL in PRP and whole blood, respectively. Moreover, ODN2395, an oligonucleotide, induced platelet aggregation and adhesion to vascular endothelial cells. SYK inhibition, which mediated thrombogenic activity via glycoprotein VI on platelets, ameliorated platelet aggregation in the system, demonstrating that the mechanism of platelet aggregation was induced by soluble collagen and oligonucleotide. Our evaluation system partially recapitulated the aggregation mechanisms in blood vessels and can contribute to the discovery of safe drugs to mitigate the risk of thrombocytopenia.

SARS-CoV-2 infection modifies the transcriptome of the megakaryocytes in the bone marrow

ABSTRACT

Megakaryocytes (MKs), integral to platelet production, predominantly reside in the bone marrow (BM) and undergo regulated fragmentation within sinusoid vessels to release platelets into the bloodstream. Inflammatory states and infections influence MK transcription, potentially affecting platelet functionality. Notably, COVID-19 has been associated with altered platelet transcriptomes. In this study, we investigated the hypothesis that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection could affect the transcriptome of BM MKs. Using spatial transcriptomics to discriminate subpopulations of MKs based on proximity to BM sinusoids, we identified ∼19 000 genes in MKs. Machine learning techniques revealed that the transcriptome of healthy murine BM MKs exhibited minimal differences based on proximity to sinusoid vessels. Furthermore, at peak SARS-CoV-2 viremia, when the disease primarily affected the lungs, MKs were not significantly different from those from healthy mice. Conversely, a significant divergence in the MK transcriptome was observed during systemic inflammation, although SARS-CoV-2 RNA was never detected in the BM, and it was no longer detectable in the lungs. Under these conditions, the MK transcriptional landscape was enriched in pathways associated with histone modifications, MK differentiation, NETosis, and autoimmunity, which could not be explained by cell proximity to sinusoid vessels. Notably, the type I interferon signature and calprotectin (S100A8/A9) were not induced in MKs under any condition. However, inflammatory cytokines induced in the blood and lungs of COVID-19 mice were different from those found in the BM, suggesting a discriminating impact of inflammation on this specific subset of cells. Collectively, our data indicate that a new population of BM MKs may emerge through COVID-19-related pathogenesis.