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Soluble CLEC-2 is anticipated to have various clinical applications as a novel biomarker for in vivo platelet activation, assessable using plasma obtained through routine sampling procedures. While sCLEC-2 has been measured using ELISA, we have developed a highly sensitive chemiluminescence enzyme immunoassay (CLEIA) reagent that can yield results in approximately 19 minutes. This study aims to assess its fundamental performance and explore the molecular forms of sCLEC-2 measured in patient samples. We examined the sensitivity, precision, linearity, influence of endogenous substances, residual platelets, as well as the correlation with the ELISA method, for the sCLEC-2 CLEIA reagent. The CLEIA method demonstrated sufficient sensitivity for levels observed in healthy donors, and its basic performance was satisfactory. It exhibited a strong correlation with the previously described ELISA method, with reference ranges that did not significantly differ from the ELISA data. The sCLEC-2 reference range for males was significantly higher than that for females. Since it is known that sCLEC-2 exists in shed form and microparticle form, we investigated molecular forms of sCLEC-2 measured by the CLEIA in in vitro-activated platelets and in patients' plasma using gel filtration. It is considered that the CLEIA method shows significantly stronger reactivity with the shed form compared to the microparticle form. Studies using gel filtration of patient samples also suggest that the shed form is being primarily measured. The sCLEC-2 CLEIA reagent exhibits robust performance and is promising for clinical applications.

Platelets (PLTs) facilitate tumor progression and the spread of metastasis. They also interact with cancer cells in various cancer types. Furthermore, PLTs form complexes with gastric cancer (GC) cells via direct contact and promote their malignant behaviors. The objective of the present study was to explore the molecular mechanisms driving these interactions and to evaluate the potential for preventing peritoneal dissemination by inhibiting PLT activation in GC cells. The present study examined the roles of PLT activation pathways in the increased malignancy of GC cells facilitated by PLT-cancer cells. Transforming growth factor-β receptor kinase inhibitor (TRKI), Src family kinase inhibitor (PP2) and Syk inhibitor (R406) were used to identify the molecules influencing these interactions. Their therapeutic effects were verified via cell experiments and validated using a mouse GC peritoneal dissemination model. Notably, only the PLT activation pathway-related inhibitors TRKI and PP2, but not R406, inhibited the PLT-enhanced migration and invasion of GC cells. In vivo analyses revealed that PLT-enhanced peritoneal dissemination was suppressed by PP2. Overall, the present study revealed the important role of the Srk family in the interactions between PLTs and GC cells, suggesting kinase inhibitors as promising therapeutic agents to mitigate the progression of peritoneal metastasis in patients with GC., Competing Interests: The authors declare that they have no competing interests., (Copyright: © 2024 Nakayama et al.)

Background: An iron overload status induces ferroptosis, an iron-dependent nonapoptotic cell death, in various pathological conditions. We previously reported that hemin (heme), protoporphyrin-IX with ferric iron, activates platelets via C-type lectin-like receptor-2 (CLEC-2) and glycoprotein VI/FcRγ, but protoporphyrin-IX alone blocks CLEC-2-dependent platelet activation. Therefore, we hypothesized that free iron has the ability to activate platelets., Objectives: This study aimed to elucidate platelet activation mechanisms of iron (ferric chloride), including the identification of signaling pathways and receptors, and to examine whether platelets regulate ferroptosis., Methods: Platelet aggregometry, platelet activation marker expression, and protein phosphorylation were examined in ferric chloride-stimulated human and murine platelets. Inhibitors of platelet activation signaling pathways and receptor-deleted platelets were utilized to identify the responsible signaling pathway and receptor. The effect of platelets on ferroptosis of endothelial cells was investigated in vitro., Results: Ferric chloride induced platelet activation dependent on Src family kinase pathways in humans and mice. Ferric chloride-induced platelet aggregation was almost lost in CLEC-2-depleted murine platelets and wild-type platelets preincubated with recombinant CLEC-2 proteins. Furthermore, coculture of wild-type platelets, but not CLEC-2-deficient platelets, attenuated ferroptosis of endothelial cells in vitro., Conclusion: Ferric chloride activates platelets via CLEC-2 and Src family kinase pathways, and platelets have a protective role in the ferroptosis of endothelial cells dependent on CLEC-2., Competing Interests: Declaration of competing interests The authors declare no competing financial interests., (Copyright © 2024 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Purpose of Review: Platelets are essential for hemostasis and are also vital in lymphatic and lung development and the maintenance of vascular integrity. Platelet activation receptor C-type lectin-like receptor 2 (CLEC-2) and its endogenous ligand podoplanin (PDPN) in lymphatic endothelial cells (LECs) and other cells regulate these processes. This review aims to comprehensively summarize the roles of platelet CLEC-2 and PDPN. This review also focuses on discussing the underlying mechanisms by which platelet CLEC-2 and PDPN mediate blood/lymphatic separation., Findings: CLEC-2/PDPN-induced platelet activation in the primary lymph sacs, developmental lymphovenous junctions, neonatal mesentery, and the site of tumor lymphangiogenesis prevents blood/lymphatic vessel misconnection. Further, CLEC-2/PDPN-induced platelet activation is essential for lung development. Mice deficient in CLEC-2 or PDPN show blood-filled lymphatics, lung malformations, and cerebrovascular abnormalities. CLEC-2 deletion in steady-state adult mice did not result in blood/lymphatic vessel mixing. In adulthood, CLEC-2 maintains vascular integrity and that of high endothelial venules in lymph nodes. CLEC-2 deletion in adulthood results in hemorrhage under inflammatory conditions, and hemolymph nodes., Summary: The platelet CLEC-2/LEC PDPN interaction prevents blood/lymphatic vessel mixing at active remodeling sites of the blood/lymphatic system, but not in steady-state adult mice. This interaction also regulates vascular integrity when vascular permeability increases before and after birth., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Unlike for anticoagulants, no good monitoring methods exist for antiplatelet agents, and their monitoring is considered unnecessary. In the platelet aggregation test, which is the standard test for platelet function, aggregation is evaluated by adding a platelet activator to platelets in a cuvette. Therefore, it provides information on the maximum potential of platelets to induce aggregation, but not the actual in vivo degree of platelet activation. In vivo platelet activation markers are not widely used because they require a special blood collection method, although some tests are covered by insurance. My colleagues and I identified the platelet activation receptor C-type lectin-like receptor 2 (CLEC-2) and found that CLEC-2 is cleaved and released during platelet activation. We established a plasma-soluble CLEC-2 (sCLEC-2) assay system with the aim of using it as a marker of in vivo platelet activation. Elevation of sCLEC-2 has been reported in various thrombotic diseases. The multi-center prospective cohort study CLECSTRO is now underway to investigate the usefulness of sCLEC-2 for diagnosis, typing, and prognostic estimation in acute ischemic stroke.

Thrombocytopenia, anasarca, fever, renal dysfunction, and organomegaly (TAFRO) syndrome is an inflammatory disorder with an unclear pathogenesis. We herein report a case of TAFRO syndrome in remission in a patient who experienced recurrent intracranial bleeding despite a normal platelet count and coagulation system. A further investigation suggested the presence of anti-glycoprotein VI (GPVI) autoantibodies in the plasma, which induced platelet dysfunction and bleeding tendency. No new bleeding or relapse of TAFRO syndrome occurred after immunosuppressive therapy was initiated. These findings may help elucidate the autoimmune pathogenesis of TAFRO syndrome.

Predicting the clinical course and allocating limited medical resources appropriately is crucial during the COVID-19 pandemic. Platelets are involved in microthrombosis, a critical pathogenesis of COVID-19; however, the role of soluble CLEC-2 (sCLEC-2), a novel platelet activation marker, in predicting the prognosis of COVID-19 remains unexplored. We enrolled 108 patients with COVID-19, hospitalized between January 2021 and May 2022, to evaluate the clinical use of sCLEC-2 as a predictive marker. sCLEC-2 levels were measured in plasma sampled on admission, as well as interleukin-6, cell-free DNA, von Willebrand factor, and thrombomodulin. We retrospectively classified the patients into two groups - those who required oxygenation during hospitalization (oxygenated group) and those who did not (unoxygenated group) - and compared their clinical and laboratory characteristics. The correlation between sCLEC-2 and the other parameters was validated. The sCLEC-2 level was significantly higher in the oxygenated group (188.8 pg/mL vs. 296.1 pg/mL). Multivariate analysis identified high sCLEC-2 levels (odds ratio per 10 pg/mL:1.25) as an independent predictor of oxygen therapy requirement. sCLEC-2 was positively correlated with cell-free DNA, supporting the association between platelet activation and neutrophil extracellular traps. In conclusion, sCLEC-2 is a clinically valuable marker in predicting oxygen therapy requirements for patients with COVID-19.

Kappa-carrageenan (KCG), which is used to induce thrombosis in laboratory animals for antithrombotic drug screening, can trigger platelet aggregation. However, the cell-surface receptor and related signaling pathways remain unclear. In this study, we investigated the molecular basis of KCG-induced platelet activation using light-transmittance aggregometry, flow cytometry, western blotting, and surface plasmon resonance assays using platelets from platelet receptor-deficient mice and recombinant proteins. KCG-induced tail thrombosis was also evaluated in mice lacking the platelet receptor. We found that KCG induces platelet aggregation with α-granule secretion, activated integrin αIIbβ3, and phosphatidylserine exposure. As this aggregation was significantly inhibited by the Src family kinase inhibitor and spleen tyrosine kinase (Syk) inhibitor, a tyrosine kinase-dependent pathway is required. Platelets exposed to KCG exhibited intracellular tyrosine phosphorylation of Syk, linker activated T cells, and phospholipase C gamma 2. KCG-induced platelet aggregation was abolished in platelets from C-type lectin-like receptor-2 (CLEC-2)-deficient mice, but not in platelets pre-treated with glycoprotein VI-blocking antibody, JAQ1. Surface plasmon resonance assays showed a direct association between murine/human recombinant CLEC-2 and KCG. KCG-induced thrombosis and thrombocytopenia were significantly inhibited in CLEC-2-deficient mice. Our findings show that KCG induces platelet activation via CLEC-2.

Background: Cancer-associated thrombosis (CAT) is the leading cause of morbidity and mortality. Cancer-associated fibroblasts (CAFs) are a prominent component of the tumor microenvironment that contributes to cancer progression through direct cell-cell interactions and the release of extracellular vesicles (EVs). However, the role of CAFs in CAT remains unclear., Objective: This study aims to investigate whether CAFs aggravate CAT and the underlying molecular mechanism using a preclinical mouse lung cancer model., Methods: We designed a Lewis lung carcinoma (LLC) tumor-bearing mouse model. CAFs were characterized using fluorescence immunohistostaining. The presence of podoplanin, a platelet-activating membrane protein through C-type lectin-like receptor 2 (CLEC-2), in EVs isolated from primary CAFs or LLC tumor tissues was assessed by immunoblotting. The platelet activation and aggregation abilities of the EVs were quantified using flow cytometry. Podoplanin plasma levels were measured by enzyme-linked immunosorbent assay. Venous thrombosis was induced in the femoral vein using 2.5% ferric chloride. The anti-CLEC-2 monoclonal antibody 2A2B10 was used to deplete CLEC-2 on the surface of the platelets., Results: CAFs expressing CD90, PDGFRβ, HSP47, CD34, and vimentin, co-expressed podoplanin and induced platelet activation and aggregation in a CLEC-2-dependent manner. Tumor-bearing mice showed elevated podoplanin plasma levels. CAF-EV injection and tumor-bearing mice showed shorter occlusion time in the venous thrombosis model. Although tumor growth was not altered, antibody-induced CLEC-2 depletion suppressed venous thrombosis in the tumor-bearing state but not in the healthy condition., Conclusion: CAFs and CAF-derived EVs induce CLEC-2-dependent platelet aggregation and aggravate venous thrombosis., Competing Interests: Declaration of competing interests T. Shirai, N. T., T. Sasaki, S. Oishi, R. Y., K. T., and K. S-I. declare no conflicts of interest directly relevant to the content of this article. Results of this work were disclosed, in part, as oral presentations at the annual conference of the Japanese Society of Thrombosis and Hemostasis and as poster presentation at the International Society of Thrombosis and Hemostasis in 2022., (Copyright © 2023 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Platelets form complexes with gastric cancer (GC) cells via direct contact, enhancing their malignant behavior. In the present study, the molecules responsible for GC cell-platelet interactions were examined and their therapeutic application in inhibiting the peritoneal dissemination of GC was investigated. First, the inhibitory effects of various candidate surface molecules were investigated on platelets and GC cells, such as C-type lectin-like receptor 2 (CLEC-2), glycoprotein VI (GPVI) and integrin αIIbβ3, in the platelet-induced enhancement of GC cell malignant potential. Second, the therapeutic effects of molecules responsible for the development and progression of GC were investigated in a mouse model of peritoneal dissemination. Platelet-induced enhancement of the migratory ability of GC cells was markedly inhibited by an anti-GPVI antibody and inhibitor of galectin-3, a GPVI ligand. However, neither the CLEC-2 inhibitor nor the integrin-blocking peptide significantly suppressed this enhanced migratory ability. In experiments using mouse GC cells and platelets, the migratory and invasive abilities enhanced by platelets were significantly suppressed by the anti-GPVI antibody and galectin-3 inhibitor. Furthermore, in vivo analyses demonstrated that the platelet-induced enhancement of peritoneal dissemination was significantly suppressed by the coadministration of anti-GPVI antibody and galectin-3 inhibitor, and was nearly eliminated by the combined treatment. The inhibition of adhesion resulting from GPVI-galectin-3 interaction may be a promising therapeutic strategy for preventing peritoneal dissemination in patients with GC., Competing Interests: The authors declare that they have no competing interests., (Copyright: © Nakayama et al.)

Lymphatic vessels form a systemic network that maintains interstitial fluid homeostasis and regulates immune responses and is strictly separated from the circulatory system. During embryonic development, lymphatic endothelial cells originate from blood vascular endothelial cells in the cardinal veins and form lymph sacs. Platelets are critical for separating lymph sacs from the cardinal veins through interactions between CLEC-2 (C-type lectin-like receptor-2) and PDPN (podoplanin) in lymphatic endothelial cells. Therefore, deficiencies of these genes cause blood-filled lymphatic vessels, leading to abnormal lymphatic vessel maturation. The junction between the thoracic duct and the subclavian vein has valves and forms physiological thrombi dependent on CLEC-2/PDPN signaling to prevent blood backflow into the thoracic duct. In addition, platelets regulate lymphangiogenesis and maintain blood/lymphatic separation in pathological conditions, such as wound healing and inflammatory diseases. More recently, it was reported that the entire hemostatic system is involved in lymphangiogenesis. Thus, the hemostatic system plays a crucial role in the establishment, maintenance, and rearrangement of lymphatic networks and contributes to body fluid homeostasis, which suggests that the hemostatic system is a potential target for treating lymphatic disorders. This review comprehensively summarizes the role of the hemostatic system in lymphangiogenesis and lymphatic vessel function and discusses challenges and future perspectives., Competing Interests: Disclosures None.

Introduction: Soluble C-type lectin-like receptor 2 (sCLEC-2) is a new biomarker for platelet activation, which can be easily measured by usual blood collection. We conducted the CLECSTRO, a prospective, observational cohort study, to evaluate the clinical implications of sCLEC-2 in patients with acute ischaemic stroke (AIS) and transient ischaemic attack (TIA)., Methods and Analysis: The participants are patients with AIS/TIA and control patients required for differentiation from AIS/TIA. The target population is 600, including the patients and controls, who would be recruited from eight stroke centres across Japan. The inclusion criteria are AIS within 24 hours of onset and a modified Rankin Scale (mRS) score of 0-2, TIA within 7 days of onset, and contemporary patients required for differentiation from AIS/TIA. Plasma sCLEC-2 will be measured by high-sensitive chemiluminescent enzyme immunoassay using residual blood samples from routine laboratory examinations at the first visit in all patients and 7 days later or at discharge in patients with AIS/TIA. The outcomes include plasma levels of sCLEC-2 in patients with AIS/TIA and controls, sCLEC-2/D-dimer ratio in non-cardioembolic and cardioembolic AIS/TIA, correlation of sCLEC-2 with recurrence or worsening of stroke, severity of stroke, infarct size, ABCD 2 score in TIA and outcome (mRS) at 7 days and 3 months., Ethics and Dissemination: This study was approved by the Ethical Committee of the University of Yamanashi as the central ethical committee in agreement with the ethical committees of all collaborative stroke centres. Informed consent will be obtained by an opt-out form from the patients at each stroke centre according to the Ethical Guidelines for Medical and Biological Research Involving Human Subjects by the Japanese Ministry of Health, Labour and Welfare., Trial Registration Numbers: NCT05579405, UMIN000048954., Competing Interests: Competing interests: SU reports consultant fees from LSI Medience Corporation. KS-I has a patent related to the sCLEC-2 assay (JP-6078845). MK is an advisor of LSI Medience Corporation. HW and MK are inventors of a patent application related to sCLEC-2 measurement in AIS and TIA (JP application 2021-091606)., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

The scoring systems for disseminated intravascular coagulation (DIC) criteria require several adequate cutoff values, vary, and are complicated. Accordingly, a simpler and quicker diagnostic method for DIC is needed. Under such circumstances, soluble C-type lectin-like receptor 2 (sCLEC-2) received attention as a biomarker for platelet activation., Materials and Methods: The diagnostic usefulness of sCLEC-2 and several formulas, including sCLEC-2xD-dimer, sCLEC-2/platelet count (sCLEC-2/PLT), and sCLEC-2/PLT × D-dimer (sCLEC-2xD-dimer/PLT), were evaluated among 38 patients with DIC, 39 patients with pre-DIC and 222 patients without DIC or pre-DIC (non-DIC)., Results: Although the plasma level of sCLEC-2 alone was not a strong biomarker for the diagnosis of DIC or pre-DIC, the sCLEC-2xD-dimer/PLT values in patients with DIC were significantly higher than those in patients without DIC, and in a receiver operating characteristic (ROC) analysis for the diagnosis of DIC, sCLEC-2xD-dimer/PLT showed the highest AUC, sensitivity, and odds ratio. This formula is useful for the diagnosis of both pre-DIC and DIC. sCLEC-2xD-dimer/PLT values were significantly higher in non-survivors than in survivors., Conclusion: The sCLEC-2xD-dimer/PLT formula is simple, easy, and highly useful for the diagnosis of DIC and pre-DIC without the use of a scoring system.

Coronavirus disease 2019 (COVID-19) has spread, with thrombotic complications being increasingly frequently reported. Although thrombosis is frequently complicated in septic patients, there are some differences in the thrombosis noted with COVID-19 and that noted with bacterial infections. The incidence (6-26%) of thrombosis varied among reports in patients with COVID-19; the incidences of venous thromboembolism and acute arterial thrombosis were 4.8-21.0% and 0.7-3.7%, respectively. Although disseminated intravascular coagulation (DIC) is frequently associated with bacterial infections, a few cases of DIC have been reported in association with COVID-19. Fibrin-related markers, such as D-dimer levels, are extremely high in bacterial infections, whereas soluble C-type lectin-like receptor 2 (sCLEC-2) levels are high in COVID-19, suggesting that hypercoagulable and hyperfibrinolytic states are predominant in bacterial infections, whereas hypercoagulable and hypofibrinolytic states with platelet activation are predominant in COVID-19. Marked platelet activation, hypercoagulability and hypofibrinolytic states may cause thrombosis in patients with COVID-19.

Coagulation activation is associated with cancer progression and morbidity. Recently, mechanisms through which coagulation proteases drive the tumor microenvironment (TME) have been elucidated. This review aims to develop a new strategy dependent on the coagulation system for treating osteosarcoma (OS). We focused on tissue factor (TF), the main initiator of the extrinsic coagulant pathway, as a target for OS treatment. It was found that cell surface-TF, TF-positive extracellular vesicles, and TF-positive circulating tumor cells could drive progression, metastasis, and TME in carcinomas, including OS. Thus, targeting tumor-associated coagulation by focusing on TF, the principle catalyst of the extrinsic pathway, TF is a promising target for OS., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

C-type lectin-like receptor 2 (CLEC-2) is a platelet-activated receptor expressed on the surface of platelet membranes. Soluble CLEC-2 (sCLEC-2) has been receiving attention as a predictive marker for thrombotic predisposition. The present study examined the relationship between sCLEC-2 level and degree of coagulation disorder in septic patients. Seventy septic patients were divided into the sepsis-induced disseminated intravascular coagulation (DIC) (SID) group (n = 44) and non-SID group (n = 26). The sCLEC-2 levels were compared between the two groups. Because we suspected that the sCLEC-2 level was affected by the platelet count, we calculated the sCLEC-2/platelet count ratio (C2PAC index). We further divided septic patients into four groups using the Japanese Association for Acute Medicine (JAAM) DIC scoring system (DIC scores: 0-1, 2-3, 4-5, and 6-8). The C2PAC index was significantly higher in the SID group (2.6 ± 1.7) compared with the non-SID group (1.2 ± 0.5) ( P < .001). The C2PAC indexes in the four JAAM DIC score groups were 0.9 ± 0.3, 1.1 ± 0.3, 1.7 ± 0.7, and 3.6 ± 1.0, respectively, and this index increased significantly as the DIC score increased ( P < .001). According to the receiver-operating curve analysis, the area under the curve (AUC) and optimal cutoff value for the diagnosis of SID were 0.8051 and 1.4 (sensitivity, 75.0%; specificity, 76.9%), respectively. When the C2PAC index and D-dimer level, one of the main fibrinolytic markers, were selected as predictive markers for SID diagnosis in stepwise multiple logistic regression analysis, it was possible to diagnose SID with a high probability (AUC, 0.9528; sensitivity, 0.9545; specificity, 0.8846). The C2PAC index is a useful predictor of SID progression and diagnosis in septic patients.

The ISTH London 2022 Congress is the first held (mostly) face-to-face again since the COVID-19 pandemic took the world by surprise in 2020. For 2 years we met virtually, but this year's in-person format will allow the ever-so-important and quintessential creativity and networking to flow again. What a pleasure and joy to be able to see everyone! Importantly, all conference proceedings are also streamed (and available recorded) online for those unable to travel on this occasion. This ensures no one misses out. The 2022 scientific program highlights new developments in hemophilia and its treatment, acquired and other inherited bleeding disorders, thromboinflammation, platelets and coagulation, clot structure and composition, fibrinolysis, vascular biology, venous thromboembolism, women's health, arterial thrombosis, pediatrics, COVID-related thrombosis, vaccine-induced thrombocytopenia with thrombosis, and omics and diagnostics. These areas are elegantly reviewed in this Illustrated Review article. The Illustrated Review is a highlight of the ISTH Congress. The format lends itself very well to explaining the science, and the collection of beautiful graphical summaries of recent developments in the field are stunning and self-explanatory. This clever and effective way to communicate research is revolutionary and different from traditional formats. We hope you enjoy this article and will be inspired by its content to generate new research ideas., (© 2022 The Authors. Research and Practice in Thrombosis and Haemostasis published by Wiley Periodicals LLC on behalf of International Society on Thrombosis and Haemostasis (ISTH).)

Bone marrow development and endochondral bone formation occur simultaneously. During endochondral ossification, periosteal vasculatures and stromal progenitors invade the primary avascular cartilaginous anlage, which induces primitive marrow development. We previously determined that bone marrow podoplanin (PDPN)-expressing stromal cells exist in the perivascular microenvironment and promote megakaryopoiesis and erythropoiesis. In this study, we aimed to examine the involvement of PDPN-expressing stromal cells in postnatal bone marrow generation. Using histological analysis, we observed that periosteum-derived PDPN-expressing stromal cells infiltrated the cartilaginous anlage of the postnatal epiphysis and populated on the primitive vasculature of secondary ossification center. Furthermore, immunophenotyping and cellular characteristic analyses indicated that the PDPN-expressing stromal cells constituted a subpopulation of the skeletal stem cell lineage. In vitro xenovascular model cocultured with human umbilical vein endothelial cells and PDPN-expressing skeletal stem cell progenies showed that PDPN-expressing stromal cells maintained vascular integrity via the release of angiogenic factors and vascular basement membrane-related extracellular matrices. We show that in this process, Notch signal activation committed the PDPN-expressing stromal cells into a dominant state with basement membrane-related extracellular matrices, especially type IV collagens. Our findings suggest that the PDPN-expressing stromal cells regulate the integrity of the primitive vasculatures in the epiphyseal nascent marrow. To the best of our knowledge, this is the first study to comprehensively examine how PDPN-expressing stromal cells contribute to marrow development and homeostasis., Competing Interests: Conflict of interest The authors declare that they have no conflicts of interest with the contents of this article., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Although thrombosis in coronavirus disease 2019 (COVID-19) infection has attracted attention, the mechanism underlying its development remains unclear. The relationship between platelet activation and the severity of COVID-19 infection was compared with that involving other infections. Plasma soluble C-type lectin-like receptor 2 (sCLEC-2) levels were measured in 46 patients with COVID-19 infection and in 127 patients with other infections. The plasma sCLEC-2 levels in patients with COVID-19 infection {median (25th, 75th percentile), 489 (355, 668) ng/L} were significantly higher ( p < 0.001) in comparison to patients suffering from other pneumonia {276 (183, 459) ng/L}, and the plasma sCLEC-2 levels of COVID-19 patients with severe {641 (406, 781) ng/L} or critical illness {776 (627, 860) ng/L} were significantly higher ( p < 0.01, respectively) in comparison to those with mild illness {375 (278, 484) ng/L}. The ratio of the sCLEC-2 levels to platelets in COVID-19 patients with critical illness of infection was significantly higher ( p < 0.01, p < 0.001 and p < 0.05, respectively) in comparison to COVID-19 patients with mild, moderate or severe illness. Plasma sCLEC-2 levels were significantly higher in patients with COVID-19 infection than in those with other infections, suggesting that platelet activation is triggered and facilitated by COVID-19 infection.

Coronavirus disease 2019 is diagnosed based on the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in nasopharyngeal swabs or saliva samples using reverse-transcription quantitative polymerase chain reaction. Nasopharyngeal swabs should be collected by medical professionals who are covered with full personal protective equipment (PPE), while saliva samples can be collected by patients themselves without any PPE. However, collecting saliva is difficult for people who are unable to follow instructions, including infants or unconscious patients. Owing to the high viscosity of saliva, special attention is required to handle saliva samples in laboratories. To solve these problems, we compared lingual and buccal mucosal swabs (oral swabs) with nasopharyngeal swabs and saliva samples. Among 13 patients who had a positive result for SARS-CoV-2 RNA in their nasopharyngeal swabs, 8 and 10 patients had a positive result for SARS-CoV-2 RNA in their saliva (concordance rate, 61.5%) and oral swabs (76.9%), respectively. Among the eight patients with a positive result for SARS-CoV-2 RNA in saliva, seven (87.5%) had SARS-CoV-2 detected in their oral swabs. We could not obtain saliva samples from four patients, but we found perfect concordance of SARS-CoV-2 positivity between the nasopharyngeal and oral swabs. Therefore, oral swabs can be used for SARS-CoV-2 RNA detection.

Background: Acute cerebral infarction (ACI) includes cardiogenic ACI treated with anticoagulants and atherosclerotic ACI treated with antiplatelet agents. The differential diagnosis between cardiogenic and atherosclerotic ACI is still difficult., Materials and Methods: The plasma sCLEC-2 and D-dimer levels were measured using the STACIA system., Results: The plasma sCLEC-2 level was significantly high in patients with ACI, especially those in patients with atherosclerotic or lacunar ACI, and plasma D-dimer levels were significantly high in patients with cardioembolic ACI. The plasma levels of sCLEC-2 and the sCLEC-2/D-dimer ratios in patients with atherosclerotic or lacunar ACI were significantly higher than those in patients with cardioembolic ACI. The plasma D-dimer levels in patients with atherosclerotic or lacunar ACI were significantly lower than those in patients with cardioembolic ACI. The plasma levels of sCLEC-2 and the sCLEC-2/D-dimer ratios were significantly higher in patients with atherosclerotic or lacunar ACI or acute myocardial infarction in comparison to patients with cardioembolic ACI or those with deep vein thrombosis., Conclusion: Using both the plasma sCLEC-2 and D-dimer levels may be useful for the diagnosis of ACI, and differentiating between atherosclerotic and cardioembolic ACI.

Coagulation factors are produced from hepatocytes, whereas production of coagulation factor VIII (FVIII) from primary tissues and cell species is still controversial. Here, we tried to characterize primary FVIII-producing organ and cell species using genetically engineered mice, in which enhanced green fluorescent protein (EGFP) was expressed instead of the F8 gene. EGFP-positive FVIII-producing cells existed only in thin sinusoidal layer of the liver and characterized as CD31 high , CD146 high , and lymphatic vascular endothelial hyaluronan receptor 1 (Lyve1) + . EGFP-positive cells can be clearly distinguished from lymphatic endothelial cells in the expression profile of the podoplanin - and C-type lectin-like receptor-2 (CLEC-2) + . In embryogenesis, EGFP-positive cells began to emerge at E14.5 and subsequently increased according to liver maturation. Furthermore, plasma FVIII could be abolished by crossing F8 conditional deficient mice with Lyve1-Cre mice. In conclusion, in mice, FVIII is only produced from endothelial cells exhibiting CD31 high , CD146 high , Lyve1 + , CLEC-2 + , and podoplanin - in liver sinusoidal endothelial cells., (© 2021. The Author(s).)