Incidence of superficial venous thrombosis in primary care and risk of subsequent venous thromboembolic sequelae: a retrospective cohort study performed with routine healthcare data from the Netherlands

Identification of biological significance of different stages of varicose vein development based on mRNA sequencing

Normal veins could develop to varicose vein (VV) by some risk factors, and might further progress to shallow vein thrombosis (SVT). However, the molecular mechanism of key genes associated with the progression and regression of VV are still not thorough enough. In this study, the healthy control (HC), VV, and SVT vascular samples were collected for transcriptome sequencing. The differentially expressed genes (DEGs) were screened by "DESeq2", including DEGs1 (HC vs. VV), DEGs2 (HC vs. SVT) and DEGs3 (VV vs. SVT). And their functional enrichment analyses were conducted by "ClusterProfiler". The receiver operating characteristic (ROC) curve was used to obtain the key genes (KGs) of the pathogenesis of VV and SVT. The qRT-PCR assay was performed to validate the expressions of KGs. Immune cell infiltration analyses were conducted based on ssGSEA method. The competitive endogenous RNAs (ceRNAs) regulatory network was constructed. The target drugs of KGs were predicted using DrugBank database. The biofunctions of DACT3 were further investigated through a series of experiments in vitro. All of these DEGs were associated with inflammation and immunity related functions. Immune cell infiltration was significantly different between VV and SVT. Six key genes including PLP2, DACT3, LRRC25, PILRA, MSX1 and APOD that were associated with the progression and regression of VV were screened. The expression of LRRC25 and PILRA was significantly negatively associated with central memory T cell, and significantly positively associated with B cell. Besides, XIST was the critical regulator of multiple KGs. Cimetidine was potential drug for VV and SVT therapy. Overexpression of DACT3 significantly inhibited the proliferation and migration of vascular smooth muscle cells (VSMCs), and affected their cell cycle and phenotypic transition. This study identified six key genes associated with the progression and regression of VV. Among them, DACT3 was proved to hinder VV progression. These findings may help to deepen understanding its underlying mechanisms.

Treatment of Superficial Vein Thrombosis: Recent Advances, Unmet Needs and Future Directions

Once considered relatively benign, superficial vein thrombosis (SVT) of the lower limbs is linked to deep vein thrombosis (DVT) or pulmonary embolism (PE) in up to one fourth of cases. Treatment goals include alleviating local symptoms and preventing SVT from recurring or extending into DVT or PE. Fondaparinux 2.5 mg once daily for 45 days is the treatment of choice for most patients with SVT. Potential alternatives include intermediate-dose low-molecular-weight heparin or the direct oral factor Xa inhibitor rivaroxaban, however, these require further evidence. Despite these treatment options, significant gaps remain, including the role of systemic or topical anti-inflammatory agents alone or combined with anticoagulants, and the optimal duration of anticoagulation for patients at varying risk levels. Additionally, the efficacy and safety of factor Xa inhibitors other than rivaroxaban, management of upper extremity SVT, and optimal treatment for SVT near the sapheno-femoral or sapheno-popliteal junctions are not well understood. This narrative review aims to summarize current evidence on anticoagulant treatment for SVT, highlight key unmet needs in current approaches, and discuss how ongoing studies may address these gaps.

Predictive factors of clot propagation in patients with superficial venous thrombosis towards deep venous thrombosis and pulmonary embolism: a systematic review and meta-analysis

OBJECTIVE

A subset of patients with superficial venous thrombosis (SVT) experiences clot propagation towards deep venous thrombosis (DVT) and/or pulmonary embolism (PE). The aim of this systematic review is to identify all clinically relevant cross-sectional and prognostic factors for predicting thrombotic complications in patients with SVT.

DESIGN

Systematic review.

DATA SOURCES

PubMed/MEDLINE and Embase were systematically searched until 3 March 2023.

ELIGIBILITY CRITERIA

Original research studies with patients with SVT, DVT and/or PE as the outcome and presenting cross-sectional or prognostic predictive factors.

DATA EXTRACTION AND SYNTHESIS OF RESULTS

The CHecklist for critical Appraisal and data extraction for systematic Reviews of prediction Modelling (CHARMS) checklist for prognostic factor studies was used for systematic extraction of study characteristics. Per identified predictive factor, relevant estimates of univariable and multivariable predictor-outcome associations were extracted, such as ORs and HRs. Estimates of association for the most frequently reported predictors were summarised in forest plots, and meta-analyses with heterogeneity were presented. The Quality in Prognosis Studies (QUIPS) tool was used for risk of bias assessment and Grading of Recommendations, Assessment, Development and Evaluations (GRADE) for assessing the certainty of evidence.

RESULTS

Twenty-two studies were included (n=10 111 patients). The most reported predictive factors were high age, male sex, history of venous thromboembolism (VTE), absence of varicose veins and cancer. Pooled effect estimates were heterogenous and ranged from OR 3.12 (95% CI 1.75 to 5.59) for the cross-sectional predictor cancer to OR 0.92 (95% CI 0.56 to 1.53) for the prognostic predictor high age. The level of evidence was rated very low to low. Most studies were scored high or moderate risk of bias.

CONCLUSIONS

Although the pooled estimates of the predictors high age, male sex, history of VTE, cancer and absence of varicose veins showed predictive potential in isolation, variability in study designs, lack of multivariable adjustment and high risk of bias prevent firm conclusions. High-quality, multivariable studies are necessary to be able to identify individual SVT risk profiles.

PROSPERO REGISTRATION NUMBER

CRD42021262819.

A systematic review and meta-analysis for the association between duration of anticoagulation therapy and the risk of venous thromboembolism in patients with lower limb superficial venous thrombosis

OBJECTIVE

The aim of this study was to determine the association between the duration of systemic anticoagulation therapy (ACT) and the risk of further venous thromboembolism (VTE) in patients with superficial venous thrombosis (SVT).

METHODS

A systematic review and meta-analysis were performed using searches of Medline and Cochrane Library databases in September 2023. Papers that provided VTE incidence within mid-term follow-up of ≥45 days in patients who received any ACT were included. Patients were categorized into subgroups according to the course of treatment: (1) no ACT (0 days); (2) ACT of ≤14 days; (3) ACT of 15 to 30 days; (4) ACT of 31 to 45 days; and (5) ACT of >45 days. Reported events were transformed to events per 100 patient-years, and a random-effects model was used to calculate pooled rates for proportions. The primary outcome (VTE) was a combination of SVT progression or recurrence with the occurrence of deep vein thrombosis (DVT) and pulmonary embolism (PE). Secondary outcomes included major and clinically relevant non-major or minor bleeding.

RESULTS

Twenty-four studies (10 randomized controlled trials and 14 cohort studies) combining outcomes in 12,341 patients were included in the quantitative synthesis. Minimum VTE and SVT recurrence or progression rates were observed with the ACT duration of 31 to 45 days of 16.2 (95% confidence interval [CI], 10.4-23.3) and 8.2 (95% CI, 3.1-15.8) events per 100 patient-years, respectively. Minimum DVT and PE rates observed with the treatment duration of 15 to 30 days were 5.5 (95% CI, 2.8-9.1) and 0.9 (95% CI, 0.5-1.3) events per 100 patient-years, respectively. Short-term treatment of ≤14 days was associated with the highest rates of VTE of 59.7 (95% CI, 37.7-86.4), DVT of 13.7 (95% CI, 9.6-18.4), and PE of 3.1 (95% CI, 1.4-5.6) events per 100 patient-years. Major bleeding rates were unrelated to the duration of ACT and did not exceed 0.5 events per 100 patient-years. The highest rate of clinically relevant non-major or minor bleeding was observed with ACT duration of 31 to 45 days of 14.2 (95% CI, 5.5-26.8) events per 100 patient-years. The most common risk factors for VTE included male sex, cancer, personal history of DVT, PE, or SVT, and thrombosis of non-varicose veins.

CONCLUSIONS

Prolonged systemic anticoagulation is associated with the tendency to decrease VTE rates in patients with lower limb SVT.

Superficial Venous Thrombosis: A Comprehensive Review

Superficial venous thrombosis (SVT), an inflammatory-thrombotic process of a superficial vein, is a relatively common event that may have several different underlying causes. This phenomenon has been generally considered benign, and its prevalence has been historically underestimated; the estimated incidence ranges from about 0.3 to 1.5 event per 1000 person-years, while the prevalence is approximately 3 to 11%, with different reports depending on the population studied. However, such pathology is not free of complications; indeed, it could extend to the deep circulation and embolize to pulmonary circulation. For this reason, an ultrasound examination is recommended to evaluate the extension of SVT and to exclude the involvement of deep circulation. Also, SVT may be costly, especially in the case of recurrence. Therefore, accurate management is necessary to prevent sequelae and costs related to the disease. This review aims to analyse the epidemiology of SVT, its complications, optimal medical treatment, and open questions with future perspectives.

Management and outcomes of superficial vein thrombosis: a single-center retrospective study

Background

Guidelines suggest but cannot recommend the optimal management of superficial vein thrombosis (SVT).

Objectives

To identify the prevalence of asymptomatic deep vein thrombosis (DVT) at the time of SVT diagnosis, and to report the treatment and 3-month complications of patients with only SVT more than 3 cm from deep vein junction (or unknown distance).

Methods

We performed a single-center retrospective review of patients referred to the Ottawa Hospital thrombosis unit with ultrasound (US)-diagnosed SVT, and followed patients with only SVT for 3 months.

Results

Three hundred sixteen patients with SVT were included. Of the 218 patients without DVT symptoms at presentation, 19 (8.7%; 95% CI, 5.7%-13.2%) were found to have asymptomatic concomitant DVT (11 proximal and 8 distal), and 45 (20.6%) had SVT within 3 cm of the saphenofemoral or saphenopopliteal junctions. Among the 192 patients diagnosed with SVT only, we observed 3-month thrombotic complications in 56 (29.2%; 95% CI, 23.2%-36.0%) patients, with a total of 69 events: 11 (5.7%) DVTs, 2 (1.0%) pulmonary embolisms, 37 (19.2%) SVT extensions, and 19 (9.8%) SVT recurrences. Eighty-two percent (9/11) of the 3-month DVT and pulmonary embolism events occurred in patients who initially received conservative management. Therapeutic treatment doses were most effective.

Conclusion

At the time of SVT diagnosis, many patients had asymptomatic DVT and SVT near the deep venous system, supporting the systematic use of initial US in patients clinically diagnosed with SVT. The observed differences in 3-month complication rates, according to the treatment provided, highlight the need for large-scale randomized controlled trials to establish optimal management.

The Diagnostic Utility of Natural Killer Cell Subsets in Deep Vein Thrombosis

Background

Natural killer (NK) cells are important components of adaptive and innate immune responses. NK cell subsets have different functions and may play a role in vascular disorders. This study aimed to evaluate the proportions of NK cells and their subsets to determine whether they can be used as markers of venous thrombosis and to identify whether there was a link between NK cell proportion and citrullinated histone (H3) levels.

Patients and Methods

This study included 100 participants divided into Group I (n=50, patients with deep venous thrombosis (DVT)) and Group II (n=50, age- and sex-matched healthy controls). Group I was further categorized into Group Ia (n=25, patients with acute DVT) and Group Ib (n=25, patients with chronic DVT). The proportions of NK cells and their subsets were evaluated by flow cytometry using CD3/CD16/CD56. The levels of citrullinated histones (H3) were estimated using enzyme-linked immunosorbent assay (ELISA).

Results

Compared to the control group, DVT patients had a significantly lower proportion of (CD56 dim/CD16+) NK cells, a significantly higher proportion of (CD56-/CD16+) NK cells and a high level of citrullinated histone (H3).

Conclusion

NK cell subsets and citrullinated histone (H3) could be used as markers for DVT and as targets for therapeutic drugs to inhibit the formation or progression of thrombosis.

Common Practice in the Treatment of Superficial Vein Thrombosis Involving the Sapheno-Femoral Junction: Results from a National Survey of the Italian Society of Angiology and Vascular Medicine (SIAPAV)

Background and Objectives: Prophylactic doses of low-molecular-weight heparins or fondaparinux showed their efficacy and safety for treatment of all superficial vein thrombosis (SVT) of the lower limbs, yet not for those extended to the last 3 cm of the great saphenous vein, close to the sapheno-femoral junction, or considered as a deep-vein thrombosis. Some experts suggest that these patients should be managed with full anticoagulant doses but evidence to support this recommendation is lacking, suggesting the need for a properly designed trial. Materials and Methods: Before starting a new trial, the Italian Society of Angiology and Vascular Medicine (SIAPAV) decided to verify the common therapeutic approaches for patients with an SVT in Italian vascular centers based on a hypothetical significant variation in each daily clinical practice. A standardized questionnaire of 10 questions was administered to all SIAPAV affiliates by means of the official Society website. Results: From 1 December 2022 to 20 January 2023 a total of 191 members (31.8%) answered the questionnaire, showing a detailed and a substantial heterogeneity in the therapeutic approach to SVT patients among experienced vascular physicians and angiologists. Detailed results are reported in the relative section. Conclusions: The therapeutic approach of SVT extended to the iuxta-femoral segment of the great saphenous vein is still a matter of debate, and data to support therapeutic strategies are lacking. The wide heterogeneity in the management of SVT patients, including those with more extended thrombosis, confirmed that a randomized controlled clinical trial investigating the efficacy and the safety of a tailored therapeutic regimen in this particular subgroup of patients is strongly warranted.

Does eradication of superficial vein incompetence after superficial vein thrombosis reduce the risk of recurrence and of deep vein thrombosis? A pilot study evaluating clinical practice in Örebro county, Sweden

Background

Elective eradication of superficial vein incompetence (SVI) is advocated after superficial vein thrombosis (SVT) to prevent venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism (PE), and to prevent recurrent SVT. However, this practice currently lacks evidence and not all SVT patients are referred.

Method

Pilot study based on retrospective review of medical records for patients in Örebro county, Sweden; diagnosed with SVT during 2019. Patients in primary care without venous intervention were compared with patients from a vascular service treated with eradication for SVI, regarding prevalence of VTE and recurrent SVT during one-year follow-up.

Results

Out of 236 records reviewed, 97(41%) were included, 44 in the vascular care, and 53 in primary care. Erroneous diagnosis and coding were common causes for exclusion. The groups differed in ultrasound verified SVT 25(47.2%) and 35(79.5%) ( p = .001), LMWH treatment 13(24.5%) and 24(54.5%) ( p = .002), and history of prior SVT 19(35.8%) and 31(70.5%) ( p = .001). There was no difference in the incidence of VTE during follow-up, 1(1.9%) and 1(2.3%) ( p = 1.000), or recurrent SVT, 7(13.2%) and 6(13.6%), respectively ( p = .951).

Conclusions

This pilot study cannot confirm if elective eradication of SVI after SVT reduces the risk of VTE and recurrent SVT, however, the incidence of VTE was low in both groups. Limitations of the study are the small sample size and the lack of duplex ultrasound in all cases in both groups at diagnosis and at follow-up. Further prospective studies on homogenous populations are needed.

Oberflächliche Venenthrombose der Beinvenen – Eine systematische Übersicht – Teil 1: Definition, Ätiologie, Diagnostik

Einleitung Die oberflächliche Venenthrombose (OVT) der Beinvenen ist mit einer Inzidenz von 0,5–1/1000 Einwohner/Jahr ein häufiges und mit einer Frequenz assoziierter thromboembolischer Ereignisse in bis zu 25 % der Fälle ein ernst zu nehmendes Krankheitsbild. In der vorliegenden Übersichtsarbeit sollen alle relevanten Aspekte der OVT basierend auf der aktuellen wissenschaftlichen Literatur behandelt werden.

Methoden Die systematische Übersicht umfasst das Wissen über die OVT basierend auf dem gesamten, systemisch recherchierten Erkenntnismaterial in den Datenbanken PubMed und Google Scholar. Eine Literaturrecherche in PubMed von Publikationen (1968–2018) mit den Suchbegriffen „Superficial vein thrombosis; thrombophlebitis“ ergab 102 aussagekräftige Arbeiten, die nach Vorlage der Originalarbeit ausgewertet wurden. Teil 1 der Arbeit behandelt Aspekte zur Definition, Klassifikation, Ätiologie und Diagnostik.

Ergebnisse Die OVT manifestiert sich klinisch neben den typischen Entzündungszeichen als strangförmige Induration, die Ausdruck eines thrombotischen Verschlusses epifaszialer Venen ist. Ätiologisch bedeutsam ist das Vorhandensein von Varikose (68 % der Fälle), Adipositas (23 %), Gerinnungsstörungen (18 %) und Tumorleiden (8 %). Das Durchschnittsalter der Betroffenen beträgt 62 Jahre, in 60 % der Fälle sind Frauen betroffen. Zunehmendes Lebensalter ist ein relevanter Risikofaktor. Diagnostisch ist es wichtig, das genaue Ausmaß der OVT zu beschreiben, insbesondere die Thrombuslänge und die Entfernung zum tiefen Venensystem. Dies, einschließlich der Beurteilung des tiefen Beinvenensystems, sollte bei jedem Patienten mit möglicher OVT zeitnah mittels Ultraschalldiagnostik erfolgen. Eine hier vorgeschlagene Klassifikation von 4 Ausprägungsgraden der OVT kann die Zuordnung zur aktuell empfohlenen Therapie erleichtern.

Schlussfolgerung Aufgrund der Häufigkeit und des Risikos potenziell lebensbedrohender Komplikationen sollte der OVT der Beinvenen eine größere Beachtung zukommen, insbesondere mit Blick auf eine spezialisierte Diagnostik durch Phlebologen.

Analysis of vascular involvement in 460 patients with Behçet's syndrome: Clinical characteristics and associated factors

OBJECTIVES

To describe demographic and clinical characteristics of vascular involvement in patients with Behçet's syndrome (BS) and to evaluate associations with such involvement.

METHODS

We retrospectively evaluated records of 2118 BS patients. In total, 460 patients diagnosed with superficial thrombophlebitis (ST) and/or major vascular events (venous and/or arterial involvements) were included in current analysis. Isolated ST with no accompanying deep venous thrombosis might be accepted as part of skin involvement; therefore, we defined two different outcomes for vascular involvement ("any vascular event" and "major vascular events") and performed univariable and multivariable logistic regression to assess factors associated with these outcome variables.

RESULTS

Overall, 68 (14.8%) patients had isolated ST, and 392 (85.2%) had major vascular events. The mean age of vascular BS was 33.8 (SD: 10.5) years and median follow-up was 13.9 (Q1-Q3: 8.3-22.9) years. The primary sites of major vascular events were deep venous thrombosis (n=358, 77.8%), pulmonary arterial involvement (n=66, 14.3%), extrapulmonary arterial involvement (n=52, 11.3%), and intracardiac thrombosis (n=14, 3.0%), respectively. Male sex was significantly associated with a higher risk for both outcome variables. When it was added to analysis, ST itself was the strongest explanatory variable that was associated with major vascular events in all multivariable models (ORs=11.9, 12.0, 13.0, and 18.9). While HLA-B51 was significantly associated with any vascular event, there was no similar observation for major vascular events.

CONCLUSION

Male sex is a well-known risk factor for major vascular events in BS, but our study established that presence of ST was the strongest risk factor.

Management of superficial venous thrombosis based on individual risk profiles: protocol for the development and validation of three prognostic prediction models in large primary care cohorts

BACKGROUND

Superficial venous thrombosis (SVT) is considered a benign thrombotic condition in most patients. However, it also can cause serious complications, such as clot progression to deep venous thrombosis (DVT) and pulmonary embolism (PE). Although most SVT patients are encountered in primary healthcare, studies on SVT nearly all were focused on patients seen in the hospital setting. This paper describes the protocol of the development and external validation of three prognostic prediction models for relevant clinical outcomes in SVT patients seen in primary care: (i) prolonged (painful) symptoms within 14 days since SVT diagnosis, (ii) for clot progression to DVT or PE within 45 days and (iii) for clot recurrence within 12 months.

METHODS

Data will be used from four primary care routine healthcare registries from both the Netherlands and the UK; one UK registry will be used for the development of the prediction models and the remaining three will be used as external validation cohorts. The study population will consist of patients ≥18 years with a diagnosis of SVT. Selection of SVT cases will be based on a combination of ICPC/READ/Snowmed coding and free text clinical symptoms. Predictors considered are sex, age, body mass index, clinical SVT characteristics, and co-morbidities including (history of any) cardiovascular disease, diabetes, autoimmune disease, malignancy, thrombophilia, pregnancy or puerperium and presence of varicose veins. The prediction models will be developed using multivariable logistic regression analysis techniques for models i and ii, and for model iii, a Cox proportional hazards model will be used. They will be validated by internal-external cross-validation as well as external validation.

DISCUSSION

There are currently no prediction models available for predicting the risk of serious complications for SVT patients presenting in primary care settings. We aim to develop and validate new prediction models that should help identify patients at highest risk for complications and to support clinical decision making for this understudied thrombo-embolic disorder. Challenges that we anticipate to encounter are mostly related to performing research in large, routine healthcare databases, such as patient selection, endpoint classification, data harmonisation, missing data and avoiding (predictor) measurement heterogeneity.

Management and Outcomes of Patients with Isolated Superficial Vein Thrombosis under Real Life Conditions (INSIGHTS-SVT)

OBJECTIVE

Management and outcomes of superficial vein thrombosis (SVT) are highly variable and not well described. Therefore, the INvestigating SIGnificant Health TrendS in the management of SVT (INSIGHTS-SVT) study collected prospective data under real life conditions.

METHODS

Prospective observational study of objectively confirmed acute isolated SVT. The primary outcome was a composite of symptomatic deep vein thrombosis (DVT), pulmonary embolism (PE), and extension or recurrence of SVT at three months. The primary safety outcome was clinically relevant bleeding.

RESULTS

A total of 1 150 patients were included (mean age 60.2 ± 14.7 years; 64.9% women; mean BMI 29.4 ± 6.3 kg/m²). SVT was below the knee in 54.5%, above the knee in 26.7%, above and below the knee in 18.8%. At baseline, 93.6% received pharmacological treatment (65.7% fondaparinux, 23.2% heparins, 4.3% direct oral anticoagulants [DOACs], 14.5% analgesics), 77.0% compression treatment, and 1.9% surgery; 6.4% did not receive any anticoagulation. The primary outcome occurred in 5.8%; 4.7% had recurrent or extended SVT, 1.7% DVT, and 0.8% PE. Clinically relevant non-major bleeding occurred in 1.2% and major bleeding in 0.3%. Complete clinical recovery of SVT was reported in 708 patients (62.4%). Primary outcome adjusted by propensity score and for treatment duration was lower with fondaparinux compared with low molecular weight heparin (4.4% vs. 9.6%; hazard ratio [HR] 0.51; 95% confidence interval [CI] 0.3 - 0.9; p = .017). On multivariable analysis, associated factors for primary outcome included another SVT prior to the present SVT event (HR 2.3), age per year (HR 0.97), duration of drug treatment per week (HR 0.92), and thrombus length (HR 1.03).

CONCLUSION

At three month follow up, patients with isolated SVT are at risk of thromboembolic complications (mainly recurrent or extended SVT), despite anticoagulation. In this real life study, about one third had received either heparins, oral anticoagulants, or no anticoagulation.

Management of Superficial Vein Thrombosis in Patients with Varicose Veins: A Survey among Members of National Surgical Society from Republic of Moldova

Purpose

Management of superficial vein thrombosis (SVT) in patients with varicose veins (VV) is not currently standardized. We performed a survey aimed to demonstrate patterns in the management of SVT in the Republic of Moldova.

Materials and Methods

This was a descriptive study whereby members of the National Surgical Society were asked to complete an online questionnaire. In the questionnaire, multiple-choice questions were supplemented with four clinical vignettes of real patients with SVT.

Results

The questionnaire was completed by 102 participants (31.1% response rate). In the treatment of SVT, duplex ultrasound was routinely used by 74.5% of respondents, and anticoagulants were used by 70.5%. The full therapeutic dose of anticoagulants was recommended by 63.3% of surgeons, intermediate dose by 21.1%, and prophylactic dose by 15.6%. Only 50% of respondents were prescribed anticoagulants for 1 month or more. In case of surgical intervention for SVT, crossectomy and stripping were performed by 84.0% of surgeons, while isolated crossectomy by 10.7%. In all clinical vignettes, the majority of respondents opted for urgent surgical treatment. The rate of proponents of surgery varied from 43% in cases of isolated thrombosis of tributaries, and up to 72.5% in cases of thrombosis up to the sapheno-femoral junction.

Conclusion

Management of patients with SVT and VV in the Republic of Moldova is far from standardized. Prescribed doses of anticoagulants, as well as the duration of anticoagulation are highly variable and often contradict the recommendations of current guidelines. Urgent crossectomy and stripping dominate the pattern of current therapeutic approaches.

Natural killer cells induce neutrophil extracellular trap formation in venous thrombosis

Essentials Neutrophil extracellular traps (NETs) are generated during deep vein thrombosis (DVT). The role of interferon γ (IFNγ) and natural killer (NK) cells in NET formation was studied. IFNγ promote venous thrombosis through NET formation. NK cell depletion reduces DVT. SUMMARY: Background Neutrophils contribute to venous thrombosis through the release of neutrophil extracellular traps (NETs), but the mechanism triggering their formation remains unclear. In vitro data show that interferon (IFN)-γ induces the formation of NETs. Objectives To determine whether IFN-γ and the transcription factor T-box expressed on T cells (Tbet) promote venous thrombosis through neutrophil activation. Methods Venous thrombosis was induced by flow restriction in the inferior vena cava in IFN-γ-/- , Tbet-/- or wild-type (WT) mice. After 48 h, thrombus size was measured by the use of high-frequency ultrasound. NET formation was determined by immunofluorescence. Results and Conclusions Thrombus formation was reduced in Tbet-/- and IFN-γ-/- mice, suggesting that Tbet/IFN-γ-expressing cells are required for venous thrombosis. The number of NETs formed during thrombosis was significantly lower in Tbet-/- and IFN-γ-/- mice. NET formation was also decreased in WT mice treated with an IFN-γ-blocking antibody. Injection of recombinant IFN-γ into IFN-γ-/- mice rescued the phenotype. Natural killer (NK) cells were specifically depleted prior to venous thrombosis induction. NK cell depletion results in decreased NET formation and smaller thrombi, suggesting that NK cells are required for thrombus development. In depleted mice, adoptive transfer of WT NK cells induced a similar thrombosis burden as in WT mice. In contrast, adoptive transfer of IFN-γ -/- NK cells resulted in thrombi similar in size to those in depleted mice. In vitro, we showed that WT neutrophils released fewer NETs when they were cocultured with IFN-γ-/- NK cells. This study demonstrates that NK cell-dependent IFN-γ production is crucial for thrombus development by promoting the formation of NETs by neutrophils.