From the Guidelines
Tissue factor is a glycoprotein that triggers the extrinsic pathway of the coagulation cascade by initiating thrombin formation from the zymogen prothrombin. It is expressed in cells that are normally not exposed to flowing blood, such as subendothelial cells and cells surrounding the blood vessels, including fibroblasts and smooth muscle cells 1. The primary function of tissue factor is to serve as the initiator of the coagulation cascade, which is the body's mechanism for forming blood clots to prevent excessive bleeding when blood vessels are damaged.
Key Characteristics of Tissue Factor
- Normally not exposed to blood but becomes accessible when blood vessels are injured
- Binds with Factor VII, activating it and triggering a series of enzymatic reactions that ultimately lead to the formation of fibrin
- Abundant in cells surrounding blood vessels, providing a protective barrier that activates clotting when vessels are damaged
- Abnormal expression can contribute to pathological conditions like thrombosis, disseminated intravascular coagulation, and may play a role in cancer progression 1
Measurement of Tissue Factor
Recent studies have compared various assays for measuring extracellular vesicle tissue factor in plasma samples, highlighting the importance of sensitive and specific methods for detecting tissue factor activity and antigen 1. The study found that functional assays using a blocking anti-TF antibody or immunocapture were the most specific and sensitive, with lower variability compared to antigen assays or activity assays using high-speed centrifugation 1.
Clinical Implications
Understanding the role of tissue factor in coagulation and its measurement is crucial for managing conditions associated with abnormal coagulation, such as thrombosis and disseminated intravascular coagulation. The use of sensitive and specific assays for tissue factor, as identified in recent studies 1, can improve the diagnosis and treatment of these conditions, ultimately reducing morbidity and mortality.
From the Research
Definition and Function of Tissue Factor
- Tissue factor (TF) is a transmembrane glycoprotein that initiates the coagulation cascade through its interaction with factor VII 2, 3, 4, 5, 6.
- TF belongs to the cytokine receptor protein superfamily and contributes to the transduction of cellular signaling 2.
- It plays a key role in the initiation of blood coagulation, vascular sealing, and thrombotic pathology 3.
Role in Hemostasis and Thrombosis
- TF is the primary initiator of blood coagulation and plays an essential role in hemostasis 6.
- It provides additional hemostatic protection to vital organs, such as the brain, lung, and heart 6.
- Under pathological conditions, TF can trigger both arterial and venous thrombosis 6.
- TF expression on perivascular cells and epithelial cells forms a hemostatic barrier 6.
Nonhemostatic Roles
- TF has nonhemostatic roles, including cell signaling, inflammation, vasculogenesis, and tumor growth and metastasis 4.
- TF-dependent activation of the coagulation cascade generates coagulation proteases that induce signaling in various cells 6.
Expression and Measurement
- TF is expressed on different cellular types and circulating extracellular vesicles 2.
- The measurement of TF activity could have diagnostic and/or prognostic meaning in different clinical conditions 2.
- The activated factor VII-antithrombin (FVIIa-AT) complex is proposed as an indirect biomarker of the TF-FVIIa interaction and functionally active TF expression 2.