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     The image is immunohistochemistry of paraffin-embedded Human thyroid cancer tissue using P12283(F2 Antibody) at dilution 1/35. (Original magnification: ×200)    

  
  

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     The image is immunohistochemistry of paraffin-embedded Human prostate cancer tissue using P12283(F2 Antibody) at dilution 1/35. (Original magnification: ×200)    

  
  

The F2 antibody, also called anti-prothrombin antibody, is an autoantibody targeting prothrombin (coagulation factor II), a key protein in the blood clotting cascade. First identified in the 1950s, it gained clinical significance due to its association with antiphospholipid syndrome (APS), a thrombotic disorder characterized by recurrent thrombosis or pregnancy complications. Unlike classic antiphospholipid antibodies that recognize phospholipid-protein complexes, F2 antibodies directly bind prothrombin or its complexes with phosphatidylserine. These antibodies are detected via ELISA and contribute to APS pathogenesis by interfering with coagulation regulation. They may promote thrombus formation by increasing thrombin generation or inhibiting anticoagulant pathways.

F2 antibodies are present in 30-50% of APS patients, often coexisting with lupus anticoagulant or anti-cardiolipin antibodies. Their clinical utility remains debated due to heterogeneity in detection methods and variable correlation with specific symptoms. While IgG isotypes are more strongly linked to thrombosis, IgM variants show weaker clinical associations. Beyond APS, elevated F2 antibodies occur in systemic lupus erythematosus, infections, and drug-induced autoimmunity. Current research focuses on standardizing assays, clarifying pathogenic mechanisms, and exploring therapeutic targets. Despite being less routinely tested than other antiphospholipid antibodies, F2 antibodies provide diagnostic and prognostic value in specific APS subgroups, highlighting the complexity of autoimmune coagulopathies.