The PROS1 gene encodes Protein S, a vitamin K-dependent glycoprotein primarily synthesized in the liver, endothelial cells, and megakaryocytes. Functioning as a critical cofactor in the protein C anticoagulant pathway, Protein S enhances the ability of activated protein C (APC) to inactivate procoagulant factors Va and VIIIa, thereby regulating blood coagulation and preventing excessive clot formation. Additionally, Protein S exhibits direct anticoagulant activity by binding to factors Xa and Va independently of APC. Deficiencies in Protein S, caused by mutations in the PROS1 gene (e.g., point mutations, deletions), are linked to hereditary thrombophilia, increasing the risk of venous thromboembolism. Autoantibodies against Protein S are rare but associated with autoimmune disorders, such as systemic lupus erythematosus, exacerbating thrombotic tendencies. PROS1-targeted antibodies are essential tools in research and diagnostics, enabling quantification of Protein S levels via ELISA, Western blot, or immunohistochemistry to assess deficiencies or dysregulation. They also aid in studying Protein S interactions in coagulation pathways, cellular apoptosis, and inflammation. Commercially available PROS1 antibodies are validated for specificity across species, supporting both basic research and clinical investigations into thrombotic disorders and immune-mediated coagulopathies.