Multicentre Evaluation of IL Test™ Free PS: A Fully Automated Assay to Quantify Free Protein S

The natural anticoagulant protein S; hemostatic functions and deficiency

Protein S (PS) is a vital endogenous anticoagulant. It plays a crucial role in regulating coagulation by acting as a cofactor for the activated protein C (APC) and tissue factor pathway inhibitor (TFPI) pathways. Additionally, it possesses direct anticoagulant properties by impeding the intrinsic tenase and prothrombinase complexes. Protein S oversees the coagulation process in both the initiation and propagation stages through these roles. The significance of protein S in regulating blood clotting can be inferred from the significant correlation between deficits in protein S and an elevated susceptibility to venous thrombosis. This is likely because activated protein C and tissue factor pathway inhibitor exhibit low efficacy as anticoagulants when no cofactors exist. The precise biochemical mechanisms underlying the roles of protein S cofactors have yet to be fully elucidated. Nevertheless, recent scientific breakthroughs have significantly enhanced comprehension findings for these functions. The diagnosis of protein S deficiency, both from a technical and genetic standpoint, is still a subject of debate due to the complex structural characteristics of the condition. This paper will provide an in-depth review of the molecular structure of protein S and its hemostatic effects. Furthermore, we shall address the insufficiency of protein S and its methods of diagnosis and treatment.

Genotype and laboratory and clinical phenotypes of protein s deficiency

The diagnosis of thrombophilia caused by protein S deficiency remains difficult. From 2005 to 2010, we documented 135 patients with suspected hereditary protein S deficiency for whom mutational analysis of the PROS1 gene had been performed by direct double-stranded sequencing of the amplified 15 exons including splice sites. Multiplex ligation-dependent probe amplification was performed on 12 of 15 exons in cases with no mutation found but a large deletion in the PROS1 gene was suspected. Mutations were identified in 49 patients, 9 by familial screening. Altogether, 17 new and 11 previously described mutations of PROS1 were identified among the 49 patients. After the exclusion of acquired protein S deficiency due to pregnancy or hormonal contraceptives, there remained only 1 case with protein S activity levels less than 40% that could not be explained by sequence variations or deletions in the examined regions of the PROS1 gene. After the exclusion of conditions associated with acquired protein S deficiency, persistently low protein S activity levels are highly indicative of a genetic alteration in PROS1. We observed a clear correlation between the laboratory phenotype and the type of mutation.

Coagulation, inflammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex

Protein S (PS) has an established role as an important cofactor to activated protein C (APC) in the degradation of coagulation cofactors Va and VIIIa. This anticoagulant role is evident from the consequences of its deficiency, when there is an increased risk of venous thromboembolism. In human plasma, PS circulates approximately 40% as free PS (FPS) and 60% in complex with C4b-binding protein (C4BP). Formation of this complex results in loss of PS cofactor function, and C4BP can then modulate the anticoagulant activity of APC. It had long been predicted that the complex could act as a bridge between coagulation and inflammation due to the involvement of C4BP in regulating complement activation. This prediction was recently supported by the demonstration of binding of the PS-C4BP complex to apoptotic cells. This review aims to summarize recent findings on the structure and functions of PS, the basis and importance of its deficiency, its interaction with C4BP, and the possible physiologic and pathologic importance of the PS-C4BP interaction.