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Description
The defined antibody specificity is restricted to protein S as tested at the level of sensitivity of immuno-precipitation techniques and ELISA techniques. A single precipitin line is obtained in immunoelectrophoresis, bidimensional electrophoresis and double radial immunodiffusion (Ouchterlony) against normal plasma, which shows a reaction of identity with the precipitated purified protein S. The antiserum also reacts with the protein S component in complexes with protein C or with C4b binding protein. No reaction is obtained with any other plasma protein
Immunogen
Protein S is a vitamin K dependent plasma glycoprotein (MW 69,000) which belongs to a group of coagulation inhibitors consisting itself of proteinases. It circulates in the blood in a free active form and in an inactive form bound to C4b binding protein. Protein S is also released by thrombin stimulation from platelet alpha-granules. Protein S acts a s a cofactor for activated protein C (pCa) enhancing the cleavage of factors Va and VIIIa, producing anticoagulation by decreasing the conversion of prothrombin to thrombin. It also stimulates the fibrinolytic system. Protein S looses much of its coagulant cofactor activity after cleavage by thrombin, a process which is inhibited by thrombomodulin in the presence of free calcium ions. Plasma concentration of protein S may be significantly reduced below normal adult levels (2.5 mg/ml) in patients with hereditary deficiency of protein S or suffering a combination of deep vein thrombosis, superficial thrombophlebitis and pulmonary embolism. Substances such as bacterial endotoxins, tumour necrosis factor and immune mediator interleukin 1 also reduce the protein S level in plasma. Oral contraceptives also depress pS activity. A reduction in plasma protein S during pregnancy usually returns to normal after parturition. Freund's complete adjuvant is used in the first step of the immunization procedure.