title: Low total protein S antigen but high protein S activity due to decreased C4b-binding protein in neonates.
abstract: Protein S, a vitamin K-dependent cofactor for activated protein C, exists in normal adult plasma in a free anticoagulantly active form and in an inactive form complexed to C4b-binding protein. Immunologic and functional levels of protein S and C4b-binding protein in plasma were determined for 20 newborn infants and compared with adult normal pooled plasma. Total protein S antigen levels averaged 23%, similar to other vitamin K-dependent plasma proteins. However, the protein S anticoagulant activity was 74% of that of adult normal plasma. This apparent discrepancy of activity to antigen was shown to be due to low or undetectable levels of C4b-binding protein, which results in the presence of most if not all of protein S in its free and active form. The relatively high level of anticoagulantly active protein S in infants may enhance the potential of the protein C pathway, thereby minimizing risks of venous thrombosis in this group.
authors.affiliation: Second Department of Internal Medicine, University of Vienna, Austria.
authors.forename: H P
authors.initials: HP
authors.lastname: Schwarz
authors.forename: W
authors.initials: W
authors.lastname: Muntean
authors.forename: H
authors.initials: H
authors.lastname: Watzke
authors.forename: B
authors.initials: B
authors.lastname: Richter
authors.forename: J H
authors.initials: JH
authors.lastname: Griffin
mesh_terms: D000941:Antigens / Q000032:analysis*; D002352:Carrier Proteins / Q000378:metabolism*; D003169:Complement Inactivator Proteins; D006023:Glycoproteins / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007122:Immunoelectrophoresis; D007158:Immunologic Techniques; D007231:Infant, Newborn / Q000276:immunology / Q000378:metabolism*; D017293:Protein S
chemical_list: D000941:Antigens; D002352:Carrier Proteins; D003169:Complement Inactivator Proteins; D006023:Glycoproteins; D017293:Protein S