Measurement of factor Xa-antithrombin III in plasma: relationship to prothrombin activation in vivo
Additional Document Info
The M(r) of the complexes formed when factor Xa reacts with antithrombin III (ATIII) in plasma were estimated by gel filtration and SDS-polyacrylamide electrophoresis. The predominant species of factor Xa-ATIII detected after plasma and plasma to which factor Xa had been added were gel filtered on Sephadex G-200 and Sepharose 4B had apparent M(r) > 200,000, in which factor Xa-ATIII was associated with vitronectin. Addition of factor Xa-ATIII to ATIII-depleted plasma also resulted in the formation of factor Xa-ATIII-vitronectin complexes with M(r) > 200,000. Using polyclonal antibodies to human factor Xa-ATIII and ATIII as the capture and detector antibodies, respectively, a sensitive and specific enzyme-linked immunosorbent assay was developed to quantify factor Xa-ATIII in plasma. The relationship between factor Xa-ATIII production and prothrombinase activity in vivo was investigated by quantifying factor Xa-ATIII and prothrombin fragment 1 + 2 endogenous to the plasmas of blood donors and patients with Hodgkin's and non-Hodgkin's lymphoma. Whereas the concentrations of prothrombin fragment 1 + 2 in the 84 normal plasmas increased with age, those of factor Xa-ATIII (mean +/- SD of 34.7 +/- 13.8 pM) did not, and no correlation existed between the concentrations of the two parameters in normal plasmas. In contrast, a highly significant correlation between the concentrations of these two parameters was found in the plasmas of the cancer patients which coincidentally also had higher concentrations of both factor Xa-ATIII and prothrombin fragment 1 + 2 than the normal plasmas. Thus, ATIII may differentially influence prothrombinase formation and activity in normal individuals and cancer patients.