To investigate the process of activation mechanism of blood coagulation by leukocytes, binding of radiolabelled Factor X and the activation of Factor X on the cell surface of leukocytes were studied by using cultured leukemia cell line, Molt-4 cells. Cells were cultured in RPMI 1640 medium with 10% inactivated fetal, calf serum at a concentration of 1x106cells/ml. After 6 hours' stimulation with 1 ug/ml of endotoxin(LPS: Escherichia coli 026:B6), cells were separated by centrifugation, washed three times with Tris containing NaCl buffer(pH 7.5, TBS), and then suspended in TBS containing 0.5% bovine serum albumin(TBS-BSA) to the concentration of 5x106 cells/ml. Factors X, VII and IX were purified from fresh-frozen human plasma by the method of Bajaj in a modified version. Factor VIII was purified from cryoprecipitate as starting material. Factor X labelled with 1-125 by the method of McFarlane showed a single band on autoradiography. Specific radioactivity was 0.3 mCi/mg. For the study on binding of Factor X, TBS-BSA solution containing 4 mM of CaClp, various amounts of radiolabelled Factor X with/without purified Factors VII, VIII and IX were added to the LPS-stimulated washed cell suspension and mixed well. N-butyl-phtalate was layered over the reaction mixture after incubation at room temperature for various minutes. Total amount of bound Factor X was calculated from the radioactivity of the cell pellet separated by centrifugation of the reaction mixture. The Xa activity generated in the supernatants was assayed using S2222.Results: Factor X bound specifically to the LPS-stimulated Molt-4 cells. Amount of bound Factor X and the dissociation constant was 1.0 ng/5x10bcells (5.2x103sites/cell) and 5x106M, respectively. More amounts of Factor X bound when Factors VIII and IX were present in the reaction mixture than their absence. Five times more Factor Xa was generated when Factors VII, VIII and IX were present in the reaction mixture as compared with presence of Factor VII, alone. These results suggest that blood coagulation cascade proceeds on the LPS-stimulated leukocyte surface.
343 Tissue factor expressed on monocytes induces inter-cellular gap formation of vascular endothelial cells via the extrinsic blood coagulation cascade
