An antifibrinolytic effect associated with an anti-factor V antibody in a patient with severe thrombophilia.
OBJECTIVE
The case of a patient with thrombotic manifestations and severe activated protein C resistance due to an anti-factor V antibody has recently been described. Since activated protein C (APC) is also profibrinolytic we wanted to determine whether the presence of antibodies interfering with the anticoagulant activity of APC also inhibits its profibrinolytic effect.


METHODS
Plasma clots were formed in the presence of tissue plasminogen activator, thrombin, phospholipids, Ca++, and various concentrations of APC, and the rate of lysis was monitored over time by the reduction in turbidity. Generation of endogenous thrombin and activation of thrombin activatable fibrinolysis inhibitor (TAFI) were also determined during fibrinolysis by clotting and spectrophotometric assays, respectively.


RESULTS
Addition of APC to the patient's plasma failed to stimulate fibrinolysis even at a concentration 4 times higher than that needed to produce the maximal effect in control plasma. Removal of IgG from the patient's plasma fully restored the fibrinolytic response to APC. Accordingly, addition of the patient's IgG to control plasma caused a concentration-dependent inhibition of APC-dependent fibrinolysis. The patient's IgG did not, however, inhibit the profibrinolytic effect of heparin. Determination of thrombin and activated TAFI generation during clot lysis showed that APC inhibited the generation of these enzymes by less than 20% in plasma supplemented with the patient's IgG as opposed to >80% in a control sample.


CONCLUSIONS
Our data suggest that the anti-factor V antibody inhibits fibrinolysis by antagonizing the anticoagulant effect of APC thereby favoring thrombin generation and TAFI activation. Impaired fibrinolysis may represent an additional mechanism contributing to thrombosis in patients with severe APC resistance phenotype.
Colucci
Mario
M
Department of Biomedical Sciences, University of Bari, Italy. mario.colucci@dimo.uniba.it
Simioni
Paolo
P
Piro
Donatella
D
Prandoni
Paolo
P
Pagnan
Antonio
A
Semeraro
Nicola
N
D020016:Activated Protein C Resistance / Q000235:genetics*; D000925:Anticoagulants / Q000494:pharmacology; D001323:Autoantibodies / Q000276:immunology*; D025901:Carboxypeptidase B2 / Q000502:physiology; D004789:Enzyme Activation; D005165:Factor V / Q000276:immunology*; D005260:Female; D005342:Fibrinolysis / Q000276:immunology*; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D008875:Middle Aged; D011486:Protein C / Q000494:pharmacology; D011994:Recombinant Proteins / Q000494:pharmacology; D013917:Thrombin / Q000096:biosynthesis; D019851:Thrombophilia / Q000276:immunology*; D013924:Thrombophlebitis / Q000276:immunology; D010959:Tissue Plasminogen Activator / Q000494:pharmacology
D000925:Anticoagulants; D001323:Autoantibodies; D007074:Immunoglobulin G; D011486:Protein C; D011994:Recombinant Proteins; D005165:Factor V; D006493:Heparin; D025901:Carboxypeptidase B2; D013917:Thrombin; D010959:Tissue Plasminogen Activator