MODULATION OF AN ACQUIRED COAGULATION-FACTOR-V INHIBITOR WITH INTRAVENOUS IMMUNE GLOBULIN

Purpose: We report that treatment of an immune mediated postoperative Factor V (FV) deficiency with intravenous immune globulin (IVIg) resul ted in serological and clinical disappearance of the inhibitor. Patien ts and Methods: A 9-year-old girl was exposed to bovine thrombin durin g cardiovascular surgery and subsequently developed severe, refractory hemorrhage caused by acquired FV deficiency (FV activity <5%). Despit e blood product transfusions, hemorrhage continued, and the patient wa s given IVIg, 400 mg/kg daily, for 9 days. Results: Prolonged clotting times immediately trended toward normal, and the hemorrhage ceased by the fifth IVIg treatment day, concomitant with increasing plasma FV a ctivity and disappearance of human FV inhibitor activity. The patient' s plasma initially had a much higher inhibitor titer against bovine FV (122-215 Bethesda units) than against human FV (3-4 Bethesda units). Circulating antibodies (IgM and IgG) to bovine and human thrombin and FV were detected by enzyme-linked immunosorbent assay (ELISA). After c ompletion of IVIg treatment, IgG antibodies to bovine FV and thrombin persisted, as did high-titer inhibition of bovine FV, whereas the subp opulation of IgG and IgM antibodies reactive with human FV were undete ctable. Conclusions: The inhibitor likely developed from a heterogenet ic immune response to bovine FV contaminating the topical thrombin pre paration used during surgery. To our knowledge, this is the first demo nstration of immunological clearance of an acquired FV antibody associ ated with the use of IVIg. The data suggest an antiidiotypic mechanism of IVIg in modulating clearance of antihuman FV antibodies.