Effect of intravenous immunoglobulin on a spontaneous inhibitor to factor VIII

A 71-year-old woman with a spontaneous anti-factor VIII inhibitor fractured her right wrist and 2 months later her left femur. She received treatment with porcine factor VIII for the first fracture and developed a secondary anti-porcine antibody response (from 10 to 200 Bethesda units). Following the second fracture she received intravenous immunoglobulin (i.v. IgG) (0.4 g/kg day for 5 days) in an attempt to reduce antibody activity. Despite further treatment with porcine factor VIII, the antibody level declined instead of rising as expected and the anti-human antibody activity also declined. We were not able to demonstrate neutralizing activity to her antibody but did demonstrate a reduced helper: suppressor ratio and reduced B-cell numbers and function after treatment with i.v. IgG. These changes were transient and as B-cell function improved over the following 4 months, her anti-human activity returned toward its previous level. Anti-porcine activity remained at its previous low level. We speculate that one of the mechanisms of action of i.v. IgG may be a direct cellular effect influencing both T-suppressor and B-lymphocyte function.