The effect of intravenous immunoglobulin on placental transfer of a platelet-specific antibody: anti-P1A1

The isolated perfused lobule of human placenta was used as an in-vitro model to study the effect of intravenous immunoglobulin (IVGG) on the placental transfer of a human platelet-specific antibody (anti-P1A1). Normal human IgG was shown to transfer from the maternal to the fetal circulation of the placental model after a lag period of 2-3 h. IVGG also transferred across the placenta but only after a longer lag period (3-4 h) than normal human IgG at the same concentration, which suggests that IVGG may contain a factor that inhibits the transfer of its own component IgG. The sensitive Western immunoblotting technique was used to demonstrate progressive transfer of anti-P1A1 antibody to the fetal circulation after a 2-3 h lag period. When IVGG and anti-P1A1 antibody were added simultaneously to the maternal circulation, the transfer of platelet-specific antibody was strongly inhibited by IVGG. The inhibitory effect of IVGG on anti-P1A1 antibody transfer was consistent for three different batches of the same IVGG product (Sandoglobulin). These studies provide the first scientific data to support the use of IVGG to inhibit antiplatelet antibody transfer as part of the antenatal management of neonatal alloimmune thrombocytopenia.