In-vitro inhibition of antiplatelet autoantibodies by intravenous immunoglobulins and Rh immunoglobulins.

Autoimmune thrombocytopenia (AITP) is caused by autoantibodies to platelet glycoprotein antigens. Intravenous immunoglobulin (i.v.IgG) and Rh immunoglobulin infusions have found great significance in the treatment of AITP patients not responding to corticosteroids and other modes of therapy. In our study, it was observed that immunoglobulins (i.v.IgG & Rh), and their Fab fragments inhibited the binding of antiplatelet autoantibodies to normal platelets, from 15.8 to 90.7% and 25.6 to 90.08% respectively; whereas, their Fc portion did not show any inhibition. The presence of specific anti-idiotypic antibodies to antiplatelet autoantibodies was established by using monoclonal antibodies to Glycoprotein IIb/IIa and Glycoprotein Ib/IX, as the specific idiotype source. The i.v.IgG and Rh immunoglobulin products reacted with the monoclonal antibodies, only through their Fab and not through the Fc portions, thereby confirming its specific anti-idiotype activity.