Development of anti-idiotypic antibodies to HLA antigens during pregnancy.

Thirty one pregnant women whose sera were initially positive for anti HLA antibodies were retested for lymphocytotoxicity 7-9 months after delivery. In the second testing 10 women were found to have lost the cytotoxic antibodies. These sera were tested for presence of anti-idiotypic antibodies by complement dependent cytotoxicity (CDC). In all ten sera tested, CDC blocking antibody was detected by inhibition technique at different dilutions. These antibodies directed specifically against the HLA antigen of the spouse. This CDC blocking factor could be the anti-idiotypic antibody (Ab2) directed against the cytotoxic anti-HLA antibody (Ab1). In one woman who conceived a second time, repeat sample obtained at the 7th month of the second pregnancy showed reappearance of the specific anti-HLA antibody. This may suggest that the Ab1-Ab2 network is under dynamic regulation.