AN 80-KDA SYNCYTIOTROPHOBLAST ALLOANTIGEN BOUND TO MATERNAL ALLOANTIBODY IN TERM PLACENTA

PROBLEM: We have shown that most of the IgG present on term syncytiotr ophoblast, membrane, microvesicles is bound to an 80 kDa protein antig en (R80K). METHODS: Microvesicles were prepared from term human placen ta, and the IgG eluted at pH3. RESULTS: When IgG antibody was eluted a t pH3 and reacted with acid-treated vesicles of other placentae, the a lloantibody always bound to the preparation from which it was obtained , but only to about 10% of acid-treated preparations from other placen tae. A similar polymorphic protein found in association with IgG antib ody was found in term horse placentae. Cross-reactivity of the antibod ies between species was not found. Using binding of labelled antibody, complement dependent cytotoxicity and FAGS two-color analysis, the hu man polymorphic antigen was present on peripheral brood monocytes and B-lymphocytes. The R80k antigen on intact microvesicles was resistant to trypsin, but after acid elution of IgG, trypsin released a soluble 50 kDa fragment which reacted with the acid-eluted IgG antibody. CONCL USION: The presence of antibodies to R80K in all term placentae studie d, including first pregnancies, suggests that development of this allo antibody may be a normal requirement for successful pregnancy.