Isolation of antibody to human placental alkaline phosphatase (PLAP) from extracts of human placentae

PROBLEM: Human placental alkaline phosphatase (PLAP) is a unique placental antigen bound to the syncytiotrophoblast, which may be able to elicit a spe cific immune response in pregnancy. METHOD OF STUDY: Antibody to PLAP was purified from placental extracts by: a) acid elution of membrane vesicles: b) purifying complexes of PLAP with h uman antibody on monoclonal antibodies to PLAP followed by denaturation of the enzyme; and c) by denaturation of PLAP in placental extracts and purifi cation of antibody to PLAP on PLAP columns. RESULTS AND CONCLUSIONS: Specific antibody to PLAP is present in placental extracts, and is mostly bound to placental membrane preparations. PLAP is t herefore immunogenic in pregnancy and could serve as a useful monitor of pr egnancy-specific immunological responses. Since a similar enzyme appears in some cancers, it is possible that the immunization against PLAP in pregnan cy will help to protect against the development of ovarian and endometrial cancer (the 'fetal antigen' hypothesis).