A quantitative assay for the measurement of immune responses directed against the human placenta.

A quantitative in vitro immune assay based on the classical chromium release assay has been developed to detect immune responses directed against alien antigens expressed by the developing foetus and present on the maternal-facing surface of the human placenta. A plasma membrane fraction from the surface of the placenta was prepared and the vesicles thus formed were radiolabelled with 51 Cr. The 51Cr-labelled vesicles, by various criteria, were found to be suitable for use as targets in a 'release assay'. Further, by means of experimentally immunised animals, the target membranes were shown to be capable of detecting both cellular and humoral anti-placental activity.