ELUTION AND PARTIAL CHARACTERIZATION OF IMMUNOGLOBULINS BOUND TO OVINE PLACENTA

Immunoglobulins were eluted from ovine placentae and characterized by immunoprecipitation, electrophoresis, western blotting and ELISA. IgG was shown to comprise the bulk of placental-bound immunoglobulins whil e smaller amounts of IgM and only trace amounts of IgA were demonstrat ed. Results suggest that ovine placental IgG eluted by surgical cannul ation of the uterine blood vessels in situ is similar to that eluted f rom postpartum placentae in vitro, implying that there may be some tra nsfer of antibodies across the maternal side of the placental barrier to the trophoblast. These antibodies are rich in IgG(1) and IgG(2), ha ve a relative molecular weight of 158 kDa, and bind to an 80 kDa pepti de prepared from pre-acidified ovine placental cotyledons. We propose that the binding of placental IgG to the 80 kDa antigen may prevent im munological rejection of the foetus by competitively excluding cytotox ic cells of maternal origin such as NK cells. Also, given that a simil ar antigen (80 kDa) has been reported in humans and equines, and shown to be saturated with IgG in term placentae, we propose that this anti gen may be conserved in several mammalian species for reproductive pur poses. Consequently, we suggest that the ovine placental IgG and the 8 0 kDa antigen may be suitable as models for the study of maternal-foet al interactions in mammalian pregnancies.