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 while smaller amounts of IgM and only trace amounts of IgA were demonstrated. Results suggest that ovine placental IgG eluted by surgical cannulation of the uterine blood vessels in situ is similar to that eluted from postpartum placentae in vitro, implying that there may be some transfer of antibodies across the maternal side of the placental barrier to the trophoblast. These antibodies are rich in IgG1 and IgG2, have a relative molecular weight of 158 kDa, and bind to an 80 kDa peptide prepared from pre-acidified ovine placental cotyledons. We propose that the binding of placental IgG to the 80 kDa antigen may prevent immunological rejection of the foetus by competitively excluding cytotoxic cells of maternal origin such as NK cells. Also, given that a similar antigen (80 kDa) has been reported in humans and equines, and shown to be saturated with IgG in term placentae, we propose that this antigen may be conserved in several mammalian species for reproductive purpose. Consequently, we suggest that the ovine placental IgG and the 80 kDa antigen may be suitable as models for the study of maternal-foetal interactions in mammalian pregnancies.