Immunoglobulin-secreting cells in close proximity to the mid-gestation mouse embryo

A reverse haemolytic plaque assay has been used to detect cells secreting IgM and IgG from areas in close proximity to mid-gestation mouse embryos. These cells were obtained from the fetal-placental unit and from the decidual mass of mice on the 9th or 10th day of syngeneic pregnancy. Cryohistology using affinity prepared goat antibodies specific for mouse Ig isotypes, coupled to horseradish peroxidase by a second antibody, showed that free Ig and cells containing Ig, are located closely but externally to the extra-embryonic membranes and also in areas close to the developing placenta in the decidua basalis. We suggest that some of the identified Ig-forming cells may be producing antibodies specific for antigens on the extra-embryonic membranes and may thus be acting as blocking (enhancing) antibodies.