The passage of antibodies from the maternal circulation into the embryo in rabbits

Abstract

Active immunity to Brucella abortus was induced in adult female rabbits. They were mated a week after the last injection of antigen and were killed and the yolk-sac contents of the embryos tested for agglutinins 8½ days after copulation. Specific agglutinins were found to be present in the yolk-sac contents in all cases. The titre varied significantly from embryo to embryo in the same litter, and was in some as high as that in the maternal serum at the time of killing. Passive immunity to Br. abortus was imparted to female rabbits 7 to 9 days pregnant by intravenous injection of immune serum of high titre. The rabbits were killed and the yolk-sac fluid of the embryos tested for agglutinins 10 to 17 hr. after injection. Specific agglutinins were present in most of the embryos from five of the six rabbits injected before 8 days post-coitum. All the embryos in the sixth rabbit were regressing. Specific agglutinins were not found in any of the embryos from two rabbits injected after 9 days post-coitum, by which time the yolk-sac fluid has ceased to increase in volume. Positive results were obtained both when rabbit and bovine immune sera were used. Active immunity to Br. abortus was induced in pregnant rabbits by injections beginning after the 15th day post-coitum. The serum of the newborn young, removed from their immune mothers before they had suckled, was tested and specific agglutinins were found to be present with a titre corresponding to that of the maternal serum. It was concluded that agglutinins, whether actively or passively acquired, pass freely from the maternal circulation into the yolk-sacs of 7- and 8-day rabbit embryos. This constitutes a delicate test of the passage of protein without alteration through the yolk-sac wall. The yolk-sac wall does not appear to be selective, since it is at least as permeable to foreign proteins as it is to those of maternal origin. Agglutinins pass from the maternal circulation into the embryo after the disappearance of the bilaminar wall of the yolk-sac also, either by way of the yolk-sac splanchnopleur or the allantochorionic placenta or both. The bearing of these results on current theories of placental permeability are discussed.