A, B, and H isoantigens in the human fetus

We studied the appearance of isoantigens A, B, and H during the fertilization age in human embryos and fetuses with the specific red cell adherence (SRCA) test. The first positive reaction was found in endothelial cells of a 4-wk-old embryo. In 6-wk-old embryos the isoantigens appeared on the luminal surface of the epithelium of the stomach and small intestine. In other organs the blood group isoantigens were detected at different stages of development; in 12-wk-old fetuses the distribution became identical with that of adults. In pancreatic exocrine glands from fetuses of all blood groups up to 5 mo old, H antigen alone was present. Brunner's glands of the duodenum reacted positively for both A and B blood group antigens of the fetus and also for H antigen, which supports the assumption that some secretory glands produce the precursor H substance throughout fetal and adult life.