Isohemagglutinin Activity in the First Day of Life

IT HAS BEEN well established that blood group antigens, substances A and B, are genetically determined and develop during intrauterine life.^1,2 In contrast, the blood group antibodies, the so-called "natural" isohemagglutinins, are believed by most authors to appear first, three to six months after birth.^3,4 Whether these isohemagglutinins are inborn or the result of an antigenic stimulus has been a subject of experimentation and long debate. The theory that isohemagglutinin production takes place after birth from exposure to group A and B antigens found normally in ingested food and in the developing intestinal flora has many proponents.^5-7 However, the presence of isohemagglutinins in neonatal sera⁸ has been demonstrated, and it is thought that these are maternal in origin and transferred through the placenta.^4,9 Nevertheless, in recent years it has been well documented that the fetus produces small amounts of γM-globulins¹⁰ and is capable of