Since the discovery early in this century that the body's immune system is capable of initiating the rejection of foreign cells, there has been continuing speculation about why the fetus is exempt from this reaction.
Suggestions that the placenta prevents passage of antigenic material between the mother and fetus have been disproved, and it is now known that fetal and maternal cells are exchanged through the placenta and that both humoral and cellular immunity to fetal antigens develop in the mother.
Recently, in an attempt to find out whether the normal immunity of such women might be in some way blocked, J. B. Dossetor, MD, PhD, professor of medicine and director of the transplant research laboratory, and T. Kovithavongs, MD, assistant professor of medicine, both of the University of Alberta in Edmonton, looked for the presence of suppressor cells in the blood of multiparous women. They found that multiparous women