Inhibition by alpha-fetoprotein fractions of hemagglutination reactions between A and B antigens of human red blood cells and specific antisera.

It is shown that fetal alpha-fetoprotein (AF)-rich fractions, isolated by chemical methods, can inhibit the agglutination reaction of human AB red blood cells (RBC) with specific antisera. Hemagglutination was not inhibited by other amniotic fluid or umbilical cord serum proteins in equivalent concentrations or by other pregnancy-associated hormones. The inhibitory effect is related to the amount of antibodies and AF fractions. It seems that AF interferes with the interaction between the antibody and the cell-surface antigens by preventing the binding of the antibodies to the cells. It is suggested that the ability of AF to inhibit hemagglutination reactions in vitro may play a role during pregnancy on the immune reaction between anti-A and anti-B antibodies and the corresponding RBC antigens, as well as on the manifestations or hemolytic disease of the newborn.