Natural isohemagglutinin productionby the fetus

Natural isothemagglutinins were detected in the serum of 79 of 137 (57 per cent) randomly selected full-term newborn infants. Whether these isohemagglutinins were of the γM or γG type was determined by: (1) comparing isohemagglutinin titers before and after mercaptoethanol treatment of serum, since the latter selectively reduces bisulphide bonds of γM-globulin, thus inhibiting its antibody action; and (2) separating γM-globulins from γG-globulins of sera by Sephadex-gel filtration and testing for isohemagglutinin activity in the serum fractions. Only two infants had serum γA-globulins. Results showed that in a considerable proportion of neonatal sera, isohemagglutinins are of the γM type. Therefore, it is concluded that most fetuses produce their own isohemagglutinins.