Anti-I Antibody in Normal Human Newborn Infants.

A cold agglutinin with anti-I specificity is present in a high percentage of cord sera. Evidence is produced that this antibody, like the ‘naturally-occurring’ anti-I present in adult serum, is not a γG-globulin; thus the antibody, both in cord serum and in adult serum, is inactivated by treatment with 2-mercaptoethanol, is not eluted with γG-globulin using DEAE-cellulose chromatography and is recovered in the fast sedimenting fractions after ultracentrifugation. Furthermore, the antibody does not disappear from the circulation of newborn infants as do γG antibodies which cross the human placenta. These findings indicate that the antibody in cord serum is a γM-globulin and that its production often begins before birth. [ABSTRACT FROM AUTHOR]