Naturally-occurring macroglobulin antibody of foetal origin in the normal human newborn.

Normal human umbilical cord serum and matched maternal serum were found to contain haemagglutinating substances with specificity for determinants found on Bence Jones (BJ) proteins. A majority of the cord sera examined contain such agglutinators for some type L BJ protein but only rarely for type K proteins. Cord serum agglutinators were found in concentrations which exceeded those of the matched maternal serum and a minority of cord sera contained such agglutinators in the absence of similar activity in the maternal serum. This is felt to constitute strong presumptive evidence of their foetal origin. The agglutinating substances in both the cord and maternal sera behaved as macroproteins on gel filtration chromatography and were sensitive to mercaptoethanol treatment. Cord sera, in contrast to maternal sera, were almost uniformly devoid of other macroprotein antibody activity such as Forssman antibody, antibody to γG-globulin and ABO saline antibody when the latter were sought in maternal—newborn combinations incompatible for these erythrocyte antigens. Concentration of pooled serum L-chain proteins after gel filtration chromatography revealed maternal serum levels of 8–16 μg (protein) per ml, while the pooled cord serum contained approximately 2 μg per ml of this class of protein. The naturally-occurring macroglobulin antibodies of normal human newborn appear to have specificity directed toward L-chain sites which are relatively obstructed by the H-polypeptide chain as measured by haemagglutination inhibition. The specificity of this system for the autologous free L-chain of the maternal and newborn serum has not been established. The possible biological function of such an immunological system is discussed.