IgG subclasses compared in maternal and cord serum and breast milk.

Total and specific IgG subclass antibodies against 14 pneumococcal capsular polysaccharide antigens on the cord serum from 11 healthy term infants at birth and on serum from their mothers at delivery were evaluated. The same evaluation was performed five days after delivery on the serum and the milk obtained from the six mothers who were breast feeding their infants. Mean neonatal: maternal serum ratio of total IgG1 was significantly higher than the ratios of total IgG2, IgG3, and IgG4 and higher than the ratios of pneumococcal IgG subclass antibodies. Total IgG3 and IgG4 ratios were higher than the specific antibody ratios of the same IgG subclass. Type 1 and type 14 IgG1 antibodies were the highest antipneumococcal ratios. Although the maternal milk:serum ratios of total IgG subclasses were very low, significant amounts of specific antibodies were found in the milk, at about half the concentration observed in mother's serum.