Immunoprotective factors in breast milk and sera of mother-infant pairs.

We analysed breast milk and serum samples from 33 healthy Nigerian mother-infant pairs for concentrations of IgG, IgM, IgA, C3, C4 and lysozyme. We found that the mean IgG and IgM concentrations in maternal sera were three to four times higher than the levels in infant sera, and five to ten times higher than in breast milk. The IgA and lysozyme concentrations in breast milk were, however, slightly higher than the levels in infant sera, suggesting an active localized synthesis of these factors in the mammary gland. While 54.5% of the milk samples lacked measurable concentrations of IgM by radial immunodiffusion, IgA was consistently present in all the milk samples. The mean C3 concentration in maternal sera was 164 mg/100 ml, compared to 145 mg/100 ml and 11.5 mg/100 ml in infant sera and breast milk respectively. The C4 concentration was also considerably lower in breast milk than in maternal and infant sera.