Levels of human milk-specific immunoglobulin A antibodies during lactation.

Abstract

The secretory immunoglubulin of the Immunoglobulin A class (SIgA) appears to be the most important of the soluble substances in human milk in terms of protection against diarrheal disease in breastfed infants. Longterm follow-up studies of milk antibodies in human milk have indicated that the concentration of IgA specific antibodies fluctuates during lactation with the most dramatic changes noted among women living in areas where hygienic conditions are poor. Total SIgA concentration and IgA-specific antibodies against Escherichia coli labile toxin (EcLT) Shigella B6 somatic antigen (SB6) and rotaviruses were determined in 20 lactating mothers from a rural area in Guatemala over a 16-week period. The mean concentration of SIgA was highest at the beginning of lactation and reached a plateau at 2-3 weeks postpartum. The levels of specific antibodies against EcLT SB6 and rotaviruses fluctuated in each of the women independently of total SIgA concentration and of one another. In 90% of subjects at least 1 of the specific antibodies reached nondetectable levels at some point in the study. These fluctuations may be related to the presence of homologous antigens in the maternal intestine. It is suggested that the presence of the antigen in the intestine of the mother inhibits the migration of primed IgA committed lymphocytes from the intestine to the mammary gland. This phenomenon has important practical implications. If a lactopositive breastfeeding mother becomes infected by an intestinal pathogen the levels of her milk antibodies will reach very low levels. In turn if her infant is infected by that pathogen there is an increased likelihood that the infection will result in diarrhea.