Effects of Milk Antibodies and other Proteins on the Commensal Flora

Secretory immunoglobulin A (SIgA) is intimately involved in the transfer of maternal immunity to the newborn breast-fed infant.  Recent research demonstrates the significance of SIgA in the initial development of the newborn’s microbiota, and in the establishment of a tolerogenic immunological disposition towards non-pathogenic organisms and environmental antigens.

SIgA has long been known to prevent pathogen binding to the host epithelium through immune exclusion involving numerous mechanisms.  This process primarily involves T-cell dependent, somatically hypermutated monoclonal antibodies with high specificity towards pathogen surface antigens, and the success of the immune response is dependent upon the specific antigen recognition. Whereas this role is important, there is an alternate, dual role for SIgA in the health of the host—protection and promotion of commensal colonization and maintenance of homeostatic immunity.   

Breast milk is the primary supply of such polyclonal poly-reactive SIgA in the initial stages of neonatal colonization, and provides vital pathogen resistance while promoting colonization of commensal microbiota.