New knowledge in human milk immunoglobulin.

One of the anti-infection principles of maternal milk is the predominant milk immunoglobulin, secretory IgA. This immunoglobulin contains antibodies against many pathogens and potential pathogens, viruses as well as bacteria, including several members of Enterobacteriacae. The antigenic stimuli for these milk antibodies seem to take place in the Peyer's patches of the intestine. Lymphoid cells leaving the patches after antigenic exposure seem to home to the mammary glands via the lymph and blood circulation. As a result, the milk contains secretory IgA antibodies against, among other things, the intestinal bacteria of the mother. These milk antibodies might reflect the spectrum of bacteria and viruses in the community and may be important for the protection of the breast-fed baby. Via the same homing mechanism the maternal milk obtains antibodies against dietary antigens, including cow's milk proteins. Studies of infants on mixed feeding suggest that the secretory IgA antibodies against the bovine proteins diminish the antigenic exposure, indicating the possibility of an anti-allergic mechanism.