The neonate is deficient in the main antibody that protects mucosal membranes, the secretory IgA. While developing this immune system the breast-fed baby is provided with 0.25-0.5 grams per day of secretory IgA antibodies via the milk. These antibodies which function in concert with other defense factors in milk such as lactoferrin are directed against a number of micro-organisms that threaten the neonate. Recent studies suggest that it may be possible by vaccination of the mother to increase the immunity provided the breast-fed infant via the milk secretory IgA antibodies. Breast-feeding results in a lower frequency of infections in the infant, not only developing countries, but also in societies like Canada and USA. In developing countries the most dangerous period of a child's life begins with weaning when the protection of the breast milk vanishes and often heavily contaminated food is introduced. The large number of infections, especially diarrhea, that follow may be a major factor impairing growth and development with accompanying undernutrition. Utilization of available nutrients is much improved if these infections can be prevented.
PIP: IgA antibodies have unique properties for the defense of the mucous membrane. The structure of IgA antibodies is described. IgA antibodies are found in the mucus layer on mucosal membranes and in the lumen of the gut. Secretory IgA is an important part of the host defense at the mucosal level in the gastrointestinal, as well as the respiratory and genito-urinary tracts. A mechanism of IgA's action in the gastrointestinal tract is postulated. The connections between breastfeeding and the paucity of the newborn's own antibodies are discussed. IgA is the predominant immunoglobulin in human milk. An enteromammaric link, which would provide a system for transfer of IgA antibodies from the intestine to the mammary gland, is explored. The mode of function of secretory IgA antibodies is explained. The roles of other host defense factors in milk, such as lactoferrin, lysozyme, and macrophages and granulocytes, are discussed. Studies claiming that breastfed babies have fewer infections than nonbreastfed babies are reviewed. In developing countries, the difference is dramatic, but when breastfed babies are weaned, infections from contaminated food and water begin. Progress in Costa Rica due to the provision of clean water, sanitation, oral rehydration and vaccination programs is described. The possibility of directing the mucosal immunity of the mother via the breast milk, also of the breastfed infant via vaccination procedure, is explored.