The immunological components of human milk and their effect on immune development in infants.

There have been considerable advances in our understanding of the diverse mixture of bioactive components in human milk that influence the immune status of infants by not only providing protection but also facilitating development, tolerance, and an appropriate inflammatory response. It could be suggested that milk is the communication vehicle between the maternal immune system and the infant, a system actively directing and educating the immune, metabolic, and microflora systems within the infant, while conferring multiple means of protection from pathogens. The physiological and protective functions of many of the immune components in human milk have been deduced not from studies in infants but from what is known in other species and in vitro models. This update briefly reviews immune development in infants and focuses on current knowledge of how both the "classical" immune and the nonimmune ingredients found in mature human milk promote immune development, facilitate the development of tolerance, and regulate the inflammatory response of infants.