Abstract
Human milk is a dynamic source of nutrients and bioactive factors; unique in providing for the human infant’s optimal growth and development. The growing infant’s immune system has a number of developmental immune deficiencies placing the infant at increased risk of infection. This review focuses on how human milk directly contributes to the infant’s innate immunity. Remarkable new findings clarify the multifunctional nature of human milk bioactive components. New research techniques have expanded our understanding of the potential for human milk’s effect on the infant that will never be possible with milk formulas. Human milk microbiome directly shapes the infant’s intestinal microbiome, while the human milk oligosaccharides drive the growth of these microbes within the gut. New techniques such as genomics, metabolomics, proteomics, and glycomics are being used to describe this symbiotic relationship. An expanded role for antimicrobial proteins/peptides within human milk in innate immune protection is described. The unique milieu of enhanced immune protection with diminished inflammation results from a complex interaction of anti-inflammatory and antioxidative factors provided by human milk to the intestine. New data support the concept of mucosal-associated lymphoid tissue and its contribution to the cellular content of human milk. Human milk stem cells (hMSCs) have recently been discovered. Their direct role in the infant for repair and regeneration is being investigated. The existence of these hMSCs could prove to be an easily harvested source of multilineage stem cells for the study of cancer and tissue regeneration. As the infant’s gastrointestinal tract and immune system develop, there is a comparable transition in human milk over time to provide fewer immune factors and more calories and nutrients for growth. Each of these new findings opens the door to future studies of human milk and its effect on the innate immune system and the developing infant.
Highlights
The innate immune system is the first line of defense against infection and is activated within minutes, reacting in a nonspecific, preprogrammed, and patterned manner to various infectious or foreign stimuli [1]
This review focuses on how human milk directly contributes to the infant’s innate immunity
There is a large body of evidence documenting the benefits of human breast milk for human infants, in diminishing morbidity and mortality and protecting against specific infections during the period of breastfeeding [4,5,6]
Summary
The innate immune system is the first line of defense against infection and is activated within minutes, reacting in a nonspecific, preprogrammed, and patterned manner to various infectious or foreign (non-self) stimuli [1]. Breast Milk Immunity nature of the uterus, placenta, and amniotic fluid, the evolution of human milk from colostrum through transitional milk to mature milk provides nutrition and protection appropriate for the timeaffected development of the infant [3]. There is a large body of evidence documenting the benefits of human breast milk for human infants, in diminishing morbidity and mortality and protecting against specific infections during the period of breastfeeding [4,5,6]. Research into the specific factors in human breast milk, which lead to the remarkable health benefits of exclusive breastfeeding, has been ongoing for decades; there are still intriguing mysteries of how human milk contributes to the development and regulation of both the infant’s innate [10] and adaptive immune function [11,12,13]. This review will focus on the current understanding of the critical interactions between human breast milk and the infant’s developing innate immune system (Figure 1) [12, 16,17,18]
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