Abstract
Exclusive human milk feeding of the newborn is recommended during the first 6 months of life to promote optimal health outcomes during early life and beyond. Human milk contains a variety of bioactive factors such as hormones, cytokines, leukocytes, immunoglobulins, lactoferrin, lysozyme, stem cells, human milk oligosaccharides (HMOs), microbiota, and microRNAs. Recent findings highlighted the potential importance of adding HMOs into infant formula for their roles in enhancing host defense mechanisms in neonates. Therefore, understanding the roles of human milk bioactive factors on immune function is critical to build the scientific evidence base around breastfeeding recommendations, and to enhance positive health outcomes in formula fed infants through modifications to formulas. However, there are still knowledge gaps concerning the roles of different milk components, the interactions between the different components, and the mechanisms behind health outcomes are poorly understood. This review aims to show the current knowledge about HMOs, milk microbiota, immunoglobulins, lactoferrin, and milk microRNAs (miRNAs) and how these could have similar mechanisms of regulating gut and microbiota function. It will also highlight the knowledge gaps for future research.
Highlights
The immune system is the primary line of defense against environmental exposures such as allergens, bacteria, and viruses
The current review focus is on lactoferrin, immunoglobulins, human milk oligosaccharides (HMOs), milk microbiota, and miRNAs components of human milk and their role in infants’ gut microbiota colonization, gut health and immune system modulation
immunoglobulin A (IgA), secretory IgA (sIgA), IgM, and immunoglobulin G (IgG) concentrations are significantly higher in fresh human milk compared to donor milk [62], which is important to infants in the neonatal intensive care unit due to frequent use of donor milk
Summary
The immune system is the primary line of defense against environmental exposures such as allergens, bacteria, and viruses. IgG is the main immunoglobulin found in serum and is associated with long-term immunity It activates the complement cascade to remove pathogens, but has been shown to protect against viral infections at the mucosal level through neutralization [57, 58]. IgA, sIgA, IgM, and IgG concentrations are significantly higher in fresh human milk compared to donor milk [62], which is important to infants in the neonatal intensive care unit due to frequent use of donor milk This is not unexpected as most donor milk is from mothers of infants that are at least 6 months of age and these samples undergo Holder pasteurization. Human milk with higher LDFH-I levels is associated with protection against norovirus as well [94] In both of these gastrointestinal viruses, HMOs have been shown to improve outcomes.
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