Composition of human milk – a journey of discovery

Scientists continue to discover and characterise new components in human milk, and the journey is far from over. In 2007, researchers discovered milk stem cells (Cregan et al.). Soon after that, in 2009, a comprehensive study (Molinari et al.) of the proteome map of human milk revealed 261 proteins that had never before been identified. Following this in 2015, an article (Alsaweed et al.) described over 300 novel milk microRNA molecules, components that are known to play a key role in the regulation of gene expression.

Key findings

Human milk is more than nutrition. Multifunctional proteins including sIgA, lactoferrin and lysozyme, as well as free fatty acids, act as anti-infective agents supporting infant health.

These agents work together to inactivate, destroy or bind to specific microbes, preventing their attachment to mucosal surfaces.

Living maternal cells are transferred through the milk to the infant. These include blood-derived leukocytes, cells of the mammary epithelium, stem cells and cell fragments, which provide immune-protection to the infant.

A large number of human milk oligossaccharides are also transferred to the infant and have been reported to have an important immunological function acting as probiotics that promote the intestinal growth of commensal bacteria. They also act as decoys or receptor analogues to inhibit the binding of pathogens, – including rotaviruses – to intestinal surfaces.

Human milk also contains commensal bacteria that become part of the gut microflora and influence inflammatory and immunomodulary processes. Not only do commensal bacteria prevent overgrowth of pathogenic bacteria, they also acidify the gut, ferment lactose, breakdown lipids and proteins, and produce vitamins K and biotin.

Download the infographic here: "What makes breastmilk so unique?"

Study abstracts
Identification of nestin-positive putative mammary stem cells in human breast milk

Stem cells in mammary tissue have been well characterised by using the mammary stem cell marker, cytokeratin (CK) 5 and the mature epithelial markers CK14, ...

Cregan MD, Fan Y, Appelbee A, Brown ML, Klopcic B, Koppen J, Mitoulas LR, Piper KM, Choolani MA, Chong YS, Hartmann PE (2007)

Cell Tissue Res 329, 129-136
Proteome mapping of human skim milk proteins in term and preterm milk

The abundant proteins in human milk have been well characterized and are known to provide nutritional, protective, and developmental advantages to both term and preterm ...

Molinari CE, Casadio YS, Hartmann BT, Livk A, Bringans S, Arthur PG, Hartmann PE (2012)

J Proteome Res 11, 1696-1714
References

Alsaweed,M. et al. Human milk microRNA and total RNA differ depending on milk fractionation. Journal of Cellular Biochemistry doi:10.1002/jcb.25207, (2015)

Newburg,D.S. & Walker,W.A. Protection of the neonate by the innate immune system of developing gut and of human milk. Pediatr Res 61, 2-8 (2007)

Hassiotou,F. et al. Maternal and infant infections stimulate a rapid leukocyte response in breastmilk. Clin Transl Immunology 2, e3 (2013)

Hassiotou,F. et al. Breastmilk is a novel source of stem cells with multilineage differentiation potential. Stem Cells 30, 2164-2174 (2012)

Bode,L. Human milk oligosaccharides: Every baby needs a sugar mama. Glycobiology 22, 1147-1162 (2012)

Garrido,D., Kim,J.H., German,J.B., Raybould,H.E., & Mills,D.A. Oligosaccharide binding proteins from Bifidobacterium longum subsp. Infantis reveal a preference for host glycans. PLoS One 6, e17315 (2011)

Sela,D.A. et al. An infant-associated bacterial commensal utilizes breast milk sialyloligosaccharides. J Biol Chem 286, 11909-11918 (2011)

Wu,S., Grimm,R., German,J.B., & Lebrilla,C.B. Annotation and structural analysis of sialylated human milk oligosaccharides. J Proteome Res 10, 856-868 (2011)