Breast milk contains a complex community of living cells that may help explain how it supports infant nutrition and immune protection, according to new research revealing previously hidden details about their behaviour.

Scientists from The University of Western Australia used advanced imaging techniques to examine individual human milk cells, uncovering differences in how they process nutrients and suggesting new ways to investigate the relationship between lactation and maternal health.

The study, published in ACS Nano, provides a closer look at the biological processes inside human milk. Researchers say the findings could help scientists better understand the functions of these cells and their potential importance for mothers and babies.

Scientists Discover Different Roles Among Breast Milk Cells

The researchers examined several types of cells found in human milk, including lactocytes, which produce milk, and immune cells such as neutrophils, macrophages and dendritic cells.

Using a combination of microscopy techniques, they investigated the cells' internal structures, chemical composition and metabolic activity.

Lead author Qiongxiang (Lynn) Lin, a PhD candidate, said researchers still know relatively little about the functions of the different living cells in human milk.

'With our new approach, we can look inside individual cells at the nanoscale and begin to understand how their structure, chemical composition and metabolism are connected,' Lin said.

The researchers found that these cells use nutrients in distinct ways, suggesting they have specialised roles rather than functioning as a single, uniform population.

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How Sugar and Protein Are Used Inside Breast Milk

One of the study's findings concerned glucose, a type of sugar that cells can use for energy and other biological processes.

Using stable isotope tracing, the team followed glucose-derived carbon and found it was preferentially incorporated into lipid droplets inside macrophages. These immune cells also showed gene activity associated with processing fats.

The researchers separately tracked amino acids, which are the building blocks of proteins. They found that certain groups of lactocytes were particularly active in protein production, secretion and energy use.

Lin said the findings demonstrated that human milk cells use nutrients in different ways, revealing metabolic activity that conventional profiling methods may not fully capture.

Could These Cells Help Protect Babies From Infection?

The study identified sulphur- and iron-enriched granules within neutrophils, immune cells involved in defending the body against infection.

Professor Donna Geddes, director of the university's Centre for Human Lactation Research and Translation, said the cells' distinct functions help support the composition and volume of human milk.

She also highlighted the potential importance of the neutrophil findings, noting that these immune cells contribute to bacterial killing and help protect babies from infection.

However, the research did not establish that these particular cellular findings lead to measurable improvements in infant health. Further research is needed to determine how the observed processes translate into benefits for babies.

What the Discovery Could Mean for Maternal Health

The researchers combined their imaging results with single-cell RNA sequencing, allowing them to connect individual cells' structures with their gene activity and nutrient use.

Associate Professor K. Swaminathan Iyer, director of the ARC Training Centre for Biomedical Analysis, said the approach could help researchers investigate how human milk cells change between individuals, throughout lactation and under different maternal health conditions.

The team is particularly interested in whether conditions such as gestational diabetes alter the cellular and metabolic characteristics of human milk.

The findings provide a foundation for further research into how maternal health and lactation influence the cellular composition of human milk.

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Frequently Asked Questions

  • What types of living cells are found in human breast milk?
    The study examined milk-producing lactocytes and immune cells including neutrophils, macrophages and dendritic cells.
  • How do breast milk cells use nutrients differently?
    The researchers found that the cells have specialised metabolic roles. Macrophages preferentially incorporated glucose-derived carbon into lipid droplets, while some lactocytes were particularly active in protein production, secretion and energy use.
  • What did the study find about neutrophils in breast milk?
    Neutrophils contained high concentrations of sulphur and iron in cellular granules. These immune cells are involved in bacterial killing and may help defend against infection, although the study did not prove a measurable health benefit for babies.
  • How was the breast milk cell research carried out?
    Scientists from The University of Western Australia used advanced microscopy, stable isotope tracing and single-cell RNA sequencing to examine the cells' structures, chemical composition, nutrient use and gene activity.
  • Does the research change infant-feeding advice?
    No. The findings provide a basis for further research into lactation and maternal-infant health, but they do not establish immediate changes to infant-feeding advice or prove that the observed cellular processes improve infant health.