It's widely known that breastfeeding impacts the health of both mother and child, but the underlying biology that leads to these effects has been understudied. In a review article publishing in the Cell Press journal Trends in Immunology on February 26, researchers highlight recent studies showing T cells—white blood cells that play a pivotal role in the immune system—shape the baby's immune system, support healthy gut bacteria, and reduce the risk of breast cancer for the mother.
"Lactation is not just a nutritional process; it is an immune-regulated state with lasting consequences for both maternal and infant health," says senior author Deepshika Ramanan of the Salk Institute for Biological Studies.
"We highlight emerging evidence that immune cells, particularly T cells, support milk production. Mammary T cells also have lasting effects on maternal health and infant immunity."
Recently, research in both mouse models and human milk has transformed our understanding of how different immune cell types contribute to lactation. Historically, lactation-associated immune changes were thought to involve mainly myeloid cells, which do not impact milk production.
"Several recent studies demonstrate that T cell subsets expand during lactation, with functions spanning mammary gland maturation and milk production to long-term protection against breast cancer," says author Abigail Jaquish of the Salk Institute for Biological Studies.
Research shows that another potential function of these maternal T cells could be protection of the infant. For example, the T cells found in milk may help shape a baby's immune system, support healthy gut bacteria, and even provide direct immune protection.
The team says that understanding how the immune system supports lactation can provide insight into why breastfeeding is associated with long-term maternal benefits—such as reduced breast cancer risk—and how milk may influence infant growth and immune development. Studying immune regulation during lactation may also help explain why some individuals experience difficulties with milk production or infections such as mastitis and could ultimately inform strategies to improve maternal and infant health outcomes, they add.
Many fundamental questions in this field remain, however. Researchers still do not fully understand how different T cell subsets function during lactation, which microbial cues might guide their recruitment to the mammary gland, and how immune-epithelial communication provides breast cancer protection.
"On the infant side, we are only beginning to understand whether and how immune cells transferred through breast milk directly shape neonatal immune development," Ramanan says.
"We hope the advances in the field resonate with clinicians and public health researchers by reframing lactation as an immune-driven process with long-term health implications," Jaquish says. "We expect the review to spark new cross-disciplinary conversations and highlight the need for increased focus on lactation in immunology research."
