Recent research is reshaping the understanding of breastfeeding, revealing it to be far more than a nutritional process. Scientists now believe lactation is a complex, immune-regulated state with lasting health consequences for both mothers and infants, driven in large part by the activity of T cells – critical components of the immune system.
For years, the immunological changes associated with lactation were primarily attributed to myeloid cells. However, a review article published February 26 in Trends in Immunology highlights emerging evidence demonstrating that T cells play a pivotal role in supporting milk production, shaping an infant’s immune system, fostering healthy gut bacteria, and even reducing a mother’s risk of breast cancer.
“Lactation is not just a nutritional process; it is an immune-regulated state with lasting consequences for both maternal and infant health,” said Deepshika Ramanan, senior author of the review and a researcher at the Salk Institute for Biological Studies.
The research, drawing from studies in both mouse models and human milk samples, indicates that various T cell subsets expand during lactation, contributing to mammary gland maturation, milk production, and long-term protection against breast cancer, according to Abigail Jaquish, as well of the Salk Institute.
This protective effect against breast cancer appears to be particularly significant following a complete cycle of lactation and involution – the process of the mammary gland returning to its non-pregnant state. A study published in Nature in October 2025 found that parity (having given birth) and lactation are associated with increased numbers of CD8+ T cells within normal breast tissue. In mouse models, pregnancy followed by lactation and involution led to reduced tumor growth and increased immune cell infiltration, effects that were reversed when CD8+ T cells were depleted.
The benefits extend to infants as well. T cells present in breast milk may directly influence a baby’s developing immune system and contribute to a healthy gut microbiome. Researchers are now investigating the extent to which these transferred immune cells directly shape neonatal immune development.
While the understanding of these immunological mechanisms is growing, significant questions remain. Scientists are working to determine how different T cell subsets function during lactation, what microbial signals attract them to the mammary gland, and how communication between immune cells and epithelial cells provides breast cancer protection.
“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 stated. “We expect the review to spark modern cross-disciplinary conversations and highlight the need for increased focus on lactation in immunology research.”
Researchers acknowledge that further study is needed to fully elucidate the complex interplay between the immune system and lactation, potentially leading to strategies to improve maternal and infant health outcomes and address challenges like milk production difficulties or mastitis.
