Breastfeeding, long recognized for its nutritional benefits, is increasingly understood as a complex immunological process with far-reaching implications for both maternal and infant health. Recent research is revealing how immune cells, particularly T cells, play a pivotal role in shaping a baby’s developing immune system, fostering healthy gut bacteria, and even reducing a mother’s risk of breast cancer. This emerging understanding of lactation as an “immune-regulated state” is prompting a reevaluation of its long-term health consequences and opening new avenues for improving maternal and infant care.
For decades, the focus on immunity during lactation centered on myeloid cells, a type of immune cell that doesn’t directly influence milk production. However, a growing body of evidence demonstrates that various T cell subsets expand during lactation, contributing to mammary gland maturation, milk production, and long-term protection against disease. This shift in perspective, detailed in a recent review published in the journal Trends in Immunology on February 26, 2026, highlights the dynamic interplay between the immune system and lactation.
T Cells: Key Players in Lactation and Beyond
T cells, a type of white blood cell crucial to the immune system, are now recognized as central to the benefits of breastfeeding. Researchers have found that these cells not only support milk production but too establish a lasting presence in the mammary gland, offering sustained immune benefits. “Lactation is not just a nutritional process; it is an immune-regulated state with lasting consequences for both maternal and infant health,” explains Deepshika Ramanan, senior author of the Trends in Immunology review and researcher at the Salk Institute for Biological Studies.
Studies in both mouse models and human milk have transformed our understanding of how different immune cell types contribute to lactation. Abigail Jaquish, also of the Salk Institute for Biological Studies, notes that “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.” This protective effect against breast cancer is particularly noteworthy, as parity (the number of times a woman has given birth) and breastfeeding are both associated with a reduced risk of the disease. A study published in Nature in 2025 found that breastfeeding was associated with longer overall survival and an increase in CD8+ tissue-resident memory T (TRM) cells in breast cancer patients. Read more about this research in Nature Immunology.
Immune Support for Infants Through Breast Milk
The benefits of lactation extend beyond the mother, with research suggesting that T cells in breast milk play a critical role in shaping the infant’s immune system. These cells may help establish healthy gut bacteria, provide direct immune protection, and contribute to the development of a robust immune response. The precise mechanisms by which these immune cells influence infant development are still being investigated, but the potential impact is significant.
Understanding how the immune system supports lactation could also shed light on why some individuals experience difficulties with milk production or develop infections like mastitis. Further research into immune regulation during lactation may ultimately lead to strategies for improving maternal and infant health outcomes.
Unanswered Questions and Future Research
Despite the recent advances, many fundamental questions remain unanswered. Researchers are working to understand how different T cell subsets function during lactation, what microbial cues 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.
The researchers hope their function will encourage clinicians and public health professionals to view lactation as an immune-driven process with long-term health implications. They anticipate that this review will spark new cross-disciplinary conversations and emphasize the need for increased focus on lactation in immunology research. Learn more about the review in Trends in Immunology.
The ongoing investigation into the immunological aspects of lactation promises to refine our understanding of maternal and infant health, potentially leading to improved strategies for supporting breastfeeding and optimizing outcomes for both mother and child. The next steps involve further unraveling the complex interactions between immune cells, the mammary gland, and the developing infant immune system.
What are your thoughts on the evolving understanding of breastfeeding and its immunological benefits? Share your comments and experiences below.
