It has been understood for some time now that a mother's milk confers her nursing infant with immunity to certain pathogens. This process of transferring antibodies – the part of the immune system that finds and neutralizes the disease-causing agents – to the baby is known as “passive immunity”. But new research has found that there may be another layer to how a mother's milk provides her child with immunity.

Published in the Journal of Immunology, the study on mice has found that specific immune cells in the mother’s milk pass through the wall of the infant's intestine and travel to the thymus – the primary lymphoid organ of the immune system. Here, the maternal cells have been found to “educate” the developing cells of the infant, so that the immune system will be able to launch an attack on the specific pathogens that the mother has already experienced but that the infant has yet to encounter. The team have named this newly described process “maternal educational immunity”.

While these experiments have only been carried out in mice, the results are intriguing. It suggests that a new way of vaccinating a baby could be through vaccinating the mother.

In one series of experiments, the researchers tested out their theory using the bacterium Mycobacterium tuberculosis (TB), the microbe responsible for an estimated 1.5 million deaths per year. They discovered that the mouse pups nursed on females that were immunized against TB were found to produce the correct antibody to fight it, despite not having been immunized themselves. If the principles described in this study also hold true in humans, it could be a novel way to treat babies in the developing world, where the majority of TB cases occur.

Currently, babies vaccinated against TB have a generally poor response, giving them immunity to the worst of the symptoms, but not preventing the pulmonary symptoms that occur in the lungs.

“We hope that by vaccinating the mother, who will eventually nurse the baby, we will improve infant immunity against TB,” explains Ameae Walker, who led the research, in a statement. “It's like vaccinating the baby without actually vaccinating the baby. In some instances, our work has shown that immunity against TB is far more effective if acquired through the milk than if acquired through direct vaccination of the baby. Of course, clinical trials will need to be conducted to test whether this is the case in humans.”