When young mice start nibbling on solid food for the first time, something remarkable happens inside their bodies: their immune systems begin a complex recalibration that shapes how they will respond to food and germs for the rest of their lives. Now, scientists at LMU Munich have discovered exactly how this process works—and the findings could one day help people deal with allergies and autoimmune diseases.
The immune system has a tough job during early childhood. It must learn to ignore harmless things like food and friendly bacteria while still staying alert for actual dangers. Getting this balance wrong can lead to allergies, asthma, or autoimmune conditions later in life. One major moment in this balancing act is when babies switch from milk to solid food, and researchers have long wondered how that dietary change affects the immune system.
A team led by Professor Barbara Schraml at the Biomedical Center has now found the answer. Working with mice, they discovered a signaling pathway that carries information about dietary changes directly to immune cells in the spleen, a key organ that helps filter blood and fight infections. The pathway begins when young mice start eating grain-based solid food. Their immune cells, called lymphocytes, boost production of a messenger molecule called interferon-gamma. This molecule then triggers a chain reaction that activates a specific type of dendritic cell, known as cDC1. These activated cells produce another molecule called CXCL9, which helps reshape the behavior of T cells—soldiers of the immune system that learn to recognize substances from food.
"Dietary signals are thus relayed through the immune system, helping to recalibrate the developing pool of T cells as the immune system comes into contact with a greater variety of substances from food and the environment," Schraml explained.
The researchers made another surprising discovery: this regulatory circuit works even in mice raised without any gut bacteria, meaning it does not depend on the changes in gut microbes that normally happen when young animals start eating solid food. The team suspects compounds in grain feed—possibly beta-glucans from cereal grains or traces of microbial molecules—might be the dietary signals driving the immune response.
Perhaps most hopeful of all, the scientists found that adult mice also showed this same responsiveness to dietary changes. The cDC1 cells stayed sensitive to what the animals were eating throughout their lives. This suggests diet could be a tool for shaping immunity not just in children, but in grown-ups too.
"Our results show that food provides the immune system not only with nutrients, but also with information," Schraml said. "The discovery that cDC1 remain responsive to dietary changes in adults opens up the long-term possibility of investigating whether immune responses can be influenced by targeted dietary interventions."
The findings were published in the journal Nature Communications. While the research was conducted in mice, it points toward a future where doctors might one day use specific foods or diets to help people strengthen their immune systems or reduce allergic reactions. For now, the discovery gives scientists a clearer map of how the immune system learns to tell friend from foe—and how mealtimes might play a bigger role in health than anyone expected.