Allergies are more common in young childrenlisegagne/Getty By Ruby Prosser ScullyYoung immune systems are sensitive to food allergens if they don’t have the right gut bacteria, a study in mice suggests. Sung-Wook Hong of the Institute for Basic Science in South Korea and his colleagues have been investigating the effects of the microbiome on allergies and the immune system. They wondered why mice raised in a sterile environment without any gut microbes suddenly produce high levels of a type of antibody when they are weaned onto solid food. These immunoglobulin E (IgE) antibodies form the arm of our immune system that mediates allergic responses to certain chemicals. When IgE antibodies detect allergens, they trigger the release of inflammatory chemicals that lead to the symptoms of allergies. Advertisement Read more: Allergy explosion: They are on the rise, and here’s why To understand why IgE spikes in microbe-free mice during weaning, the team fed young mice either a normal diet or one formulated with just the necessary amino acids, vitamins and glucose – nothing that could provoke the immune system. They found that the mice on the normal diet spontaneously developed an immune response, while the ones on the antigen-free diet did not. This suggests that the lack of a healthy gut microbiome is linked to a food-triggered immune response in mice, says Hong. Read more: A child’s mix of gut bacteria may determine if they get allergies However, when the team delayed introducing normal solid food until the microbe-free mice were adults, they found that they produced less IgE antibodies. The team found that a special type of immune cell, called T follicular helper cells, were involved in the IgE response seen in the mice. This kind of T cell is mostly generated early in life. This finding helps explain why allergies are more common in children than adults, says Hong. When the team let the microbe-free mice mix with normal mice, they found that they stopped producing as many T follicular helper cells, and their levels of IgE antibodies fell. Read more: Breast milk contains fungi which may help seed a baby’s microbiome “One of the implications of this study is that what is happening to your microbiota at the time of introduction of the food antigens is important,” says Emma Hamilton-Williams at the University of Queensland, Australia. “In that first year of life, the gut microbiota is really developing and changing quickly, so there definitely seems to be a connection,” she says. In humans, good gut bacteria can be killed off by antibiotics, illness or radiation. The findings raise questions about how soon certain foods should be given to young children after antibiotics, says Elissa Deenick at the University of New South Wales. Journal reference: Science Advances, DOI: 10.1126/sciadv.aaw1507 Read more: Probiotics are mostly useless and can actually hurt you More on these topics: immune system microbiology food and drink allergies