The microbes that colonise an infant's gut in the first weeks of life may help decide whether the immune system learns tolerance or tips towards allergy. A Karolinska Institutet study in Nature Microbiology, based on the Swedish ALADDIN birth cohort, analysed faecal samples from children and their mothers and followed the children from birth to five years of age, connecting early microbial ecology to later allergic outcomes.
Children with high early-life levels of bifidobacteria that produce aromatic lactic acids developed fewer allergy antibodies, known as IgE, and had a lower risk of atopic eczema at two years of age. One bacterial metabolite stood out: 4-hydroxyphenyl lactate, which in laboratory experiments reduced IgE production in immune cells by approximately 60 per cent, suggesting a concrete molecular route from microbe to immune restraint.
The study, whose authors include Johan Alm, also identified the circumstances that favour these protective bacteria: vaginal delivery, exclusive breastfeeding during the first two months of life and early contact with older siblings. The researchers suggest that supporting such bacteria through breastfeeding, diet or potentially probiotics could eventually contribute to allergy prevention, while noting that any such intervention remains to be tested in trials.