Early-life colonization by aromatic-lactate-producing bifidobacteria lowers the risk of allergic sensitization

Early-life microbial exposures shape immune development and allergy risk. Food allergen sensitization, reflected by the presence of food allergen-specific immunoglobulin E (IgE), is an early indication of impaired immune tolerance. Here we show that early-life transmission of aromatic lactate-producing bifidobacteria strains in 147 children followed from birth to 5 years of age, facilitated by vaginal delivery, exposure to older siblings and exclusive breastfeeding for the first 2 months, led to increased levels of aromatic lactates in the infant gut. This microbiota–metabolite signature was inversely associated with the development of food allergen-specific IgE until 5 years and atopic dermatitis at 2 years. The observed effect was mediated by 4-hydroxy-phenyllactate, which inhibited IgE, but not IgG, production in ex vivo human immune cell cultures. Together, these findings define an early-life microbiota–metabolite–immune axis linking microbial transmission and feeding practices with reduced allergic sensitization.