Disruption of the Early-Life Microbiota Alters Peyer's Patch Development and Germinal Center Formation in Gastrointestinal-Associated Lymphoid Tissue

During postnatal development, both the maturing microbiome and the host im-mune system are susceptible to environmental perturbations such as antibiotic use. The impact of timing in which antibiotic exposure occurs was investigated by treating mice from days 5-9 with amoxicillin or azithromycin, two of the most commonly prescribed medications in children. Both early-life antibiotic regimens disrupted Peyer's patch development and immune cell abundance, with a sustained decrease in germinal center formation and diminished intesti-nal immunoglobulin A (IgA) production. These effects were less pronounced in adult mice. Through comparative analysis of microbial taxa, Bifidobacterium longum abundance was found to be associated with germinal center frequency. When re-introduced to antibiotic-exposed mice, B. longum partially rescued the immunological deficits. These findings suggest that early-life antibiotic use af-fects the development of intestinal IgA-producing B cell functions and that pro -biotic strains could be used to restore normal development after antibiotic exposure.