Maternal diet and gut microbiome composition modulate early‐life immune development

In early life, the intestinal mucosa and immune system undergo a critical developmental process to contain the expanding gut microbiome while promoting tolerance toward commensals, yet the influence of maternal diet and microbial composition on offspring immune maturation remains poorly understood. We colonized germ‐free mice with a consortium of 14 strains, fed them a standard fiber‐rich chow or a fiber‐free diet, and then longitudinally assessed offspring development during the weaning period. Unlike pups born to dams fed the fiber‐rich diet, pups of fiber‐deprived dams demonstrated delayed colonization with Akkermansia muciniphila, a mucin‐foraging bacterium that can also use milk oligosaccharides. The pups of fiber‐deprived dams exhibited an enrichment of colonic transcripts corresponding to defense response pathways and a peak in Il22 expression at weaning. Removal of A. muciniphila from the community, but maintenance on the fiber‐rich diet, was associated with reduced proportions of RORγt‐positive innate and adaptive immune cell subsets. Our results highlight the potent influence of maternal dietary fiber intake and discrete changes in microbial composition on the postnatal microbiome assemblage and early immune development.