Diet-derived LPS determines intestinal IgA induction and repertoire characteristics independently of the microbiota.

A hallmark of the main secreted antibody immunoglobulin A (IgA) is its mutational load that accumulates throughout life. Although this is mainly interpreted in terms of continuing microbial induction, we show that dietary composition during early life can promote IgA induction, its repertoire, and mutational diversification independently of microbial exposure. Using germ-free and colonized mice fed different diets formulated with proprietary grain-based processing or from purified chemicals with different principal macronutrient calorie sources, we found that dietary lipopolysaccharide contamination led to Toll-like receptor (TLR) 4 signaling and promoted germinal center activity in the intestinal immune compartment. The effects of lipopolysaccharide on mucosal immune induction were phenocopied only when presented within colloidal liposomes rather than in dispersed solution. These findings indicate that dietary composition and its formulation can leave a durable impression on the resultant IgA repertoire.