Select symbionts drive high IgA levels in the mouse intestine

Immunoglobulin A (IgA) is an important factor to maintain homeostasis at mucosal surfaces. Levels of luminal IgA can vary widely; the current model suggests total IgA levels are driven by individual immune responses to specific microbes. Here, we found the prebiotic, pectin oligosaccharide (pec-oligo), induced high-IgA levels in the small intestine in a T cell-dependent manner. Surprisingly, this IgA-high phenotype was retained after cessation of pec-oligo treatment and was readily transmissible by bacteria both horizontally and vertically in the absence of pec-oligo. Interestingly, we noted a mismatch comparing the bacterial taxa enriched in the overall pec-oligo bacterial community versus the IgA-coated microbes in this same community. We found a small group of ethanol-resistant microbes, highly enriched for Lachnospiraceae bacterium A2, drove the IgA-high phenotype. Our findings support a model of intestinal adaptive immunity in which a limited number of microbes can promote durable changes in IgA directed to many symbionts.