Role of the early life gut microbiome on immunoglobulin A and colonic immune development

ABSTRACT The gut microbiome and immune system develop in concert, influenced by environment, diet, infections, and antibiotics. Secretory immunoglobulin A (sIgA) in breastmilk is the primary mediator of coordinated immune and microbiome development, modulating host-bacterial interactions. Breastmilk sIgA is the main source of IgA be- fore the first month of life, and formula-fed infants lack sIgA exposure during this critical period. Antibiotics ad- ministered during infancy lead to dramatic changes in microbiome composition during a critical period for regu- lation of gut inflammation. Preterm infants are more likely to be exposed to antibiotics, are more susceptible to bacterial infection, have less mature gut microbiomes, and have persistent alterations in immune development relative to their term counterparts. Animal models are essential to precisely control the complexity and variables of human immune and microbiome development. Gnotobiotic mouse models have been used to determine how individual strains impact immune development in adults. However, <25% of species tested in these models have >5% prevalence among infants. Therefore, new models are necessary to determine the impacts of microbes that colonize human infants on the developing immune system. We have developed a gnotobiotic mouse model of colonizing germ-free mating pairs with bacterial isolates or fecal samples from human infants. Pups are born microbiome-humanized, avoiding the negative immune consequences of lack of microbial exposure. Just as in human neonates, the gut microbiome of these mice matures over time, and we find that microbiome similarity correlates with cellular and secreted markers of immune response. The rationale for our proposal is to use this model to understand how human-associated microbes impact immune development, sIgA bacterial binding, and susceptibility to antibiotic-mediated disruption and bacterial pathogen colonization. In Aim 1, we colonize gnoto- biotic dams with the most abundant and prevalent bacterial isolates or combinations colonizing human infants from two clinical cohorts of 80,000 fecal samples from over 1,050 hospitalized preterm or community term infants. By using germ free breeding pairs homozygous or heterozygous IgA knockout mice, we will evaluate how ma- ternal or infant sIgA impacts immune development. In Aim 2, we colonize wild-type germ-free mice with preterm or term fecal samples and evaluate immune disruption relative to antibiotic treatment. In Aim 3, we evaluate immune tolerance and susceptibility to E. coli challenge with rescue with IgA supplementation. Our proposal is innovative because our interdisciplinary research team will complement data from unique human cohorts in a gnotobiotic mouse model that recapitulates microbiome and immune development and disruption by antibiotics and infectious challenge. This proposal is significant because we will use sophisticated multivariate analyses to precisely determine how prevalent infant-associated microbes differentially affect immune development. Our work is impactful because we will advance understanding of the co-development of the gut microbiome and immune system and establish a predictive framework for promoting healthy microbiome-immune interactions.