Mechanisms of maternal Immunoglobulin A control over the neonatal microbiota and the development of Necrotizing Enterocolitis

University Of Pittsburgh At Pittsburgh, Pittsburgh PA

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Abstract

ABSTRACT In infants the microbiota develops along a standard trajectory, where early colonization with facultative anaerobes (Enterobacteriaceae) transitions to dominance by Bifidobacteria until children begin to consume solid food. Deviations in the trajectory of intestinal bacterial colonization are associated with disease. In particular, preterm infants are dominated by Enterobacteriaceae for much longer than term infants, and these bacteria can invade the preterm intestinal epithelium, contributing to the of development of Necrotizing Enterocolitis (NEC). NEC is a devastating disease that is still lethal to ¼ of infants that develop it and leads to long term complications for many others. Breast milk contains bioactive molecules that directly modulate infant bacterial colonization, including antibodies, such as Immunoglobulin A (IgA). IgA is the predominant antibody found in breast milk and is secreted into milk by B cells that travel to the mammary gland from the mother’s intestine. In preterm infants, IgA binding to Enterobacteriaceae is inversely correlated to the development of NEC. We have demonstrated that the anti-bacterial reactivity of milk-derived IgA varies significantly between individuals and that a lack of IgA binding to intestinal bacteria in neonates leads to significantly increased intestinal Enterobacteriaceae, immune cell activation and accumulation. However, how IgA shapes host/bacteria and bacteria/bacteria interactions that define the assembly of the neonatal microbiota remains poorly understood. Our hypothesis is that maternal IgA, provided in breast milk, regulates the composition and transcriptome of neonatal intestinal bacteria, the activation of immune cells and the development of NEC. Using both samples collected from preterm infants and gnotobiotic mice carrying a defined bacterial consortium we will test this hypothesis. To identify how IgA shapes the absolute abundance of various members of the microbiota, we developed (Microbiota Flow Cytometry; MicFLY) a method that provides accurate single cell resolution of bacteria at all taxonomic levels. MicFLY can also be used to sort bacteria prior to RNAseq (MicFLYseq). Here, in three aims, we propose to use MicFLY and MicFLYseq to determine how milk-derived IgA shapes the development of the neonatal microbiota and NEC. In Aim 1, using a cohort of daily collected infant fecal samples we will define how feeding modality and IgA binding shape the formation of the preterm microbiota and NEC. In Aim 2 we will determine how IgA binding shapes intestinal bacterial transcription to modulate immune-driven inflammation and the development of NEC. In Aim 3 we will use gnotobiotic mice to test whether infant bacterial colonization is shaped by the anti-bacterial reactivity of maternal intestinal IgA. Together this proposal will define the assembly of the infant microbiota at the single cell level, determine the role of IgA in modulating intestinal bacterial transcription and colonization and identify how IgA control of the microbiota reduces the incidence of NEC. Our proposal has the potential to uncover how milk-derived IgA could be used to improve infant health and reduce the incidence of NEC.