Exposure to diverse microbial flora accelerates the development of infant immunity

Abstract

Abstract The newborn immune system is considered underdeveloped and ill-equipped to defend itself against many pathogens. Indeed, infection is the leading cause of hospitalization and death for infants under 6 months. Relative to the adult immune system, little is known about infant immunity or the signals that orchestrate immunologic maturation. The constraints of human research and the use of sterile animal models limit advancements in this area. Commonly used animal models are raised in “specific pathogen free” (SPF) conditions to minimize the confounding effects of diverse microbial exposure. We sought to understand the physiologic effects of exposure to those diverse microbes on infant immune development. We co-housed laboratory mice with pet store mice from conception to expose them to diverse microbial flora. Microbial exposure led to a dramatic shift in immune cell composition with increases in the proportion of T cell memory, helper T cell subsets, macrophages, and neutrophils, as well as general increases in the number of most immune cell subsets as early as 2 weeks of age. The gap between the microbially-exposed mice and SPF mice continued to widen at 3 and 6 weeks of age. We also observed increased TNFα, IL-6, IL-5, IL-17, and RANTES expression at 3 weeks of age. By 6 weeks most of the cytokines/chemokines tested where increased. These observations demonstrate that exposure to diverse microbial flora during early life dramatically alters the trajectory of the developing immune system. A better understanding of how healthy immune systems develop, and the risks and benefits of modulating infant immunity could lead to important advancements in treatments for early life infection and novel infant vaccination approaches. Supported by Grants from: Medical School/University of Minnesota Foundation Award Program Masonic Cross-Departmental Grants in Children's Health Research University of Minnesota Department of Pediatrics "R" Award