Neonatal Immune Adaptation of the Gut and Its Role during Infections

Abstract

The intestinal tract is engaged in a relationship with a dense and complex microbial ecosystem, the microbiota. The establishment of this symbiosis is essential for host physiology, metabolism, and immune homeostasis. Because newborns are essentially sterile, the first exposure to microorganisms and environmental endotoxins during the neonatal period is followed by a crucial sequence of active events leading to immune tolerance and homeostasis. Contact with potent immunostimulatory molecules starts immediately at birth, and the discrimination between commensal bacteria and invading pathogens is essential to avoid an inappropriate immune stimulation and/or host infection. The dysregulation of these tight interactions between host and microbiota can be responsible for important health disorders, including inflammation and sepsis. This review summarizes the molecular events leading to the establishment of postnatal immune tolerance and how pathogens can avoid host immunity and induce neonatal infections and sepsis.

Discordant temporal development of bacterial phyla and the emergence of core in the fecal microbiota of young children

“…The gradual development of microbiota may reflect the stepwise development of host physiology. For example, the most important cellular components of the gastrointestinal immune system are already present in fetal life (Tourneur and Chassin, 2013), but a newborn still has immature intestinal mucosal layer, immunological and metabolic functions (Fernandez et al, 2011;Jakobsson et al, 2014;Levy and Wynn, 2014;Pichichero, 2014). After a few months, infants are able to absorb fat-soluble compounds efficiently because of maturation of bile salt (Fernandez et al, 2011).…”

Caries and Periodontitis: Contesting the Conventional Wisdom on Their Aetiology

“…It is therefore also essential for the newborn baby to be exposed to numerous microorganisms in order to stimulate its own immune system. It is generally considered that the immune system inherited from the mother through the placenta consists mainly of IgG antibodies and it takes between 6 months up to 3 years before the baby's own immune system has reached a functional level, although the neonatal period seems to be most important for the immune adaptation and exposure to microorganisms [Karlsson et al, 1999;Tourneur and Chassin, 2013]. As a result, most of the microorganisms established early in life are regarded by tolerance as commensals and do not provoke a significant immune response so long as they colonize only the epithelial barriers and teeth and do not penetrate the mucosal lining or occur at niches not "normal" for them.…”

Bifidobacterium breve alters immune function and ameliorates DSS-induced inflammation in weanling rats

“…F ollowing delivery, mammalian neonates come out from a germ-free uterus to a highly contaminated extrauterine environment, in which they are exposed to many bacteria and antigens (1). During this process, trillions of microbes come to inhabit the mammalian neonatal intestine, and a complex symbiosis system termed microbiota is formed (1).…”

“…During this process, trillions of microbes come to inhabit the mammalian neonatal intestine, and a complex symbiosis system termed microbiota is formed (1). Microbiota is considered important for normal immunological development of the host.…”

“…For example, reports have shown reduced diversity in the intestinal microbiota and an association of reduced beneficial microbes, such as lactobacilli and bifidobacteria, with increased risk of allergic disease (2). Generally, bifidobacteria, a beneficial microbe, are more dominant in the intestinal microbiota of breastfed infants than in formula-fed infants (1,3). Additionally, the immune function of breastfed infants is reportedly different from that of formula-fed infants (4), and as a result, breastfeeding is thought to protect infants from diseases such as allergy and pneumonia (4).…”