Spatial and temporal key steps in early-life intestinal immune system development and education

A newborn's perspective on immune responses to food

In this review, we will highlight infants' immune responses to food, emphasizing the unique aspects of early-life immunity and the critical role of breast milk as a food dedicated to infants. Infants are susceptible to inflammatory responses rather than immune tolerance at the mucosal and skin barriers, necessitating strategies to promote oral tolerance that consider this susceptibility. Breast milk provides nutrients for growth and cell metabolism, including immune cells. The content of breast milk, influenced by maternal genetics and environmental exposures, prepares the infant's immune system for the outside world, including solid foods. To do this, breast milk promotes immune system development through antigen-specific and non-antigen-specific immune education by exposing the newborn to food and respiratory allergens and acting on three key targets for food allergy prevention: the gut microbiota, epithelial cells, and immune cells. Building knowledge of how the maternal exposome and human milk composition influence offspring's healthy immune development will lead to recommendations that meet the specific needs of the developing immune system and increase the chances of promoting an appropriate immune response to food in the long term.

Early-life vitamin A treatment rescues neonatal infection-induced durably impaired tolerogenic properties of celiac lymph nodes

Gut-draining mesenteric and celiac lymph nodes (mLNs and celLNs) critically contribute to peripheral tolerance toward food and microbial antigens by supporting the de novo induction of regulatory T cells (Tregs). These tolerogenic properties of mLNs and celLNs are stably imprinted within stromal cells (SCs) by microbial signals and vitamin A (VA), respectively. Here, we report that a single, transient gastrointestinal infection in the neonatal, but not adult, period durably abrogates the efficient Treg-inducing capacity of celLNs by altering the subset composition and gene expression profile of celLNSCs. These cells carry information about the early-life pathogen encounter until adulthood and durably instruct migratory dendritic cells entering the celLN with reduced tolerogenic properties. Mechanistically, transiently reduced VA levels cause long-lasting celLN functional impairment, which can be rescued by early-life treatment with VA. Together, our data highlight the therapeutic potential of VA to prevent sequelae post gastrointestinal infections in infants.

Probiotics induce intestinal IgA secretion in weanling mice potentially through promoting intestinal APRIL expression and modulating the gut microbiota composition

Intestinal infections are strongly associated with infant mortality, and intestinal immunoglobulin A (IgA) is important to protect infants from intestinal infections after weaning. This study aims to screen probiotics that can promote the production of intestinal IgA after weaning and further explore their potential mechanisms of action. In this study, probiotics promoting intestinal IgA production were screened in weanling mouse models. The results showed that oral administration of Bifidobacterium bifidum (B. bifidum) FL228.1 and Bifidobacterium bifidum (B. bifidum) FL276.1 significantly enhanced IgA levels in the small intestine and upregulated the expression of a proliferation-inducing ligand (APRIL) and its upstream regulatory factor toll-like receptor 4 (TLR4). Furthermore, B. bifidum FL228.1 upregulated the relative abundance of Lactobacillus, while B. bifidum FL276.1 increased the relative abundance of Marvinbryantia and decreased Mucispirillum, further elevating intestinal IgA levels. In summary, B. bifidum FL228.1 and B. bifidum FL276.1 can induce IgA production in the intestinal tract of weanling mice by promoting intestinal APRIL expression and mediating changes in the gut microbiota, thus playing a significant role in enhancing local intestinal immunity in infants.

Maternal polysorbate 80 exposure causes intestinal ILCs and CD4+ T cell developmental abnormalities in mouse offspring

This study aimed to investigate the transgenerational impacts of maternal intake of polysorbate 80 (P80), an emulsifier widely used in modern society, on the development of offspring immunity. Our results revealed that maternal P80 treatment led to impaired differentiation of innate lymphoid cells (ILCs) and CD4+ T cells in the small intestinal lamina propria (SiLP), resulting in intestinal dyshomeostasis in female offspring. Furthermore, we found that SiLP ILCs abundances were significantly altered in 0-day-old fetuses from P80-treated mothers, indicating a prenatal impact of P80-treated mothers on offspring immunity. Additionally, cesarean section and foster-nursing studies demonstrated that P80-induced altered SiLP ILCs in 0-day-old fetuses could further induce dysregulation of ILCs and CD4+ T cells in the SiLP, thus promoting intestinal dysregulation in offspring later in life. Overall, our findings suggest that maternal P80 intake could prenatally program the development of offspring immunity, exerting a significant and long-lasting impact.

Antibiotic use during pregnancy is linked to offspring gut microbial dysbiosis, barrier disruption, and altered immunity along the gut-lung axis

Antibiotic use during pregnancy is associated with increased asthma risk in children. Since approximately 25% of women use antibiotics during pregnancy, it is important to identify the pathways involved in this phenomenon. We investigate how mother-to-offspring transfer of antibiotic-induced gut microbial dysbiosis influences immune system development along the gut-lung axis. Using a mouse model of maternal antibiotic exposure during pregnancy, we immunophenotyped offspring in early life and after asthma induction. In early life, prenatal-antibiotic exposed offspring exhibited gut microbial dysbiosis, intestinal inflammation (increased fecal lipocalin-2 and IgA), and dysregulated intestinal ILC3 subtypes. Intestinal barrier dysfunction in the offspring was indicated by a FITC-dextran intestinal permeability assay and circulating lipopolysaccharide. This was accompanied by increased T-helper (Th)17 cell percentages in the offspring's blood and lungs in both early life and after allergy induction. Lung tissue additionally showed increased percentages of RORγt T-regulatory (Treg) cells at both time points. Our investigation of the gut-lung axis identifies early-life gut dysbiosis, intestinal inflammation, and barrier dysfunction as a possible developmental programming event promoting increased expression of RORγt in blood and lung CD4+ T cells that may contribute to increased asthma risk.

Prolonged dysbiosis and altered immunity under nutritional intervention in a physiological mouse model of severe acute malnutrition

Severe acute malnutrition (SAM) is a multifactorial disease affecting millions of children worldwide. It is associated with changes in intestinal physiology, microbiota, and mucosal immunity, emphasizing the need for multidisciplinary studies to unravel its full pathogenesis. We established an experimental model in which weanling mice fed a high-deficiency diet mimic key anthropometric and physiological features of SAM in children. This diet alters the intestinal microbiota (less segmented filamentous bacteria, spatial proximity to epithelium), metabolism (decreased butyrate), and immune cell populations (depletion of LysoDC in Peyer's patches and intestinal Th17 cells). A nutritional intervention leads to a fast zoometric and intestinal physiology recovery but to an incomplete restoration of the intestinal microbiota, metabolism, and immune system. Altogether, we provide a preclinical model of SAM and have identified key markers to target with future interventions during the education of the immune system to improve SAM whole defects.

Regulatory T cells in peripheral tissue tolerance and diseases

Maintenance of peripheral tolerance by CD4+Foxp3+ regulatory T cells (Tregs) is essential for regulating autoreactive T cells. The loss of function of Foxp3 leads to autoimmune disease in both animals and humans. An example is the rare, X-linked recessive disorder known as IPEX (Immune Dysregulation, Polyendocrinopathy, Enteropathy X-linked) syndrome. In more common human autoimmune diseases, defects in Treg function are accompanied with aberrant effector cytokines such as IFNγ. It has recently become appreciated that Tregs plays an important role in not only maintaining immune homeostasis but also in establishing the tissue microenvironment and homeostasis of non-lymphoid tissues. Tissue resident Tregs show profiles that are unique to their local environments which are composed of both immune and non-immune cells. Core tissue-residence gene signatures are shared across different tissue Tregs and are crucial to homeostatic regulation and maintaining the tissue Treg pool in a steady state. Through interaction with immunocytes and non-immunocytes, tissue Tregs exert a suppressive function via conventional ways involving contact dependent and independent processes. In addition, tissue resident Tregs communicate with other tissue resident cells which allows Tregs to adopt to their local microenvironment. These bidirectional interactions are dependent on the specific tissue environment. Here, we summarize the recent advancements of tissue Treg studies in both human and mice, and discuss the molecular mechanisms that maintain tissue homeostasis and prevent pathogenesis.

Xylan Prebiotics and the Gut Microbiome Promote Health and Wellbeing: Potential Novel Roles for Pentosan Polysulfate

This narrative review highlights the complexities of the gut microbiome and health-promoting properties of prebiotic xylans metabolized by the gut microbiome. In animal husbandry, prebiotic xylans aid in the maintenance of a healthy gut microbiome. This prevents the colonization of the gut by pathogenic organisms obviating the need for dietary antibiotic supplementation, a practice which has been used to maintain animal productivity but which has led to the emergence of antibiotic resistant bacteria that are passed up the food chain to humans. Seaweed xylan-based animal foodstuffs have been developed to eliminate ruminant green-house gas emissions by gut methanogens in ruminant animals, contributing to atmospheric pollution. Biotransformation of pentosan polysulfate by the gut microbiome converts this semi-synthetic sulfated disease-modifying anti-osteoarthritic heparinoid drug to a prebiotic metabolite that promotes gut health, further extending the therapeutic profile and utility of this therapeutic molecule. Xylans are prominent dietary cereal components of the human diet which travel through the gastrointestinal tract as non-digested dietary fibre since the human genome does not contain xylanolytic enzymes. The gut microbiota however digest xylans as a food source. Xylo-oligosaccharides generated in this digestive process have prebiotic health-promoting properties. Engineered commensal probiotic bacteria also have been developed which have been engineered to produce growth factors and other bioactive factors. A xylan protein induction system controls the secretion of these compounds by the commensal bacteria which can promote gut health or, if these prebiotic compounds are transported by the vagal nervous system, may also regulate the health of linked organ systems via the gut–brain, gut–lung and gut–stomach axes. Dietary xylans are thus emerging therapeutic compounds warranting further study in novel disease prevention protocols.

Revisiting the steps of Salmonella gut infection with a focus on antagonistic interbacterial interactions

A commensal microbial community is established in the mammalian gut during its development, and these organisms protect the host against pathogenic invaders. The hallmark of noninvasive Salmonella gut infection is the induction of inflammation via effector proteins secreted by the type III secretion system, which modulate host responses to create a new niche in which the pathogen can overcome the colonization resistance imposed by the microbiota. Several studies have shown that endogenous microbes are important to control Salmonella infection by competing for resources. However, there is limited information about antimicrobial mechanisms used by commensals and pathogens during these in vivo disputes for niche control. This review aims to revisit the steps that Salmonella needs to overcome during gut colonization-before and after the induction of inflammation-to achieve an effective infection. We focus on a series of reported and hypothetical antagonistic interbacterial interactions in which both contact-independent and contact-dependent mechanisms might define the outcome of the infection.