Petya Koleva

The Infant Gut Microbiome: Evidence for Obesity Risk and Dietary Intervention

Increasing globally, particularly in children, obesity is a serious public health issue and risk factor for overweight and metabolic disease in later life. Both in experimental animal and human studies, advances in gene sequencing technologies have yielded intriguing possibilities for the role of the gut microbiome in later development of overweight status. Before translating study findings into practice, we must first reconcile inconsistencies between animal experimentation, and human adult and infant studies. Recent evidence for associations with gut microbiota and infant weight gain or child weight status, implicate Bacteroides and Lactobacillus species. Dietary manipulation with human milk and pre/probiotic formulations holds promise for preventing obesity.

Fetal programming of overweight through the microbiome: boys are disproportionately affected

Maternal and childhood obesity in pregnancy are worrisome public health issues facing our world today. New gene sequencing methods have advanced our knowledge of the disruptive effect of birth interventions and postnatal exposures on the maturation of gut microbiota and immunity during infancy. Yet, little is known about the impact of maternal pregnancy overweight on gut microbes and related processes, and how this may affect overweight risk in offspring. To address this gap in knowledge, we surveyed human studies for evidence in children, infants and pregnant women to piece together the limited literature and generate hypotheses for future investigation. From this literature, we learned that higher Lactobacillus yet lower Bacteroides spp. colonization of gut microbiota within 3 months of birth predicted risk for infant and child overweight. The abundance of bifidobacteria and staphylococci also appeared to play a role in the association with overweight, as did infant fecal immunoglobulin A levels, glycoproteins of the gut immune system that are acquired from breast milk and produced by the infant. We proposed that pregnancy overweight influences the compositional structure of gut microbiota in infants through vertical transfer of microbiota and/or their metabolites during pregnancy, delivery and breastfeeding. Finally, we brought forward emerging evidence on sex dimorphism, as well as ethnic and geographic variation, in reported associations between maternal overweight-induced gut microbiota dysbiosis and overweight risk.

Microbial programming of health and disease starts during fetal life.

The pioneer microbiota of the neonatal gut are essential for gut maturation, and metabolic and immunologic programming. Recent research has shown that early bacterial colonization may impact the occurrence of disease later in life (microbial programming). Despite early conflicting evidence, it has long been considered that the womb is a sterile environment and human microbial colonization begins at birth. In the last few years, several findings have reiterated the presence of microbes in infant first stool (meconium) and pointed to the existence of in utero microbial colonization of the infant gut. The dominant bacterial taxa detected in meconium specimens belong to the Enterobacteriaceae family (Escherichia genus) and lactic acid bacteria (notably members of the genera Leuconostoc, Enterococcus, and Lactococcus). Maternal atopy promotes dominance of Enterobacteriaceae in newborn meconium, which in turn may lead to respiratory problems in the infant. This microbial interaction with the host immune system may in fact, originate during fetal life. Our review evaluates the evidence for an intrauterine origin of meconium microbiota, their composition and influences, and potential clinical implications on infant health.

Chemically Defined Diet Alters the Protective Properties of Fructo-Oligosaccharides and Isomalto-Oligosaccharides in HLA-B27 Transgenic Rats

Non-digestible oligosaccharides (NDO) were shown to reduce inflammation in experimental colitis, but it remains unclear whether microbiota changes mediate their colitis-modulating effects. This study assessed intestinal microbiota and intestinal inflammation after feeding chemically defined AIN-76A or rat chow diets, with or without supplementation with 8 g/kg body weight of fructo-oligosaccharides (FOS) or isomalto-oligosaccharides (IMO). The study used HLA-B27 transgenic rats, a validated model of inflammatory bowel disease (IBD), in a factorial design with 6 treatment groups. Intestinal inflammation and intestinal microbiota were analysed after 12 weeks of treatment. FOS and IMO reduced colitis in animals fed rat chow, but exhibited no anti-inflammatory effect when added to AIN-76A diets. Both NDO induced specific but divergent microbiota changes. Bifidobacteria and Enterobacteriaceae were stimulated by FOS, whereas copy numbers of Clostridium cluster IV were decreased. In addition, higher concentrations of total short-chain fatty acids (SCFA) were observed in cecal contents of rats on rat chow compared to the chemically defined diet. AIN-76A increased the relative proportions of propionate, iso-butyrate, valerate and iso-valerate irrespective of the oligosaccharide treatment. The SCFA composition, particularly the relative concentration of iso-butyrate, valerate and iso-valerate, was associated (P≤0.004 and r≥0.4) with increased colitis and IL-1 β concentration of the cecal mucosa. This study demonstrated that the protective effects of fibres on colitis development depend on the diet. Although diets modified specific cecal microbiota, our study indicates that these changes were not associated with colitis reduction. Intestinal inflammation was positively correlated to protein fermentation and negatively correlated with carbohydrate fermentation in the large intestine.

CD71 + erythroid suppressor cells impair adaptive immunity against Bordetella pertussis

Infant’s immune system cannot control infection or respond to vaccination as efficiently as older individuals, a phenomenon that has been attributed to immunological immaturity. Recently, we challenged this notion and proposed the presence of actively immunosuppressive and physiologically enriched CD71+ erythroid cells in neonates. Here we utilized Bordetella pertussis, a common neonatal respiratory tract pathogen, as a proof of concept to investigate the role of these cells in adaptive immunity. We observed that CD71+ cells have distinctive immunosuppressive properties and prevent recruitment of immune cells to the mucosal site of infection. CD71+ cells ablation unleashed induction of B. pertussis-specific protective cytokines (IL-17 and IFN-γ) in the lungs and spleen upon re-infection or vaccination. We also found that CD71+ cells suppress systemic and mucosal B. pertussis-specific antibody responses. Enhanced antigen-specific adaptive immunity following CD71+ cells depletion increased resistance of mice to B. pertussis infection. Furthermore, we found that human cord blood CD71+ cells also suppress T and B cell functions in vitro. Collectively, these data provide important insight into the role of CD71+ erythroid cells in adaptive immunity. We anticipate our results will spark renewed investigation in modulating the function of these cells to enhance host defense to infections in newborns.

Erythroid Suppressor Cells Compromise Neonatal Immune Response against Bordetella pertussis

Newborns are highly susceptible to infection. The underlying mechanism of neonatal infection susceptibility has generally been associated with neonatal immune cell immaturity. In this study, we challenged this notion and built upon our recent discovery that neonates are physiologically enriched with erythroid TER119+CD71+ cells (Elahi et al. 2013. Nature 504: 158–162). We have used Bordetella pertussis, a common neonatal respiratory tract infection, as a proof of concept to investigate the role of these cells in newborns. We found that CD71+ cells have distinctive immune-suppressive properties and suppress innate immune responses against B. pertussis infection. CD71+ cell ablation unleashed innate immune response and restored resistance to B. pertussis infection. In contrast, adoptive transfer of neonatal CD71+ cells into adult recipients impaired their innate immune response to B. pertussis infection. Enhanced innate immune response to B. pertussis was characterized by increased production of protective cytokines IFN-γ, TNF-α, and IL-12, as well as recruitment of NK cells, CD11b+, and CD11c+ cells in the lung. Neonatal and human cord blood CD71+ cells express arginase II, and this enzymatic activity inhibits phagocytosis of B. pertussis in vitro. Thus, our study challenges the notion that neonatal infection susceptibility is due to immune cell–intrinsic defects and instead highlights active immune suppression mediated by abundant CD71+ cells in the newborn. Our findings provide additional support for the novel theme in neonatal immunology that immunosuppression is essential to dampen robust immune responses in the neonate. We anticipate that our results will spark renewed investigation in modulating the function of these cells and developing novel strategies for enhancing host defense to infections in newborns.

Maternal depressive symptoms linked to reduced fecal Immunoglobulin A concentrations in infants

Secretory Immunoglobulin A (sIgA) plays a critical role to infant gut mucosal immunity. Delayed IgA production is associated with greater risk of allergic disease. Murine models of stressful events during pregnancy and infancy show alterations in gut immunity and microbial composition in offspring, but little is known about the stress-microbiome-immunity pathways in humans. We investigated differences in infant fecal sIgA concentrations according to the presence of maternal depressive symptoms during and after pregnancy. A subsample of 403 term infants from the Canadian Healthy Infant Longitudinal Development (CHILD) cohort were studied. Their mothers completed the Center of Epidemiologic Studies Depression Scale when enrolled prenatally and again postpartum. Quantified by Immundiagnostik sIgA ELISA kit, sIgA from infant stool was compared across maternal depressive symptom categories using Mann-Whitney U-tests and logistic regression models that controlled for various covariates. Twelve percent of women reported clinically significant depressive symptoms only prenatally, 8.7% had only postpartum symptoms and 9.2% had symptoms both pre and postnatally. Infants born to mothers with pre and postnatal symptoms had significantly lower median sIgA concentrations than those in the reference group (4.4 mg/g feces vs. 6.3 mg/g feces; p = 0.033). The odds for sIgA concentrations in the lowest quartile was threefold higher (95% CI: 1.25-7.55) when mothers had pre and postnatal symptoms, after controlling for breastfeeding status, infant age, antibiotics exposure and other covariates. Postnatal symptoms were not associated with fecal sIgA, independently of breastfeeding status. Infants born to mothers with depressive symptoms appear to have lower fecal sIgA concentrations, predisposing them to higher risk for allergic disease.

CD71+ Erythroid Suppressor Cells Promote Fetomaternal Tolerance through Arginase-2 and PDL-1

Survival of the allogeneic pregnancy depends on the maintenance of immune tolerance to paternal alloantigens at the fetomaternal interface. Multiple localized mechanisms contribute to the fetal evasion from the mother’s immune rejection as the fetus is exposed to a wide range of stimulatory substances such as maternal alloantigens, microbes and amniotic fluids. In this article, we demonstrate that CD71+ erythroid cells are expanded at the fetomaternal interface and in the periphery during pregnancy in both humans and mice. These cells exhibit immunosuppressive properties, and their abundance is associated with a Th2 skewed immune response, as their depletion results in a proinflammatory immune response at the fetomaternal interface. In addition to their function in suppressing proinflammatory responses in vitro, maternal CD71+ erythroid cells inhibit an aggressive allogeneic response directed against the fetus such as reduction in TNF-α and IFN-γ production through arginase-2 activity and PD-1/programmed death ligand-1 (PDL-1) interactions. Their depletion leads to the failure of gestation due to the immunological rejection of the fetus. Similarly, fetal liver CD71+ erythroid cells exhibit immunosuppressive activity. Therefore, immunosuppression mediated by CD71+ erythroid cells on both sides (mother/fetus) is crucial for fetomaternal tolerance. Thus, our results reveal a previously unappreciated role for CD71+ erythroid cells in pregnancy and indicate that these cells mediate homeostatic immunosuppressive/immunoregulatory responses during pregnancy.

Sex-specific impact of asthma during pregnancy on infant gut microbiota

Asthma during pregnancy is associated with retardation of fetal growth in a sex-specific manner. Lactobacilli microbes influence infant growth. This study aimed to determine whether lactobacilli and other microbes are reduced in the gut of infants born to an asthmatic mother, and whether this differs by the sex of the infant. Mother-infant pairs (N=1021) from the Canadian Healthy Infant Longitudinal Development full-term cohort were studied. The abundance of infant faecal microbiota at 3–4 months, profiled by gene sequencing, was compared between both women with and without asthma treatment during pregnancy. Infant sex, maternal ethnicity, pre-pregnancy overweight and atopy status, birth mode, breastfeeding status and intrapartum antibiotic treatment were tested as covariates. Independent of birth mode and other covariates, male, Caucasian infants born to women with prenatal asthma harboured fewer lactobacilli in the gut at 3–4 months of age. If asthmatic mothers had pre-pregnancy overweight, the abundance of Lactobacillus in males was further reduced in the infant gut, whereas the microbiota of female infants was enriched with Bacteroidaceae. Similar differences in infant gut microbial composition according to maternal prenatal asthma status were also more evident among women with food or environmental allergies. Gut lactobacilli were less abundant in male infants, but Bacteroidaceae were more abundant in female infants at 3–4 months of age, following maternal asthma during pregnancy. Gut lactobacilli are less abundant at 3–4 months in male but not female infants following maternal prenatal asthma http://ow.ly/jXnl30fU9xH

Worldwide Variation in Human Milk Metabolome: Indicators of Breast Physiology and Maternal Lifestyle?

Human milk provides essential substrates for the optimal growth and development of a breastfed infant. Besides providing nutrients to the infant, human milk also contains metabolites which form an intricate system between maternal lifestyle, such as the mother’s diet and the gut microbiome, and infant outcomes. This study investigates the variation of these human milk metabolites from five different countries. Human milk samples (n = 109) were collected one month postpartum from Australia, Japan, the USA, Norway, and South Africa and were analyzed by nuclear magnetic resonance. The partial least squares discriminant analysis (PLS-DA) showed separation between either maternal countries of origin or ethnicities. Variation between countries in concentration of metabolites, such as 2-oxoglutarate, creatine, and glutamine, in human milk, between countries, could provide insights into problems, such as mastitis and/or impaired functions of the mammary glands. Several important markers of milk production, such as lactose, betaine, creatine, glutamate, and glutamine, showed good correlation between each metabolite. This work highlights the importance of milk metabolites with respect to maternal lifestyle and the environment, and also provides the framework for future breastfeeding and microbiome studies in a global context.