Maternal diet modulates the infant microbiome and intestinal Flt3L necessary for dendritic cell development and immunity to respiratory infection

A gut-focused perinatal dietary intervention is associated with lower alpha diversity of the infant gut microbiota: results from a randomised controlled trial

OBJECTIVES

In experimental models, the prenatal diet influences gut microbiota composition in mothers and offspring; however, it is unclear whether this occurs in humans. We investigated the effects of a gut-focused perinatal dietary intervention on maternal and infant gut microbiota composition four weeks after birth.

METHODS

This randomised controlled trial randomised pregnant women to receive dietary advice as part of standard care, or additionally receive a dietary intervention focused on the Australian Dietary Guidelines and increasing prebiotic and probiotic/fermented food intakes (ACTRN12616000936426). Study assessments occurred from gestation week 26 (baseline) to four weeks postpartum (follow-up). Faecal samples, collected at baseline for mothers, and follow-up for mothers and infants, underwent 16SrRNA sequencing. The primary outcome was a between-group mean difference in infant faecal Shannon index. Secondary outcomes included between-group differences in other microbiota measures, including maternal change from baseline CLR-transformed Prevotella abundance.

RESULTS

Forty-four women and 45 infants completed the study. The mean Shannon index of infants in the intervention group was -0.35 (95% CI: -0.64, -0.06, SD: 0.52) units lower than control group infants, corresponding to a medium effect size (Cohen's D: -0.74, 95% CI: -1.34, -0.13). The findings were similar using other metrics of α-diversity. There were no between-group differences in β-diversity, nor any differentially abundant taxa in infants. The intervention increased abundances of the genus Prevotella in mothers compared to controls.

DISCUSSION

This gut-focused perinatal dietary intervention was associated with differences in the maternal and infant gut microbiota composition. Larger studies are required to replicate and extend these findings.

Lifelong partners: Gut microbiota-immune cell interactions from infancy to old age

Our immune system and gut microbiota are intricately coupled from birth, both going through maturation during early life and senescence during aging almost in a synchronized fashion. The symbiotic relationship between the human host and microbiota is critically dependent on a healthy immune system to keep our microbiota in check, while the microbiota provides essential functions to promote the development and fitness of our immune system. The partnership between our immune system and microbiota is particularly important during early life, when microbial ligands and metabolites shape the development of the immune cells and immune tolerance; during aging, having sufficient beneficial gut bacteria is critical for the maintenance of intact mucosal barriers, immune metabolic fitness, and strong immunity against pathogens. The immune system during childhood is programmed, with the support of the microbiota, to develop robust immune tolerance, and limit autoimmunity and metabolic dysregulation, which are prevalent during aging. This review comprehensively explores the mechanistic underpinnings of gut microbiota-immune cell interactions during infancy and old age, with the goal to gain a better understanding of potential strategies to leverage the gut microbiota to combat age-related immune decline.

Jian'er Qiangshen Ointment Treating Bronchial Asthma by Inhibiting Lung Inflammation and Regulating Intestinal Microbiota

OBJECTIVE

To investigate the ameliorative effects and mechanisms of Jian'er Qiangshen Ointment (JEQS) on asthma.

METHODS

Twenty-four BALB/c mice were randomly and equally divided into four groups: blank control, ovalbumin (OVA), OVA + dexamethasone (DXMS), and OVA + JEQS. Lung tissue sections were isolated for H&E and Masson staining, and inflammatory factor levels were measured. Ultra-high performance liquid chromatography-time-of-flight mass spectrometry (UHPLC-TOF-MS) was employed to analyze and identify blood components in mice following intragastric administration of JEQS extract. Network pharmacology analysis was subsequently utilized to predict the pharmacological targets and mechanisms of JEQS in asthma treatment. 16S rRNA sequencing was conducted to determine bacterial community composition and diversity.

RESULT

Animal experiments indicated that compared to the OVA group, the OVA + drug groups (DXMS and JEQS) exhibited milder asthma symptoms and significantly improved pathological changes. JEQS significantly reduced IFN-γ, IL-4, IL-5, and IL-13 levels in lung tissue.

CONCLUSION

Through network pharmacology and 16S rRNA sequencing, JEQS ointment was found to alleviate asthma-related inflammatory responses and improve asthma symptoms via multi-target mechanisms and modulation of intestinal microbiota. Network pharmacology revealed 28 effective components in JEQS for asthma treatment, with α-linolenic acid, 9-oxononanoic acid, inosine, linoleic acid, and amygdalin as primary active constituents. One hundred core targets were identified, including AKT1, IL-6, ALB, TNF, and MAPK3. 16S rRNA sequencing demonstrated increased proportions of Proteobacteria and Actinobacteria following JEQS treatment. Probiotics such as Clostridium, Escherichia, Bacteroides, and Candidatus Saccharimonas became dominant microbiota.

The gut microbiota-immune-brain axis: Therapeutic implications

The microbiota-gut-brain axis has major implications for human health including gastrointestinal physiology, brain function, and behavior. The immune system represents a key pathway of communication along this axis with the microbiome implicated in neuroinflammation in health and disease. In this review, we discuss the mechanisms as to how the gut microbiota interacts with the brain, focusing on innate and adaptive immunity that are often disrupted in gut-brain axis disorders. We also consider the implications of these observations and how they can be advanced by interdisciplinary research. Leveraging an increased understanding of how these interactions regulate immunity has the potential to usher in a new era of precision neuropsychiatric clinical interventions for psychiatric, neurodevelopmental, and neurological disorders.

Maternal Gut Inflammation Aggravates Acute Liver Failure Through Facilitating Ferroptosis via Altering Gut Microbial Metabolism in Offspring

Microbial transmission from mother to infant is important for offspring microbiome formation and health. However, it is unclear whether maternal gut inflammation (MGI) during lactation influences mother-to-infant microbial transmission and offspring microbiota and disease susceptibility. In this study, it is found that MGI during lactation altered the gut microbiota of suckling pups by shaping the maternal microbiota in the gut and mammary glands. MGI-induced changes in the gut microbiota of suckling pups lasted into adulthood, resulting in the exacerbation of acute liver failure (ALF) caused by acetaminophen (APAP) in offspring. Specifically, MGI reduced the abundance of Lactobacillus reuteri (L. reuteri) and its metabolite indole-3-acetic acid (IAA) level in adult offspring. L. reuteri and IAA alleviated ALF in mice by promoting intestinal IL-22 production. Mechanistically, IL-22 limits APAP-induced excessive oxidative stress and ferroptosis by activating STAT3. The intestinal abundances of L. reuteri and IAA are inversely associated with the progression of patients with ALF. Overall, the study reveals the role of MGI in mother-to-infant microbial transmission and disease development in offspring, highlighting potential strategies for intervention in ALF based on the IAA-IL-22-STAT3 axis.

Tubular epithelial cell-derived Flt3L is required for type 1 conventional dendritic cell (cDC1) activation and expansion in promoting the recovery in acute kidney injury

INTRODUCTION

Dendritic cells (DCs) play a crucial role in the recovery following acute kidney injury (AKI). Fms-related tyrosine kinase 3 ligand (Flt3L) is essential for the generation and maintenance of DCs. However, the cellular source of Flt3L in the kidney and its contribution on renal DC function during AKI remain unclear.

METHODS

An online available dataset and specimens collected from AKI were used to analyze FLT3L expression. Wild type (WT) mice, T cell-deficient (TcraKO), and type 1 conventional DC (cDC1)-deficient (Irf8KO) mice underwent ischemia-reperfusion (IR) injury to induce AKI. These mice were treated with either mouse recombinant Flt3L (rFlt3L) or the Flt3 inhibitor gilteritinib. In vitro, experiments with human and murine bone marrow (BM) cells, HK-2 cell line, Jurkat T cells, the monocyte cell line THP1, CD4+ T cells and cDC1s were conducted to validate the link between Flt3L and DCs.

RESULTS

Circulating FLT3L levels were significantly elevated in patients with AKI. This correlated with the degree of kidney dysfunction observed in these patients. Flt3L was expressed in and released by tubular epithelial cells, with minimal expression in immune cells. Flt3L primarily promoted the activation and expansion of cDC1s and polarization of CD4+T cells in vitro, an effect that was blocked by dephosphorylation of AKT and ERK signaling with gilteritinib. In vivo, gilteritinib worsened the outcomes after AKI by decreasing kidney cDC1s expansion. Conversely, therapeutic administration of rFlt3L promoted renal cDC1 accumulation and improved kidney function in mice with AKI. However, in Irf8KO mice, rFlt3 failed to improve outcomes.

CONCLUSION

Flt3L is upregulated in both humans and mice during IRI-induced AKI and is likely produced by tubular epithelial cells. It mainly promotes the expansion and activation of kidney cDC1 cells, thereby reducing the severity of AKI in mice. These findings suggest that Flt3L-dependent, cDC1-targeted immunotherapy could be a promising strategy for treating AKI.

Novel anti-inflammatory properties of mannose oligosaccharides in the treatment of inflammatory bowel disease via LGALS3 modulation

This study investigates the role of Gum Arabic Mannose Oligosaccharides (GA-MOS) in modulating gut microbiota and alleviating symptoms of Inflammatory Bowel Disease (IBD). Employing both in vitro and in vivo models, we explored how GA-MOS influences microbial communities, particularly focusing on their capacity to enhance health-associated bacteria and reduce pathogenic species within the gut environment. Our findings reveal that GA-MOS treatment significantly altered the gut microbiota composition, increasing the abundance of anti-inflammatory bacteria while decreasing pro-inflammatory species, thus contributing to a reduction in gut inflammation and an improvement in intestinal barrier function. Detailed molecular analyses further demonstrated that these changes in microbiota were associated with modifications in the host's immune response, particularly through the suppression of key inflammatory pathways and cytokines involved in IBD progression. These results underscore the potential of dietary polysaccharides like GA-MOS as therapeutic agents in managing dysbiosis and inflammatory conditions in the gut, offering a promising approach for enhancing microbial health and overall disease management in IBD. This study provides novel insights into the bioactive properties of MOS and their interactions with gut microbiota, suggesting broader implications for their use in microbiome-centered therapies.

Clinical implications of maternal multikingdom transmissions and early-life microbiota

Mother-to-infant transmission of the bacteriome, virome, mycobiome, archaeome, and their mobile genetic elements has been recognised in nature as an important step for the infant to acquire and maintain a healthy early-life (from birth till age 3 years) microbiota. A comprehensive overview of other maternal multikingdom transmissions remains unavailable, except for that of the bacteriome. Associations between microorganisms and diseases throughout the human life span have been gradually discovered; however, whether these microorganisms are maternally derived and how they concomitantly interact with other microbial counterparts remain poorly understood. This Review first discusses the current understanding of maternal multikingdom transmissions, their contributions to the development of early-life microbiota, and the primary factors that influence the transmission processes. The clinical implications of the inherited microbiota on human health in early life have been emphasised upon next, along with highlighting of knowledge gaps that should be addressed in future research. Finally, interventions to restore typical vertical transmission or disturbed early-life microbiota have been discussed as potential therapeutic approaches.

Explore Alteration of Lung and Gut Microbiota in a Murine Model of OVA-Induced Asthma Treated by CpG Oligodeoxynucleotides

Aim

We sought to investigate the impact of CpG oligodeoxynucleotides (CpG-ODN) administration on the lung and gut microbiota in asthmatic mice, specifically focusing on changes in composition, diversity, and abundance, and to elucidate the microbial mechanisms underlying the therapeutic effects of CpG-ODN and identify potential beneficial bacteria indicative of its efficacy.

Methods

HE staining were used to analyze inflammation in lung, colon and small intestine tissues. High-throughput sequencing technology targeting 16S rRNA was employed to analyze the composition, diversity, and correlation of microbiome in the lung, colon and small intestine of control, model and CpG-ODN administration groups.

Results

(1) Histopathologically, both lung and intestinal tissue in asthmatic mice exhibited significant structural damage and inflammatory response, whereas the structure of both lung and intestinal tissue approached normal levels, accompanied by a notable improvement in the inflammatory response after CpG-ODN treatment. (2) In the specific microbiota composition analysis, bacterial dysbiosis observed in the asthmatic mice, accompanied by enrichment of Proteobacteria found to cause lung and intestinal epithelial damage and inflammatory reaction. After CpG-ODN administration, bacterial dysbiosis was improved, and a notable enrichment of beneficial bacteria, indicating a novel microecology. Meanwhile Oscillospira and Clostridium were identified as two biomarkers of the CpG-ODN treatment. (3) Heatmap analysis revealed significant correlations among lung, small intestine, and colon microbiota.

Conclusion

CpG-ODN treatment can ameliorate OVA-induced asthma in mice. One side, preserving the structural integrity of the lung and intestine, safeguarding the mucosal physical barrier, the other side, improving the dysbiosis of lung and gut microbiota in asthmatic mice. Beneficial bacteria and metabolites take up microecological advantages, regulate immune cells and participate in the mucosal immune response to protect the immune barrier. Meanwhile, Oscillospira and Clostridium as biomarkers for CpG-ODN treatment, has reference significance for exploring precise Fecal microbiota transplantation treatment for asthma.

Antibiotic-mediated dysbiosis leads to activation of inflammatory pathways

Introduction

The gut microbiota plays a pivotal role in influencing host health, through the production of metabolites and other key signalling molecules. While the impact of specific metabolites or taxa on host cells is well-documented, the broader impact of a disrupted microbiota on immune homeostasis is less understood, which is particularly important in the context of the increasing overuse of antibiotics.

Methods

Female C57BL/6 mice were gavaged twice daily for four weeks with Vancomycin, Polymyxin B, or PBS (control). Caecal microbiota composition was assessed via 16S rRNA sequencing and caecal metabolites were quantified with NMR spectroscopy. Immune profiles of spleen and mesenteric lymph nodes (MLNs) were assessed by flow cytometry, and splenocytes assessed for ex vivo cytokine production. A generalised additive model approach was used to examine the relationship between global antibiotic consumption and IBD incidence.

Results

Antibiotics significantly altered gut microbiota composition, reducing alpha-diversity. Acetate and butyrate were significantly reduced in antibiotic groups, while propionate and succinate increased in Vancomycin and PmB-treated mice, respectively. The MLNs and spleen showed changes only to DC numbers. Splenocytes from antibiotic-treated mice stimulated ex vivo exhibited increased production of TNF. Epidemiological analysis revealed a positive correlation between global antibiotic consumption and IBD incidence.

Discussion

Our findings demonstrate that antibiotic-mediated dysbiosis results in significantly altered short-chain fatty acid levels but immune homeostasis in spleen and MLNs at steady state is mostly preserved. Non-specific activation of splenocytes ex vivo, however, revealed mice with perturbed microbiota had significantly elevated production of TNF. Thus, this highlights antibiotic-mediated disruption of the gut microbiota may program the host towards dysregulated immune responses, predisposing to the development of TNF-associated autoimmune or chronic inflammatory disease.

Short-chain fatty acids in fetal development and metabolism

Short-chain fatty acids (SCFAs), primarily derived from gut microbiota, play a role in regulating fetal development; however, the mechanism remains unclear. Fetal SCFAs levels depends on maternal SCFAs transported via the placenta. Metabolic stress, particularly from diabetes and obesity, can disrupt maternal SCFAs levels, impairing fetal metabolic reprogramming. Dysregulated SCFAs may negatively impact the development of the fetal cardiovascular, nervous, and immune systems, potentially contributing to adverse outcomes in adulthood. This review focuses on recent advances regarding the role of maternal SCFAs in shaping the metabolic profile of offspring, especially in the context of various maternal metabolic disorders. Given that SCFAs may influence fetal development through the placenta-embryo axis, targeted SCFAs supplementation could be a promising strategy against developmental diseases associated with intrauterine risk factors.

Pre-pregnancy obesity is associated with an altered maternal metabolome and reduced Flt3L expression in preterm birth

Mechanisms linking pre-pregnancy obesity to increased preterm birth risk are unclear. Here, we examined the impact of pre-pregnancy obesity on metabolites, Fms-related tyrosine kinase 3 ligand (Flt3L), and proinflammatory cytokine profiles in preterm birth. We used cytokine bead array, ELISA and Gas Chromatography-Mass Spectrometry (GC-MS) to determine cytokine and metabolite profiles in maternal and cord blood samples from 124 pregnant women in Australia, who gave birth at term (n = 86) or preterm (n = 38). Besides the expected variations in birth weight and gestational age, all demographic characteristics, including pre-pregnancy body mass index, were similar between the term and preterm birth groups. Mothers in the preterm birth group had reduced Flt3L (P = 0.002) and elevated IL-6 (P = 0.002) compared with term birthing mothers. Among mothers who gave birth preterm, those with pre-pregnancy obesity had lower Flt3L levels (P = 0.02) compared with lean mothers. Flt3L and IL-6 were similar in cord blood across both groups, but TNFα levels (P = 0.02) were reduced in preterm newborns. Metabolomic analysis revealed significant shifts in essential metabolites in women with pre-pregnancy obesity, some of which were linked to preterm births. Our findings suggest that maternal pre-pregnancy obesity alters the metabolome and reduces Flt3L expression, potentially increasing risk of preterm birth.

Mechanisms and risk factors for perinatal allergic disease

Allergies are among the top causes of chronic disease in children. Their pathogenesis classically involves T helper 2 (Th2)-type inflammation driven by IgE-mediated allergen sensing. Triggers influencing allergic disease occur early in life, including before birth. The immature fetal immune system and mucosal barriers undergo periods of plasticity that are open to longitudinal programming by maternal influence. Evidence supports the importance of the maternal immune system in shaping perinatal immunity, as the transfer of cytokines, antibodies, and cells promotes offspring protection from pathogens. However, the same components may lead to allergic predisposition. Maternal-fetal interactions are further modified by epigenetic, metabolic, dietary, and microbiome-mediated effects. Here, we review how diverse maternal exposures and mediators signal across the placenta and through nursing perinatally to promote future tolerance or enhance reactivity against allergens. Improved understanding of the mechanisms predisposing for allergic disease in early life can guide the development of new therapeutics and preventative lifestyle modifications.

A maternal high-fat diet predisposes to infant lung disease via increased neutrophil-mediated IL-6 trans-signaling

A poor maternal diet during pregnancy predisposes the infant to severe lower respiratory tract infections (sLRIs), which, in turn, increases childhood asthma risk; however, the underlying mechanisms remain poorly understood. Here, we show that the offspring of high-fat diet (HFD)-fed mothers (HFD-reared pups) developed an sLRI following pneumovirus inoculation in early life and subsequent asthma in later life upon allergen exposure. Prior to infection, HFD-reared pups developed microbial dysbiosis and low-grade systemic inflammation (LGSI), characterized by hyperneutropoiesis in the liver and elevated inflammatory cytokine expression, most notably granulocyte-colony stimulating factor (G-CSF), interleukin-17A (IL-17A), IL-6 and soluble IL-6 receptor (sIL-6R) (indicative of IL-6 trans-signaling) in the circulation and multiple organs but most prominently the liver. Inhibition of IL-6 trans-signaling using sgp130Fc transgenic mice or via specific genetic deletion of IL-6Ra on neutrophils conferred protection against both diseases. Taken together, our findings suggest that a maternal HFD induces neonatal LGSI that predisposes to sLRI and subsequent asthma via neutrophil-mediated IL-6 trans-signaling.

Dual therapy with corticosteroid ablates the beneficial effect of DP2 antagonism in chronic experimental asthma

Prostaglandin D2 (PGD2) signals via the DP1 and DP2 receptors. In Phase II trials, DP2 antagonism decreased airway inflammation and airway smooth muscle (ASM) area in moderate-to-severe asthma patients. However, in Phase III, DP2 antagonism failed to lower the rate of exacerbations, and DP2 as a target was shelved. Here, using a preclinical model of chronic experimental asthma, we demonstrate that rhinovirus-induced exacerbations increase PGD2 release, mucus production, transforming growth factor (TGF)-β1 and type-2 inflammation. DP2 antagonism or DP1 agonism ablates these phenotypes, increases epithelial EGF expression and decreases ASM area via increased IFN-γ. In contrast, dual DP1-DP2 antagonism or dual corticosteroid/DP2 antagonism, which attenuates endogenous PGD2, prevented ASM resolution. We demonstrate that DP2 antagonism resolves ASM remodelling via PGD2/DP1-mediated upregulation of IFN-γ expression, and that dual DP2 antagonism/corticosteroid therapy, as often occurred in the human trials, impairs the efficacy of DP2 antagonism by suppressing endogenous PGD2 and IFN-γ production.

The interplay between diet and the gut microbiome: implications for health and disease

Diet has a pivotal role in shaping the composition, function and diversity of the gut microbiome, with various diets having a profound impact on the stability, functionality and diversity of the microbial community within our gut. Understanding the profound impact of varied diets on the microbiome is crucial, as it will enable us not only to make well-informed dietary decisions for better metabolic and intestinal health, but also to prevent and slow the onset of specific diet-related diseases that stem from suboptimal diets. In this Review, we explore how geographical location affects the gut microbiome and how different diets shape its composition and function. We examine the mechanisms by which whole dietary regimes, such as the Mediterranean diet, high-fibre diet, plant-based diet, high-protein diet, ketogenic diet and Western diet, influence the gut microbiome. Furthermore, we underscore the need for exhaustive studies to better understand the causal relationship between diet, host and microorganisms for the development of precision nutrition and microbiome-based therapies.

Reduce, reinforce, and replenish: safeguarding the early-life microbiota to reduce intergenerational health disparities

Socioeconomic (SE) disparity and health inequity are closely intertwined and associated with cross-generational increases in the rates of multiple chronic non-communicable diseases (NCDs) in North America and beyond. Coinciding with this social trend is an observed loss of biodiversity within the community of colonizing microbes that live in and on our bodies. Researchers have rightfully pointed to the microbiota as a key modifiable factor with the potential to ease existing health inequities. Although a number of studies have connected the adult microbiome to socioeconomic determinants and health outcomes, few studies have investigated the role of the infant microbiome in perpetuating these outcomes across generations. It is an essential and important question as the infant microbiota is highly sensitive to external forces, and observed shifts during this critical window often portend long-term outcomes of health and disease. While this is often studied in the context of direct modulators, such as delivery mode, family size, antibiotic exposure, and breastfeeding, many of these factors are tied to underlying socioeconomic and/or cross-generational factors. Exploring cross-generational socioeconomic and health inequities through the lens of the infant microbiome may provide valuable avenues to break these intergenerational cycles. In this review, we will focus on the impact of social inequality in infant microbiome development and discuss the benefits of prioritizing and restoring early-life microbiota maturation for reducing intergenerational health disparities.

Microbiota-derived short chain fatty acids in pediatric health and diseases: from gut development to neuroprotection

The infant gut microbiota undergoes significant changes during early life, which are essential for immune system maturation, nutrient absorption, and metabolic programming. Among the various microbial metabolites, short-chain fatty acids (SCFAs), primarily acetate, propionate, and butyrate, produced through the fermentation of dietary fibers by gut bacteria, have emerged as critical modulators of host-microbiota interactions. SCFAs serve as energy sources for colonic cells and play pivotal roles in regulating immune responses, maintaining gut barrier integrity, and influencing systemic metabolic pathways. Recent research highlights the potential neuroprotective effects of SCFAs in pediatric populations. Disruptions in gut microbiota composition and SCFA production are increasingly associated with a range of pediatric health issues, including obesity, allergic disorders, inflammatory bowel disease (IBD), and neurodevelopmental disorders. This review synthesizes current knowledge on the role of microbiota-derived SCFAs in pediatric health, emphasizing their contributions from gut development to neuroprotection. It also underscores the need for further research to unravel the precise mechanisms by which SCFAs influence pediatric health and to develop targeted interventions that leverage SCFAs for therapeutic benefits.

The emerging roles of microbiome and short-chain fatty acids in the pathogenesis of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease that affects premature infants and leads to long-term pulmonary complications. The pathogenesis of BPD has not been fully elucidated yet. In recent years, the microbiome and its metabolites, especially short-chain fatty acids (SCFAs), in the gut and lungs have been demonstrated to be involved in the development and progression of the disease. This review aims to summarize the current knowledge on the potential involvement of the microbiome and SCFAs, especially the latter, in the development and progression of BPD. First, we introduce the gut-lung axis, the production and functions of SCFAs, and the role of SCFAs in lung health and diseases. We then discuss the evidence supporting the involvement of the microbiome and SCFAs in BPD. Finally, we elaborate on the potential mechanisms of the microbiome and SCFAs in BPD, including immune modulation, epigenetic regulation, enhancement of barrier function, and modulation of surfactant production and the gut microbiome. This review could advance our understanding of the microbiome and SCFAs in the pathogenesis of BPD, which also helps identify new therapeutic targets and facilitate new drug development.

The role of plasmacytoid dendritic cells (pDCs) in immunity during viral infections and beyond

Type I and III interferons (IFNs) are essential for antiviral immunity and act through two different but complimentary pathways. First, IFNs activate intracellular antimicrobial programs by triggering the upregulation of a broad repertoire of viral restriction factors. Second, IFNs activate innate and adaptive immunity. Dysregulation of IFN production can lead to severe immune system dysfunction. It is thus crucial to identify and characterize the cellular sources of IFNs, their effects, and their regulation to promote their beneficial effects and limit their detrimental effects, which can depend on the nature of the infected or diseased tissues, as we will discuss. Plasmacytoid dendritic cells (pDCs) can produce large amounts of all IFN subtypes during viral infection. pDCs are resistant to infection by many different viruses, thus inhibiting the immune evasion mechanisms of viruses that target IFN production or their downstream responses. Therefore, pDCs are considered essential for the control of viral infections and the establishment of protective immunity. A thorough bibliographical survey showed that, in most viral infections, despite being major IFN producers, pDCs are actually dispensable for host resistance, which is achieved by multiple IFN sources depending on the tissue. Moreover, primary innate and adaptive antiviral immune responses are only transiently affected in the absence of pDCs. More surprisingly, pDCs and their IFNs can be detrimental in some viral infections or autoimmune diseases. This makes the conservation of pDCs during vertebrate evolution an enigma and thus raises outstanding questions about their role not only in viral infections but also in other diseases and under physiological conditions.

The gut-airway microbiome axis in health and respiratory diseases

Communication between the gut and remote organs, such as the brain or the cardiovascular system, has been well established and recent studies provide evidence for a potential bidirectional gut-airway axis. Observations from animal and human studies indicate that respiratory insults influence the activity of the gut microbiome and that microbial ligands and metabolic products generated by the gut microbiome shape respiratory immunity. Information exchange between these two large mucosal surface areas regulates microorganism-immune interactions, with significant implications for the clinical and treatment outcomes of a range of respiratory conditions, including asthma, chronic obstructive pulmonary disease and lung cancer. In this Review, we summarize the most recent data in this field, offering insights into mechanisms of gut-airway crosstalk across spatial and temporal gradients and their relevance for respiratory health.

Mechanisms of antibody mediated immunity - Distinct in early life

Immune responses in early life are characterized by a failure to robustly generate long-lasting protective responses against many common pathogens or upon vaccination. This is associated with a reduced ability to generate T-cell dependent high affinity antibodies. This review highlights the differences in T-cell dependent antibody responses observed between infants and adults, in particular focussing on the alterations in immune cell function that lead to reduced T follicular helper cell-B cell crosstalk within germinal centres in early life. Understanding the distinct functional characteristics of early life humoral immunity, and how these are regulated, will be critical in guiding age-appropriate immunological interventions in the very young.

Extra-pulmonary control of respiratory defense

Pneumonia persists as a public health crisis, representing the leading cause of death due to infection. Whether respiratory tract infections progress to pneumonia and its sequelae such as acute respiratory distress syndrome and sepsis depends on numerous underlying conditions related to both the causative agent and host. Regarding the former, pneumonia burden remains staggeringly high, despite the effectiveness of pathogen-targeting strategies such as vaccines and antibiotics. This demands a greater understanding of host features that collaborate to promote immune resistance and tissue resilience in the infected lung. Such features inside the pulmonary compartment have drawn much attention, where major advances have been made related to resident and recruited immune activity. By comparison, extra-pulmonary processes guiding pneumonia susceptibility are relatively elusive, constituting the focus of this review. Here we will highlight examples of when, how, and why tissues outside of the lungs dispatch signals that modulate local immunity in the airspaces. Topics include the liver, gut, bone marrow, brain and more, all of which contribute in direct and indirect ways to pneumonia outcome. When tuned appropriately, it has become clear that these responses can serve protective roles, and this will be considered distinctly from what would otherwise be aberrant responses characteristic of pneumonia-induced organ injury and sepsis. Further advances in this area may reveal novel targetable areas for clinical intervention that are not confined to the intra-pulmonary space.

CXCR3+ effector regulatory T cells associate with disease tolerance during lower respiratory pneumovirus infection

Lifestyle factors like poor maternal diet or antibiotic exposure disrupt early life microbiome assembly in infants, increasing the risk of severe lower respiratory infections (sLRI). Our prior studies in mice indicated that a maternal low-fibre diet (LFD) exacerbates LRI severity in infants by impairing recruitment of plasmacytoid dendritic cells (pDC) and consequently attenuating expansion of lung regulatory T (Treg) cells during pneumonia virus of mice (PVM) infection. Here, we investigated whether maternal dietary fibre intake influences Treg cell phenotypes in the mediastinal lymph nodes (mLN) and lungs of PVM-infected neonatal mice. Using high dimensional flow cytometry, we identified distinct clusters of regulatory T cells (Treg cells), which differed between lungs and mLN during infection, with notably greater effector Treg cell accumulation in the lungs. Compared to high-fibre diet (HFD)-reared pups, frequencies of various effector Treg cell subsets were decreased in the lungs of LFD-reared pups. Particularly, recruitment of chemokine receptor 3 (CXCR3+) expressing Treg cells was attenuated in LFD-reared pups, correlating with lower lung expression of CXCL9 and CXCL10 chemokines. The recruitment of this subset in response to PVM infection was similarly impaired in pDC depleted mice or following anti-CXCR3 treatment, increasing immunopathology in the lungs. In summary, PVM infection leads to the sequential recruitment and expansion of distinct Treg cell subsets to the lungs and mLN. The attenuated recruitment of the CXCR3+ subset in LFD-reared pups increases LRI severity, suggesting that strategies to enhance pDCs or CXCL9/CXCL10 expression will lower immune-mediated pathogenesis.

Early life microbiome influences on development of the mucosal innate immune system

The gut microbiota is well known to possess immunomodulatory capacities, influencing a multitude of cellular signalling pathways to maintain host homeostasis. Although the formation of the immune system initiates before birth in a sterile environment, an emerging body of literature indicates that the neonatal immune system is influenced by a first wave of external stimuli that includes signals from the maternal microbiota. A second wave of stimulus begins after birth and must be tightly regulated during the neonatal period when colonization of the host occurs concomitantly with the maturation of the immune system, requiring a fine adjustment between establishing tolerance towards the commensal microbiota and preserving inflammatory responses against pathogenic invaders. Besides integrating cues from commensal microbes, the neonatal immune system must also regulate responses triggered by other environmental signals, such as dietary antigens, which become more complex with the introduction of solid food during the weaning period. This "window of opportunity" in early life is thought to be crucial for the proper development of the immune system, setting the tone of subsequent immune responses in adulthood and modulating the risk of developing chronic and metabolic inflammatory diseases. Here we review the importance of host-microbiota interactions for the development and maturation of the immune system, particularly in the early-life period, highlighting the known mechanisms involved in such communication. This discussion is focused on recent data demonstrating microbiota-mediated education of innate immune cells and its role in the development of lymphoid tissues.

Maternal Brown Rice Diet during Pregnancy Promotes Adipose Tissue Browning in Offspring via Reprogramming PKA Signaling and DNA Methylation

SCOPE

Brown rice, the most consumed food worldwide, has been shown to possess beneficial effects on the prevention of metabolic diseases. However, the way in which maternal brown rice diet improves metabolism in offspring and the regulatory mechanisms remains unclear. The study explores the epigenetic regulation of offspring energy metabolic homeostasis by maternal brown rice diet during pregnancy.

METHODS AND RESULTS

Female mice are fed brown rice during pregnancy, and then body phenotypes, the histopathological analysis, and adipose tissues biochemistry assay of offspring mice are detected. It is found that maternal brown rice diet significantly reduces body weight and fat mass, increases energy expenditure and heat production in offspring. Maternal brown rice diet increases uncoupling protein 1 (UCP1) protein level and upregulates the mRNA expression of thermogenic genes in adipose tissues. Mechanistically, protein kinase A (PKA) signaling is likely responsible in the induced thermogenic program in offspring adipocytes, and the progeny adipocytes browning program is altered due to decreased level of DNA methyltransferase 1 protein and hypomethylation of the transcriptional coregulator positive regulatory domain containing 16 (PRDM16).

CONCLUSIONS

These findings demonstrate that maternal brown rice during pregnancy improves offspring mice metabolic homeostasis via promoting adipose browning, and its mechanisms may be mediated by DNA methylation reprogramming.

Dietary nutrients during gestation cause obesity and related metabolic changes by altering DNA methylation in the offspring

Growing evidence shows that maternal nutrition from preconception until lactation has an important effect on the development of non-communicable diseases in the offspring. Biological responses to environmental stress during pregnancy, including undernutrition or overnutrition of various nutrients, are transmitted in part by DNA methylation. The aim of the present narrative review is to summarize literature data on altered DNA methylation patterns caused by maternal macronutrient or vitamin intake and its association with offspring's phenotype (obesity and related metabolic changes). With our literature search, we found evidence for the association between alterations in DNA methylation pattern of different genes caused by maternal under- or overnutrition of several nutrients (protein, fructose, fat, vitamin D, methyl-group donor nutrients) during 3 critical periods of programming (preconception, pregnancy, lactation) and the development of obesity or related metabolic changes (glucose, insulin, lipid, leptin, adiponectin levels, blood pressure, non-alcoholic fatty liver disease) in offspring. The review highlights that maternal consumption of several nutrients could individually affect the development of offspring's obesity and related metabolic changes via alterations in DNA methylation.

SARS-CoV-2 infection elucidates unique features of pregnancy-specific immunity

Pregnancy is a risk factor for increased severity of SARS-CoV-2 and other respiratory infections. The mechanisms underlying this risk have not been well-established, partly due to a limited understanding of how pregnancy shapes immune responses. To gain insight into the role of pregnancy in modulating immune responses at steady state and upon perturbation, we collected peripheral blood mononuclear cells (PBMC), plasma, and stool from 226 women, including 152 pregnant individuals (n = 96 with SARS-CoV-2 infection and n = 56 healthy controls) and 74 non-pregnant women (n = 55 with SARS-CoV-2 and n = 19 healthy controls). We found that SARS-CoV-2 infection was associated with altered T cell responses in pregnant compared to non-pregnant women. Differences included a lower percentage of memory T cells, a distinct clonal expansion of CD4-expressing CD8 + T cells, and the enhanced expression of T cell exhaustion markers, such as programmed cell death-1 (PD-1) and T cell immunoglobulin and mucin domain-3 (Tim-3), in pregnant women. We identified additional evidence of immune dysfunction in severely and critically ill pregnant women, including a lack of expected elevation in regulatory T cell (Treg) levels, diminished interferon responses, and profound suppression of monocyte function. Consistent with earlier data, we found maternal obesity was also associated with altered immune responses to SARS-CoV-2 infection, including enhanced production of inflammatory cytokines by T cells. Certain gut bacterial species were altered in pregnancy and upon SARS-CoV-2 infection in pregnant individuals compared to non-pregnant women. Shifts in cytokine and chemokine levels were also identified in the sera of pregnant individuals, most notably a robust increase of interleukin-27 (IL-27), a cytokine known to drive T cell exhaustion, in the pregnant uninfected control group compared to all non-pregnant groups. IL-27 levels were also significantly higher in uninfected pregnant controls compared to pregnant SARS-CoV-2-infected individuals. Using two different preclinical mouse models of inflammation-induced fetal demise and respiratory influenza viral infection, we found that enhanced IL-27 protects developing fetuses from maternal inflammation but renders adult female mice vulnerable to viral infection. These combined findings from human and murine studies reveal nuanced pregnancy-associated immune responses, suggesting mechanisms underlying the increased susceptibility of pregnant individuals to viral respiratory infections.

The Respiratory Microbiome in Paediatric Chronic Wet Cough: What Is Known and Future Directions

Chronic wet cough for longer than 4 weeks is a hallmark of chronic suppurative lung diseases (CSLD), including protracted bacterial bronchitis (PBB), and bronchiectasis in children. Severe lower respiratory infection early in life is a major risk factor of PBB and paediatric bronchiectasis. In these conditions, failure to clear an underlying endobronchial infection is hypothesised to drive ongoing inflammation and progressive tissue damage that culminates in irreversible bronchiectasis. Historically, the microbiology of paediatric chronic wet cough has been defined by culture-based studies focused on the detection and eradication of specific bacterial pathogens. Various 'omics technologies now allow for a more nuanced investigation of respiratory pathobiology and are enabling development of endotype-based models of care. Recent years have seen substantial advances in defining respiratory endotypes among adults with CSLD; however, less is understood about diseases affecting children. In this review, we explore the current understanding of the airway microbiome among children with chronic wet cough related to the PBB-bronchiectasis diagnostic continuum. We explore concepts emerging from the gut-lung axis and multi-omic studies that are expected to influence PBB and bronchiectasis endotyping efforts. We also consider how our evolving understanding of the airway microbiome is translating to new approaches in chronic wet cough diagnostics and treatments.

Interleukin-22 suppresses major histocompatibility complex II in mucosal epithelial cells

Major histocompatibility complex (MHC) II is dynamically expressed on mucosal epithelial cells and is induced in response to inflammation and parasitic infections, upon exposure to microbiota, and is increased in chronic inflammatory diseases. However, the regulation of epithelial cell-specific MHC II during homeostasis is yet to be explored. We discovered a novel role for IL-22 in suppressing epithelial cell MHC II partially via the regulation of endoplasmic reticulum (ER) stress, using animals lacking the interleukin-22-receptor (IL-22RA1), primary human and murine intestinal and respiratory organoids, and murine models of respiratory virus infection or with intestinal epithelial cell defects. IL-22 directly downregulated interferon-γ-induced MHC II on primary epithelial cells by modulating the expression of MHC II antigen A α (H2-Aα) and Class II transactivator (Ciita), a master regulator of MHC II gene expression. IL-22RA1-knockouts have significantly higher MHC II expression on mucosal epithelial cells. Thus, while IL-22-based therapeutics improve pathology in chronic disease, their use may increase susceptibility to viral infections.

IL-22: Immunity's bittersweet symphony

Epithelial cells play a crucial role in barrier defense. Here, Moniruzzaman et al. (2023. J. Exp. Med.https://doi.org/10.1084/jem.20230106) discovered that interleukin-22 (IL-22) represses MHC class II expression by epithelial cells with an opposite impact on chronic inflammatory disease and viral infection.

Immunometabolism of dendritic cells in health and disease

Dendritic cells (DCs) are crucial mediators that bridge the innate and adaptive immune responses. Cellular rewiring of metabolism is an emerging regulator of the activation, migration, and functional specialization of DC subsets in specific microenvironments and immunological conditions. DCs undergo metabolic adaptation to exert immunogenic or tolerogenic effects in different contexts. Also, beyond their intracellular metabolic and signaling roles, metabolites and nutrients mediate the intercellular crosstalk between DCs and other cell types, and such crosstalk orchestrates DC function and immune responses. Here, we provide a comprehensive review of the metabolic regulation of DC biology in various contexts and summarize the current understanding of such regulation in directing immune homeostasis and inflammation, specifically with respect to infections, autoimmunity, tolerance, cancer, metabolic diseases, and crosstalk with gut microbes. Understanding context-specific metabolic alterations in DCs may identify mechanisms for physiological and pathological functions of DCs and yield potential opportunities for therapeutic targeting of DC metabolism in many diseases.

IL-33-induced neutrophilic inflammation and NETosis underlie rhinovirus-triggered exacerbations of asthma

Rhinovirus-induced neutrophil extracellular traps (NETs) contribute to acute asthma exacerbations; however, the molecular factors that trigger NETosis in this context remain ill-defined. Here, we sought to implicate a role for IL-33, an epithelial cell-derived alarmin rapidly released in response to infection. In mice with chronic experimental asthma (CEA), but not naïve controls, rhinovirus inoculation induced an early (1 day post infection; dpi) inflammatory response dominated by neutrophils, neutrophil-associated cytokines (IL-1α, IL-1β, CXCL1), and NETosis, followed by a later, type-2 inflammatory phase (3-7 dpi), characterised by eosinophils, elevated IL-4 levels, and goblet cell hyperplasia. Notably, both phases were ablated by HpARI (Heligmosomoides polygyrus Alarmin Release Inhibitor), which blocks IL-33 release and signalling. Instillation of exogenous IL-33 recapitulated the rhinovirus-induced early phase, including the increased presence of NETs in the airway mucosa, in a PAD4-dependent manner. Ex vivo IL-33-stimulated neutrophils from mice with CEA, but not naïve mice, underwent NETosis and produced greater amounts of IL-1α/β, IL-4, and IL-5. In nasal samples from rhinovirus-infected people with asthma, but not healthy controls, IL-33 levels correlated with neutrophil elastase and dsDNA. Our findings suggest that IL-33 blockade ameliorates the severity of an asthma exacerbation by attenuating neutrophil recruitment and the downstream generation of NETs.

Propionate primes the DC pump in neonates

The protective benefits of breastmilk are well-appreciated, yet lack mechanistic detail. In this issue of Immunity, Sikder et al. reveal how breastmilk-microbiota-derived propionate induces Flt3L expression, dendritic cell maturation, regulatory T cell recruitment, and antiviral immunity in the lung.