THE INTESTINAL COMMENSAL, Bacteroides fragilis, MODULATES HOST RESPONSES TO VIRAL INFECTION AND THERAPY: LESSONS FOR EXPLORATION DURING Mycobacterium tuberculosis INFECTION

Nontoxigenic Bacteroides fragilis: A double-edged sword

The contribution of commensal microbes to human health and disease is unknown. Bacteroides fragilis (B. fragilis) is an opportunistic pathogen and a common colonizer of the human gut. Nontoxigenic B. fragilis (NTBF) and enterotoxigenic B. fragilis (ETBF) are two kinds of B. fragilis. NTBF has been shown to affect the host immune system and interact with gut microbes and pathogenic microbes. Previous studies indicated that certain strains of B. fragilis have the potential to serve as probiotics, based on their observed relationship with the immune system. However, several recent studies have shown detrimental effects on the host when beneficial gut bacteria are found in the digestive system or elsewhere. In some pathological conditions, NTBF may have adverse reactions. This paper presents a comprehensive analysis of NTBF ecology from the host-microbe perspective, encompassing molecular disease mechanisms analysis, bacteria-bacteria interaction, bacteria-host interaction, and the intricate ecological context of the gut. Our review provides much-needed insights into the precise application of NTBF.

Zedoary turmeric oil injection ameliorates lung inflammation via platelet factor 4 and regulates gut microbiota disorder in respiratory syncytial virus-infected young mice

BACKGROUND

Respiratory syncytial virus (RSV)-induced lung inflammation is one of the main causes of hospitalization and easily causes disruption of intestinal homeostasis in infants, thereby resulting in a negative impact on their development. However, the current clinical drugs are not satisfactory. Zedoary turmeric oil injection (ZTOI), a patented traditional Chinese medicine (TCM), has been used for clinical management of inflammatory diseases. However, its in vivo efficacy against RSV-induced lung inflammation and the underlying mechanism remain unclear.

PURPOSE

The present study was designed to confirm the in vivo efficacy of ZTOI against lung inflammation and intestinal disorders in RSV-infected young mice and to explore the potential mechanism.

STUDY DESIGN AND METHODS

Lung inflammation was induced by RSV, and cytokine antibody arrays were used to clarify the effectiveness of ZTOI in RSV pneumonia. Subsequently, key therapeutic targets of ZTOI against RSV pneumonia were identified through multi-factor detection and further confirmed. The potential therapeutic material basis of ZTOI in target tissues was determined by non-target mass spectrometry. After confirming that the pharmacological substances of ZTOI can reach the intestine, we used 16S rRNA-sequencing technology to study the effect of ZTOI on the intestinal bacteria.

RESULTS

In the RSV-induced mouse lung inflammation model, ZTOI significantly reduced the levels of serum myeloperoxidase, serum amyloid A, C-reactive protein, and thymic stromal lymphoprotein; inhibited the mRNA expression of IL-10 and IL-6; and decreased pathological changes in the lungs. Immunofluorescence and qPCR experiments showed that ZTOI reduced RSV load in the lungs. According to cytokine antibody arrays, platelet factor 4 (PF4), a weak chemotactic factor mainly synthesized by megakaryocytes, showed a concentration-dependent change in lung tissues affected by ZTOI, which could be the key target for ZTOI to exert anti-inflammatory effects. Additionally, sesquiterpenes were enriched in the lungs and intestines, thereby exerting anti-inflammatory and regulatory effects on gut microbiota.

CONCLUSION

ZTOI can protect from lung inflammation via PF4 and regulate gut microbiota disorder in RSV-infected young mice by sesquiterpenes, which provides reference for its clinical application in RSV-induced lung diseases.

Berberine: Potential preventive and therapeutic strategies for human colorectal cancer

Colorectal cancer (CRC) is a common digestive tract tumor, with incidences continuing to rise. Although modern medicine has extended the survival time of CRC patients, its adverse effects and the financial burden cannot be ignored. CRC is a multi-step process and can be caused by the disturbance of gut microbiome and chronic inflammation's stimulation. Additionally, the presence of precancerous lesions is also a risk factor for CRC. Consequently, scientists are increasingly interested in identifying multi-target, safe, and economical herbal medicine and natural products. This paper summarizes berberine's (BBR) regulatory mechanisms in the occurrence and development of CRC. The findings indicate that BBR regulates gut microbiome homeostasis and controls mucosal inflammation to prevent CRC. In the CRC stage, BBR inhibits cell proliferation, invasion, and metastasis, blocks the cell cycle, induces cell apoptosis, regulates cell metabolism, inhibits angiogenesis, and enhances chemosensitivity. BBR plays a role in the overall management of CRC. Therefore, using BBR as an adjunct to CRC prevention and treatment could become a future trend in oncology.

Impact of dietary carbohydrate, fat or protein restriction on the human gut microbiome: a systematic review

Restriction of dietary carbohydrates, fat and/or protein is often used to reduce body weight and/or treat (metabolic) diseases. Since diet is a key modulator of the human gut microbiome, which plays an important role in health and disease, this review aims to provide an overview of current knowledge of the effects of macronutrient-restricted diets on gut microbial composition and metabolites. A structured search strategy was performed in several databases. After screening for inclusion and exclusion criteria, thirty-six articles could be included. Data are included in the results only when supported by at least three independent studies to enhance the reliability of our conclusions. Low-carbohydrate (<30 energy%) diets tended to induce a decrease in the relative abundance of several health-promoting bacteria, including Bifidobacterium, as well as a reduction in short-chain fatty acid (SCFA) levels in faeces. In contrast, low-fat diets (<30 energy%) increased alpha diversity, faecal SCFA levels and abundance of some beneficial bacteria, including Faecalibacterium prausnitzii. There were insufficient data to draw conclusions concerning the effects of low-protein (<10 energy%) diets on gut microbiota. Although the data of included studies unveil possible benefits of low-fat and potential drawbacks of low-carbohydrate diets for human gut microbiota, the diversity in study designs made it difficult to draw firm conclusions. Using a more uniform methodology in design, sample processing and sharing raw sequence data could foster our understanding of the effects of macronutrient restriction on gut microbiota composition and metabolic dynamics relevant to health. This systematic review was registered at https://www.crd.york.ac.uk/prospero as CRD42020156929.

Porphyromonas gingivalis aggravates colitis via a gut microbiota-linoleic acid metabolism-Th17/Treg cell balance axis

Periodontitis is closely related to inflammatory bowel disease (IBD). An excessive and non-self-limiting immune response to the dysbiotic microbiome characterizes the two. However, the underlying mechanisms that overlap still need to be clarified. We demonstrate that the critical periodontal pathogen Porphyromonas gingivalis (Pg) aggravates intestinal inflammation and Th17/Treg cell imbalance in a gut microbiota-dependent manner. Specifically, metagenomic and metabolomic analyses shows that oral administration of Pg increases levels of the Bacteroides phylum but decreases levels of the Firmicutes, Verrucomicrobia, and Actinobacteria phyla. Nevertheless, it suppresses the linoleic acid (LA) pathway in the gut microbiota, which was the target metabolite that determines the degree of inflammation and functions as an aryl hydrocarbon receptor (AHR) ligand to suppress Th17 differentiation while promoting Treg cell differentiation via the phosphorylation of Stat1 at Ser727. Therapeutically restoring LA levels in colitis mice challenged with Pg exerts anti-colitis effects by decreasing the Th17/Treg cell ratio in an AHR-dependent manner. Our study suggests that Pg aggravates colitis via a gut microbiota-LA metabolism-Th17/Treg cell balance axis, providing a potential therapeutically modifiable target for IBD patients with periodontitis.

A new perspective on gut-lung axis affected through resident microbiome and their implications on immune response in respiratory diseases

The highly diverse microbial ecosystem of the human body colonizes the gastrointestinal tract has a profound impact on the host's immune, metabolic, endocrine, and other physiological processes, which are all interconnected. Specifically, gut microbiota has been found to play a crucial role in facilitating the adaptation and initiation of immune regulatory response through the gastrointestinal tract affecting the other distal mucosal sites such as lungs. A tightly regulated lung-gut axis during respiratory ailments may influence the various molecular patterns that instructs priming the disease severity to dysregulate the normal function. This review provides a comprehensive summary of current research on gut microbiota dysbiosis in respiratory diseases including asthma, pneumonia, bronchopneumonia, COPD during infections and cancer. A complex-interaction among gut microbiome, associated metabolites, cytokines, and chemokines regulates the protective immune response activating the mucosal humoral and cellular response. This potential mechanism bridges the regulation patterns through the gut-lung axis. This paper aims to advance the understanding of the crosstalk of gut-lung microbiome during infection, could lead to strategize to modulate the gut microbiome as a treatment plan to improve bad prognosis in various respiratory diseases.

Abnormal Development of Microbiota May Be a Risk Factor for Febrile Urinary Tract Infection in Infancy

Febrile urinary tract infection (fUTI) is common in infants, but specific risk factors for developing it remain unclear. As most fUTIs are caused by ascending infections of intestinal bacteria, dysbiosis-an imbalance in gut microbial communities-may increase fUTI risk. This study was conducted to test the hypothesis that abnormal development of gut microbiota during infancy increases the risk of developing fUTI. Stool samples were collected from 28 infants aged 3-11 months with first-onset fUTI (fUTI group) and 51 healthy infants of the same age (HC group). After bacterial DNA extraction, 16S rRNA expression was measured and the diversity of gut microbiota and constituent bacteria were compared between the two groups. The alpha diversity of gut microbiota (median Shannon index and Chao index) was significantly lower in the fUTI group (3.0 and 42.5) than in the HC group (3.7 and 97.0; p < 0.001). The beta diversity also formed different clusters between the two groups (p < 0.001), suggesting differences in their microbial composition. The linear discriminant analysis effect size showed that the fUTI group proportionally featured significantly more Escherichia-Shigella in the gut microbiota (9.5%) than the HC group (3.1%; p < 0.001). In summary, abnormal gut microbiota development during infancy may increase the risk of fUTI.

Gut Bacteroides act in a microbial consortium to cause susceptibility to severe malaria

Malaria is caused by Plasmodium species and remains a significant cause of morbidity and mortality globally. Gut bacteria can influence the severity of malaria, but the contribution of specific bacteria to the risk of severe malaria is unknown. Here, multiomics approaches demonstrate that specific species of Bacteroides are causally linked to the risk of severe malaria. Plasmodium yoelii hyperparasitemia-resistant mice gavaged with murine-isolated Bacteroides fragilis develop P. yoelii hyperparasitemia. Moreover, Bacteroides are significantly more abundant in Ugandan children with severe malarial anemia than with asymptomatic P. falciparum infection. Human isolates of Bacteroides caccae, Bacteroides uniformis, and Bacteroides ovatus were able to cause susceptibility to severe malaria in mice. While monocolonization of germ-free mice with Bacteroides alone is insufficient to cause susceptibility to hyperparasitemia, meta-analysis across multiple studies support a main role for Bacteroides in susceptibility to severe malaria. Approaches that target gut Bacteroides present an opportunity to prevent severe malaria and associated deaths.

Effects of Enteromorpha prolifera polysaccharides on growth performance, intestinal barrier function and cecal microbiota in yellow-feathered broilers under heat stress

BACKGROUND

Global warming leading to heat stress (HS) is becoming a major challenge for broiler production. This study aimed to explore the protective effects of seaweed (Enteromorpha prolifera) polysaccharides (EPS) on the intestinal barrier function, microbial ecology, and performance of broilers under HS. A total of 144 yellow-feathered broilers (male, 56 days old) with 682.59 ± 7.38 g were randomly assigned to 3 groups: 1) TN (thermal neutral zone, 23.6 ± 1.8 °C), 2) HS (heat stress, 33.2 ± 1.5 °C for 10 h/d), and 3) HSE (HS + 0.1% EPS). Each group contained 6 replicates with 8 broilers per replicate. The study was conducted for 4 weeks; feed intake and body weights were measured at the end of weeks 2 and 4. At the end of the feeding trial, small intestine samples were collected for histomorphology, antioxidant, secretory immunoglobulin A (sIgA) content, apoptosis, gene and protein expression analysis; cecal contents were also collected for microbiota analysis based on 16S rDNA sequencing.

RESULTS

Dietary EPS promoted the average daily gain (ADG) of broilers during 3-4 weeks of HS (P < 0.05). At the end of HS on broilers, the activity of total superoxide dismutase (T-SOD), glutathione S-transferase (GST), and the content of sIgA in jejunum were improved by EPS supplementation (P < 0.05). Besides, dietary EPS reduced the epithelial cell apoptosis of jejunum and ileum in heat-stressed broilers (P < 0.05). Addition of EPS in HS group broilers' diet upregulated the relative mRNA expression of Occludin, ZO-1, γ-GCLc and IL-10 of the jejunum (P < 0.05), whereas downregulated the relative mRNA expression of NF-κB p65, TNF-α and IL-1β of the jejunum (P < 0.05). Dietary EPS increased the protein expression of Occludin and ZO-1, whereas it reduced the protein expression of NF-κB p65 and MLCK (P < 0.01) and tended to decrease the protein expression of TNF-α (P = 0.094) in heat-stressed broilers. Furthermore, the proportions of Bacteroides and Oscillospira among the three groups were positively associated with jejunal apoptosis and pro-inflammatory cytokine expression (P < 0.05) and negatively correlated with jejunal Occludin level (P < 0.05). However, the proportions of Lactobacillus, Barnesiella, Subdoligranulum, Megasphaera, Collinsella, and Blautia among the three groups were positively related to ADG (P < 0.05).

CONCLUSIONS

EPS can be used as a feed additive in yellow-feathered broilers. It effectively improves growth performance and alleviates HS-induced intestinal injury by relieving inflammatory damage and improving the tight junction proteins expression. These beneficial effects may be related to inhibiting NF-κB/MLCK signaling pathway activation and regulation of cecal microbiota.

Gut Microbiota and Respiratory Infections: Insights from Mendelian Randomization

The role of the gut microbiota in modulating the risk of respiratory infections has garnered increasing attention. However, conventional clinical trials have faced challenges in establishing the precise relationship between the two. In this study, we conducted a Mendelian randomization analysis with single nucleotide polymorphisms employed as instrumental variables to assess the causal links between the gut microbiota and respiratory infections. Two categories of bacteria, family Lactobacillaceae and genus Family XIII AD3011, were causally associated with the occurrence of upper respiratory tract infections (URTIs). Four categories of gut microbiota existed that were causally associated with lower respiratory tract infections (LRTIs), with order Bacillales and genus Paraprevotella showing a positive association and genus Alistipes and genus Ruminococcaceae UCG009 showing a negative association. The metabolites and metabolic pathways only played a role in the development of LRTIs, with the metabolite deoxycholine acting negatively and menaquinol 8 biosynthesis acting positively. The identification of specific bacterial populations, metabolites, and pathways may provide new clues for mechanism research concerning therapeutic interventions for respiratory infections. Future research should focus on elucidating the potential mechanisms regulating the gut microbiota and developing effective strategies to reduce the incidence of respiratory infections. These findings have the potential to significantly improve global respiratory health.

The gut and lung microbiota in pulmonary tuberculosis: susceptibility, function, and new insights into treatment

INTRODUCTION

Tuberculosis (TB) is a chronic infectious disease caused by mycobacterium tuberculosis (Mtb) that poses a major threat to human health.

AREAS COVERED

Herein, we aim to review the alteration of the microbiota in gut and respiratory during TB development, the potential function and mechanisms of microbiota in the pathogenesis of Mtb infection, and the impact of antibiotic treatment on the microbiota. In addition, we discuss the potential new paradigm for the use of microbiota-based treatments such as probiotics and prebiotics in the treatment of TB.

EXPERT OPINION

Studies have shown that trillions of micro-organisms live in the human gut and respiratory tract, acting as gatekeepers in maintaining immune homeostasis and respiratory physiology and playing a beneficial or hostile role in the development of TB. Anti-TB antibiotics may cause microecological imbalances in the gut and respiratory tract, and microbiome-based therapeutics may be a promising strategy for TB treatment. Appropriate probiotics and prebiotics supplementation, along with antimycobacterial treatment, will improve the therapeutic effect of TB treatment and protect the gut and respiratory microbiota from dysbiosis.

Paeonia lactiflora Pall. Polysaccharide alleviates depression in CUMS mice by inhibiting the NLRP3/ASC/Caspase-1 signaling pathway and affecting the composition of their intestinal flora

ETHNOPHARMACOLOGICAL RELEVANCE

Paeonia lactiflora Pall. (PL) has been commonly used to de-stressing the liver and relieve depression in traditional Chinese medicine for over a thousand years. Recently, it has been widely used in studies on anti-depressant, anti-inflammatory and regulation of intestinal flora. However, the polysaccharide component has received less attention than the saponin component of PL.

AIM OF THE STUDY

This study aimed to elucidate the effects of Paeonia lactiflora polysaccharide (PLP) on depressive behavior in mice in a chronic unpredictable mild stress (CUMS) model and its possible action mechanisms.

MATERIALS AND METHODS

A model of chronic depression induced by the CUMS approach. Behavioral experiments were used to assess the success of the CUMS model and the therapeutic impact of PLP. Then the extent of damage to the colonic mucosa was assessed by H&E staining; the extent of neuronal damage was assessed by Nissler staining. Inflammatory factor expression was assessed at different sites in the mouse by enzyme-linked immunoassay (Elisa). The alterations of fecal microflora were detected by 16S rRNA gene sequencing. In the colonic tissues, NLRP3, ASC and Caspase-1 mRNA and protein levels detected by quantitative real-time PCR (qRT-PCR) and Western blot(WB).

RUSULTS

PLP can improve depressive behavior in CUMS mice, and colonic mucosal and neuronal damage. Elisa assay showed that PLP could reduce interleukin-1β (IL-1β), interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α) levels, and increase 5-Hydroxytryptamine(5-HT) levels in CUMS mice. 16S sequencing analysis showed that PLP could regulate the intestinal flora of CUMS mice and increase their species richness. In addition, PLP significantly inhibited NLRP3/ASC/Caspase-1 signalling pathways activation in the colonic tissues of CUMS mice.

CONCLUSIONS

PLP modulates depression-related intestinal ecological dysregulation, increases species richness, and inhibits inflammatory factors levels and NLRP3 inflammasome activation to reduce colonic mucosal and neurons damage, thereby improving depression-like behavior and neurotransmitter release in CUMS mice.

An Archetypical Model for Engrafting Bacteroides fragilis into Conventional Mice Following Reproducible Antibiotic Conditioning of the Gut Microbiota

Bacteroides fragilis is a commonly investigated commensal bacterium for its protective role in host diseases. Here, we aimed to develop a reproducible antibiotic-based model for conditioning the gut microbiota and engrafting B. fragilis into a conventional murine host. Initially, we selected different combinations of antibiotics, including metronidazole, imipenem, and clindamycin, and investigated their efficacy in depleting the mouse Bacteroides population. We performed 16S rRNA sequencing of DNA isolated from fecal samples at different time points. The α-diversity was similar in mice treated with metronidazole (MET) and differed only at weeks 1 (p = 0.001) and 3 (p = 0.009) during metronidazole/imipenem (MI) treatment. Bacteroides compositions, during the MET and MI exposures, were similar to the pre-antibiotic exposure states. Clindamycin supplementation added to MET or MI regimens eliminated the Bacteroides population. We next repeated metronidazole/clindamycin (MC) treatment in two additional independent experiments, followed by a B. fragilis transplant. MC consistently and reproducibly eliminated the Bacteroides population. The depleted Bacteroides did not recover in a convalescence period of six weeks post-MC treatment. Finally, B. fragilis was enriched for ten days following engraftment into Bacteroides-depleted mice. Our model has potential use in gut microbiota studies that selectively investigate Bacteroides' role in diseases of interest.

Spatial transcriptomes and microbiota reveal immune mechanism that respond to pathogen infection in the posterior intestine of Sebastes schlegelii

The intestine is a site of immune cell priming at birth. Therefore, spatial transcriptomes were performed to define how the transcriptomic landscape was spatially organized in the posterior intestine of Sebastes schlegelii following Edwardsiella piscicida infection. In the healthy condition, we identified a previously unappreciated molecular regionalization of the posterior intestine. Following bacterial infection, most immune-related genes were identified in mucosa layer. Moreover, investigation of immune-related genes and genes in immune-related KEGG pathways based on spatial transcriptomes shed light on which sections of these genes are in the posterior intestine. Meanwhile, the high expression of genes related to regeneration also indicated that the posterior intestine was responding to the invasion of pathogens by constantly proliferating new cells. In addition, the increasing microbiota communities indicated that these bacteria maintained posterior intestine integrity and shaped the mucosal immune system. Taken together, spatial transcriptomes and microbiota compositions have significant implications for understanding the immune mechanism that responds to E. piscicida infection in the posterior intestine of S. schlegelii, which also provides a theoretical basis for the spatial distribution of immune genes and changes in bacterial flora in other teleosts in the process of resisting pathogens.

The gut microbiome: A line of defense against tuberculosis development

The tuberculosis (TB) burden remains a significant global public health concern, especially in less developed countries. While pulmonary tuberculosis (PTB) is the most common form of the disease, extrapulmonary tuberculosis, particularly intestinal TB (ITB), which is mostly secondary to PTB, is also a significant issue. With the development of sequencing technologies, recent studies have investigated the potential role of the gut microbiome in TB development. In this review, we summarized studies investigating the gut microbiome in both PTB and ITB patients (secondary to PTB) compared with healthy controls. Both PTB and ITB patients show reduced gut microbiome diversity characterized by reduced Firmicutes and elevated opportunistic pathogens colonization; Bacteroides and Prevotella were reported with opposite alteration in PTB and ITB patients. The alteration reported in TB patients may lead to a disequilibrium in metabolites such as short-chain fatty acid (SCFA) production, which may recast the lung microbiome and immunity via the "gut-lung axis". These findings may also shed light on the colonization of Mycobacterium tuberculosis in the gastrointestinal tract and the development of ITB in PTB patients. The findings highlight the crucial role of the gut microbiome in TB, particularly in ITB development, and suggest that probiotics and postbiotics might be useful supplements in shaping a balanced gut microbiome during TB treatment.

Bacteroides fragilis derived metabolites, identified by molecular networking, decrease Salmonella virulence in mice model

In the gut microbiota, resident bacteria prevent pathogens infection by producing specific metabolites. Among bacteria belonging to phylum Bacteroidota, we have previously shown that Bacteroides fragilis or its cell-free supernatant inhibited in vitro Salmonella Heidelberg translocation. In the present study, we have analyzed this supernatant to identify bioactive molecules after extraction and subsequent fractionation using a semi-preparative reversed-phase Liquid Chromatography High-Resolution Tandem Mass Spectrometry (LC-HRMS/MS). The results indicated that only two fractions (F3 and F4) strongly inhibited S. Heidelberg translocation in a model mimicking the intestinal epithelium. The efficiency of the bioactive fractions was evaluated in BALB/c mice, and the results showed a decrease of S. Heidelberg in Peyer’s patches and spleen, associated with a decrease in inflammatory cytokines and neutrophils infiltration. The reduction of the genus Alistipes in mice receiving the fractions could be related to the anti-inflammatory effects of bioactive fractions. Furthermore, these bioactive fractions did not alter the gut microbiota diversity in mice. To further characterize the compounds present in these bioactive fractions, Liquid Chromatography High-Resolution Tandem Mass Spectrometry (LC-HRMS/MS) data were analyzed through molecular networking, highlighting cholic acid (CA) and deoxycholic acid. In vitro, CA had inhibitory activity against the translocation of S. Heidelberg by significantly decreasing the expression of Salmonella virulence genes such as sipA. The bioactive fractions also significantly downregulated the flagellar gene fliC, suggesting the involvement of other active molecules. This study showed the interest to characterize better the metabolites produced by B. fragilis to make them means of fighting pathogenic bacteria by targeting their virulence factor without modifying the gut microbiota.

Ingestion, Immunity, and Infection: Nutrition and Viral Respiratory Tract Infections

Respiratory infections place a heavy burden on the health care system, particularly in the winter months. Individuals with a vulnerable immune system, such as very young children and the elderly, and those with an immune deficiency, are at increased risk of contracting a respiratory infection. Most respiratory infections are relatively mild and affect the upper respiratory tract only, but other infections can be more serious. These can lead to pneumonia and be life-threatening in vulnerable groups. Rather than focus entirely on treating the symptoms of infectious disease, optimizing immune responsiveness to the pathogens causing these infections may help steer towards a more favorable outcome. Nutrition may have a role in such prevention through different immune supporting mechanisms. Nutrition contributes to the normal functioning of the immune system, with various nutrients acting as energy sources and building blocks during the immune response. Many micronutrients (vitamins and minerals) act as regulators of molecular responses of immune cells to infection. It is well described that chronic undernutrition as well as specific micronutrient deficiencies impair many aspects of the immune response and make individuals more susceptible to infectious diseases, especially in the respiratory and gastrointestinal tracts. In addition, other dietary components such as proteins, pre-, pro- and synbiotics, and also animal- and plant-derived bioactive components can further support the immune system. Both the innate and adaptive defense systems contribute to active antiviral respiratory tract immunity. The initial response to viral airway infections is through recognition by the innate immune system of viral components leading to activation of adaptive immune cells in the form of cytotoxic T cells, the production of neutralizing antibodies and the induction of memory T and B cell responses. The aim of this review is to describe the effects of a range different dietary components on anti-infective innate as well as adaptive immune responses and to propose mechanisms by which they may interact with the immune system in the respiratory tract.

Gut-Lung Axis: Microbial Crosstalk in Pediatric Respiratory Tract Infections

The gut microbiota is an important regulator for maintaining the organ microenvironment through effects on the gut-vital organs axis. Respiratory tract infections are one of the most widespread and harmful diseases, especially in the last 2 years. Many lines of evidence indicate that the gut microbiota and its metabolites can be considered in therapeutic strategies to effectively prevent and treat respiratory diseases. However, due to the different gut microbiota composition in children compared to adults and the dynamic development of the immature immune system, studies on the interaction between children's intestinal flora and respiratory infections are still lacking. Here, we describe the changes in the gut microbiota of children with respiratory tract infections and explain the relationship between the microbiota of children with their immune function and disease development. In addition, we will provide perspectives on the direct manipulation of intestinal microbes to prevent or treat pediatric respiratory infections.