Dietary nucleic acid and intestinal microbiota synergistically promote a shift in the Th1/Th2 balance toward Th1-skewed immunity

Microbiota and Immunity during Respiratory Infections: Lung and Gut Affair

Bacterial and viral respiratory tract infections are the most common infectious diseases, leading to worldwide morbidity and mortality. In the past 10 years, the importance of lung microbiota emerged in the context of pulmonary diseases, although the mechanisms by which it impacts the intestinal environment have not yet been fully identified. On the contrary, gut microbial dysbiosis is associated with disease etiology or/and development in the lung. In this review, we present an overview of the lung microbiome modifications occurring during respiratory infections, namely, reduced community diversity and increased microbial burden, and of the downstream consequences on host-pathogen interaction, inflammatory signals, and cytokines production, in turn affecting the disease progression and outcome. Particularly, we focus on the role of the gut-lung bidirectional communication in shaping inflammation and immunity in this context, resuming both animal and human studies. Moreover, we discuss the challenges and possibilities related to novel microbial-based (probiotics and dietary supplementation) and microbial-targeted therapies (antibacterial monoclonal antibodies and bacteriophages), aimed to remodel the composition of resident microbial communities and restore health. Finally, we propose an outlook of some relevant questions in the field to be answered with future research, which may have translational relevance for the prevention and control of respiratory infections.

High concentration of extracellular nucleotides suppresses cell growth via delayed cell cycle progression in cancer and noncancer cell lines

Tumor necrosis frequently occurs in malignant tumors, showing rapid growth and invasion. This phenomenon is generally regarded as simple ischemic necrosis due to insufficient tumor vessels and blood supply. However, the necrotic tissue contains high amount of nuclear substances, DNA, and nucleoproteins that may affect the surrounding tumor cells by promoting or suppressing the tumor cell growth in vivo. This study focused on the effects of an externally administered water-soluble nuclear crude extract (SNE) containing nuclear protein and oligonucleotides on several human cancer and noncancer cell lines. The results demonstrated that the SNE suppressed cell growth in cancer and noncancer cells in vitro. Through the flow cytometry analysis of the nuclear DNA content, it was observed that the SNE increased and decreased cell proportion in the S and G2/M phases, respectively, thereby suggesting that the cell growth inhibition was due to cell cycle delay, and not due to apoptosis. These studies suggest that the high-concentration of extracellular nucleotides generated as a result of tumor necrosis and/or released from infiltrated neutrophils could suppress the growth of surrounding cancer and intrinsic cells, which provides us some insights into an alternative anticancer strategy for patients with highly malignant necrotic tumor.

The HPA axis dysregulation in severe mental illness: Can we shift the blame to gut microbiota?

Accumulating evidence indicates that patients with severe mental disorders, including major depression, bipolar disorder and schizophrenia present with various alterations of the gut microbiota and increased intestinal permeability. In addition, the hypothalamic-pituitary-adrenal (HPA) axis dysregulation and subclinical inflammation have been reported in this group of patients. Although it has been found that the HPA axis dysregulation appears as a consequence of psychosocial stress, especially traumatic life events, the exact mechanisms of this observation remain unclear. Animal model studies have unraveled several mechanisms linking the gut microbiota with the HPA axis dysfunction. Indeed, the gut microbiota can activate the HPA axis through several mediators that cross the blood-brain barrier and include microbial antigens, cytokines and prostaglandins. There is also evidence that various microbial species can affect ileal corticosterone production that may impact the activity of the HPA axis. However, some metabolites released by various microbes, e.g., short-chain fatty acids, can attenuate the HPA axis response. Moreover, several bacteria release neurotransmitters that can directly interact with vagal afferents. It has been postulated that the HPA axis activation can impact the gut microbiota and intestinal permeability. In this article, we discuss various mechanisms linking the gut microbiota with the HPA axis activity and summarize current evidence for a cross-talk between the gut-brain axis and the HPA axis from studies of patients with mood and psychotic disorders. Finally, we show potential clinical implications that can arise from future studies investigating the HPA axis activity with respect to the gut microbiota in severe mental disorders.

TLR Activation and Allergic Disease: Early Life Microbiome and Treatment

PURPOSE OF REVIEW

Allergy and asthma are growing problems in the developed world. The accelerated increase of these diseases may be related to microbiome modification that leads to aberrant activation of Toll-like receptors (TLRs). Current research supports the concept that changes in microbial communities in early life impact TLR activation, resulting in an altered risk for the development of asthma and allergies.

RECENT FINDINGS

Prenatal and early childhood events that generate microbiome modification are closely related with TLR activation. Early childhood exposure to a rich array of TLR agonists, particularly lipopolysaccharide, strongly predicts protection against allergic disease later in life even when other lifestyle factors are accounted for. Genetic deletion of TLR signaling components in mice results in reduced function of tolerogenic cell populations in the gut. In contrast, weak TLR signaling can promote allergic sensitization later in life. This review summarizes the role of TLR signaling in microbiome-mediated protection against allergy.

Exploring the Impact of Food on the Gut Ecosystem Based on the Combination of Machine Learning and Network Visualization

Prebiotics and probiotics strongly impact the gut ecosystem by changing the composition and/or metabolism of the microbiota to improve the health of the host. However, the composition of the microbiota constantly changes due to the intake of daily diet. This shift in the microbiota composition has a considerable impact; however, non-pre/probiotic foods that have a low impact are ignored because of the lack of a highly sensitive evaluation method. We performed comprehensive acquisition of data using existing measurements (nuclear magnetic resonance, next-generation DNA sequencing, and inductively coupled plasma-optical emission spectroscopy) and analyses based on a combination of machine learning and network visualization, which extracted important factors by the Random Forest approach, and applied these factors to a network module. We used two pteridophytes, Pteridium aquilinum and Matteuccia struthiopteris, for the representative daily diet. This novel analytical method could detect the impact of a small but significant shift associated with Matteuccia struthiopteris but not Pteridium aquilinum intake, using the functional network module. In this study, we proposed a novel method that is useful to explore a new valuable food to improve the health of the host as pre/probiotics.

Protective Effects of Hydrolyzed Nucleoproteins from Salmon Milt against Ethanol-Induced Liver Injury in Rats

Dietary nucleotides play a role in maintaining the immune responses of both animals and humans. Oral administration of nucleic acids from salmon milt have physiological functions in the cellular metabolism, proliferation, differentiation, and apoptosis of human small intestinal epithelial cells. In this study, we examined the effects of DNA-rich nucleic acids prepared from salmon milt (DNSM) on the development of liver fibrosis in an in vivo ethanol-carbon tetrachloride cirrhosis model. Plasma aspartate transaminase and alanine transaminase were significantly less active in the DNSM-treated group than in the ethanol plus carbon tetrachloride (CCl₄)-treated group. Collagen accumulation in the liver and hepatic necrosis were observed histologically in ethanol plus CCl₄-treated rats; however, DNSM-treatment fully protected rats against ethanol plus CCl₄-induced liver fibrosis and necrosis. Furthermore, we examined whether DNSM had a preventive effect against alcohol-induced liver injury by regulating the cytochrome p450 2E1 (CYP2E1)-mediated oxidative stress pathway in an in vivo model. In this model, CYP2E1 activity in ethanol plus CCl₄-treated rats increased significantly, but DNSM-treatment suppressed the enzyme's activity and reduced intracellular thiobarbituric acid reactive substances (TBARS) levels. Furthermore, the hepatocytes treated with 100 mM ethanol induced an increase in cell death and were not restored to the control levels when treated with DNSM, suggesting that digestive products of DNSM are effective for the prevention of alcohol-induced liver injury. Deoxyadenosine suppressed the ethanol-induced increase in cell death and increased the activity of alcohol dehydrogenase. These results suggest that DNSM treatment represents a novel tool for the prevention of alcohol-induced liver injury.

DNA-fragments are transcytosed across CaCo-2 cells by adsorptive endocytosis and vesicular mediated transport

Dietary DNA is degraded into shorter DNA-fragments and single nucleosides in the gastrointestinal tract. Dietary DNA is mainly taken up as single nucleosides and bases, but even dietary DNA-fragments of up to a few hundred bp are able to cross the intestinal barrier and enter the blood stream. The molecular mechanisms behind transport of DNA-fragments across the intestine and the effects of this transport on the organism are currently unknown. Here we investigate the transport of DNA-fragments across the intestinal barrier, focusing on transport mechanisms and rates. The human intestinal epithelial cell line CaCo-2 was used as a model. As DNA material a PCR-fragment of 633 bp was used and quantitative real time PCR was used as detection method. DNA-fragments were found to be transported across polarized CaCo-2 cells in the apical to basolateral direction (AB). After 90 min the difference in directionality AB vs. BA was >10³ fold. Even undegraded DNA-fragments of 633 bp could be detected in the basolateral receiver compartment at this time point. Transport of DNA-fragments was sensitive to low temperature and inhibition of endosomal acidification. DNA-transport across CaCo-2 cells was not competed out with oligodeoxynucleotides, fucoidan, heparin, heparan sulphate and dextrane sulphate, while linearized plasmid DNA, on the other hand, reduced transcytosis of DNA-fragments by a factor of approximately 2. Our findings therefore suggest that vesicular transport is mediating transcytosis of dietary DNA-fragments across intestinal cells and that DNA binding proteins are involved in this process. If we extrapolate our findings to in vivo conditions it could be hypothesized that this transport mechanism has a function in the immune system.

Effect of recycled litter on immune cells in the cecal tonsils of chickens

This experiment was conducted to study selected aspects of the gut immune response in broiler chicks reared on fresh or recycled litter that were fed diets with and without subtherapeutic antibiotic supplementation. All of the chicks were reared in pens that contained either fresh pine shavings (fresh litter) or litter that was recycled for 3 consecutive flocks (recycled litter). The experiment was a 2 × 2 factorial arrangement of treatments with 4 replicate pens (n = 4) per treatment. At 10 and 35 d of age, the cecal tonsils were analyzed for intestinal immune measurements. The cecal tonsils of birds reared on recycled litter had increased IL-1 mRNA (P < 0.01) and a lower percentage of CD4(+)CD25(+) cells at 10 and 35 d of age when compared with those of chicks reared on fresh litter. Birds fed diets supplemented with bacitracin had a reduction in CD4(+) cells (P = 0.01) at 10 d of age when compared with that of chicks that were not fed the antibiotic. The combination of bacitracin supplementation and fresh litter resulted in an approximate 10-fold increase in IL-10 mRNA (P = 0.01) at 10 d of age when compared with that of the unsupplemented chicks in fresh litter. Among those chicks that were not supplemented with bacitracin, the recycled-litter treatment resulted in 25-fold (P = 0.01) and 39-fold (P = 0.02) higher IL-4 mRNA levels at 10 and 35 d of age, respectively, when compared with those of the chicks reared on fresh litter. In conclusion, the intestinal immune response of birds reared on recycled litter is skewed toward an inflammatory response, whereas the fresh litter treatment was skewed toward an anti-inflammatory response. Bacitracin supplementation did not interact with the litter type to alter IL-1 mRNA levels in cecal tonsils, suggesting the low efficiency of bacitracin in alleviating the inflammatory response induced by recycled litter.

Dysregulation of allergic airway inflammation in the absence of microbial colonization

RATIONALE

The incidence of allergic disorders is increasing in developed countries and has been associated with reduced exposure to microbes and alterations in the commensal bacterial flora.

OBJECTIVES

To ascertain the relevance of commensal bacteria on the development of an allergic response, we used a model of allergic airway inflammation in germ-free (GF) mice that lack any exposure to pathogenic or nonpathogenic microorganisms.

METHODS

Allergic airway inflammation was induced in GF, specific pathogen-free (SPF), or recolonized mice by sensitization and challenge with ovalbumin. The resulting cellular infiltrate and cytokine production were measured.

MEASUREMENTS AND MAIN RESULTS

Our results show that the total number of infiltrating lymphocytes and eosinophils were elevated in the airways of allergic GF mice compared with control SPF mice, and that this increase could be reversed by recolonization of GF mice with the complex commensal flora of SPF mice. Exaggerated airway eosinophilia correlated with increased local production of Th2-associated cytokines, elevated IgE production, and an altered number and phenotype of conventional dendritic cells. Regulatory T-cell populations and regulatory cytokine levels were unaltered, but GF mice exhibited an increased number of basophils and decreased numbers of alveolar macrophages and plasmacytoid dendritic cells.

CONCLUSIONS

These data demonstrate that the presence of commensal bacteria is critical for ensuring normal cellular maturation, recruitment, and control of allergic airway inflammation.

Characterization of immunostimulatory CpG-rich sequences from different Bifidobacterium species

The beneficial effects of Bifidobacterium are partly due to its immunostimulatory properties. These immunostimulatory properties may be linked to the presence of unmethylated CpG motifs specific to bacterial DNA, which may induce a TH1 response by activating Toll-like receptors (TLR). Using in silico analyses, PCR amplification, and dot blotting, we characterized the CpG content of various bifidobacterial strains and evaluated the immunostimulatory properties and genomic heterogeneity of these motifs in the genus. Our in silico study, based on entire genome sequences from five bifidobacterial strains, showed that Bifidobacterium genomes contain numerous CpG motifs, including 5'-purine-purine-CG-pyrimidine-pyrimidine-3' and 5'-purine-TCG-pyrimidine-pyrimidine-3' motifs, and biologically active sequences previously identified in lactic acid bacteria. We identified four CpG-rich sequences with Bifidobacterium longum NCC2705. Two sequences with a percent G+C of about 68% included 14 and 16 CpG motifs. Two sequences with a percent G+C of about 60% included 16 and 6 CpG motifs. These sequences induce the production of monocyte chemoattractant protein 1 (MCP-1) and tumor necrosis factor alpha (TNF-alpha) through a pattern of TLR9 stimulation on RAW 264.7 macrophages. No link could be established between their immunostimulatory properties, the number of CpG motifs, and percent G+C. We investigated inter- and intraspecies heterogeneity in 71 strains of various origins. These sequences were highly conserved in the genus. No link was found between the presence of the CpG-rich sequence and the origin of the strains (healthy, allergic, or preterm infants). The high frequency of CpG motifs in the DNA of Bifidobacterium may play an important role in the immunostimulatory properties of commensal or probiotic bifidobacterial strains.

Nucleoprotein Diet Ameliorates Arthritis Symptoms in Mice Transgenic for Human T-Cell Leukemia Virus Type I (HTLV-1)

Because rheumatoid arthritis (RA), an autoimmune disease, the patients often recognize side-effects due to the medication, alternative therapeutic strategies might potentially offer a clinical advantage. We evaluated the effect of nucleoprotein from salmon soft roe on animal model of arthritis. Mice transgenic for human T-cell leukemia virus type I (HTLV-1 Tg) were divided into three experimental groups and supplemented on either nucleoprotein-free (nonNP), or 0.6% or 1.2% nucleoprotein mixed (NP0.6 or NP1.2) diet for 3 months. The mice were evaluated arthritis by morphology, and measured with rheumatoid factor (RF). Moreover, macrophages and oxidative metabolites were assessed in the ankle and/or serum. Anti-oxidative potentials in nucleoprotein were determined with biological anti-oxidative potential (BAP) test, and electron spin resonance (ESR) analysis. NonNP-diet HTLV-1 Tg mice increased an arthritis symptoms and RF. The symptoms were ameliorated in NP-diet groups. Macrophages detected by F4/80 staining, and oxidative metabolites in the serum and/or joints were clearly decreased in 1.2% NP-diet HTLV-1 Tg mice. Nucleoprotein and DNA-nucleotide, but less protamine, had direct anti-oxidative potency with BAP test and/or ESR in vitro. These observations suggest that dietary nucleoprotein ameliorates arthritis symptoms in HTLV-1 Tg mice and offers hope as an alternative treatment for this debilitating medical condition.

Administration of antibiotics during infancy promoted the development of atopic dermatitis-like skin lesions in NC/Nga mice

This study aimed to determine whether oral antibiotic administration during infancy is associated with the spontaneous development of atopic dermatitis-like skin lesions by modulating intestinal microbiota. Female NC/Nga mice at 3 weeks of age were orally administered kanamycin or polymyxin B. Clinical symptoms, scratching behavior, and serum antibody levels were evaluated. Changes in intestinal microbiota were determined by culture-independent analysis and cultural analysis. The kanamycin-treated mice showed higher clinical scores and scratching frequency than the control mice. IgE levels were significantly higher in the kanamycin-treated mice than in the control mice. Transient changes in intestinal microbiota were observed under kanamycin treatment. Polymyxin B treatment failed to affect scratching behavior. These results suggest that oral administration of kanamycin during infancy promoted the development of atopic dermatitis-like skin lesions in NC/Nga mice and was associated with a transient change in intestinal microbiota.

Factors influencing the incidence and prevalence of food allergy

Food allergy is an increasing problem in Europe and elsewhere and severe reactions to food are also becoming more common. As food allergy is usually associated with other forms of allergic sensitisation it is likely that many risk factors are common to all forms of allergy. However the potential severity of the disease and the specific public heath measures required for food allergy make it important to identify the specific risk factors for this condition. Food allergy is unusual in that it often manifests itself very early in life and commonly remits with the development of tolerance. Hypotheses that explain the distribution of food allergy include specific genetic polymorphisms, the nature of the allergens involved and the unique exposure to large quantities of allergen through the gut. Progress has been made in developing more specific and testable hypotheses but the evidence for any of these is still only preliminary. Further collaborative research is required to develop an appropriate public health response to this growing problem.

The managed immune system: protecting the womb to delay the tomb

The developing immune system serves as a novel target for disruption by environmental chemicals and drugs, and one that can significantly influence later-life health risks. Specific immune maturational events occur during critical windows of pre- and early postnatal development that are not effectively modeled using adult exposure-assessment or general developmental toxicity screens. The range of postnatal health risks linked to developmental immunotoxicity (DIT) is influenced, in part, by the natural progression of prenatal-neonatal development. In this progression, the pregnancy itself imposes a Th2-bias in utero, and this produces a delay in the acquisition of Th1 functional capacity in the newborn. The status of Th1 regulatory and Th17 populations may also be important in immune function/dysfunction considerations. The necessary shift from a Th2 preferred capacity in late gestation to a more balance functional capacity in the neonate can be disrupted by xenobiotics leaving the child with increased vulnerability to a range of potential diseases. Knowledge of environmental factors that facilitate effective immune functional maturation as well as those xenobiotics capable of disrupting the process is important in strategies to reduce the incidence of diseases such as childhood asthma. Because hormesis has been shown to be an important factor in modulation of the adult immune system, it becomes even more important to understand potentially opposing dose-response effects for the immune system of the fetus, neonate, and juvenile. The direct linkage between immune dysfunction and chronic disease has become abundantly apparent in recent years. Therefore, a more comprehensive and effective approach for the protection of the developing immune system can help to reduce the incidence of later-life chronic diseases.

Gnotobiotic mouse immune response induced by Bifidobacterium sp. strains isolated from infants

Bifidobacterium, which is a dominant genus in infants' fecal flora and can be used as a probiotic, has shown beneficial effects in various pathologies, including allergic diseases, but its role in immunity has so far been little known. Numerous studies have shown the crucial role of the initial intestinal colonization in the development of the intestinal immune system, and bifidobacteria could play a major role in this process. For a better understanding of the effect of Bifidobacterium on the immune system, we aimed at determining the impact of Bifidobacterium on the T-helper 1 (T(H)1)/T(H)2 balance by using gnotobiotic mice. Germfree mice were inoculated with Bifidobacterium longum NCC2705, whose genome is sequenced, and with nine Bifidobacterium strains isolated from infants' fecal flora. Five days after inoculation, mice were killed. Transforming growth factor beta1 (TGF-beta1), interleukin-4 (IL-4), IL-10, and gamma interferon (IFN-gamma) gene expressions in the ileum and IFN-gamma, tumor necrosis factor alpha (TNF-alpha), IL-10, IL-4, and IL-5 secretions by splenocytes cultivated for 48 h with concanavalin A were quantified. Two Bifidobacterium species had no effect (B. adolescentis) or little effect (B. breve) on the immune system. Bifidobacterium bifidum, Bifidobacterium dentium, and one B. longum strain induced T(H)1 and T(H)2 cytokines at the systemic and intestinal levels. One B. longum strain induced a T(H)2 orientation with high levels of IL-4 and IL-10, both secreted by splenocytes, and of TGF-beta gene expression in the ileum. The other two strains induced T(H)1 orientations with high levels of IFN-gamma and TNF-alpha splenocyte secretions. Bifidobacterium's capacity to stimulate immunity is species specific, but its influence on the orientation of the immune system is strain specific.

Food allergy and anaphylaxis

Food allergy is a common cause of anaphylaxis, and its incidence is rising. The development of allergy is multifactorial, and the mechanisms of tolerance are complex. The natural history of food allergy varies by causative food; some allergies are mostly outgrown, while others are usually life-long. Anaphylaxis caused by food allergy may differ clinically from other causes of anaphylaxis. Death is usually caused by respiratory failure, and patients who have asthma are at greatest risk for severe reactions. At this time, avoiding allergenic triggers, and when that fails, timely administration of epinephrine, are the main approaches to food allergy. Although several experimental medications promise to dramatically change the field of food allergy, none of these treatments are currently available outside of research settings.

Using house dust extracts to understand the immunostimulatory activities of living environments

Laboratory and epidemiological studies have provided indirect but compelling evidence that toll-like receptor (TLR) signaling pathways play an important role in host responsiveness to ambient immunostimulatory factors. Nonetheless, direct evidence is limited. This paper will present our experience investigating the innate immunostimulatory activities of sterile house dust extracts (HDEs). In initial studies, bone marrow derived dendritic cells (BMDDCs) were cultured with HDEs, and cytokine production and co-stimulatory molecule expression were evaluated. In additional experiments, the TLR dependence of these responses was determined. HDEs induced concentration-dependent BMDDC activation. Moreover, the relative bioactivities of HDEs correlated with their endotoxin content. Finally, HDE-mediated responses were found to be partially dependent on TLR2, TLR4, and TLR9 and almost completely dependent on MyD88. These investigations provide the first direct evidence that TLR signaling pathways play a key role in innate responsiveness to non-infectious factors ubiquitous in living environments.

Role of the innate immune system and host-commensal mutualism

Host organisms live in intimate contact with indigenous microflora. The interactions between the host and commensal microbiota are highly complex and heterogeneous. A growing body of evidence indicates that commensal symbionts provide many benefits to the host physiology, particularly in the gastrointestinal system. The molecular mechanisms of the mutualistic interactions between the host and commensals are largely unknown but can be due either to bioactivity of the commensals or to the reaction of the host immune system to the commensal-derived products. Recent advances in our understanding of the innate immune system allow re-evaluation of some of the older findings regarding the mechanisms of benefits conferred by microflora. Here we review the examples of the benefits of host-commensal interactions that are due to recognition of commensal microbial products by the host innate immune system.