Small intestinal nematode infection of mice is associated with increased enterobacterial loads alongside the intestinal tract

A Novel Non-invasive Method to Detect RELM Beta Transcript in Gut Barrier Related Changes During a Gastrointestinal Nematode Infection

Currently, methods for monitoring changes of gut barrier integrity and the associated immune response via non-invasive means are limited. Therefore, we aimed to develop a novel non-invasive technique to investigate immunological host responses representing gut barrier changes in response to infection. We identified the mucous layer on feces from mice to be mainly composed of exfoliated intestinal epithelial cells. Expression of RELM-β, a gene prominently expressed in intestinal nematode infections, was used as an indicator of intestinal cellular barrier changes to infection. RELM-β was detected as early as 6 days post-infection (dpi) in exfoliated epithelial cells. Interestingly, RELM-β expression also mirrored the quality of the immune response, with higher amounts being detectable in a secondary infection and in high dose nematode infection in laboratory mice. This technique was also applicable to captured worm-infected wild house mice. We have therefore developed a novel non-invasive method reflecting gut barrier changes associated with alterations in cellular responses to a gastrointestinal nematode infection.

Fecal Microbiota Transplantation Decreases Intestinal Loads of Multi-Drug Resistant Pseudomonas aeruginosa in Murine Carriers

Intestinal carriage of multi-drug resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa (Psae) constitutes a pivotal prerequisite for subsequent fatal endogenous infections in patients at risk. We here addressed whether fecal microbiota transplantation (FMT) could effectively combat MDR-Psae carriage. Therefore, secondary abiotic mice were challenged with MDR-Psae by gavage. One week later, mice were subjected to peroral FMT from either murine or human donors on 3 consecutive days. Irrespective of murine or human origin of fecal transplant, intestinal MDR-Psae loads decreased as early as 24 h after the initial FMT. Remarkably, the murine FMT could lower intestinal MDR-Psae burdens by approximately 4 log orders of magnitude within 1 week. In another intervention study, mice harboring a human gut microbiota were perorally challenged with MDR-Psae and subjected to murine FMT on 3 consecutive days, 1 week later. Strikingly, within 5 days, murine FMT resulted in lower loads and carrier rates of MDR-Psae in mice with a human gut microbiota. In conclusion, FMT might be a promising antibiotics-independent option to combat intestinal MDR-Psae carriage and thus prevent from future endogenous infections of patients at risk.

Multidrug-Resistant Pseudomonas aeruginosa Accelerate Intestinal, Extra-Intestinal, and Systemic Inflammatory Responses in Human Microbiota-Associated Mice With Subacute Ileitis

The globally rising incidences of multidrug-resistant (MDR) Pseudomonas aeruginosa (Psae) in humans and live-stock animals has prompted the World Health Organization to rate MDR Psae as serious threat for human health. Only little is known, however, regarding factors facilitating gastrointestinal Psae-acquisition by the vertebrate host and subsequently induced inflammatory sequelae. In the present study, we addressed whether subacute ileitis predisposed mice harboring a human gut microbiota for intestinal MDR Psae carriage and whether inflammatory responses might be induced following peroral challenge with the opportunistic pathogen. To accomplish this, secondary abiotic mice were associated with a human gut microbiota by fecal microbiota transplantation. Ten days later (i.e., on day 0), subacute ileitis was induced in human microbiota associated (hma) mice by peroral low-dose Toxoplasma gondii infection. On day 5 post-infection, mice were perorally challenged with 10⁹ colony forming units of a clinical MDR Psae isolate by gavage and the fecal bacterial loads surveyed thereafter. Four days post-peroral challenge, only approximately one third of mice with a human gut microbiota and subacute ileitis harbored the opportunistic pathogen in the intestinal tract. Notably, the gut microbiota composition was virtually unaffected by the Psae-carriage status during subacute ileitis of hma mice. The Psae challenge resulted, however, in more pronounced intestinal epithelial apoptotic cell and T lymphocyte responses upon ileitis induction that were not restricted to the ileum, but also affected the large intestines. Higher Psae-induced abundances of T cells could additionally be observed in extra-intestinal compartments including liver, kidney, lung, and heart of hma mice with subacute ileitis. Furthermore, higher apoptotic cell numbers, but lower anti-inflammatory IL-10 concentrations were assessed in the liver of Psae as compared to mock treated mice with ileitis. Remarkably, Psae-challenge was accompanied by even more pronounced systemic secretion of pro-inflammatory cytokines such as TNF and IL-6 at day 9 post ileitis induction. In conclusion, whereas in one third of hma mice with subacute ileitis Psae could be isolated from the intestines upon peroral challenge, the opportunistic pathogen was responsible for inflammatory sequelae in intestinal, extra-intestinal, and even systemic compartments and thus worsened subacute ileitis outcome irrespective of the Psae-carrier status.

Chinese liver fluke Clonorchis sinensis infection changes the gut microbiome and increases probiotic Lactobacillus in mice

Chinese liver fluke Clonorchis sinensis changes the host's immune system. Recently, it has been reported that helminths including C. sinensis can ameliorate immune-related diseases such as allergy. In addition, recent studies showed that helminth infection can alleviate immune-mediated disorders by altering the gut microbiome. However, changes in the gut microbiome due to C. sinensis have not been reported yet. In this study, changes in the gut microbiome of C57BL/6 mice infected with C. sinensis metacercariae were evaluated over time. Stool was analyzed by 16S rRNA amplicon analysis using high-throughput sequencing technology. There was no apparent difference in species richness and diversity between the infected and control groups. However, the composition of the microbiome was different between the infected and control groups at 20 days and 30 days post-infection, and the difference disappeared at 50 days post-infection. In particular, this microbiome alteration was associated with a change in the relative abundance of genus Lactobacillus and the probiotic Lactobacillus species that are known to have an immune-modulation role in immune-mediated diseases.

Exclusive dependence of IL-10Rα signalling on intestinal microbiota homeostasis and control of whipworm infection

The whipworm Trichuris trichiura is a soil-transmitted helminth that dwells in the epithelium of the caecum and proximal colon of their hosts causing the human disease, trichuriasis. Trichuriasis is characterized by colitis attributed to the inflammatory response elicited by the parasite while tunnelling through intestinal epithelial cells (IECs). The IL-10 family of receptors, comprising combinations of subunits IL-10Rα, IL-10Rβ, IL-22Rα and IL-28Rα, modulates intestinal inflammatory responses. Here we carefully dissected the role of these subunits in the resistance of mice to infection with T. muris, a mouse model of the human whipworm T. trichiura. Our findings demonstrate that whilst IL-22Rα and IL-28Rα are dispensable in the host response to whipworms, IL-10 signalling through IL-10Rα and IL-10Rβ is essential to control caecal pathology, worm expulsion and survival during T. muris infections. We show that deficiency of IL-10, IL-10Rα and IL-10Rβ results in dysbiosis of the caecal microbiota characterised by expanded populations of opportunistic bacteria of the families Enterococcaceae and Enterobacteriaceae. Moreover, breakdown of the epithelial barrier after whipworm infection in IL-10, IL-10Rα and IL-10Rβ-deficient mice, allows the translocation of these opportunistic pathogens or their excretory products to the liver causing organ failure and lethal disease. Importantly, bone marrow chimera experiments indicate that signalling through IL-10Rα and IL-10Rβ in haematopoietic cells, but not IECs, is crucial to control worm expulsion and immunopathology. These findings are supported by worm expulsion upon infection of conditional mutant mice for the IL-10Rα on IECs. Our findings emphasize the pivotal and complex role of systemic IL-10Rα signalling on immune cells in promoting microbiota homeostasis and maintaining the intestinal epithelial barrier, thus preventing immunopathology during whipworm infections.

A comprehensive analysis of the faecal microbiome and metabolome of Strongyloides stercoralis infected volunteers from a non-endemic area

Data from recent studies support the hypothesis that infections by human gastrointestinal (GI) helminths impact, directly and/or indirectly, on the composition of the host gut microbial flora. However, to the best of our knowledge, these studies have been conducted in helminth-endemic areas with multi-helminth infections and/or in volunteers with underlying gut disorders. Therefore, in this study, we explore the impact of natural mono-infections by the human parasite Strongyloides stercoralis on the faecal microbiota and metabolic profiles of a cohort of human volunteers from a non-endemic area of northern Italy (S+), pre- and post-anthelmintic treatment, and compare the findings with data obtained from a cohort of uninfected controls from the same geographical area (S-). Analyses of bacterial 16S rRNA high-throughput sequencing data revealed increased microbial alpha diversity and decreased beta diversity in the faecal microbial profiles of S+ subjects compared to S-. Furthermore, significant differences in the abundance of several bacterial taxa were observed between samples from S+ and S- subjects, and between S+ samples collected pre- and post-anthelmintic treatment. Faecal metabolite analysis detected marked increases in the abundance of selected amino acids in S+ subjects, and of short chain fatty acids in S- subjects. Overall, our work adds valuable knowledge to current understanding of parasite-microbiota associations and will assist future mechanistic studies aimed to unravel the causality of these relationships.

Parasitic Nematodes Exert Antimicrobial Activity and Benefit From Microbiota-Driven Support for Host Immune Regulation

Intestinal parasitic nematodes live in intimate contact with the host microbiota. Changes in the microbiome composition during nematode infection affect immune control of the parasites and shifts in the abundance of bacterial groups have been linked to the immunoregulatory potential of nematodes. Here we asked if the small intestinal parasite Heligmosomoides polygyrus produces factors with antimicrobial activity, senses its microbial environment and if the anti-nematode immune and regulatory responses are altered in mice devoid of gut microbes. We found that H. polygyrus excretory/secretory products exhibited antimicrobial activity against gram^+/− bacteria. Parasites from germ-free mice displayed alterations in gene expression, comprising factors with putative antimicrobial functions such as chitinase and lysozyme. Infected germ-free mice developed increased small intestinal Th2 responses coinciding with a reduction in local Foxp3⁺RORγt⁺ regulatory T cells and decreased parasite fecundity. Our data suggest that nematodes sense their microbial surrounding and have evolved factors that limit the outgrowth of certain microbes. Moreover, the parasites benefit from microbiota-driven immune regulatory circuits, as an increased ratio of intestinal Th2 effector to regulatory T cells coincides with reduced parasite fitness in germ-free mice.

Micromanaging Immunity in the Murine Host vs. the Mosquito Vector: Microbiota-Dependent Immune Responses to Intestinal Parasites

The digestive tract plays a central role in nutrient acquisition and harbors a vast and intricate community of bacteria, fungi, viruses and parasites, collectively known as the microbiota. In recent years, there has been increasing recognition of the complex and highly contextual involvement of this microbiota in the induction and education of host innate and adaptive immune responses under homeostasis, during infection and inflammation. The gut passage and colonization by unicellular and multicellular parasite species present an immense challenge to the host immune system and to the microbial communities that provide vital support for its proper functioning. In mammals, parasitic nematodes induce distinct shifts in the intestinal microbial composition. Vice versa, the commensal microbiota has been shown to serve as a molecular adjuvant and immunomodulator during intestinal parasite infections. Moreover, similar interactions occur within insect vectors of deadly human pathogens. The gut microbiota has emerged as a crucial factor affecting vector competence in Anopheles mosquitoes, where it modulates outcomes of infections with malaria parasites. In this review, we discuss currently known involvements of the host microbiota in the instruction, support or suppression of host immune responses to gastrointestinal nematodes and protozoan parasites in mice, as well as in the malaria mosquito vector. A deeper understanding of the mechanisms underlying microbiota-dependent modulation of host and vector immunity against parasites in mammals and mosquitoes is key to a better understanding of the host-parasite relationships and the identification of more efficient approaches for intervention and treatment of parasite infections of both clinical and veterinary importance.

Intestinal fluke Metagonimus yokogawai infection increases probiotic Lactobacillus in mouse cecum

Helminth infection can alleviate immune-mediated disorders such as allergies and autoimmune diseases, by altering the gut microbiome. However, changes in gut microbiome due to intestinal trematodes remain unelucidated. Here, we evaluated the changes in the gut microbiome of ICR mice infected with Metagonimus yokogawai, a hypo-virulent intestinal trematode. Four weeks after infection, mouse cecal content was analyzed by 16S rRNA amplicon analysis. Although there was no apparent difference in species richness and diversity, the microbiome composition was different in the infected and control groups. Furthermore, several Lactobacillus species with known immunomodulatory role in immune-mediated diseases were increased in the infected group.

Epithelial-Cell-Derived Phospholipase A2 Group 1B Is an Endogenous Anthelmintic

Immunity to intestinal helminth infections has been well studied, but the mechanism of helminth killing prior to expulsion remains unclear. Here we identify epithelial-cell-derived phospholipase A₂ group 1B (PLA₂g1B) as a host-derived endogenous anthelmintic. PLA₂g1B is elevated in resistant mice and is responsible for killing tissue-embedded larvae. Despite comparable activities of other essential type-2-dependent immune mechanisms, Pla2g1b^−/− mice failed to expel the intestinal helminths Heligmosomoides polygyrus or Nippostrongylus brasiliensis. Expression of Pla2g1b by epithelial cells was dependent upon intestinal microbiota, adaptive immunity, and common-gamma chain-dependent signaling. Notably, Pla2g1b was downregulated in susceptible mice and inhibited by IL-4R-signaling in vitro, uncoupling parasite killing from expulsion mechanisms. Resistance was restored in Pla2g1b^−/− mice by treating infective H. polygyrus L3 larvae with PLA₂g1B, which reduced larval phospholipid abundance. These findings uncover epithelial-cell-derived Pla2g1b as an essential mediator of helminth killing, highlighting a previously overlooked mechanism of anti-helminth immunity.

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Pla2g1b expression correlated with resistance to intestinal helminth infection

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PLA₂g1B is essential for resistance to intestinal helminth infection in mice

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PLA₂g1B directly reduces phospholipid abundance in infective larvae

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Pla2g1b is expressed by epithelial cells and is negatively regulated by IL-4Rα

Schistosoma mansoni infection is associated with quantitative and qualitative modifications of the mammalian intestinal microbiota

In spite of the extensive contribution of intestinal pathology to the pathophysiology of schistosomiasis, little is known of the impact of schistosome infection on the composition of the gut microbiota of its mammalian host. Here, we characterised the fluctuations in the composition of the gut microbial flora of the small and large intestine, as well as the changes in abundance of individual microbial species, of mice experimentally infected with Schistosoma mansoni with the goal of identifying microbial taxa with potential roles in the pathophysiology of infection and disease. Bioinformatic analyses of bacterial 16S rRNA gene data revealed an overall reduction in gut microbial alpha diversity, alongside a significant increase in microbial beta diversity characterised by expanded populations of Akkermansia muciniphila (phylum Verrucomicrobia) and lactobacilli, in the gut microbiota of S. mansoni-infected mice when compared to uninfected control animals. These data support a role of the mammalian gut microbiota in the pathogenesis of hepato-intestinal schistosomiasis and serves as a foundation for the design of mechanistic studies to unravel the complex relationships amongst parasitic helminths, gut microbiota, pathophysiology of infection and host immunity.

The impact of a helminth-modified microbiome on host immunity

Intestinal helminths have well-characterized modulatory effects on mammalian immune pathways. Ongoing helminth infection has been associated with both the suppression of allergies and an altered susceptibility to microbial infections. Enteric helminths share a niche with the intestinal microbiota, and the presence of helminths alters the microbiota composition and the metabolic signature of the host. Recent studies have demonstrated that the helminth-modified intestinal microbiome has the capacity to modify host immune responses even in the absence of live helminth infection. This article discusses the mechanisms by which helminths modify the intestinal microbiome of mammals, and reviews the evidence for a helminth-modified microbiome directly influencing host immunity during infectious and inflammatory diseases. Understanding the multifaceted mechanisms that underpin helminth immunomodulation will pave the way for novel therapies to combat infectious and inflammatory diseases.

Anti-inflammatory Effects of the Octapeptide NAP in Human Microbiota-Associated Mice Suffering from Subacute Ileitis

The octapeptide NAP is well known for its neuroprotective properties. We here investigated whether NAP treatment could alleviate pro-inflammatory immune responses during experimental subacute ileitis. To address this, mice with a human gut microbiota were perorally infected with one cyst of Toxoplasma gondii (day 0) and subjected to intraperitoneal synthetic NAP treatment from day 1 until day 8 postinfection (p.i.). Whereas placebo (PLC) control animals displayed subacute ileitis at day 9 p.i., NAP-treated mice exhibited less pronounced pro-inflammatory immune responses as indicated by lower numbers of intestinal mucosal T and B lymphocytes and lower interferon (IFN)-γ concentrations in mesenteric lymph nodes. The NAP-induced anti-inflammatory effects were not restricted to the intestinal tract but could also be observed in extra-intestinal including systemic compartments, given that pro-inflammatory cytokines were lower in liver, kidney, and lung following NAP as compared to PLC application, whereas at day 9 p.i., colonic and serum interleukin (IL)-10 concentrations were higher in the former as compared to the latter. Remarkably, probiotic commensal bifidobacterial loads were higher in the ileal lumen of NAP as compared to PLC-treated mice with ileitis. Our findings thus further support that NAP might be regarded as future treatment option directed against intestinal inflammation.

Helminth-Bacterial Interactions: Cause and Consequence

Intestinal helminths, along with mutualistic microbes, have cohabited the intestine of mammals throughout evolution. Interactions between helminths, bacteria, and their mammalian hosts may shape not only host-helminth and host-microbiome interactions, but also the relationship between helminths and the microbiome. This 'ménage à trois' situation may not be completely balanced in that it may favor either the host or the parasite, possibly at the cost of the other partner. Similarly, helminths may favor the establishment of a particular microbiome with either positive or negative consequences for the overall health and well-being of the host. Recent studies indicate that infection with intestinal helminths can and does impact the intestinal microbiome, with important consequences for each partner in this tripartite relationship.

Helminths and intestinal barrier function

Approximately one-sixth of the worlds' population is infected with helminths and this class of parasite takes a major toll on domestic livestock. The majority of species of parasitic helminth that infect mammals live in the gut (the only niche for tapeworms) where they contact the hosts' epithelial cells. Here, the helminth-intestinal epithelial interface is reviewed in terms of the impact on, and regulation of epithelial barrier function, both intrinsic (epithelial permeability) and extrinsic (mucin, bacterial peptides, commensal bacteria) elements of the barrier. The data available on direct effects of helminths on epithelial permeability are scant, fragmentary and pales in comparison with knowledge of mobilization of immune reactions and effector cells in response to helminth parasites and how these impact intestinal barrier function. The interaction of helminth-host and helminth-host-bacteria is an important determinant of gut form and function and precisely defining these interactions will radically alter our understanding of normal gut physiology and pathophysiological reactions, revealing new approaches to infection with parasitic helminths, bacterial pathogens and idiopathic auto-inflammatory disease.

Parasite-Microbiota Interactions With the Vertebrate Gut: Synthesis Through an Ecological Lens

The vertebrate gut teems with a large, diverse, and dynamic bacterial community that has pervasive effects on gut physiology, metabolism, and immunity. Under natural conditions, these microbes share their habitat with a similarly dynamic community of eukaryotes (helminths, protozoa, and fungi), many of which are well-known parasites. Both parasites and the prokaryotic microbiota can dramatically alter the physical and immune landscape of the gut, creating ample opportunities for them to interact. Such interactions may critically alter infection outcomes and affect overall host health and disease. For instance, parasite infection can change how a host interacts with its bacterial flora, either driving or protecting against dysbiosis and inflammatory disease. Conversely, the microbiota can alter a parasite's colonization success, replication, and virulence, shifting it along the parasitism-mutualism spectrum. The mechanisms and consequences of these interactions are just starting to be elucidated in an emergent transdisciplinary area at the boundary of microbiology and parasitology. However, heterogeneity in experimental designs, host and parasite species, and a largely phenomenological and taxonomic approach to synthesizing the literature have meant that common themes across studies remain elusive. Here, we use an ecological perspective to review the literature on interactions between the prokaryotic microbiota and eukaryotic parasites in the vertebrate gut. Using knowledge about parasite biology and ecology, we discuss mechanisms by which they may interact with gut microbes, the consequences of such interactions for host health, and how understanding parasite-microbiota interactions may lead to novel approaches in disease control.

Multidrug-resistant Pseudomonas aeruginosa aggravates inflammatory responses in murine chronic colitis

The World Health Organization has rated multidrug-resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa (Psae) as serious threat to human health. We here addressed whether chronic murine gut inflammation facilitates intestinal MDR Psae colonization and whether bacterial infection subsequently worsens colonic immunopathology. Converse to wildtype counterparts, Psae colonized the intestines of IL-10^−/− mice with chronic colitis following peroral challenge, but did not lead to changes in intestinal microbiota composition. Psae infection accelerated both macroscopic (i.e. clinical) and microscopic disease (i.e. colonic epithelial apoptosis), that were accompanied by increased intestinal pro-inflammatory immune responses as indicated by elevated colonic numbers of innate and adaptive immune cell subsets and enhanced secretion of pro-inflammatory cytokines such as TNF and IFN-γ in mesenteric lymph nodes of Psae-infected as compared to unchallenged IL-10^−/− mice. Remarkably, Psae-induced pro-inflammatory immune responses were not restricted to the gut, but could also be observed systemically as indicated by increased TNF and IFN-γ concentrations in sera upon Psae-infection. Furthermore, viable commensals originating from the intestinal microbiota translocated to extra-intestinal compartments such as liver, kidney and spleen of Psae-infected IL-10^−/− mice with chronic colitis only. Hence, peroral MDR Psae-infection results in exacerbated colonic as well as systemic pro-inflammatory immune responses during chronic murine colitis.

Peroral Low-Dose Toxoplasma gondii Infection of Human Microbiota-Associated Mice - A Subacute Ileitis Model to Unravel Pathogen-Host Interactions

Within 1 week following high-dose Toxoplasma gondii infection, mice develop lethal necrotizing ileitis. However, data from a subacute T. gondii-induced ileitis model are scarce. Therefore, mice harboring a human gut microbiota were perorally infected with one cyst of T. gondii. Within 9 days post-infection, the intestinal microbiota composition shifted towards higher loads of commensal enterobacteria and enterococci. Following T. gondii infection, mice were clinically only mildly affected, whereas ≈60% of mice displayed fecal blood and mild-to-moderate ileal histopathological changes. Intestinal inflammation was further characterized by increased apoptotic intestinal epithelial cells, which were accompanied by elevated proliferating gut epithelial cell numbers. As compared to naive controls, infected mice displayed elevated numbers of intestinal T lymphocytes and regulatory T-cells and increased pro-inflammatory mediator secretion. Remarkably, T. gondii-induced apoptotic and pro-inflammatory immune responses were not restricted to the gut, but could also be observed in extra-intestinal compartments including kidney, liver, and lung. Strikingly, low-dose T. gondii infection resulted in increased serum levels of pro- and anti-inflammatory cytokines. In conclusion, the here presented subacute ileitis model following peroral low-dose T. gondii infection of humanized mice allows for detailed investigations of the molecular mechanism underlying the “ménage à trois” of pathogens, human gut microbiota, and immunity.

The octapetide NAP alleviates intestinal and extra-intestinal anti-inflammatory sequelae of acute experimental colitis

The octapeptide NAP has been shown to exert neuroprotective properties and reduce neuro-inflammatory responses. The aim of the present study was to investigate if NAP provides anti-inflammatory effects in acute murine colitis. To address this, C57BL/6 j mice were challenged with 3.5% dextran sulfate sodium from day 0 until day 6 to induce colitis, either treated intraperitoneally with NAP or placebo (NaCl 0.9%) from day 1 until day 6 post-induction (p.i.) and subjected to in depth macroscopic, microscopic and immunological evaluations. Whereas NAP application did not alleviate macroscopic (i.e. clinical) sequelae of colitis, lower numbers of apoptotic, but higher counts of proliferating/regenerating colonic epithelial cells could be observed in NAP as compared to placebo treated mice at day 7 p.i. Furthermore, lower numbers of adaptive immune cells such as T lymphocytes and regulatory T cells were abundant in the colonic mucosa and lamina propria upon NAP versus placebo treatment that were accompanied by less colonic secretion of pro-inflammatory mediators including IFN-γ and nitric oxide at day 7 p.i. In mesenteric lymph nodes, pro-inflammatory IFN-γ, TNF and IL-6 concentrations were increased in placebo, but not NAP treated mice at day 7 p.i., whereas interestingly, elevated anti-inflammatory IL-10 levels could be observed in NAP treated mice only. The assessed anti-inflammatory properties of NAP were not restricted to the intestinal tract, given that in extra-intestinal compartments such as the kidneys, IFN-γ levels increased in placebo, but not NAP treated mice upon colitis induction. NAP induced effects were accompanied by distinct changes in intestinal microbiota composition, given that colonic luminal loads of bifidobacteria, regarded as anti-inflammatory, "health-promoting" commensal species, were two orders of magnitude higher in NAP as compared to placebo treated mice and even naive controls. In conclusion, NAP alleviates intestinal and extra-intestinal pro-inflammatory sequelae of acute experimental colitis and may provide novel treatment options of intestinal inflammatory diseases in humans.

Differential human gut microbiome assemblages during soil-transmitted helminth infections in Indonesia and Liberia

BACKGROUND

The human intestine and its microbiota is the most common infection site for soil-transmitted helminths (STHs), which affect the well-being of ~ 1.5 billion people worldwide. The complex cross-kingdom interactions are not well understood.

RESULTS

A cross-sectional analysis identified conserved microbial signatures positively or negatively associated with STH infections across Liberia and Indonesia, and longitudinal samples analysis from a double-blind randomized trial showed that the gut microbiota responds to deworming but does not transition closer to the uninfected state. The microbiomes of individuals able to self-clear the infection had more alike microbiome assemblages compared to individuals who remained infected. One bacterial taxon (Lachnospiracae) was negatively associated with infection in both countries, and 12 bacterial taxa were significantly associated with STH infection in both countries, including Olsenella (associated with reduced gut inflammation), which also significantly reduced in abundance following clearance of infection. Microbial community gene abundances were also affected by deworming. Functional categories identified as associated with STH infection included arachidonic acid metabolism; arachidonic acid is the precursor for pro-inflammatory leukotrienes that threaten helminth survival, and our findings suggest that some modulation of arachidonic acid activity in the STH-infected gut may occur through the increase of arachidonic acid metabolizing bacteria.

CONCLUSIONS

For the first time, we identify specific members of the gut microbiome that discriminate between moderately/heavily STH-infected and non-infected states across very diverse geographical regions using two different statistical methods. We also identify microbiome-encoded biological functions associated with the STH infections, which are associated potentially with STH survival strategies, and changes in the host environment. These results provide a novel insight of the cross-kingdom interactions in the human gut ecosystem by unlocking the microbiome assemblages at taxonomic, genetic, and functional levels so that advances towards key mechanistic studies can be made.

The relationships between faecal egg counts and gut microbial composition in UK Thoroughbreds infected by cyathostomins

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We profiled the faecal microbial communities of horses with cyathostomin infections, pre- and post-anthelmintic treatment.

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Methanomicrobia and Dehalobacterium were expanded in the microbiota of horses with low cyathostomin faecal egg counts.

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A reduction in TM7 and an expansion in Adlercreutzia followed anthelmintic treatment in horses with high faecal egg counts.

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Novel intervention strategies against cyathostomins based on the manipulation of the gut flora may be developed.

A growing body of evidence, particularly in humans and rodents, supports the existence of a complex network of interactions occurring between gastrointestinal (GI) helminth parasites and the gut commensal bacteria, with substantial effects on both host immunity and metabolic potential. However, little is known of the fundamental biology of such interactions in other animal species; nonetheless, given the considerable economic losses associated with GI parasites, particularly in livestock and equines, as well as the global threat of emerging anthelmintic resistance, further explorations of the complexities of host-helminth-microbiota interactions in these species are needed. This study characterises the composition of the equine gut commensal flora associated with the presence, in faecal samples, of low (Clow) and high (Chigh) numbers of eggs of an important group of GI parasites (i.e. the cyathostomins), prior to and following anthelmintic treatment. High-throughput sequencing of bacterial 16S rRNA amplicons and associated bioinformatics and statistical analyses of sequence data revealed strong clustering according to faecal egg counts (P = 0.003). A trend towards increased populations of Methanomicrobia (class) and Dehalobacterium (genus) was observed in Clow in comparison with Chigh. Anthelmintic treatment in Chigh was associated with a significant reduction of the bacterial Phylum TM7 14 days post-ivermectin administration, as well as a transient expansion of Adlercreutzia spp. at 2 days post-treatment. This study provides a first known insight into the discovery of the intimate mechanisms governing host-parasite-microbiota interactions in equines, and sets a basis for the development of novel, biology-based intervention strategies against equine GI helminths based on the manipulation of the commensal gut flora.

Helminth-induced alterations of the gut microbiota exacerbate bacterial colitis

Infection with the intestinal helminth parasite Heligmosomoides polygyrus exacerbates the colitis caused by the bacterial enteropathogen Citrobacter rodentium. To clarify the underlying mechanism, we analyzed fecal microbiota composition of control and helminth-infected mice and evaluated the functional role of compositional differences by microbiota transplantation experiments. Our results showed that infection of Balb/c mice with H. polygyrus resulted in significant changes in the composition of the gut microbiota, characterized by a marked increase in the abundance of Bacteroidetes and decreases in Firmicutes and Lactobacillales. Recipients of the gut microbiota from helminth-infected wide-type, but not STAT6-deficient, Balb/c donors had increased fecal pathogen shedding and significant worsening of Citrobacter-induced colitis compared to recipients of microbiota from control donors. Recipients of helminth-altered microbiota also displayed increased regulatory T cells and IL-10 expression. Depletion of CD4+CD25+ T cells and neutralization of IL-10 in recipients of helminth-altered microbiota led to reduced stool C. rodentium numbers and attenuated colitis. These results indicate that alteration of the gut microbiota is a significant contributor to the H. polygyrus-induced exacerbation of C. rodentium colitis. The helminth-induced alteration of the microbiota is Th2-dependent and acts by promoting regulatory T cells that suppress protective responses to bacterial enteropathogens.

Recent advances in gut immunology

In recent years, there have been significant advances in our understanding of the mucosal immune system. In addition to unravelling some of the complexities of this system, including the discovery of completely new cells types, further insights into the three-way interactions between mucosal immune cells, the intestinal epithelium and the microbial communities colonizing the GI tract promise to redefine our understanding of how intestinal homeostasis is maintained, but also how dysregulation of these highly integrated interactions conspires to cause disease. In this review, we will discuss major recent advances in the role of key immune players in the gut, including innate lymphoid cells (ILCs), mucosa-associated invariant T cells (MAIT cells) and cells of the mononuclear phagocyte system (MPS), including how these cells interact with the intestinal epithelial and their crosstalk with components of the intestinal microbiota, and how these interactions shape host health.

Intestinal Microbiota Changes in Mice Lacking Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) - Bifidobacteria Make the Difference

Pituitary adenylate cyclase activating polypetide (PACAP) constitutes a neuropeptide that is widely distributed in the host exerting essential cytoprotective properties, whereas PACAP^–/– mice display increased susceptibility to distinct immunopathological conditions. The orchestrated interplay between the gut microbiota and the host is pivotal in immune homeostasis and resistance to disease. Potential pertubations of the intestinal microbiota in PACAP^–/– mice, however, have not been addressed so far. For the first time, we performed a comprehensive survey of the intestinal microbiota composition in PACAP^–/– and wildtype (WT) mice starting 2 weeks postpartum until 18 months of age applying quantitative culture-independent techniques. Fecal enterobacteria and enterococci were lower in PACAP^–/– than WT mice aged 1 month and ≥6 months, respectively. Whereas Mouse Intestinal Bacteroides were slightly higher in PACAP^–/– versus WT mice aged 1 and 6 months, this later in life held true for Bacteroides/Prevotella spp. (≥12 months) and lactobacilli (>15 months of age). Strikingly, health-beneficial bifidobacteria were virtually absent in the intestines of PACAP^–/– mice, even when still breastfed. In conclusion, PACAP deficiency is accompanied by distinct changes in fecal microbiota composition with virtually absent bifidobacteria as a major hallmark that might be linked to increased susceptibility to disease.

Infections by human gastrointestinal helminths are associated with changes in faecal microbiota diversity and composition

Investigations of the impact that patent infections by soil-transmitted gastrointestinal nematode parasites exert on the composition of the host gut commensal flora are attracting growing interest by the scientific community. However, information collected to date varies across experiments, and further studies are needed to identify consistent relationships between parasites and commensal microbial species. Here, we explore the qualitative and quantitative differences between the microbial community profiles of cohorts of human volunteers from Sri Lanka with patent infection by one or more parasitic nematode species (H+), as well as that of uninfected subjects (H-) and of volunteers who had been subjected to regular prophylactic anthelmintic treatment (Ht). High-throughput sequencing of the bacterial 16S rRNA gene, followed by bioinformatics and biostatistical analyses of sequence data revealed no significant differences in alpha diversity (Shannon) and richness between groups (P = 0.65, P = 0.13 respectively); however, beta diversity was significantly increased in H+ and Ht when individually compared to H-volunteers (P = 0.04). Among others, bacteria of the families Verrucomicrobiaceae and Enterobacteriaceae showed a trend towards increased abundance in H+, whereas the Leuconostocaceae and Bacteroidaceae showed a relative increase in H- and Ht respectively. Our findings add valuable knowledge to the vast, and yet little explored, research field of parasite—microbiota interactions and will provide a basis for the elucidation of the role such interactions play in pathogenic and immune-modulatory properties of parasitic nematodes in both human and animal hosts.

Enteric Helminths Promote Salmonella Coinfection by Altering the Intestinal Metabolome

Intestinal helminth infections occur predominantly in regions where exposure to enteric bacterial pathogens is also common. Helminth infections inhibit host immunity against microbial pathogens, which has largely been attributed to the induction of regulatory or type 2 (Th2) immune responses. Here we demonstrate an additional 3-way interaction in which helminth infection alters the metabolic environment of the host intestine to enhance bacterial pathogenicity. We show that an ongoing helminth infection increased colonization by Salmonella independently of T regulatory or Th2 cells. Instead, helminth infection altered the metabolic profile of the intestine, which directly enhanced bacterial expression of Salmonella pathogenicity island 1 (SPI-1) genes and increased intracellular invasion. These data reveal a novel mechanism by which a helminth-modified metabolome promotes susceptibility to bacterial coinfection.

TPL-2 restricts Ccl24-dependent immunity to Heligmosomoides polygyrus

TPL-2 (COT, MAP3K8) kinase activates the MEK1/2-ERK1/2 MAPK signaling pathway in innate immune responses following TLR, TNFR1 and IL-1R stimulation. TPL-2 contributes to type-1/Th17-mediated autoimmunity and control of intracellular pathogens. We recently demonstrated TPL-2 reduces severe airway allergy to house dust mite by negatively regulating type-2 responses. In the present study, we found that TPL-2 deficiency resulted in resistance to Heligmosomoides polygyrus infection, with accelerated worm expulsion, reduced fecal egg burden and reduced worm fitness. Using co-housing experiments, we found resistance to infection in TPL-2 deficient mice (Map3k8-/-) was independent of microbiota alterations in H. polygyrus infected WT and Map3k8-/-mice. Additionally, our data demonstrated immunity to H. polygyrus infection in TPL-2 deficient mice was not due to dysregulated type-2 immune responses. Genome-wide analysis of intestinal tissue from infected TPL-2-deficient mice identified elevated expression of genes involved in chemotaxis and homing of leukocytes and cells, including Ccl24 and alternatively activated genes. Indeed, Map3k8-/-mice had a significant influx of eosinophils, neutrophils, monocytes and Il4GFP+ T cells. Conditional knockout experiments demonstrated that specific deletion of TPL-2 in CD11c+ cells, but not Villin+ epithelial cells, LysM+ myeloid cells or CD4+ T cells, led to accelerated resistance to H. polygyrus. In line with a central role of CD11c+ cells, CD11c+ CD11b+ cells isolated from TPL-2-deficient mice had elevated Ccl24. Finally, Ccl24 neutralization in TPL-2 deficient mice significantly decreased the expression of Arg1, Retnla, Chil3 and Ear11 correlating with a loss of resistance to H. polygyrus. These observations suggest that TPL-2-regulated Ccl24 in CD11c+CD11b+ cells prevents accelerated type-2 mediated immunity to H. polygyrus. Collectively, this study identifies a previously unappreciated role for TPL-2 controlling immune responses to H. polygyrus infection by restricting Ccl24 production.

The Probiotic Compound VSL#3 Modulates Mucosal, Peripheral, and Systemic Immunity Following Murine Broad-Spectrum Antibiotic Treatment

There is compelling evidence linking the commensal intestinal microbiota with host health and, in turn, antibiotic induced perturbations of microbiota composition with distinct pathologies. Despite the attractiveness of probiotic therapy as a tool to beneficially alter the intestinal microbiota, its immunological effects are still incompletely understood. The aim of the present study was to assess the efficacy of the probiotic formulation VSL#3 consisting of eight distinct bacterial species (including Streptococcus thermophilus, Bifidobacterium breve, B. longum, B. infantis, Lactobacillus acidophilus, L. plantarum, L. paracasei, and L. delbrueckii subsp. Bulgaricus) in reversing immunological effects of microbiota depletion as compared to reassociation with a complex murine microbiota. To address this, conventional mice were subjected to broad-spectrum antibiotic therapy for 8 weeks and perorally reassociated with either VSL#3 bacteria or a complex murine microbiota. VSL#3 recolonization resulted in restored CD4+ and CD8+ cell numbers in the small and large intestinal lamina propria as well as in B220+ cell numbers in the former, whereas probiotic intervention was not sufficient to reverse the antibiotic induced changes of respective cell populations in the spleen. However, VSL#3 application was as efficient as complex microbiota reassociation to attenuate the frequencies of regulatory T cells, activated dendritic cells and memory/effector T cells in the small intestine, colon, mesenteric lymph nodes, and spleen. Whereas broad-spectrum antibiotic treatment resulted in decreased production of cytokines such as IFN-γ, IL-17, IL-22, and IL-10 by CD4+ cells in respective immunological compartments, VSL#3 recolonization was sufficient to completely recover the expression of the anti-inflammatory cytokine IL-10 without affecting pro-inflammatory mediators. In summary, the probiotic compound VSL#3 has an extensive impact on mucosal, peripheral, and systemic innate as well as adaptive immunity, exerting beneficial anti-inflammatory effects in intestinal as well as systemic compartments. Hence, VSL#3 might be considered a therapeutic immunomodulatory tool following antibiotic therapy.

Reciprocal Interactions between Nematodes and Their Microbial Environments

Parasitic nematode infections are widespread in nature, affecting humans as well as wild, companion, and livestock animals. Most parasitic nematodes inhabit the intestines of their hosts living in close contact with the intestinal microbiota. Many species also have tissue migratory life stages in the absence of severe systemic inflammation of the host. Despite the close coexistence of helminths with numerous microbes, little is known concerning these interactions. While the environmental niche is considerably different, the free-living nematode Caenorhabditis elegans (C. elegans) is also found amongst a diverse microbiota, albeit on decaying organic matter. As a very well characterized model organism that has been intensively studied for several decades, C. elegans interactions with bacteria are much more deeply understood than those of their parasitic counterparts. The enormous breadth of understanding achieved by the C. elegans research community continues to inform many aspects of nematode parasitology. Here, we summarize what is known regarding parasitic nematode-bacterial interactions while comparing and contrasting this with information from work in C. elegans. This review highlights findings concerning responses to bacterial stimuli, antimicrobial peptides, and the reciprocal influences between nematodes and their environmental bacteria. Furthermore, the microbiota of nematodes as well as alterations in the intestinal microbiota of mammalian hosts by helminth infections are discussed.

Immune Responses to Broad-Spectrum Antibiotic Treatment and Fecal Microbiota Transplantation in Mice

Compelling evidence demonstrates the pivotal role of the commensal intestinal microbiota in host physiology and the detrimental effects of its perturbations following antibiotic treatment. Aim of this study was to investigate the impact of antibiotics induced depletion and subsequent restoration of the intestinal microbiota composition on the murine mucosal and systemic immunity. To address this, conventional C57BL/6j mice were subjected to broad-spectrum antibiotic treatment for 8 weeks. Restoration of the intestinal microbiota by peroral fecal microbiota transplantation (FMT) led to reestablishment of small intestinal CD4⁺, CD8⁺, and B220⁺ as well as of colonic CD4⁺ cell numbers as early as 7 days post-FMT. However, at d28 following FMT, colonic CD4⁺ and B220⁺ cell numbers were comparable to those in secondary abiotic (ABx) mice. Remarkably, CD8⁺ cell numbers were reduced in the colon upon antibiotic treatment, and FMT was not sufficient to restore this immune cell subset. Furthermore, absence of gut microbial stimuli resulted in decreased percentages of memory/effector T cells, regulatory T cells, and activated dendritic cells in the small intestine, colon, mesenteric lymph nodes (MLN), and spleen. Concurrent antibiotic treatment caused decreased cytokine production (IFN-γ, IL-17, IL-22, and IL-10) of CD4⁺ cells in respective compartments. These effects were, however, completely restored upon FMT. In summary, broad-spectrum antibiotic treatment resulted in profound local (i.e., small and large intestinal), peripheral (i.e., MLN), and systemic (i.e., splenic) changes in the immune cell repertoire that could, at least in part, be restored upon FMT. Further studies need to unravel the distinct molecular mechanisms underlying microbiota-driven changes in immune homeostasis subsequently providing novel therapeutic or even preventive approaches in human immunopathologies.

Intestinal, extra-intestinal and systemic sequelae of Toxoplasma gondii induced acute ileitis in mice harboring a human gut microbiota

Background

Within seven days following peroral high dose infection with Toxoplasma gondii susceptible conventionally colonized mice develop acute ileitis due to an underlying T helper cell (Th) -1 type immunopathology. We here addressed whether mice harboring a human intestinal microbiota developed intestinal, extra-intestinal and systemic sequelae upon ileitis induction.

Methodology/Principal findings

Secondary abiotic mice were generated by broad-spectrum antibiotic treatment and associated with a complex human intestinal microbiota following peroral fecal microbiota transplantation. Within three weeks the human microbiota had stably established in the murine intestinal tract as assessed by quantitative cultural and culture-independent (i.e. molecular 16S rRNA based) methods. At day 7 post infection (p.i.) with 50 cysts of T. gondii strain ME49 by gavage human microbiota associated (hma) mice displayed severe clinical, macroscopic and microscopic sequelae indicating acute ileitis. In diseased hma mice increased numbers of innate and adaptive immune cells within the ileal mucosa and lamina propria and elevated intestinal secretion of pro-inflammatory mediators including IFN-γ, IL-12 and nitric oxide could be observed at day 7 p.i. Ileitis development was accompanied by substantial shifts in intestinal microbiota composition of hma mice characterized by elevated total bacterial loads and increased numbers of intestinal Gram-negative commensals such as enterobacteria and Bacteroides / Prevotella species overgrowing the small and large intestinal lumen. Furthermore, viable bacteria translocated from the inflamed ileum to extra-intestinal including systemic compartments. Notably, pro-inflammatory immune responses were not restricted to the intestinal tract as indicated by increased pro-inflammatory cytokine secretion in extra-intestinal (i.e. liver and kidney) and systemic compartments including spleen and serum.

Conclusion/Significance

With respect to the intestinal microbiota composition “humanized” mice display acute ileitis following peroral high dose T. gondii infection. Thus, hma mice constitute a suitable model to further dissect the interactions between pathogens, human microbiota and vertebrate host immunity during acute intestinal inflammation.

Comprehensive Survey of Intestinal Microbiota Changes in Offspring of Human Microbiota-Associated Mice

Secondary abiotic mice generated by broad-spectrum antibiotic treatment provide a valuable tool for association studies with microbiota derived from different vertebrate hosts. We here generated human microbiota-associated (hma) mice by human fecal microbiota transplantation of secondary abiotic mice and performed a comprehensive survey of the intestinal microbiota dynamics in offspring of hma mice over 18 weeks following weaning as compared to their mothers applying both cultural and molecular methods. Mice were maintained under standard hygienic conditions with open cages, handled under aseptic conditions, and fed autoclaved chow and water. Within 1 week post weaning, fecal loads of commensal enterobacteria and enterococci had decreased, whereas obligate anaerobic bacteria such as Bacteroides/Prevotella species and clostridia were stably colonizing the intestines of hma offspring at high loads. Lactobacilli numbers were successively increasing until 18 weeks post weaning in both hma offspring and mothers, whereas by then, bifidobacteria were virtually undetectable in the former only. Interestingly, fecal lactobacilli and bifidobacteria were higher in mothers as compared to their offspring at 5 and 18 weeks post weaning. We conclude that the intestinal microbiota composition changes in offspring of hma mice, but also their mothers over time particularly affecting aerobic and microaerobic species.

Making Mouse Models That Reflect Human Immune Responses

Humans are infected with a variety of acute and chronic pathogens over the course of their lives, and pathogen-driven selection has shaped the immune system of humans. The same is likely true for mice. However, laboratory mice we use for most biomedical studies are bred in ultra-hygienic environments, and are kept free of specific pathogens. We review recent studies that indicate that pathogen infections are important for the basal level of activation and the function of the immune system. Consideration of these environmental exposures of both humans and mice can potentially improve mouse models of human disease.

Acute ileitis facilitates infection with multidrug resistant Pseudomonas aeruginosa in human microbiota-associated mice

Background

The rising incidence of multidrug resistant (MDR) Gram-negative bacteria including Pseudomonas aeruginosa has become a serious issue in prevention of its spread particularly among hospitalized patients. It is, however, unclear whether distinct conditions such as acute intestinal inflammation facilitate P. aeruginosa infection of vertebrate hosts.

Methods and results

To address this, we analysed P. aeruginosa infection in human microbiota-associated (hma) mice with acute ileitis induced by peroral Toxoplasma gondii challenge. When perorally infected with P. aeruginosa at day 3 post ileitis induction, hma mice displayed higher intestinal P. aeruginosa loads as compared to hma mice without ileitis. However, the overall intestinal microbiota composition was not disturbed by P. aeruginosa (except for lowered bifidobacterial populations), and the infection did not further enhance ileal immune cell responses. Pro-inflammatory cytokines including IFN-γ and IL-12p70 were similarly increased in ileum and mesenteric lymph nodes of P. aeruginosa infected and uninfected hma mice with ileitis. The anti-inflammatory cytokine IL-10 increased multifold upon ileitis induction, but interestingly more distinctly in P. aeruginosa infected as compared to uninfected controls. Immune responses were not restricted to the intestines as indicated by elevated pro-inflammatory cytokine levels in liver and kidney upon ileitis induction. However, except for hepatic TNF-α levels, P. aeruginosa infection did not result in more distinct pro-inflammatory cytokine secretion in liver and kidney of hma mice with ileitis. Whereas viable intestinal bacteria were more frequently detected in systemic compartments such as spleen and cardiac blood of P. aeruginosa infected than uninfected mice at day 7 following ileitis induction, P. aeruginosa infection did not exacerbate systemic pro-inflammatory sequelae, but resulted in lower IL-10 serum levels.

Conclusion

Acute intestinal inflammation facilitates infection of the vertebrate host with MDR bacteria including P. aeruginosa and might also pose particularly hospitalized patients at risk for acquisition. Since acute T. gondii induced inflammation might mask immunopathology caused by P. aeruginosa, a subacute or chronic inflammation model might be better suited to investigate the potential role of P. aeruginosa infection in the aggravation of intestinal disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-017-0154-4) contains supplementary material, which is available to authorized users.

Inflammatory arthritis and systemic bone loss are attenuated by gastrointestinal helminth parasites

Infections with different helminth species have been observed to ameliorate a variety of chronic inflammatory diseases. Herein, we show that the natural murine helminth species, Heligmosomoides polygyrus bakeri (Hp) is capable of attenuating disease severity in two different inflammatory arthritis models. Furthermore, we show that excretory-secretory (ES) products from Hp directly suppress osteoclast differentiation in vitro. Taken together, these results demonstrate that helminth infections can dampen autoimmune diseases and highlight a previously unrecognized and important role for ES products, by directly impacting on bone destruction.

Metabolites: deciphering the molecular language between DCs and their environment

Dendritic cells (DCs) determine the outcome of the immune response based on signals they receive from the environment. Presentation of antigen under various contexts can lead to activation and differentiation of T cells for immunity or dampening of immune responses by establishing tolerance, primarily through the priming of regulatory T cells. Infections, inflammation and normal cellular interactions shape DC responses through direct contact or via cytokine signaling. Although it is widely accepted that DCs sense microbial components through pattern recognition receptors (PRRs), increasing evidence advocates for the existence of a set of signals that can profoundly shape DC function via PRR-independent pathways. This diverse group of host- or commensal-derived metabolites represents a newly appreciated code from which DCs can interpret environmental cues. In this review, we discuss the existing information on the effect of some of the most studied metabolites on DC function, together with the implications this may have in immune-mediated diseases.

Interactions between the intestinal microbiome and helminth parasites

Throughout evolution, both helminths and bacteria have inhabited our intestines. As intestinal helminths and bacteria inhabit the same environmental niche, it is likely that these organisms interact with, and impact on, each other. In addition, intestinal helminths are well known to alter intestinal physiology, permeability, mucous secretion and the production of antimicrobial peptides – all of which may impact on bacterial survival and spatial organization. Yet despite rapid advances in our understanding of host–intestinal bacteria interactions, the impact of helminths on this relationship has remained largely unexplored. Moreover, although intestinal helminths are generally accepted to possess potent immuno‐modulatory activity, it is unknown whether this capacity requires interactions with intestinal bacteria. We propose that this ‘ménage à trois’ situation is likely to have exerted a strong selective pressure on the development of our metabolic and immune systems. Whilst such pressures remain in developing countries, the eradication of helminths in industrialized countries has shifted this evolutionary balance, possibly underlying the increased development of chronic inflammatory diseases. Thus, helminth–bacteria interactions may represent a key determinant of healthy homoeostasis.

Early-life enteric infections: relation between chronic systemic inflammation and poor cognition in children

The intestinal microbiota undergoes active remodeling in the first 6 to 18 months of life, during which time the characteristics of the adult microbiota are developed. This process is strongly influenced by the early diet and enteric pathogens. Enteric infections and malnutrition early in life may favor microbiota dysbiosis and small intestinal bacterial overgrowth, resulting in intestinal barrier dysfunction and translocation of intestinal bacterial products, ultimately leading to low-grade, chronic, subclinical systemic inflammation. The leaky gut-derived low-grade systemic inflammation may have profound consequences on the gut-liver-brain axis, compromising normal growth, metabolism, and cognitive development. This review examines recent data suggesting that early-life enteric infections that lead to intestinal barrier disruption may shift the intestinal microbiota toward chronic systemic inflammation and subsequent impaired cognitive development.

Macrobiota - helminths as active participants and partners of the microbiota in host intestinal homeostasis

Important insights have recently been gained in our understanding of the intricate relationship in the intestinal milieu between the vertebrate host mucosal immune response, commensal bacteria, and helminths. Helminths are metazoan worms (macrobiota) and trigger immune responses that include potent regulatory components capable of controlling harmful inflammation, protecting barrier function and mitigating tissue damage. They can secrete a variety of products that directly affect immune regulatory function but they also have the capacity to influence the composition of microbiota, which can also then impact immune function. Conversely, changes in microbiota can affect susceptibility to helminth infection, indicating that crosstalk between these two disparate groups of endobiota can play an essential role in host intestinal immune function and homeostasis.

Interactions between multiple helminths and the gut microbiota in wild rodents

The gut microbiota is vital to host health and, as such, it is important to elucidate the mechanisms altering its composition and diversity. Intestinal helminths are host immunomodulators and have evolved both temporally and spatially in close association with the gut microbiota, resulting in potential mechanistic interplay. Host–helminth and host–microbiota interactions are comparatively well-examined, unlike microbiota–helminth relationships, which typically focus on experimental infection with a single helminth species in laboratory animals. Here, in addition to a review of the literature on helminth–microbiota interactions, we examined empirically the association between microbiota diversity and composition and natural infection of multiple helminth species in wild mice (Apodemus flavicollis), using 16S rRNA gene catalogues (metataxonomics). In general, helminth presence is linked with high microbiota diversity, which may confer health benefits to the host. Within our wild rodent system variation in the composition and abundance of gut microbial taxa associated with helminths was specific to each helminth species and occurred both up- and downstream of a given helminth's niche (gut position). The most pronounced helminth–microbiota association was between the presence of tapeworms in the small intestine and increased S24–7 (Bacteroidetes) family in the stomach. Helminths clearly have the potential to alter gut homeostasis. Free-living rodents with a diverse helminth community offer a useful model system that enables both correlative (this study) and manipulative inference to elucidate helminth–microbiota interactions.

Diplomatic Assistance: Can Helminth-Modulated Macrophages Act as Treatment for Inflammatory Disease?

Helminths have evolved numerous pathways to prevent their expulsion or elimination from the host to ensure long-term survival. During infection, they target numerous host cells, including macrophages, to induce an alternatively activated phenotype, which aids elimination of infection, tissue repair, and wound healing. Multiple animal-based studies have demonstrated a significant reduction or complete reversal of disease by helminth infection, treatment with helminth products, or helminth-modulated macrophages in models of allergy, autoimmunity, and sepsis. Experimental studies of macrophage and helminth therapies are being translated into clinical benefits for patients undergoing transplantation and those with multiple sclerosis. Thus, helminths or helminth-modulated macrophages present great possibilities as therapeutic applications for inflammatory diseases in humans. Macrophage-based helminth therapies and the underlying mechanisms of their therapeutic or curative effects represent an under-researched area with the potential to open new avenues of treatment. This review explores the application of helminth-modulated macrophages as a new therapy for inflammatory diseases.

Interleukin-13 Receptor α1-Dependent Responses in the Intestine Are Critical to Parasite Clearance

Nematode infection upregulates interleukin-4 (IL-4) and IL-13 and induces STAT6-dependent changes in gut function that promote worm clearance. IL-4 and IL-13 activate the type 2 IL-4 receptor (IL-4R), which contains the IL-13Rα1 and IL-4Rα chains. We used mice deficient in IL-13Rα1 (IL-13Rα1(-/-)) to examine the contribution of IL-13 acting at the type 2 IL-4R to immune and functional responses to primary (Hb1) and secondary (Hb2) infections with the gastrointestinal nematode parasite Heligmosomoides bakeri There were differences between strains in the IL-4 and IL-13 expression responses to Hb1 but not Hb2 infection. Following Hb2 infection, deficient mice had impaired worm expulsion and higher worm fecundity despite normal production of Th2-derived cytokines. The upregulation of IL-25 and IL-13Rα2 in Hb1- and Hb2-infected wild-type (WT) mice was absent in IL-13Rα1(-/-)mice. Goblet cell numbers and resistin-like molecule beta (RELM-β) expression were attenuated significantly in IL-13Rα1(-/-)mice following Hb2 infections. IL-13Rα1 contributes to the development of alternatively activated macrophages, but the type 1 IL-4R is also important. Hb1 infection had no effects on smooth muscle function or epithelial permeability in either strain, while the enhanced mucosal permeability and changes in smooth muscle function and morphology observed in response to Hb2 infection in WT mice were absent in IL-13Rα1(-/-)mice. Notably, the contribution of claudin-2, which has been linked to IL-13, does not mediate the increased mucosal permeability following Hb2 infection. These results show that activation of IL-13Rα1 is critical for key aspects of the immune and functional responses to Hb2 infection that facilitate expulsion.

Tropical and travel-associated norovirus: current concepts

PURPOSE OF REVIEW

We highlight recent advances relevant to understanding norovirus infections in the tropics, both in populations living in developing settings and travelers to these regions.

RECENT FINDINGS

Because of the decrease in diarrheal disease associated with the global rollout of vaccines against rotavirus, norovirus is emerging as the predominant cause of diarrhea morbidity among children in the tropics, and evidence suggests that it contributes to adult disease in endemic populations and travelers. In addition to identifying potential target populations for preventive measures, we provide an update on norovirus vaccine development and concepts related to their implementation in low-income and middle-income countries.

SUMMARY

These current concepts related to norovirus-attributable disease burden, clinical significance, and economic impact can potentially be applied to tailoring efforts to prevent and mitigate the effects of this important enteropathogen.

Cohabitation in the Intestine: Interactions among Helminth Parasites, Bacterial Microbiota, and Host Immunity

Both intestinal helminth parasites and certain bacterial microbiota species have been credited with strong immunomodulatory effects. Recent studies reported that the presence of helminth infection alters the composition of the bacterial intestinal microbiota and, conversely, that the presence and composition of the bacterial microbiota affect helminth colonization and persistence within mammalian hosts. This article reviews recent findings on these reciprocal relationships, in both human populations and mouse models, at the level of potential mechanistic pathways and the implications these bear for immunomodulatory effects on allergic and autoimmune disorders. Understanding the multidirectional complex interactions among intestinal microbes, helminth parasites, and the host immune system allows for a more holistic approach when using probiotics, prebiotics, synbiotics, antibiotics, and anthelmintics, as well as when designing treatments for autoimmune and allergic conditions.

Helminths and the microbiota: parts of the hygiene hypothesis

In modern societies, diseases that are driven by dysregulated immune responses are increasing at an alarming pace, such as inflammatory bowel diseases and diabetes. There is an urgent need to understand these epidemiological trends, which are likely to be driven by the changing environment of the last few decades. There are complex interactions between human genetic factors and this changing environment that is leading to the increasing prevalence of metabolic and inflammatory diseases. Alterations to human gut bacterial communities (the microbiota) and lowered prevalence of helminth infections are potential environmental factors contributing to immune dysregulation. Helminths have co-evolved with the gut microbiota and their mammalian hosts. This three-way interaction is beginning to be characterized, and the knowledge gained may enable the design of new therapeutic strategies to treat metabolic and inflammatory diseases. However, these complex interactions need to be carefully investigated in the context of host genetic backgrounds to identify optimal treatment strategies. The complex nature of these interactions raises the possibility that only with highly personalized treatment, with knowledge of individual genetic and microbiota communities, will therapeutic interventions be successful for a majority of the individuals suffering from these complex diseases of immune dysregulation.

Plasmodium berghei ANKA causes intestinal malaria associated with dysbiosis

Gastrointestinal symptoms, such as abdominal pain and diarrhea, are frequently observed in patients with Plasmodium falciparum malaria. However, the correlation between malaria intestinal pathology and intestinal microbiota has not been investigated. In the present study, infection of C57BL/6 mice with P. berghei ANKA (PbA) caused intestinal pathological changes, such as detachment of epithelia in the small intestines and increased intestinal permeability, which correlated with development with experimental cerebral malaria (ECM). Notably, an apparent dysbiosis occurred, characterized by a reduction of Firmicutes and an increase in Proteobacteria. Furthermore, some genera of microbiota correlated with parasite growth and/or ECM development. By contrast, BALB/c mice are resistant to ECM and exhibit milder intestinal pathology and dysbiosis. These results indicate that the severity of cerebral and intestinal pathology coincides with the degree of alteration in microbiota. This is the first report demonstrating that malaria affects intestinal microbiota and causes dysbiosis.