The Intestinal Microbiota Contributes to the Ability of Helminths to Modulate Allergic Inflammation

Lalit Kumar Dubey, Nicola Harris, Luc Xavier Marie Lebon, Andrew J. Macpherson, Benjamin John Marsland, Laure Menin, Ilaria Mosconi, Alessandra Piersigilli, Alexis Rapin, Jacques Rougemont, Mario Michael Zaiss
Elsevier, 2015
Journal paper

Abstract

Intestinal helminths are potent regulators of their host's immune system and can ameliorate inflammatory diseases such as allergic asthma. In the present study we have assessed whether this anti-inflammatory activity was purely intrinsic to helminths, or whether it also involved crosstalk with the local microbiota. We report that chronic infection with the murine helminth Heligmosomoides polygyrus bakeri (Hpb) altered the intestinal habitat, allowing increased short chain fatty acid (SCFA) production. Transfer of the Hpb-modified microbiota alone was sufficient to mediate protection against allergic asthma. The helminth-induced anti-inflammatory cytokine secretion and regulatory T cell suppressor activity that mediated the protection required the G protein-coupled receptor (GPR)-41. A similar alteration in the metabolic potential of intestinal bacterial communities was observed with diverse parasitic and host species, suggesting that this represents an evolutionary conserved mechanism of host-microbe-helminth interactions.

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https://infoscience.epfl.ch/record/216633?ln=en

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The interaction of commensal intestinal bacteria with helminth parasites

Nicola Harris, Mario Michael Zaiss

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 'menage a 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.

Wiley-Blackwell2016

Intestinal parasitic worms (commonly named intestinal helminths) affect close to one quarter of the world population and cause major losses for the livestock industry. These parasites establish chronic infections by modulation the immunity of their host. The immune system of mammals has been challenged by this immuno-modulation all along the course of evolution. Although intestinal parasites constitute a threat to human health, their recent eradication from industrialized regions may not be without consequence. In fact, the loss of intestinal helminth-driven immuno-regulation has been proposed to underlie the increased frequency of immune disorders observed in developed areas. Here, we first showed that one immune-modulatory strategy of intestinal helminths involves alterations of the intestinal bacterial communities. Although a lot remained to be understood about these alterations, they were characterized by higher intestinal levels of short-chain fatty acids (SCFAs), bacterial metabolites with immuno-suppressive activity. A better understanding of how intestinal helminths modulate host immunity via the intestinal microbiome may open the door to novel strategies to fight both intestinal parasites and immune disorders. In this context, I further characterized the impact of intestinal helminths on fecal bacterial communities in children living in a rural region of Ecuador and naturally infected with Ascaris lumbricoides, a parasite affecting 1.2 billion people worldwide. I then used a mouse model to extensively characterize the impact of intestinal helminth infection on intestinal bacterial communities along the intestinal tract. Based on our main results, we hypothesized that the worm-induced mucus secretion may favor the growth of SCFA-producing bacteria in the intestine, which in turn down-regulates the host immunity by promoting regulatory T cells. As part of this work, I also developed a web-based platform to assist scientists in analyzing data from high-throughput nucleic-acid sequencing, a method commonly used to characterize microbial communities but for which data analysis remains particularly challenging.

EPFL2018

Recently, several studies done in Drosophila have revealed that efficient and rapid recovery from bacterial infection in the gut is possible only when bacterial clearance by the immune system is coordinated with repair through renewal of the epithelium damaged by infection. In this thesis, I have analyzed how the entomopathogenic bacterium Pseudomonas entomophila affects the immune response and epithelium renewal. A microarray analysis first showed that P. entomophila is recognized by the Drosophila immune system since ingestion of this bacterium stimulated the expression of antimicrobial peptide genes by the Imd pathway. In addition, stress and damage related pathways were strongly induced by P. entomophila, which correlate with its capacity to inflict severe damage. While antibacterial genes were induced in the gut following infection with P. entomophila, the immune response was not productive due to a general inhibition of translation that affected all the newly synthesized transcripts. Furthermore, the blockage of translation also inhibited the repair program by blocking the production of JAK-STAT ligands (upd3, upd2) and growth factors, which stimulate the intestinal stem cells proliferation and differentiation. I next analyzed the pathways that link cellular damage to reduction of translation. Using a genetic approach, I showed that inhibition of translation was induced by two signaling pathways: i) the phosphorylation of elongation initiation factor 2α (eIF2α) by the stress kinase GCN2 and ii) the inhibition of the TOR pathway by the AMPK kinase. Both kinases sense metabolic deprivation, suggesting that cellular damages induced by P. entomophila induce a state of “starvation”. Inhibition of translation is usually an adaptive cellular response to adjust the metabolism to the energy status of the cells. The observation that GCN2-deficient flies survived better than wild-type flies to P. entomophila indicates that pathogenesis is linked to an over-activation of stress pathways that usually help to endure the consequence of an infection. In this in vivo model of infection, I also showed that the reduction of translation was a consequence of cellular damage to the intestine caused by host-derived reactive oxygen species (through the activity of Duox) and by the direct action of a pore-forming toxin produced by the pathogen. As a consequence of this translational arrest, flies succumbed P. entomophila infection because they were unable to repair gut damage. Finally, I showed that inhibition of translation also had a strong influence on innate immune responses observed upon P. entomophila infection. The specific activation of a systemic immune response (antimicrobial peptides produced by the fat body) observed upon P. entomophila infection could be recapitulated by feeding flies with a non-lethal pathogen and an inhibitor of translation. Hence, I showed translation inhibition could be an important feature that shapes the immune response. The p38 MAPK family is involved in stress and immunity in both mammals and Drosophila. In Drosophila, three p38-MAPK-encoding genes, p38a, p38b and p38c, have been identified but their function in the gut immune response is poorly characterized. In the second part of my thesis, I have analyzed the role of these three p38 MAPKs in Drosophila intestinal immunity, especially p38c, which is strongly enriched in the gut. I first confirmed that the three p38 are involved kinases are involved in the defense to oral infection with pathogenic (but non-lethal) bacteria such as Erwinia carotovora 15. Surprisingly, p38c mutant flies were more resistant to P. entomophila and did not show the reduction in translation observed in wild-type flies. Interestingly, the transcription of the ROS producing enzyme Duox was reduced in p38c raising the hypothesis that p38 contributes to P. entomophila pathogenicity by activating Duox. Furthermore, I have obtained preliminary data indicating that p38c and the transcription factor ATF-3 act in the same pathway contributing the host immune response and lipid metabolism. Together, my thesis reveals the complex cross-talks between stress and immune pathways during microbial infection. While, it shows that stress pathways usually contribute to endure the damage caused by infection, excessive activation of these pathways can contribute to pathogenesis.

EPFL2013

EPFL2018