Acetate, a metabolic product of Heligmosomoides polygyrus, facilitates intestinal epithelial barrier breakdown in a FFAR2-dependent manner

Approximately 2 billion people worldwide and a significant part of the domestic livestock are infected with soil-transmitted helminths, of which many establish chronic infections causing substantial eco-nomic and welfare burdens. Beside intensive research on helminth-triggered mucosal and systemic immune responses, the local mechanism that enables infective larvae to cross the intestinal epithelial barrier and invade mucosal tissue remains poorly addressed. Here, we show that Heligmosomoides poly-gyrus infective L3s secrete acetate and that acetate potentially facilitates paracellular epithelial tissue invasion by changed epithelial tight junction claudin expression. In vitro, impedance-based real-time epithelial cell line barrier measurements together with ex vivo functional permeability assays in intesti-nal organoid cultures revealed that acetate decreased intercellular barrier function via the G-protein cou-pled free fatty acid receptor 2 (FFAR2, GPR43). In vivo validation experiments in FFAR2-/-mice showed lower H. polygyrus burdens, whereas oral acetate-treated C57BL/6 wild type mice showed higher burdens. These data suggest that locally secreted acetate - as a metabolic product of the energy metabolism of H. polygyrus L3s - provides a significant advantage to the parasite in crossing the intestinal epithelial barrier and invading mucosal tissues. This is the first and a rate-limiting step for helminths to establish chronic infections in their hosts and if modulated could have profound consequences for their life cycle.(c) 2022 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.

Role of myeloid cells in mediating protection against parasitic helminth larvae

Beatrice Volpe

Helminth infections affect around one fourth of the world population living in the poorest regions of our planet. Helminths mainly cause debilitating chronic effects on health, development and nutritional status of infected people. The development of a vaccine is currently thought to be the more promising solution to eradicate helminths. However, further research efforts are required to unravel host-pathogen interactions, evasion strategies and killing mechanisms. The work presented in this thesis expands our knowledge in these domains, with a special focus given to the functions employed by myeloid immune cells against various soil-transmitted helminths. Our laboratory has previously showed that macrophages can efficiently trap and kill H. polygyrus larvae in immune mice by upregulating the enzyme Arginase 1. By contrast, following primary infection, H. polygyrus can establish chronicity because protective adaptive immune mechanisms do not arise quickly enough to block larval development. In a primary setting, we observed that myeloid cells accumulate around larvae and specifically express the inducible form of nitric oxide synthase (iNOS) in response to the parasite. Furthermore, iNOS deficient mice displayed reduced worm burdens as compared to wild type controls, indicating that iNOS expression favors larval survival. Induction of iNOS by the larvae constitutes a novel mechanism of innate immune response evasion. Although the exact mechanism by which iNOS expression attenuates protection is still unclear, current evidence indicates that it involves alterations to myeloid cell function. We next sought to determine whether the described protective role for antibody-activated macrophages during rodent helminth infection hold true in a human setting. To this end, we compared the ability of antibody activated human blood-derived macrophages and eosinophils to attack A. suum larvae, a close relative to the human parasite A. lumbricoides. Eosinophils were included in the analyses as former studies on porcine eosinophils had shown that they efficiently kill Ascaris larvae. We observed that immune serum stimulated human macrophages adhered to A. suum larvae and impaired their motility. Surprisingly, Ascaris trapping mechanism was somehow different from what has been described in rodent models. Interestingly, macrophages were also less efficient than eosinophils to trap the larvae. Gene expression analysis revealed that macrophages stimulated with immune serum and larvae upregulated the eosinophil chemoattractant CCL24, suggesting that they may function more as helper cells that attract eosinophils, which in turn kill the parasite. In the final project, we investigated how macrophages detect and bind to helminth larvae given that only limited knowledge is available regarding larval recognition mechanisms. We could show that complement and/or antibodies were sufficient for the recognition of H. polygyrus and A. suum larvae, while IL-4 activation, and thus type 2 polarization, is sufficient for induction of recognition of N. brasiliensis larvae. We further explored the role of carbohydrates in this process and showed that soluble Î²-glucans could inhibit larval-macrophage interaction. This led to the discovery that the Î²-glucan binding site of the complement receptor 3 (CR3) played a crucial role in mouse macrophage recognition of N. brasiliensis larvae.

EPFL2017

Intestinal helminths modulate the gut microbiome

Alexis Rapin

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

Role of myeloid cells in mediating protection against parasitic helminth larvae

Beatrice Volpe

EPFL2017

Intestinal helminths modulate the gut microbiome

Alexis Rapin

EPFL2018