The effect of challenge and trickle Trichuris muris infections on the polarisation of the immune response

The adaptive immune response to Trichuris in wild versus laboratory mice: An established model system in context

Laboratory model organisms have provided a window into how the immune system functions. An increasing body of evidence, however, suggests that the immune responses of naive laboratory animals may differ substantially to those of their wild counterparts. Past exposure, environmental challenges and physiological condition may all impact on immune responsiveness. Chronic infections of soil-transmitted helminths, which we define as establishment of adult, fecund worms, impose significant health burdens on humans, livestock and wildlife, with limited treatment success. In laboratory mice, Th1 versus Th2 immune polarisation is the major determinant of helminth infection outcome. Here we compared antigen-specific immune responses to the soil-transmitted whipworm Trichuris muris between controlled laboratory and wild free-ranging populations of house mice (Mus musculus domesticus). Wild mice harbouring chronic, low-level infections produced lower levels of cytokines in response to Trichuris antigen than laboratory-housed C57BL/6 mice. Wild mouse effector/memory CD4+ T cell phenotype reflected the antigen-specific cytokine response across the Th1/Th2 spectrum. Increasing egg shedding was associated with body condition loss. However, local Trichuris-specific Th1/Th2 balance was positively associated with worm burden only in older wild mice. Thus, although the fundamental relationships between the CD4+ T helper cell response and resistance to T. muris infection are similar in both laboratory and wild M. m. domesticus, there are quantitative differences and age-specific effects that are analogous to human immune responses. These context-dependent immune responses demonstrate the fundamental importance of understanding the differences between model and natural systems for translating mechanistic models to 'real world' immune function.

Another decade of Trichuris muris research: An update and application of key discoveries

The mouse whipworm, Trichuris muris, has been used for over 60 years as a tractable model for human trichuriasis, caused by the related whipworm species, T. trichiura. The history of T. muris research, from the discovery of the parasite in 1761 to understanding the lifecycle and outcome of infection with different doses (high versus low dose infection), as well as the immune mechanisms associated with parasite expulsion and chronic infection have been detailed in an earlier review published in 2013. Here, we review recent advances in our understanding of whipworm biology, host-parasite interactions and basic immunology brought about using the T. muris mouse model, focussing on developments from the last decade. In addition to the traditional high/low dose infection models that have formed the mainstay of T. muris research to date, novel models involving trickle (repeated low dose) infection in laboratory mice or infection in wild or semi-wild mice have led to important insights into how immunity develops in situ in a multivariate environment, while the use of novel techniques such as the development of caecal organoids (enabling the study of larval development ex vivo) promise to deliver important insights into host-parasite interactions. In addition, the genome and transcriptome analyses of T. muris and T. trichiura have proven to be invaluable tools, particularly in the context of vaccine development and identification of secreted products including proteins, extracellular vesicles and micro-RNAs, shedding further light on how these parasites communicate with their host and modulate the immune response to promote their own survival.

High-fat diet-induced resistance to helminth infection via alternative induction of type 2 immunity

Gastrointestinal nematode infections cause morbidity and socioeconomic loss in the most deprived communities. The shift in the context of obesity has led to spatial overlap with endemic gastrointestinal nematode regions resulting in the emergence of a novel comorbidity. Despite this, the impact of a high-fat diet (HFD) on immune-regulated protection against gastrointestinal infections remains largely unknown. We employed the murine model of nematode infection, Trichuris muris, to investigate the effect of an HFD on the immune response against chronic infection. Surprisingly, diet-induced obesity drove parasite expulsion in both single and repeated trickle low doses of T. muris eggs. Mechanistically, an HFD increased the expression of the ST2 receptor on CD4+ T cells, priming an enhanced type 2 helper T (Th2) cell cytokine production following interleukin (IL)-33 stimulation ex vivo. Despite IL-33-/- mice demonstrating that IL-33 is not critical for host protective immunity to T. muris under a conventional diet, HFD-fed T-cell deplete mice adoptively transferred with ST2-/- CD4 T cells were unable to expel a T. muris infection unlike those transferred with ST2-sufficient cells. Collectively, this study demonstrates that an HFD primes CD4+ T cells to utilize the IL-33-ST2 axis in a novel induction of type 2 immunity, providing insights into the emerging comorbidities of obesity and nematode infection.

Trichuris WAP and CAP proteins: Potential whipworm vaccine candidates?

Trichuris trichiura and T. suis are gastrointestinal dwelling roundworms that infect humans and pigs, respectively. Heavy infections cause gastrointestinal symptoms and impaired growth and development. Vaccination has the potential to reduce the disease burden of whipworm infection; however, there are currently no commercially available vaccines against these parasites and very few against other gastrointestinal-dwelling nematodes of medical and agricultural importance. The naturally occurring mouse whipworm, T. muris, has been used for decades to model human trichuriasis, and the immunogenic potential of the excretory/secretory material (E/S, which can be collected following ex vivo culture of worms) has been studied in the context of vaccine candidate identification. Despite this, researchers are yet to progress an effective vaccine candidate to clinical trials. The T. muris, T. trichiura, and T. suis genomes each encode between 10 and 27 whey acidic protein (WAP) domain-containing proteins and 15 to 34 cysteine-rich secretory protein/antigen 5/pathogenesis related-1 (CAP) family members. WAP and CAP proteins have been postulated to play key roles in host-parasite interactions and may possess immunomodulatory functions. In addition, both protein families have been explored in the context of helminth vaccines. Here, we use phylogenetic and functional analysis to investigate the evolutionary relationship between WAP and CAP proteins encoded by T. muris, T. trichiura, and T. suis. We highlight several WAP and CAP proteins that warrant further study to understand their biological function and as possible vaccine candidates against T. trichiura and/or T. suis, based on the close evolutionary relationship with WAP or CAP proteins identified within T. muris E/S products.

Whipworm secretions and their roles in host-parasite interactions

Whipworm (Trichuris) is a genus of roundworms that causes gastrointestinal infections in humans and animals. Of particular interest are T. trichiura, the causative agent of human trichuriasis, a neglected tropical disease that affects 477 million people worldwide, and T. suis, the pig whipworm species, responsible for growth stunting and economic losses within the agricultural industry. The naturally occurring mouse whipworm, T. muris, has been used for decades as a model for trichuriasis, yielding knowledge on the biology of these parasites and the host response to infection. Ex vivo culture of T. muris (and to some extent, T. suis) has provided insight into the composition of the excretory/secretory (E/S) products released by worms, which include a myriad of proteins, RNAs, lipids, glycans, metabolites and extracellular vesicles. T. muris E/S has formed the basis of the search for whipworm vaccine candidates, while the immunomodulatory potential of T. suis and T. muris secretions has been investigated with the aim of improving our understanding of how these parasites modulate host immunity, as well as identifying immunomodulatory candidates with therapeutic potential in the context of inflammatory diseases. This article will review the various components found within Trichuris E/S, their potential as vaccine candidates and their immunomodulatory properties.

Trickle infection with Heligmosomoides polygyrus results in decreased worm burdens but increased intestinal inflammation and scarring

Introduction

Intestinal roundworms cause chronic debilitating disease in animals, including humans. Traditional experimental models of these types of infection use a large single-dose infection. However, in natural settings, hosts are exposed to parasites on a regular basis and when mice are exposed to frequent, smaller doses of Heligmosomoides polygyrus, the parasites are cleared more quickly. Whether this more effective host response has any negative consequences for the host is not known.

Results

Using a trickle model of infection, we found that worm clearance was associated with known resistance-related host responses: increased granuloma and tuft cell numbers, increased levels of granuloma IgG and decreased intestinal transit time, as well as higher serum IgE levels. However, we found that the improved worm clearance was also associated with an inflammatory phenotype in and around the granuloma, increased smooth muscle hypertrophy/hyperplasia, and elevated levels of Adamts gene expression.

Discussion

To our knowledge, we are the first to identify the involvement of this protein family of matrix metalloproteinases (MMPs) in host responses to helminth infections. Our results highlight the delicate balance between parasite clearance and host tissue damage, which both contribute to host pathology. When continually exposed to parasitic worms, improved clearance comes at a cost.

Food for thought - ILC metabolism in the context of helminth infections

Helminths are multicellular ancient organisms residing as parasites at mucosal surfaces of their host. Through adaptation and co-evolution with their hosts, helminths have been able to develop tolerance mechanisms to limit inflammation and avoid expulsion. The study of helminth infections as an integral part of tissue immunology allowed us to understand fundamental aspects of mucosal and barrier immunology, which led to the discovery of a new group of tissue-resident immune cells, innate lymphoid cells (ILC), over a decade ago. Here, we review the intricate interplay between helminth infections and type 2 ILC (ILC2) biology, discuss the host metabolic adaptation to helminth infections and the metabolic pathways fueling ILC2 responses. We hypothesize that nutrient competition between host and helminths may have prevented chronic inflammation in the past and argue that a detailed understanding of the metabolic restraints imposed by helminth infections may offer new therapeutic avenues in the future.

Trichuris muris Model: Role in Understanding Intestinal Immune Response, Inflammation and Host Defense

Several parasites have evolved to survive in the human intestinal tract and over 1 billion people around the world, specifically in developing countries, are infected with enteric helminths. Trichuris trichiura is one of the world’s most common intestinal parasites that causes human parasitic infections. Trichuris muris, as an immunologically well-defined mouse model of T. trichiura, is extensively used to study different aspects of the innate and adaptive components of the immune system. Studies on T. muris model offer insights into understanding host immunity, since this parasite generates two distinct immune responses in resistant and susceptible strains of mouse. Apart from the immune cells, T. muris infection also influences various components of the intestinal tract, especially the gut microbiota, mucus layer, epithelial cells and smooth muscle cells. Here, we reviewed the different immune responses generated by innate and adaptive immune components during acute and chronic T. muris infections. Furthermore, we discussed the importance of studying T. muris model in understanding host–parasite interaction in the context of alteration in the host’s microbiota, intestinal barrier, inflammation, and host defense, and in parasite infection-mediated modulation of other immune and inflammatory diseases.

Immunoregulatory molecules secreted by Trichuris muris

Trichuris, whipworm nematode infections are prevalent in humans, domestic livestock and mammals. All share an epithelial dwelling niche and similar life cycle with the chronic infections that follow implying that immune evasion mechanisms are operating. Nematode excretory secretory (ES) products have been shown to be a rich source of immunomodulatory molecules for many species. The Trichuris muris model is a natural parasite of mice and has been used extensively to study host–parasite interactions and provides a tractable platform for investigation of the immunoregulatory capacity of whipworm ES. The present review details progress in identification of the composition of T. muris ES, immunomodulatory components and their potential mechanisms of action. The adult T. muris secretome is dominated by one protein with modulatory capacity although remains to be completely characterized. In addition, the secretome contains multiple other proteins and small molecules that have immunomodulatory potential, certainly by comparison to other Trichuris species. Moreover, T. muris-derived exosomes/exosome-like vesicles contain both protein and multiple miRNAs providing an alternate delivery process for molecules with the potential to modulate host immunity.

Trichuris muris as a tool for holistic discovery research: from translational research to environmental bio-tagging

Trichuris spp. (whipworms) are intestinal nematode parasites which cause chronic infections associated with significant morbidities. Trichuris muris in a mouse is the most well studied of the whipworms and research on this species has been approached from a number of different disciplines. Research on T. muris in a laboratory mouse has provided vital insights into the host–parasite interaction through analyses of the immune responses to infection, identifying factors underpinning host susceptibility and resistance. Laboratory studies have also informed strategies for disease control through anthelmintics and vaccine research. On the contrary, research on naturally occurring infections with Trichuris spp. allows the analysis of the host–parasite co-evolutionary relationships and parasite genetic diversity. Furthermore, ecological studies utilizing Trichuris have aided our knowledge of the intricate relationships amongst parasite, host and environment. More recently, studies in wild and semi-wild settings have combined the strengths of the model organism of the house mouse with the complexities of context-dependent physiological responses to infection. This review celebrates the extraordinarily broad range of beneficiaries of whipworm research, from immunologists and parasitologists, through epidemiologists, ecologists and evolutionary biologists to the veterinary and medical communities.

Advances in vaccine development for human trichuriasis

Trichuriasis known as whipworm infection caused by Trichuris trichiura, is a highly prevalent soil-transmitted helminthiasis in low- and middle-income countries located in tropical and subtropical areas and affecting approximately 360 million people. Children typically harbour the largest burden of T. trichiura and they are usually co-infected with other soil-transmitted helminth (STH), including Ascaris lumbricoides and hookworm. The consequences of trichuriasis, such as malnutrition and physical and cognitive growth restriction, lead to a massive health burden in endemic regions. Despite the implementation of mass drug administration of anthelminthic treatment to school-age children, T. trichiura infection remains challenging to control due to the low efficacy of current drugs as well as high rates of post-treatment re-infection. Thus, the development of a vaccine that would induce protective immunity and reduce infection rate or community faecal egg output is essential. Hurdles for human whipworm vaccine development include the lack of suitable vaccine antigen targets and animal models for human T. trichiura infection. Instead, rodent whipworm T. muris infected mouse models serve as a major surrogate for testing immunogenicity and efficacy of vaccine candidates. In this review, we summarize recent advances in animal models for T. trichiura antigen discovery and testing of vaccine candidates, while providing an overall view of the current status of T. trichiura vaccine development.

Embracing nature's complexity: Immunoparasitology in the wild

A wealth of research is dedicated to understanding how resistance against parasites is conferred and how parasite-driven pathology is regulated. This research is in part driven by the hope to better treatments for parasitic diseases of humans and livestock, and in part by immunologists who use parasitic infections as biomedical tools to evoke physiological immune responses. Much of the current mechanistic knowledge has been discovered in laboratory studies using model organisms, especially the laboratory mouse. However, wildlife are also hosts to a range of parasites. Through the study of host-parasite interactions in these non-laboratory systems we can gain a deeper understanding of parasite immunology in a more natural, complex environment. With a focus on helminth parasites, we here explore the insights gained into parasite-induced immune responses through (for immunologists) non-conventional experimental systems, and how current core findings from laboratory studies are reflected in these more natural conditions. The quality of the immune response is undoubtedly a central player in susceptibility versus resistance, as many laboratory studies have shown. Yet, in the wild, parasite infections tend to be chronic diseases. Whilst reading our review, we encourage the reader to consider the following questions which may (only) be answered by studying naturally occurring parasites in the wild: a) what type of immune responses are mounted against parasites in different hosts in the wild, and how do they vary within an individual over time, between individuals of the same species and between species? b) can we use wild or semi-wild study systems to understand the evolutionary drivers for tolerance versus resistance towards a parasite? c) what determines the ability of the host to cope with an infection and is there a link with the type of immune response mounted? d) can we modulate environmental factors to manipulate a wild animal's immune response to parasitic infections, with translation potential for humans, wildlife, and livestock? and e) in context of this special issue, what lessons for Type 2 immunity can we glean from studying animals in their natural environments? Further, we aim to integrate some of the knowledge gained in semi-wild and wild settings with knowledge gained from traditional laboratory-based research, and to raise awareness for the opportunities (and challenges) that come with integrating a multitude of naturally-occurring variables into immunoparasitological research.

Overview of Immunological Responses and Immunomodulation Properties of Trichuris sp.: Prospects for Better Understanding Human Trichuriasis

Trichuris sp. infection has appeared as a pathological burden in the population, but the immunomodulation features could result in an opportunity to discover novel treatments for diseases with prominent inflammatory responses. Regarding the immunological aspects, the innate immune responses against Trichuris sp. are also responsible for determining subsequent immune responses, including the activation of innate lymphoid cell type 2 (ILC2s), and encouraging the immune cell polarization of the resistant host phenotype. Nevertheless, this parasite can establish a supportive niche for worm survival and finally avoid host immune interference. Trichuris sp. could skew antigen recognition and immune cell activation and proliferation through the generation of specific substances, called excretory/secretory (ESPs) and soluble products (SPs), which mainly mediate its immunomodulation properties. Through this review, we elaborate and discuss innate–adaptive immune responses and immunomodulation aspects, as well as the clinical implications for managing inflammatory-based diseases, such as inflammatory bowel diseases, allergic, sepsis, and other autoimmune diseases.

The role of β2 integrin in dendritic cell migration during infection

Background

Dendritic cells (DCs) play a key role in shaping T cell responses. To do this, DCs must be able to migrate to the site of the infection and the lymph nodes to prime T cells and initiate the appropriate immune response. Integrins such as β₂ integrin play a key role in leukocyte adhesion, migration, and cell activation. However, the role of β₂ integrin in DC migration and function in the context of infection-induced inflammation in the gut is not well understood. This study looked at the role of β₂ integrin in DC migration and function during infection with the nematode worm Trichuris muris. Itgb2^tm1Bay mice lacking functional β₂ integrin and WT littermate controls were infected with T. muris and the response to infection and kinetics of the DC response was assessed.

Results

In infection, the lack of functional β₂ integrin significantly reduced DC migration to the site of infection but not the lymph nodes. The lack of functional β₂ integrin did not negatively impact T cell activation in response to T. muris infection.

Conclusions

This data suggests that β₂ integrins are important in DC recruitment to the infection site potentially impacting the initiation of innate immunity but is dispensible for DC migration to lymph nodes and T cell priming in the context of T. muris infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12865-020-00394-5.

The Methyltransferase DOT1L Controls Activation and Lineage Integrity in CD4+ T Cells during Infection and Inflammation

CD4⁺ T helper (Th) cell differentiation is controlled by lineage-specific expression of transcription factors and effector proteins, as well as silencing of lineage-promiscuous genes. Lysine methyltransferases (KMTs) comprise a major class of epigenetic enzymes that are emerging as important regulators of Th cell biology. Here, we show that the KMT DOT1L regulates Th cell function and lineage integrity. DOT1L-dependent dimethylation of lysine 79 of histone H3 (H3K79me2) is associated with lineage-specific gene expression. However, DOT1L-deficient Th cells overproduce IFN-γ under lineage-specific and lineage-promiscuous conditions. Consistent with the increased IFN-γ response, mice with a T-cell-specific deletion of DOT1L are susceptible to infection with the helminth parasite Trichuris muris and are resistant to the development of allergic lung inflammation. These results identify a central role for DOT1L in Th2 cell lineage commitment and stability and suggest that inhibition of DOT1L may provide a therapeutic strategy to limit type 2 immune responses.

Investigating the importance of B cells and antibodies during Trichuris muris infection using the IgMi mouse

Abstract

The IgMi mouse has normal B cell development; its B cells express an IgM B cell receptor but cannot class switch or secrete antibody. Thus, the IgMi mouse offers a model system by which to dissect out antibody-dependent and antibody-independent B cell function. Here, we provide the first detailed characterisation of the IgMi mouse post-Trichuris muris (T. muris) infection, describing expulsion phenotype, cytokine production, gut pathology and changes in T regulatory cells, T follicular helper cells and germinal centre B cells, in addition to RNA sequencing (RNA seq) analyses of wild-type littermates (WT) and mutant B cells prior to and post infection. IgMi mice were susceptible to a high-dose infection, with reduced Th2 cytokines and elevated B cell-derived IL-10 in mesenteric lymph nodes (MLN) compared to controls. A low-dose infection regime revealed IgMi mice to have significantly more apoptotic cells in the gut compared to WT mice, but no change in intestinal inflammation. IL-10 levels were again elevated. Collectively, this study showcases the potential of the IgMi mouse as a tool for understanding B cell biology and suggests that the B cell plays both antibody-dependent and antibody-independent roles post high- and low-dose T. muris infection.

Key messages

During a high-dose T. muris infection, B cells are important in maintaining the Th1/Th2 balance in the MLN through an antibody-independent mechanism.

High levels of IL-10 in the MLN early post-infection, and the presence of IL-10-producing B cells, correlates with susceptibility to T. muris infection.

B cells maintain gut homeostasis during chronic T. muris infection via an antibody-dependent mechanism.

Electronic supplementary material

The online version of this article (10.1007/s00109-020-01954-3) contains supplementary material, which is available to authorized users.

Immunity to Soil-Transmitted Helminths: Evidence From the Field and Laboratory Models

Infection with soil-transmitted helminths (STH) remains a major burden on global health and agriculture. Our understanding of the immunological mechanisms that govern whether an individual is resistant or susceptible to infection is derived primarily from model infections in rodents. Typically, experimental infections employ an artificially high, single bolus of parasites that leads to rapid expulsion of the primary infection and robust immunity to subsequent challenges. However, immunity in natura is generated slowly, and is only partially effective, with individuals in endemic areas retaining low-level infections throughout their lives. Therefore, there is a gap between traditional model STH systems and observations in the field. Here, we review the immune response to traditional model STH infections in the laboratory. We compare these data to studies of natural infection in humans and rodents in endemic areas, highlighting crucial differences between experimental and natural infection. We then detail the literature to date on the use of "trickle" infections to experimentally model the kinetics of natural infection.

Parasite resource manipulation drives bimodal variation in infection duration

Over a billion people on earth are infected with helminth parasites and show remarkable variation in parasite burden and chronicity. These parasite distributions are captured well by classic statistics, such as the negative binomial distribution. But the within-host processes underlying this variation are not well understood. In this study, we explain variation in macroparasite infection outcomes on the basis of resource flows within hosts. Resource flows realize the interactions between parasites and host immunity and metabolism. When host metabolism is modulated by parasites, we find a positive feedback of parasites on their own resources. While this positive feedback results in parasites improving their resource availability at high burdens, giving rise to chronic infections, it also results in a threshold biomass required for parasites to establish in the host, giving rise to acute infections when biomass fails to clear the threshold. Our finding of chronic and acute outcomes in bistability contrasts with classic theory, yet is congruent with the variation in helminth burdens observed in human and wildlife populations.

In silico design of a T-cell epitope vaccine candidate for parasitic helminth infection

Trichuris trichiura is a parasite that infects 500 million people worldwide, leading to colitis, growth retardation and Trichuris dysentery syndrome. There are no licensed vaccines available to prevent Trichuris infection and current treatments are of limited efficacy. Trichuris infections are linked to poverty, reducing children's educational performance and the economic productivity of adults. We employed a systematic, multi-stage process to identify a candidate vaccine against trichuriasis based on the incorporation of selected T-cell epitopes into virus-like particles. We conducted a systematic review to identify the most appropriate in silico prediction tools to predict histocompatibility complex class II (MHC-II) molecule T-cell epitopes. These tools were used to identify candidate MHC-II epitopes from predicted ORFs in the Trichuris genome, selected using inclusion and exclusion criteria. Selected epitopes were incorporated into Hepatitis B core antigen virus-like particles (VLPs). Bone marrow-derived dendritic cells and bone marrow-derived macrophages responded in vitro to VLPs irrespective of whether the VLP also included T-cell epitopes. The VLPs were internalized and co-localized in the antigen presenting cell lysosomes. Upon challenge infection, mice vaccinated with the VLPs+T-cell epitopes showed a significantly reduced worm burden, and mounted Trichuris-specific IgM and IgG2c antibody responses. The protection of mice by VLPs+T-cell epitopes was characterised by the production of mesenteric lymph node (MLN)-derived Th2 cytokines and goblet cell hyperplasia. Collectively our data establishes that a combination of in silico genome-based CD4+ T-cell epitope prediction, combined with VLP delivery, offers a promising pipeline for the development of an effective, safe and affordable helminth vaccine.

Trickle infection and immunity to Trichuris muris

The majority of experiments investigating the immune response to gastrointestinal helminth infection use a single bolus infection. However, in situ individuals are repeatedly infected with low doses. Therefore, to model natural infection, mice were repeatedly infected (trickle infection) with low doses of Trichuris muris. Trickle infection resulted in the slow acquisition of immunity reflected by a gradual increase in worm burden followed by partial expulsion. Flow cytometry revealed that the CD4+ T cell response shifted from Th1 dominated to Th2 dominated, which coincided with an increase in Type 2 cytokines. The development of resistance following trickle infection was associated with increased worm expulsion effector mechanisms including goblet cell hyperplasia, Muc5ac production and increased epithelial cell turn over. Depletion of CD4+ T cells reversed resistance confirming their importance in protective immunity following trickle infection. In contrast, depletion of group 2 innate lymphoid cells did not alter protective immunity. T. muris trickle infection resulted in a dysbiotic mircrobiota which began to recover alpha diversity following the development of resistance. These data establish trickle infection as a robust and informative model for analysis of immunity to chronic intestinal helminth infection more akin to that observed under natural infection conditions and confirms the importance of CD4+ T cell adaptive immunity in host protection.

Infection with parasitic worms (helminths) is a considerable cause of morbidity in humans. Understanding how we respond to infection is crucial to developing novel therapies. Laboratory models of helminth infection have been a valuable tool in understanding fundamental immune responses to infection. However, typically an individual mouse will be infected with a large, single-dose of the parasite. This is in contrast to the natural scenario in which individuals will receive frequent low level exposures. However, it is unknown how repeated infection alters the development of immunity to infection. We have developed a laboratory model to tackle this question. We infected mice with the model helminth Trichuris muris on a weekly basis and assessed a range of responses in comparison with a more traditional infection regime. We found striking differences in the dynamics of the infection, the host immune response, and in changes to host gut microbial populations. Our study shows how resistance to helminth infection can develop over time in response to repeat infection, and provides a model system that better reflects human immunity to this parasite.

Helminth-microbiota cross-talk - A journey through the vertebrate digestive system

The gastrointestinal (GI) tract of vertebrates is inhabited by a vast array of organisms, i.e., the microbiota and macrobiota. The former is composed largely of commensal microorganisms, which play vital roles in host nutrition and maintenance of energy balance, in addition to supporting the development and function of the vertebrate immune system. By contrast, the macrobiota includes parasitic helminths, which are mostly considered detrimental to host health via a range of pathogenic effects that depend on parasite size, location in the GI tract, burden of infection, metabolic activity, and interactions with the host immune system. Sharing the same environment within the vertebrate host, the GI microbiota and parasitic helminths interact with each other, and the results of such interactions may impact, directly or indirectly, on host health and homeostasis. The complex relationships occurring between parasitic helminths and microbiota have long been neglected; however, recent studies point towards a role for these interactions in the overall pathophysiology of helminth disease, as well as in parasite-mediated suppression of inflammation. Whilst several discrepancies in qualitative and quantitative modifications in gut microbiota composition have been described based on host and helminth species under investigation, we argue that attention should be paid to the systems biology of the gut compartment under consideration, as variations in the abundances of the same population of bacteria inhabiting different niches of the GI tract may result in varying functional consequences for host physiology.

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.

Vaccination Against Whipworm: Identification of Potential Immunogenic Proteins in Trichuris muris Excretory/Secretory Material

Trichuris trichiura (whipworm) is one of the four major soil-transmitted helminth infections of man, affecting an estimated 465 million people worldwide. An effective vaccine that induces long-lasting protective immunity against T. trichiura would alleviate the morbidity associated with this intestinal-dwelling parasite, however the lack of known host protective antigens has hindered vaccine development. Here, we show that vaccination with ES products stimulates long-lasting protection against chronic infection in male C57BL/6 mice. We also provide a framework for the identification of immunogenic proteins within T. muris ES, and identify eleven candidates with direct homologues in T. trichiura that warrant further study. Given the extensive homology between T. muris and T. trichiura at both the genomic and transcriptomic levels, this work has the potential to advance vaccine design for T. trichiura.

Rapid environmental effects on gut nematode susceptibility in rewilded mice

Genetic and environmental factors shape host susceptibility to infection, but how and how rapidly environmental variation might alter the susceptibility of mammalian genotypes remains unknown. Here, we investigate the impacts of seminatural environments upon the nematode susceptibility profiles of inbred C57BL/6 mice. We hypothesized that natural exposure to microbes might directly (e.g., via trophic interactions) or indirectly (e.g., via microbe-induced immune responses) alter the hatching, growth, and survival of nematodes in mice housed outdoors. We found that while C57BL/6 mice are resistant to high doses of nematode (Trichuris muris) eggs under clean laboratory conditions, exposure to outdoor environments significantly increased their susceptibility to infection, as evidenced by increased worm burdens and worm biomass. Indeed, mice kept outdoors harbored as many worms as signal transducer and activator of transcription 6 (STAT6) knockout mice, which are genetically deficient in the type 2 immune response essential for clearing nematodes. Using 16S ribosomal RNA sequencing of fecal samples, we discovered enhanced microbial diversity and specific bacterial taxa predictive of nematode burden in outdoor mice. We also observed decreased type 2 and increased type 1 immune responses in lamina propria and mesenteric lymph node (MLN) cells from infected mice residing outdoors. Importantly, in our experimental design, different groups of mice received nematode eggs either before or after moving outdoors. This contrasting timing of rewilding revealed that enhanced hatching of worms was not sufficient to explain the increased worm burdens; instead, microbial enhancement and type 1 immune facilitation of worm growth and survival, as hypothesized, were also necessary to explain our results. These findings demonstrate that environment can rapidly and significantly shape gut microbial communities and mucosal responses to nematode infections, leading to variation in parasite expulsion rates among genetically similar hosts.

The environment in which an individual resides is likely to change how she or he responds to infection. However, most of our understanding about host responses to infection arises from experimental studies conducted under uniform environmental conditions in the laboratory. We wished to investigate whether findings in the laboratory translate into the wild. Therefore, in this study, we placed common strains of laboratory mice into large, outdoor enclosures to investigate how a more natural environment might impact their ability to combat intestinal worm infections. We found that while mice are able to clear worm infections in the laboratory, mice residing outdoors harbored higher worm burdens and larger worms than their laboratory cousins. The longer the mice lived outdoors, the greater the number and size of worms in their guts. We found that outdoor mice harbored more diverse gut microbes and even specific bacteria that may have impacted worm growth and survival inside the mice. Mice kept outdoors also produced decreased immune responses of the type essential for worm expulsion. Together, these results demonstrate that the external environment significantly alters how a host responds to worms and germs in her or his gut, thereby leading to variation in the outcome of infections.

Manipulation of host and parasite microbiotas: Survival strategies during chronic nematode infection

Intestinal dwelling parasites have evolved closely with the complex intestinal microbiota of their host, but the significance of the host microbiota for metazoan pathogens and the role of their own intestinal microbiota are still not fully known. We have found that the parasitic nematode Trichuris muris acquired a distinct intestinal microbiota from its host, which was required for nematode fitness. Infection of germ-free mice and mice monocolonized with Bacteroides thetaiotaomicron demonstrated that successful T. muris infections require a host microbiota. Following infection, T. muris-induced alterations in the host intestinal microbiota inhibited subsequent rounds of infection, controlling parasite numbers within the host intestine. This dual strategy could promote the long-term survival of the parasite within the intestinal niche necessary for successful chronic nematode infection.

Intestinal epithelial suppressor of cytokine signaling 3 (SOCS3) impacts on mucosal homeostasis in a model of chronic inflammation

Introduction

Suppressor of cytokine signaling 3 (SOCS3) is a tumour suppressor, limiting intestinal epithelial cell (IEC) proliferation in acute inflammation, and tumour growth, but little is known regarding its role in mucosal homeostasis. Resistance to the intestinal helminth Trichuris muris relies on an “epithelial escalator” to expel the parasite. IEC turnover is restricted by parasite‐induced indoleamine 2,3‐dioxygenase (IDO).

Methods

Mice with or without conditional knockout of SOCS3 were infected with T. muris. Crypt depth, worm burden, and proliferating cells and IDO were quantified. SOCS3 knockdown was also performed in human IEC cell lines.

Results

Chronic T. muris infection increased expression of SOCS3 in wild‐type mice. Lack of IEC SOCS3 led to a modest increase in epithelial turnover. This translated to a lower worm burden, but not complete elimination of the parasite suggesting a compensatory mechanism, possibly IDO, as seen in SOCS3 knockdown.

Conclusions

We report that SOCS3 impacts on IEC turnover following T. muris infection, potentially through enhancement of IDO. IDO may dampen the immune response which can drive IEC hyperproliferation in the absence of SOCS3, demonstrating the intricate interplay of immune signals regulating mucosal homeostasis, and suggesting a novel tumour suppressor role of SOCS3.

Immune-driven alterations in mucin sulphation is an important mediator of Trichuris muris helminth expulsion

Mucins are heavily glycosylated proteins that give mucus its gel-like properties. Moreover, the glycans decorating the mucin protein core can alter the protective properties of the mucus barrier. To investigate whether these alterations could be parasite-induced we utilized the Trichuris muris (T. muris) infection model, using different infection doses and strains of mice that are resistant (high dose infection in BALB/c and C57BL6 mice) or susceptible (high dose infection in AKR and low dose infection in BALB/c mice) to chronic infection by T. muris. During chronicity, within the immediate vicinity of the T. muris helminth the goblet cell thecae contained mainly sialylated mucins. In contrast, the goblet cells within the epithelial crypts in the resistant models contained mainly sulphated mucins. Maintained mucin sulphation was promoted by T_H2-immune responses, in particular IL-13, and contributed to the protective properties of the mucus layer, making it less vulnerable to degradation by T. muris excretory secretory products. Mucin sulphation was markedly reduced in the caecal goblet cells in the sulphate anion transporter-1 (Sat-1) deficient mice. We found that Sat-1 deficient mice were susceptible to chronic infection despite a strong T_H2-immune response. Lower sulphation levels lead to decreased efficiency of establishment of T. muris infection, independent of egg hatching. This study highlights the complex process by which immune-regulated alterations in mucin glycosylation occur following T. muris infection, which contributes to clearance of parasitic infection.

Approximately 2 billion people are infected with worms every year, causing physical, nutritional and cognitive impairment particularly in children. Mucins are large sugar-coated (glycosylated) proteins that form the intestinal mucus layer. This mucus layer protects our ‘insides’ from external insults and plays an important role during worm infection. We discovered that there is a difference in the glycosylation of mucins in people infected with worms compared to uninfected individuals. Therefore, using different mouse models we investigated the role of glycosylation, and in particular sulphation of mucins in infection. We found that mucin glycosylation is controlled by the immune response and increased sulphation correlated with the expulsion of the worm from the host. Highly sulphated mucins were protected from degradation by the worm. Moreover, mice lacking a sulphate transporter had significantly lower sulphation levels on mucins, which resulted in a reduction in the establishment of the worms and chronic infection.

The influence of trematode parasite burden on gene expression in a mammalian host

Background

Parasites can profoundly impact their hosts and are responsible for a plethora of debilitating diseases. To identify global changes in host gene expression related to parasite infection, we sequenced, assembled, and annotated the liver transcriptomes of Balb/cj mice infected with the trematode parasite Schistosoma mansoni and compared the results to uninfected mice. We used two different methodologies (i.e. de novo and reference guided) to evaluate the influence of parasite sequences on host transcriptome assembly.

Results

Our results demonstrate that the choice of assembly methodology significantly impacted the proportion of parasitic reads detected from the host library, yet the presence of non-target (xenobiotic) sequences did not create significant structural errors in the assembly. After removing parasite sequences from the mouse transcriptomes, we analyzed host gene expression under different parasite infection levels and observed significant differences in the associated immunologic and metabolic responses based on infection level. In particular, genes associated with T–helper type 1 (Th–1) and T–helper type 2 (Th–2) were up-regulated in infected mice whereas genes related to amino acid and carbohydrate metabolism were down-regulated in infected mice. These changes in gene expression scale with infection status and likely impact the evolutionary fitness of hosts.

Conclusions

Overall, our data indicate that a) infected mice reduce the expression of key metabolic genes in direct proportion to their infection level; b) infected mice similarly increase the expression of key immune genes in response to infection; c) patterns of gene expression correspond to the pathological symptoms of schistosomiasis; and d) identifying and filtering out non-target sequences (xenobiotics) improves differential expression prediction. Our findings identify parasite targets for RNAi or other therapies and provide a better understanding of the pathology and host immune repertoire involved in response to S. mansoni infections.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2950-5) contains supplementary material, which is available to authorized users.

Animal models to study acute and chronic intestinal inflammation in mammals

Acute and chronic inflammatory diseases of the intestine impart a significant and negative impact on the health and well-being of human and non-human mammalian animals. Understanding the underlying mechanisms of inflammatory disease is mandatory to develop effective treatment and prevention strategies. As inflammatory disease etiologies are multifactorial, the use of appropriate animal models and associated metrics of disease are essential. In this regard, animal models used alone or in combination to study acute and chronic inflammatory disease of the mammalian intestine paired with commonly used inflammation-inducing agents are reviewed. This includes both chemical and biological incitants of inflammation, and both non-mammalian (i.e. nematodes, insects, and fish) and mammalian (i.e. rodents, rabbits, pigs, ruminants, dogs, and non-human primates) models of intestinal inflammation including germ-free, gnotobiotic, as well as surgical, and genetically modified animals. Importantly, chemical and biological incitants induce inflammation via a multitude of mechanisms, and intestinal inflammation and injury can vary greatly according to the incitant and animal model used, allowing studies to ascertain both long-term and short-term effects of inflammation. Thus, researchers and clinicians should be aware of the relative strengths and limitations of the various animal models used to study acute and chronic inflammatory diseases of the mammalian intestine, and the scope and relevance of outcomes achievable based on this knowledge. The ability to induce inflammation to mimic common human diseases is an important factor of a successful animal model, however other mechanisms of disease such as the amount of infective agent to induce disease, invasion mechanisms, and the effect various physiologic changes can have on inducing damage are also important features. In many cases, the use of multiple animal models in combination with both chemical and biological incitants is necessary to answer the specific question being addressed regarding intestinal disease. Some incitants can induce acute responses in certain animal models while others can be used to induce chronic responses; this review aims to illustrate the strengths and weaknesses in each animal model and to guide the choice of an appropriate acute or chronic incitant to facilitate intestinal disease.

Immunity to gastrointestinal nematodes: mechanisms and myths

Immune responses to gastrointestinal nematodes have been studied extensively for over 80 years and intensively investigated over the last 30–40 years. The use of laboratory models has led to the discovery of new mechanisms of protective immunity and made major contributions to our fundamental understanding of both innate and adaptive responses. In addition to host protection, it is clear that immunoregulatory processes are common in infected individuals and resistance often operates alongside modulation of immunity. This review aims to discuss the recent discoveries in both host protection and immunoregulation against gastrointestinal nematodes, placing the data in context of the specific life cycles imposed by the different parasites studied and the future challenges of considering the mucosal/immune axis to encompass host, parasite, and microbiome in its widest sense.

Regulatory T cells limit induction of protective immunity and promote immune pathology following intestinal helminth infection

Foxp3(+) regulatory T cells (Tregs) have a well-characterized role in limiting autoimmunity and dampening deleterious immune responses. However, a potential consequence of the immunosuppressive function of Tregs can be the limitation of protective immunity to infectious pathogens. Parasitic infections are a potent stimulus for the generation of Treg responses, which may be beneficial to both the parasite and the host by promoting persistence of infection and limiting immune-mediated pathology, respectively. In this study, we explore the functional role of Tregs post-low-dose infection with the intestinal helminth parasite Trichuris muris, which yields a chronic infection because of inefficient induction of Th2 responses. Early Treg depletion postinfection resulted in expedited worm clearance, and was associated with reduced Th1-mediated inflammation of the intestinal environment. Interestingly, this protective immunity was lost, and worm burden enhanced if Tregs were depleted later once the infection was established. Early and late Treg depletion resulted in enhanced Th2 and reduced Th1 cytokine and humoral responses. Blockade of the Th2 cytokine IL-4 resulted in a moderate increase in Th1 but had no effect on worm burden. Our findings suggest that Tregs preferentially limit Th2 cell expansion, which can impact infections where clear immune polarity has not been established. Thus, the impact of Treg depletion is context and time dependent, and can be beneficial to the host in situations where Th1 responses should be limited in favor of Th2 responses.

Mycobacterium bovis BCG infection severely delays Trichuris muris expulsion and co-infection suppresses immune responsiveness to both pathogens

BACKGROUND

The global epidemiology of parasitic helminths and mycobacterial infections display extensive geographical overlap, especially in the rural and urban communities of developing countries. We investigated whether co-infection with the gastrointestinal tract-restricted helminth, Trichuris muris, and the intracellular bacterium, Mycobacterium bovis (M. bovis) BCG, would alter host immune responses to, or the pathological effect of, either infection.

RESULTS

We demonstrate that both pathogens are capable of negatively affecting local and systemic immune responses towards each other by modifying cytokine phenotypes and by inducing general immune suppression. T. muris infection influenced non-specific and pathogen-specific immunity to M. bovis BCG by down-regulating pulmonary TH1 and Treg responses and inducing systemic TH2 responses. However, co-infection did not alter mycobacterial multiplication or dissemination and host pulmonary histopathology remained unaffected compared to BCG-only infected mice. Interestingly, prior M. bovis BCG infection significantly delayed helminth clearance and increased intestinal crypt cell proliferation in BALB/c mice. This was accompanied by a significant reduction in systemic helminth-specific TH1 and TH2 cytokine responses and significantly reduced local TH1 and TH2 responses in comparison to T. muris-only infected mice.

CONCLUSION

Our data demonstrate that co-infection with pathogens inducing opposing immune phenotypes, can have differential effects on compartmentalized host immune protection to either pathogen. In spite of local and systemic decreases in TH1 and increases in TH2 responses co-infected mice clear M. bovis BCG at the same rate as BCG only infected animals, whereas prior mycobacterial infection initiates prolonged worm infestation in parallel to decreased pathogen-specific TH2 cytokine production.

Advancing a multivalent 'Pan-anthelmintic' vaccine against soil-transmitted nematode infections

Ascaris lumbricoides

The Sabin Vaccine Institute Product Development Partnership is developing a Pan-anthelmintic vaccine that simultaneously targets the major soil-transmitted nematode infections, in other words, ascariasis, trichuriasis and hookworm infection. The approach builds off the current bivalent Human Hookworm Vaccine now in clinical development and would ultimately add both a larval Ascaris lumbricoides antigen and an adult-stage Trichuris trichiura antigen from the parasite stichosome. Each selected antigen would partially reproduce the protective immunity afforded by UV-attenuated Ascaris eggs and Trichuris stichosome extracts, respectively. Final antigen selection will apply a ranking system that includes the evaluation of expression yields and solubility, feasibility of process development and the absence of circulating antigen-specific IgE among populations living in helminth-endemic regions. Here we describe a five year roadmap for the antigen discovery, feasibility and antigen selection, which will ultimately lead to the scale-up expression, process development, manufacture, good laboratory practices toxicology and preclinical evaluation, ultimately leading to Phase 1 clinical testing.

Trichuris muris: a model of gastrointestinal parasite infection

Infection with soil-transmitted gastrointestinal parasites, such as Trichuris trichiura, affects more than a billion people worldwide, causing significant morbidity and health problems especially in poverty-stricken developing countries. Despite extensive research, the role of the immune system in triggering parasite expulsion is incompletely understood which hinders the development of anti-parasite therapies. Trichuris muris infection in mice serves as a useful model of T. trichiura infection in humans and has proven to be an invaluable tool in increasing our understanding of the role of the immune system in promoting either susceptibility or resistance to infection. The old paradigm of a susceptibility-associated Th1 versus a resistance-associated Th2-type response has been supplemented in recent years with cell populations such as novel innate lymphoid cells, basophils, dendritic cells and regulatory T cells proposed to play an active role in responses to T. muris infection. Moreover, new immune-controlled mechanisms of expulsion, such as increased epithelial cell turnover and mucin secretion, have been described in recent years increasing the number of possible targets for anti-parasite therapies. In this review, we give a comprehensive overview of experimental work conducted on the T. muris infection model, focusing on important findings and the most recent reports on the role of the immune system in parasite expulsion.

Helminth infections and host immune regulation

Helminth parasites infect almost one-third of the world's population, primarily in tropical regions. However, regions where helminth parasites are endemic record much lower prevalences of allergies and autoimmune diseases, suggesting that parasites may protect against immunopathological syndromes. Most helminth diseases are spectral in nature, with a large proportion of relatively asymptomatic cases and a subset of patients who develop severe pathologies. The maintenance of the asymptomatic state is now recognized as reflecting an immunoregulatory environment, which may be promoted by parasites, and involves multiple levels of host regulatory cells and cytokines; a breakdown of this regulation is observed in pathological disease. Currently, there is much interest in whether helminth-associated immune regulation may ameliorate allergy and autoimmunity, with investigations in both laboratory models and human trials. Understanding and exploiting the interactions between these parasites and the host regulatory network are therefore likely to highlight new strategies to control both infectious and immunological diseases.

The mucosal response of hamsters exposed to weekly repeated infections with the hookworm Ancylostoma ceylanicum

An experiment was carried out to assess mucosal changes in hamsters exposed to weekly repeated low-intensity infections with the hookworm Ancylostoma ceylanicum. The experiment included control groups of naïve, uninfected hamsters and groups that received a single-pulse primary infection. Changes in the intestinal architecture and in the density of inflammatory cells in the mucosa, including mast cells, goblet cells, Paneth cells and eosinophils were examined in relation to changes in hookworm burdens. As in the single-pulse primary infection, hamsters exposed to repeated infections responded with marked changes in the intestinal architecture and in mucosal populations of inflammatory cells. However, there were distinct differences in the kinetics of the responses to these two types of infection (primary single-pulse and repeated). The reduction in villous height and the increase in crypt depth in animals exposed to repeated infections were both initially slower but eventually equalled and exceeded the responses in hamsters given a chronic primary infection, despite the presence of fewer adult worms in the former. Similarly, changes in the mitotic figures of epithelial cells in the mucosa and the mast cell response were both initially slower and less intense in repeatedly infected hamsters, but eventually exceeded the response to primary infection. Furthermore, the eosinophil response was found to be initially greater in repeated infections and overall more persistent. In contrast, both goblet and Paneth cell responses were less marked in repeatedly infected animals compared to those carrying a primary infection. These results are discussed in the context of host protective resistance to infection with A. ceylanicum.

Wild immunology: converging on the real world

Recently, the Centre for Immunity, Infection and Evolution sponsored a one-day symposium entitled "Wild Immunology." The CIIE is a new Wellcome Trust-funded initiative with the remit to connect evolutionary biology and ecology with research in immunology and infectious diseases in order to gain an interdisciplinary perspective on challenges to global health. The central question of the symposium was, "Why should we try to understand infection and immunity in wild systems?" Specifically, how does the immune response operate in the wild and how do multiple coinfections and commensalism affect immune responses and host health in these wild systems? The symposium brought together a broad program of speakers, ranging from laboratory immunologists to infectious disease ecologists, working on wild birds, unmanaged animals, wild and laboratory rodents, and on questions ranging from the dynamics of coinfection to how commensal bacteria affect the development of the immune system. The meeting on wild immunology, organized by Amy Pedersen, Simon Babayan, and Rick Maizels, was held at the University of Edinburgh on 30 June 2011.

Changes in the mucosal barrier during acute and chronic Trichuris muris infection

The intestinal mucosal barrier, part of the innate immune defence, is responsive to the external environment and changes in response to infection. There is disparate evidence for the epithelial and goblet cell products within the intrinsic barrier being part of a response to resolve infection. We comprehensively analysed the changes of mucosal glycoconjugates during acute and chronic infection by utilising the Trichuris muris (T. muris) model. Transcription factors, atonal homolog 1 (Math-1) and SAM pointed domain containing ETS transcription factor (Spdef) were activated during acute infection, which promoted stem cell fate towards a secretory cell phenotype. The thickness of the intermediate barrier, the carbohydrate-rich glycocalyx, composed of cell surface mucins increased with exposure to T. muris, with an increase in Muc4, Muc13 and Muc17. Overall, hypersecretion of glycoproteins into the extrinsic barrier (mediated by IL-13) via the gamma amino-butyric acid-α3 receptor (GABA-α3), was observed during acute infection. Furthermore, altered glycosylation was observed during acute and chronic infection; mucins were more highly charged during acute infection than during chronic infection. This study readdresses the changes within the mucosal barrier, in particular in the cell surface and secreted mucins during acute and chronic nematode infection.

The vitamin D receptor and inducible nitric oxide synthase associated pathways in acquired resistance to Cooperia oncophora infection in cattle

Cooperia oncophora is an economically important gastrointestinal nematode in ruminants. Acquired resistance to Cooperia oncophora infection in cattle develops rapidly as a result of prior infections. Naïve cattle, when given a primary infection of high-dose infective L3 larvae, develop a strong immunity to subsequent reinfection. Compared to primary infection, reinfection resulted in a marked reduction in worm establishment. In order to understand molecular mechanisms underlying the development of acquired resistance, we characterized the transcriptomic responses of the bovine small intestine to a primary infection and reinfection. A total of 23 pathways were significantly impacted during infection. The vitamin D receptor activation was strongly induced only during reinfection, suggesting that this pathway may play an important role in the development of acquired resistance via its potential roles in immune regulation and intestinal mucosal integrity maintenance. The expression of inducible nitric oxide synthase (NOS2) was strongly induced during reinfection but not during primary infection. As a result, several canonical pathways associated with NOS2 were impacted. The genes involved in eicosanoid synthesis, including prostaglandin synthase 2 (PTGS2 or COX2), remained largely unchanged during infection. The rapid development of acquired resistance may help explain the lack of relative pathogenicity by Cooperia oncophora infection in cattle. Our findings facilitate the understanding of molecular mechanisms underlying the development of acquired resistance, which could have an important implication in vaccine design.

Chronic systemic infection exacerbates ischemic brain damage via a CCL5 (regulated on activation, normal T-cell expressed and secreted)-mediated proinflammatory response in mice

Infection and systemic inflammation are risk factors for cerebrovascular diseases and poststroke infections impair outcome in stroke patients, although the mechanisms of their contribution are mostly unknown. No preclinical studies have identified how chronic infection affects ischemic brain damage and which key inflammatory mediators are involved. We used a well established model of gut infection (Trichuris muris) to study how chronic infection contributes to brain injury. We show that, in mice, infection that leads to a chronic Th1-polarized immune response dramatically (60%) exacerbates brain damage caused by experimental stroke. Chronic Th1-type infection resulted in systemic upregulation of proinflammatory mediators and profoundly altered stroke-induced early (40 min to 4 h) and late (48 h) inflammation in the brain and peripheral tissues. Using the same infection, we show that a Th1-, but not Th2-polarized response augments brain injury by increasing the Th1 chemokine CCL5 [regulated on activation, normal T-cell expressed and secreted (RANTES)] systemically. This infection-associated response paralleled altered regulatory T-cell response, accelerated platelet aggregation in brain capillaries, and increased microvascular injury and matrix metalloproteinase activation after stroke. Antibody neutralization of RANTES reversed the effect of chronic infection on brain damage, microvascular MMP-9 activation, and cellular inflammatory response. Our results suggest that chronic infection exacerbates ischemic brain damage via a RANTES-mediated systemic inflammatory response, which leads to delayed resolution of inflammation and augmented microvascular injury in the brain.

Regulation of immune responses to Strongyloides venezuelensis challenge after primary infection with different larvae doses

Nematode infections are generally followed by high rates of reinfection, leading to elevated prevalence in endemic areas. Therefore, the effective control of nematode infections depends on understanding the induction and regulation of protective mechanisms. However, most experimental models for protective immune response against nematodes use high parasite exposure, not always reflecting what occurs naturally in human populations. In this study, we tested whether infecting mice with different Strongyloides venezuelensis larvae loads would affect protective responses against reinfection. Interestingly, we found that a previous infection with 10-500 larvae conferred high rate of protection against reinfection with S. venezuelensis in mice, by destroying large numbers of migrating larvae. However, low-dose priming did not abolish adult worm maturation, as detected in high-dose primed group. Results also indicated that a previous low-dose infection delayed the development of cellular infiltrate, while a high inoculum rapidly induced these inflammatory features. Cytokine production by splenocyte cultures of challenge infected mice demonstrated that low-dose priming had increased production of IL-4 and IFN-gamma, while high-dose induced IL-4 production but not IFN-gamma. Our data support the hypothesis that low-dose nematode infection does not induce a polarized type-2 immune response, allowing adult worm survival.

Type 2 immune-inducing helminth vaccination maintains protective efficacy in the setting of repeated parasite exposures

Animal studies have demonstrated that helminth vaccines which induce type 2 immune responses can be protective. To date, however, such vaccines have not been tested against repeated parasite challenges. Since repeated antigenic challenge of patients with allergic disease results in immunologic tolerance, we hypothesized that a helminth vaccine which induces type 2 immune responses may lose its protective efficacy in the setting of repeated parasite exposures (RPEs). To test this hypothesis, we examined whether RPEs induce immunological tolerance and reduce the effectiveness of a type 2 immune-inducing vaccine. BALB/c mice vaccinated against Litomosoides sigmodontis, a filarial nematode of rodents, were repeatedly exposed to irradiated larvae for 2 or 8 weeks or to non-irradiated infectious larvae for three months. Vaccination-induced parasite-specific IgE levels, parasite antigen-driven basophil interleukin 4 (IL-4) release, and Th2 skewing of the cellular immune response remained stable in the face of RPEs. Furthermore, RPEs in vaccinated mice did not augment immunoregulatory responses, as parasite antigen-driven cellular proliferation, production of IL-10, and frequencies of CD4(+)CD25(+)FoxP3(+) regulatory T-cells were not altered by RPEs. Challenge infections with infectious L3-stage larvae resulted in lower worm burdens in vaccinated mice given RPEs than in vaccinated controls. These results demonstrate that vaccines which induce type 2 immune responses can maintain their efficacy in the setting of repeated parasite exposures.

Helminth products bypass the need for TSLP in Th2 immune responses by directly modulating dendritic cell function

Thymic stromal lymphopoietin (TSLP) is an interleukin (IL)-7-like cytokine, mainly expressed by epithelial cells, and key to the development of allergic responses. The well-documented involvement of TSLP in allergy has led to the conviction that TSLP promotes the development of inflammatory Th2 cell responses. However, we now report that the interaction of TSLP with its receptor (TSLPR) has no functional impact on the development of protective Th2 immune responses after infection with 2 helminth pathogens, Heligmosomoides polygyrus and Nippostrongylus brasiliensis. Mice deficient in the TSLP binding chain of the TSLPR (TSLPR(-/-)) exhibited normal Th2 cell differentiation, protective immunity and memory responses against these two distinct rodent helminths. In contrast TSLP was found to be necessary for the development of protective Th2 responses upon infection with the helminth Trichuris muris (T. muris). TSLP inhibited IL-12p40 production in response to T. muris infection, and treatment of TSLPR(-/-) animals with neutralizing anti-IL-12p40 monoclonal antibody (mAb) was able to reverse susceptibility and attenuate IFN-gamma production. We additionally demonstrated that excretory-secretory (ES) products from H. polygyrus and N. brasiliensis, but not T. muris, were capable of directly suppressing dendritic cell (DC) production of IL-12p40, thus bypassing the need for TSLP. Taken together, our data show that the primary function of TSLP is to directly suppress IL-12 secretion, thus supporting Th2 immune responses.

Early exposure of infants to GI nematodes induces Th2 dominant immune responses which are unaffected by periodic anthelminthic treatment

We have previously shown a reduction in anaemia and wasting malnutrition in infants <3 years old in Pemba Island, Zanzibar, following repeated anthelminthic treatment for the endemic gastrointestinal (GI) nematodes Ascaris lumbricoides, hookworm and Trichuris trichiura. In view of the low intensity of worm infections in this age group, this was unexpected, and it was proposed that immune responses to the worms rather than their direct effects may play a significant role in morbidity in infants and that anthelminthic treatment may alleviate such effects. Therefore, the primary aims of this study were to characterise the immune response to initial/early GI nematode infections in infants and the effects of anthelminthic treatment on such immune responses. The frequency and levels of Th1/Th2 cytokines (IL-5, IL-13, IFN-γ and IL-10) induced by the worms were evaluated in 666 infants aged 6–24 months using the Whole Blood Assay. Ascaris and hookworm antigens induced predominantly Th2 cytokine responses, and levels of IL-5 and IL-13 were significantly correlated. The frequencies and levels of responses were higher for both Ascaris positive and hookworm positive infants compared with worm negative individuals, but very few infants made Trichuris-specific cytokine responses. Infants treated every 3 months with mebendazole showed a significantly lower prevalence of infection compared with placebo-treated controls at one year following baseline. At follow-up, cytokine responses to Ascaris and hookworm antigens, which remained Th2 biased, were increased compared with baseline but were not significantly affected by treatment. However, blood eosinophil levels, which were elevated in worm-infected children, were significantly lower in treated children. Thus the effect of deworming in this age group on anaemia and wasting malnutrition, which were replicated in this study, could not be explained by modification of cytokine responses but may be related to eosinophil function.

Infants and very young children commonly become infected with intestinal nematode infections. However, the worm burdens are generally very light, so a beneficial effect of deworming on wasting malnutrition and anaemia in this age group which we have demonstrated was unexpected and the mechanism unclear. To investigate this, we have, for the first time, determined whether such worm infections in infants induce significant immune reactions which might be detrimental to nutrition and growth e.g. by inducing inflammation in the gut or by cytokine effects on erythropoiesis. We also determined if such responses are modulated by regular deworming over a 9 month period. Peripheral blood cells from infants infected with Ascaris and hookworms in particular responded to stimulation with worm antigens, producing predominantly Th2 cytokines. Although the Th2 cytokine responses in the periphery were not significantly altered by deworming, the levels of eosinophils, which are regulated by the Th2 cytokine, IL-5, were lower after treatment. It is possible that eosinophils play a role in gut pathology leading to wasting malnutrition and anaemia in the very young and that this effect is reduced by deworming.