A genome-scale metabolic model of parasitic whipworm

Genome-scale metabolic models are widely used to enhance our understanding of metabolic features of organisms, host-pathogen interactions and to identify therapeutics for diseases. Here we present iTMU798, the genome-scale metabolic model of the mouse whipworm Trichuris muris. The model demonstrates the metabolic features of T. muris and allows the prediction of metabolic steps essential for its survival. Specifically, that Thioredoxin Reductase (TrxR) enzyme is essential, a prediction we validate in vitro with the drug auranofin. Furthermore, our observation that the T. muris genome lacks gsr-1 encoding Glutathione Reductase (GR) but has GR activity that can be inhibited by auranofin indicates a mechanism for the reduction of glutathione by the TrxR enzyme in T. muris. In addition, iTMU798 predicts seven essential amino acids that cannot be synthesised by T. muris, a prediction we validate for the amino acid tryptophan. Overall, iTMU798 is as a powerful tool to study not only the T. muris metabolism but also other Trichuris spp. in understanding host parasite interactions and the rationale design of new intervention strategies.

Amino acid availability acts as a metabolic rheostat to determine the magnitude of ILC2 responses

Group 2 innate lymphoid cells (ILC2) are functionally poised, tissue-resident lymphocytes that respond rapidly to damage and infection at mucosal barrier sites. ILC2 reside within complex microenvironments where they are subject to cues from both the diet and invading pathogens-including helminths. Emerging evidence suggests ILC2 are acutely sensitive not only to canonical activating signals but also perturbations in nutrient availability. In the context of helminth infection, we identify amino acid availability as a nutritional cue in regulating ILC2 responses. ILC2 are found to be uniquely preprimed to import amino acids via the large neutral amino acid transporters Slc7a5 and Slc7a8. Cell-intrinsic deletion of these transporters individually impaired ILC2 expansion, while concurrent loss of both transporters markedly impaired the proliferative and cytokine-producing capacity of ILC2. Mechanistically, amino acid uptake determined the magnitude of ILC2 responses in part via tuning of mTOR. These findings implicate essential amino acids as a metabolic requisite for optimal ILC2 responses within mucosal barrier tissues.

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.

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.

Rhythmicity of intestinal IgA responses confers oscillatory commensal microbiota mutualism

Interactions between the mammalian host and commensal microbiota are enforced through a range of immune responses that confer metabolic benefits and promote tissue health and homeostasis. Immunoglobulin A (IgA) responses directly determine the composition of commensal species that colonize the intestinal tract but require substantial metabolic resources to fuel antibody production by tissue-resident plasma cells. Here, we demonstrate that IgA responses are subject to diurnal regulation over the course of a circadian day. Specifically, the magnitude of IgA secretion, as well as the transcriptome of intestinal IgA+ plasma cells, was found to exhibit rhythmicity. Oscillatory IgA responses were found to be entrained by time of feeding and were also found to be in part coordinated by the plasma cell-intrinsic circadian clock via deletion of the master clock gene Arntl. Moreover, reciprocal interactions between the host and microbiota dictated oscillatory dynamics among the commensal microbial community and its associated transcriptional and metabolic activity in an IgA-dependent manner. Together, our findings suggest that circadian networks comprising intestinal IgA, diet, and the microbiota converge to align circadian biology in the intestinal tract and to ensure host-microbial mutualism.

Anti-Trichuris mucosal responses are maintained during H. bakeri co-infection despite impaired parasite expulsion

In endemic regions concurrent infection with multiple gastrointestinal (GI) helminth species is more common than single species infection. However, the majority of model helminth infections focus on single species infections leading to a lack of understanding of how co-infection influences anti-parasite immune responses. Here, we use a model co-infection of Trichuris muris (Tm) and Heligmosomoides bakeri (Hb) to investigate the effect of Hb on anti-Tm immune responses. We observed a complete impairment of Tm expulsion in immune competent C57BL/6 mice when co-infected with Hb. This was coupled with reduced cellularity in the colonic mesenteric lymph node (cMLN) proximal to the caecum, however, cMLN cytokine responses and caecal mucosal immune responses in co-infected mice were not significantly different from mice infected with Tm alone. Interestingly, in immune-compromised mice, we found co-infection resulted in enhanced growth and fecundity of female Tm parasites. These data suggest that during helminth-helminth co-infection, immune-independent signals between species may promote survival and growth.

Defining the early stages of intestinal colonisation by whipworms

Whipworms are large metazoan parasites that inhabit multi-intracellular epithelial tunnels in the large intestine of their hosts, causing chronic disease in humans and other mammals. How first-stage larvae invade host epithelia and establish infection remains unclear. Here we investigate early infection events using both Trichuris muris infections of mice and murine caecaloids, the first in-vitro system for whipworm infection and organoid model for live helminths. We show that larvae degrade mucus layers to access epithelial cells. In early syncytial tunnels, larvae are completely intracellular, woven through multiple live dividing cells. Using single-cell RNA sequencing of infected mouse caecum, we reveal that progression of infection results in cell damage and an expansion of enterocytes expressing of Isg15, potentially instigating the host immune response to the whipworm and tissue repair. Our results unravel intestinal epithelium invasion by whipworms and reveal specific host-parasite interactions that allow the whipworm to establish its multi-intracellular niche.

Whipworms are large parasites causing chronic disease in humans and other mammals. Here, the authors show how larvae create tunnels inside the gut lining and reveal the early host response to infection via Isg15 in mice and murine caecaloids.

Hatching of parasitic nematode eggs: a crucial step determining infection

Although hatching from eggs is fundamental for nematode biology it remains poorly understood. For animal-parasitic nematodes in particular, advancement has been slow since the 1980s. Understanding such a crucial life-cycle process would greatly improve the tractability of parasitic nematodes as experimental systems, advance fundamental knowledge, and enable translational research. Here, we review the role of eggs in the nematode life cycle and the current knowledge on the hatching cascade, including the different inducing and contributing factors, and highlight specific areas of the field that remain unknown. We examine how these knowledge gaps could be addressed and discuss their potential impact and application in nematode parasite research, treatment, and control.

Profiles of inflammatory markers and their association with cardiometabolic parameters in rural and urban Uganda

Background: Inflammation may be one of the pathways explaining differences in cardiometabolic risk between urban and rural residents. We investigated associations of inflammatory markers with rural versus urban residence, and with selected cardiometabolic parameters previously observed to differ between rural and urban residents: homeostatic model assessment of insulin resistance (HOMA-IR), fasting blood glucose (FBG), blood pressure (BP) and body mass index (BMI). Methods: From two community surveys conducted in Uganda, 313 healthy individuals aged ≥ 10 years were selected by age- and sex-stratified random sampling (rural Lake Victoria island communities, 212; urban Entebbe municipality, 101). Fluorescence intensities of plasma cytokines and chemokines were measured using a bead-based multiplex immunoassay. We used linear regression to examine associations between the analytes and rural-urban residence and principal component analysis (PCA) to further investigate patterns in the relationships. Correlations between analytes and metabolic parameters were assessed using Pearson’s correlation coefficient. Results: The urban setting had higher mean levels of IL-5 (3.27 vs 3.14, adjusted mean difference [95% confidence interval] 0.12[0.01,0.23] p=0.04), IFN-⍺ (26.80 vs 20.52, 6.30[2.18,10.41] p=0.003), EGF (5.67 vs 5.07, 0.60[0.32,0.98] p<0.00001), VEGF (3.68 vs 3.28, 0.40[0.25,0.56] p<0.00001), CD40 Ligand (4.82 vs 4.51, 0.31[0.12, 0.50] p=0.001) and Serpin-E1 (9.57 vs 9.46, 0.11[0.05,0.17] p<0.00001), but lower levels of GMCSF (2.94 vs 3.05, -0.10[-0.19,-0.02] p=0.02), CCL2 (2.82 vs 3.10, -0.45[-0.70,-0.21] p<0.00001) and CXCL10 (5.48 vs 5.96, -0.49[-0.71,-0.27] p<0.00001), compared to the rural setting. In PCA, the urban setting had lower representation of some classical inflammatory mediators but higher representation of various chemoattractants and vasoactive peptides. HOMA-IR, FBG, BP and BMI were positively correlated with several principal components characterised by pro-inflammatory analytes. Conclusions: In developing countries, immunological profiles differ between rural and urban environments. Differential expression of certain pro-inflammatory mediators may have important health consequences including contributing to increased cardiometabolic risk observed in the urban environment.

Sustained Post-Developmental T-Bet Expression Is Critical for the Maintenance of Type One Innate Lymphoid Cells In Vivo

Innate lymphoid cells (ILC) play a significant role in the intestinal immune response and T-bet+ CD127+ group 1 cells (ILC1) have been linked to the pathogenesis of human inflammatory bowel disease (IBD). However, the functional importance of ILC1 in the context of an intact adaptive immune response has been controversial. In this report we demonstrate that induced depletion of T-bet using a Rosa26-Cre-ERT2 model resulted in the loss of intestinal ILC1, pointing to a post-developmental requirement of T-bet expression for these cells. In contrast, neither colonic lamina propria (cLP) ILC2 nor cLP ILC3 abundance were altered upon induced deletion of T-bet. Mechanistically, we report that STAT1 or STAT4 are not required for intestinal ILC1 development and maintenance. Mice with induced deletion of T-bet and subsequent loss of ILC1 were protected from the induction of severe colitis in vivo. Hence, this study provides support for the clinical development of an IBD treatment based on ILC1 depletion via targeting T-bet or its downstream transcriptional targets.

Trichuris muris and comorbidities - within a mouse model context

Trichuris muris is a mouse intestinal parasitic nematode that inhabits the large intestine of its host and induces a strong immune response. The effects of this strong anti-parasite response can be found locally within the intestinal niche and also systemically, having effects on multiple organs. Additionally, the anti-parasite response can have multiple effects on infectious organisms and on microbiota that the host is harbouring. It has been shown that Th1 responses induced by T. muris can affect progression of bowel inflammation, cause colitic-like intestinal inflammation, reduce barrier function and intestinal mucosal responses. In the brain, T. muris can exacerbate stroke outcome and other neurological conditions. In the lung, T. muris can suppress airway inflammation and alter immune responses to other parasites. Additionally, T. muris induced responses can inhibit anti-tumour immunity. Although this parasite maintains a localized niche in the large intestine, its effects can be far-reaching and substantially impact other infections through modulation of bystander immune responses.

The interplay between Trichuris and the microbiota

Parasitic worms are amongst the most common pathogens to infect humans and have a long-established history of inflicting disease in their hosts. There is a large body of evidence that states intestine-dwelling helminths ensure their survival by influencing the host immune response against them. In recent years, it has become apparent that the large and diverse microbial communities that exist in the gastrointestinal (GI) tract of the host and within the parasite itself have a pivotal role in worm survival and persistence. Using a variety of mouse models (including laboratory, germ-free and rewilded mice), there have been new insights into how bacteria and worms interact with each other; this includes the discovery that Trichuris is unable to hatch and/or infect their host in the absence of bacteria, and that these worms contain a Trichuris-specific gut microbiota. These interactions are determined in part by the capacity of the host, gut microbiota and worms to communicate via metabolites such as butyrate, which are microbially derived and have known immunoregulatory properties. By exploring the contribution of gut bacteria to worm infections and the intricate relationship that exists between them, an exciting and emerging field in whipworm parasitology is established.

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.

Intestinal helminth co-infection is an unrecognised risk factor for increased pneumococcal carriage density and invasive disease

Infection with Streptococcus pneumoniae is the leading cause of death in children and burden of disease is greatest where helminth infections are also common. We investigated the impact of intestinal helminth co-infection on pneumococcal carriage; a risk factor for invasive disease. We used a mouse co-infection model and clinical data to assess the impact of co-infection on carriage density. Co-infection in mice was associated with increased pneumococcal carriage density and dissemination into lungs. Helminth-infected children also exhibited increased carriage density as compared to uninfected children. Anthelmintic treatment may be a cost-effective method of reducing pneumococcal disease burden in lower-income countries.

Regulatory RNAs: A Universal Language for Inter-Domain Communication

In eukaryotes, microRNAs (miRNAs) have roles in development, homeostasis, disease and the immune response. Recent work has shown that plant and mammalian miRNAs also mediate cross-kingdom and cross-domain communications. However, these studies remain controversial and are lacking critical mechanistic explanations. Bacteria do not produce miRNAs themselves, and therefore it is unclear how these eukaryotic RNA molecules could function in the bacterial recipient. In this review, we compare and contrast the biogenesis and functions of regulatory RNAs in eukaryotes and bacteria. As a result, we discovered several conserved features and homologous components in these distinct pathways. These findings enabled us to propose novel mechanisms to explain how eukaryotic miRNAs could function in bacteria. Further understanding in this area is necessary to validate the findings of existing studies and could facilitate the use of miRNAs as novel tools for the directed remodelling of the human microbiota.

IL-17A both initiates, via IFNγ suppression, and limits the pulmonary type-2 immune response to nematode infection

Nippostrongylus brasiliensis is a well-defined model of type-2 immunity but the early lung-migrating phase is dominated by innate IL-17A production. In this study, we confirm previous observations that Il17a-KO mice infected with N. brasiliensis exhibit an impaired type-2 immune response. Transcriptional profiling of the lung on day 2 of N. brasiliensis infection revealed an increased Ifng signature in Il17a-KO mice confirmed by enhanced IFNγ protein production in lung lymphocyte populations. Depletion of early IFNγ rescued type-2 immune responses in the Il17a-KO mice demonstrating that IL-17A-mediated suppression of IFNγ promotes type-2 immunity. Notably, later in infection, once the type-2 response was established, IL-17A limited the magnitude of the type-2 response. IL-17A regulation of type-2 immunity was lung-specific and infection with Trichuris muris revealed that IL-17A promotes a type-2 immune response in the lung even when infection is restricted to the intestine. Together our data reveal IL-17A as a major regulator of pulmonary type-2 immunity such that IL-17A supports early development of a protective type-2 response by suppression of IFNγ but subsequently limits excessive type-2 responses. A failure of this feedback loop may contribute to conditions such as severe asthma, characterised by combined elevation of IL-17 and type-2 cytokines.

Contrasting impact of rural, versus urban, living on glucose metabolism and blood pressure in Uganda

Background: The burden of cardiometabolic diseases, including cardiovascular diseases and diabetes, is increasing in sub-Saharan Africa and this has been linked to urbanisation. Helminths, through their immunomodulatory properties, may protect against these disorders. We hypothesised that the rural environment protects against cardiometabolic diseases and that helminths may influence rural-urban disparity of cardiometabolic disease risk. Methods: We compared metabolic parameters of individuals aged ≥10 years living in rural, high-helminth-transmission and urban, lower-helminth-transmission settings in Uganda. Cross-sectional surveys were conducted in rural Lake Victoria island fishing communities and in urban sub-wards in Entebbe municipality. Helminth infection and outcomes, including insulin resistance (computed using the homeostatic model assessment of insulin resistance [HOMA-IR]), fasting blood glucose, fasting blood lipids, blood pressure, body mass index (BMI), waist and hip circumference, were assessed. Results: We analysed 1,898 rural and 930 urban participants. Adjusting for BMI, exercise, smoking, alcohol intake, age and sex, urban residents had lower mean fasting glucose (adjusted mean difference [95%CI] 0.18 [-0.32, -0.05] p=0.01) and HOMA-IR (-0.26 [-0.40, -0.11] p=0.001) but higher blood pressure (systolic, 5.45 [3.75, 7.15] p<0.001; diastolic, 1.93 [0.57, 3.29] p=0.006). Current helminth infection did not explain the observed differences. Conclusions: In the Ugandan context, living in rural fishing communities may protect against hypertension but worsen glucose metabolism.

Extracellular vesicles from Heligmosomoides bakeri and Trichuris muris contain distinct microRNA families and small RNAs that could underpin different functions in the host

Extracellular vesicles (EVs) have emerged as a ubiquitous component of helminth excretory-secretory products that can deliver parasite molecules to host cells to elicit immunomodulatory effects. RNAs are one type of cargo molecule that can underpin EV functions, hence there is extensive interest in characterising the RNAs that are present in EVs from different helminth species. Here we outline methods for identifying all of the small RNAs (sRNA) in helminth EVs and address how different methodologies may influence the sRNAs detected. We show that different EV purification methods introduce relatively little variation in the sRNAs that are detected, and that different RNA library preparation methods yielded larger differences. We compared the EV sRNAs in the gastrointestinal nematode Heligmosomoides bakeri with those in EVs from the distantly related gastrointestinal nematode Trichuris muris, and found that many of the sRNAs in both organisms derive from repetitive elements or intergenic regions. However, only in H. bakeri do these RNAs contain a 5' triphosphate, and Guanine (G) starting nucleotide, consistent with their biogenesis by RNA-dependent RNA polymerases (RdRPs). Distinct microRNA (miRNA) families are carried in EVs from each parasite, with H. bakeri EVs specific for miR-71, miR-49, miR-63, miR-259 and miR-240 gene families, and T. muris EVs specific for miR-1, miR-1822 and miR-252, and enriched for miR-59, miR-72 and miR-44 families, with the miR-9, miR-10, miR-80 and let-7 families abundant in both. We found a larger proportion of miRNA reads derive from the mouse host in T. muris EVs, compared with H. bakeri EVs. Our report underscores potential biases in the sRNAs sequenced based on library preparation methods, suggests specific nematode lineages have evolved distinct sRNA synthesis/export pathways, and highlights specific differences in EV miRNAs from H. bakeri and T. muris that may underpin functional adaptation to their host niches.

Development of caecaloids to study host-pathogen interactions: new insights into immunoregulatory functions of Trichuris muris extracellular vesicles in the caecum

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Development of new methods to generate, culture and characterise mouse caecaloids is described.

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Caecaloids recapitulate the caecal epithelium composition and spatial organisation.

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Caecaloids can be used to study host–caecal pathogen interactions in vitro.

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Trichuris muris EVs exert novel immunoregulatory effects on intestinal epithelial cells.

The caecum, an intestinal appendage in the junction of the small and large intestines, displays a unique epithelium that serves as an exclusive niche for a range of pathogens including whipworms (Trichuris spp.). While protocols to grow organoids from small intestine (enteroids) and colon (colonoids) exist, the conditions to culture organoids from the caecum have yet to be described. Here, we report methods to grow, differentiate and characterise mouse adult stem cell-derived caecal organoids, termed caecaloids. We compare the cellular composition of caecaloids with that of enteroids, identifying differences in intestinal epithelial cell populations that mimic those found in the caecum and small intestine. The remarkable similarity in the intestinal epithelial cell composition and spatial conformation of caecaloids and their tissue of origin enables their use as an in vitro model to study host interactions with important caecal pathogens. Thus, exploiting this system, we investigated the responses of caecal intestinal epithelial cells to extracellular vesicles secreted/excreted by the intracellular helminth Trichuris muris. Our findings reveal novel immunoregulatory effects of whipworm extracellular vesicles on the caecal epithelium, including the downregulation of responses to nucleic acid recognition and type-I interferon signalling.

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.

Whipworm and roundworm infections

Trichuriasis and ascariasis are neglected tropical diseases caused by the gastrointestinal dwelling nematodes Trichuris trichiura (a whipworm) and Ascaris lumbricoides (a roundworm), respectively. Both parasites are staggeringly prevalent, particularly in tropical and subtropical areas, and are associated with substantial morbidity. Infection is initiated by ingestion of infective eggs, which hatch in the intestine. Thereafter, T. trichiura larvae moult within intestinal epithelial cells, with adult worms embedded in a partially intracellular niche in the large intestine, whereas A. lumbricoides larvae penetrate the gut mucosa and migrate through the liver and lungs before returning to the lumen of the small intestine, where adult worms dwell. Both species elicit type 2 anti-parasite immunity. Diagnosis is typically based on clinical presentation (gastrointestinal symptoms and inflammation) and the detection of eggs or parasite DNA in the faeces. Prevention and treatment strategies rely on periodic mass drug administration (generally with albendazole or mebendazole) to at-risk populations and improvements in water, sanitation and hygiene. The effectiveness of drug treatment is very high for A. lumbricoides infections, whereas cure rates for T. trichiura infections are low. Novel anthelminthic drugs are needed, together with vaccine development and tools for diagnosis and assessment of parasite control in the field.

Contrasting impact of rural, versus urban, living on glucose metabolism and blood pressure in Uganda

Background: The burden of cardiometabolic diseases, including cardiovascular diseases and diabetes, is increasing in sub-Saharan Africa and this has been linked to urbanisation. Helminths, through their immunomodulatory properties, may protect against these disorders. We hypothesised that the rural environment protects against cardiometabolic diseases and that helminths may influence rural-urban disparity of cardiometabolic disease risk. Methods: We compared metabolic parameters of individuals aged ≥10 years living in rural, high-helminth-transmission and urban, lower-helminth-transmission settings in Uganda. Cross-sectional surveys were conducted in rural Lake Victoria island communities and in urban sub-wards in Entebbe municipality. Helminth infection and outcomes, including insulin resistance (computed using the homeostatic model assessment of insulin resistance [HOMA-IR]), fasting blood glucose, fasting blood lipids, blood pressure, body mass index (BMI), waist and hip circumference, were assessed. Results: We analysed 1,898 rural and 930 urban participants. Adjusting for BMI, exercise, smoking, alcohol intake, age and sex, urban residents had lower mean fasting glucose (adjusted mean difference [95%CI] -0.13 [-0.24, -0.01] p=0.04) and HOMA-IR (-0.13 [-0.25, -0.01] p=0.04) but higher blood pressure (systolic, 4.64 [3.23, 6.06] p<0.001; diastolic, 1.89 [0.81, 2.97] p=0.001). Current helminth infection did not explain the observed differences. Conclusions: In low-income countries, rural living may protect against hypertension but impair glucose metabolism.

Organoids - New Models for Host-Helminth Interactions

Organoids are multicellular culture systems that replicate tissue architecture and function, and are increasingly used as models of viral, bacterial, and protozoan infections. Organoids have great potential to improve our current understanding of helminth interactions with their hosts and to replace or reduce the dependence on using animal models. In this review, we discuss the applicability of this technology to helminth infection research, including strategies of co-culture of helminths or their products with organoids and the challenges, advantages, and drawbacks of the use of organoids for these studies. We also explore how complementing organoid systems with other cell types and components may allow more complex models to be generated in the future to further investigate helminth-host interactions.

High-throughput phenotyping reveals expansive genetic and structural underpinnings of immune variation

By developing a high-density murine immunophenotyping platform compatible with high-throughput genetic screening, we have established profound contributions of genetics and structure to immune variation (http://www.immunophenotype.org). Specifically, high-throughput phenotyping of 530 unique mouse gene knockouts identified 140 monogenic 'hits', of which most had no previous immunologic association. Furthermore, hits were collectively enriched in genes for which humans show poor tolerance to loss of function. The immunophenotyping platform also exposed dense correlation networks linking immune parameters with each other and with specific physiologic traits. Such linkages limit freedom of movement for individual immune parameters, thereby imposing genetically regulated 'immunologic structures', the integrity of which was associated with immunocompetence. Hence, we provide an expanded genetic resource and structural perspective for understanding and monitoring immune variation in health and disease.

ILC2s mediate systemic innate protection by priming mucus production at distal mucosal sites

Host immunity to parasitic nematodes requires the generation of a robust type 2 cytokine response, characterized by the production of interleukin 13 (IL-13), which drives expulsion. Here, we show that infection with helminths in the intestine also induces an ILC2-driven, IL-13-dependent goblet cell hyperplasia and increased production of mucins (Muc5b and Muc5ac) at distal sites, including the lungs and other mucosal barrier sites. Critically, we show that type 2 priming of lung tissue through increased mucin production inhibits the progression of a subsequent lung migratory helminth infection and limits its transit through the airways. These data show that infection by gastrointestinal-dwelling helminths induces a systemic innate mucin response that primes peripheral barrier sites for protection against subsequent secondary helminth infections. These data suggest that innate-driven priming of mucus barriers may have evolved to protect from subsequent infections with multiple helminth species, which occur naturally in endemic areas.

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.

The lung environment controls alveolar macrophage metabolism and responsiveness in type 2 inflammation

Fine control of macrophage activation is needed to prevent inflammatory disease, particularly at barrier sites such as the lungs. However, the dominant mechanisms that regulate the activation of pulmonary macrophages during inflammation are poorly understood. We found that alveolar macrophages (AlvMs) were much less able to respond to the canonical type 2 cytokine IL-4, which underpins allergic disease and parasitic worm infections, than macrophages from lung tissue or the peritoneal cavity. We found that the hyporesponsiveness of AlvMs to IL-4 depended upon the lung environment but was independent of the host microbiota or the lung extracellular matrix components surfactant protein D (SP-D) and mucin 5b (Muc5b). AlvMs showed severely dysregulated metabolism relative to that of cavity macrophages. After removal from the lungs, AlvMs regained responsiveness to IL-4 in a glycolysis-dependent manner. Thus, impaired glycolysis in the pulmonary niche regulates AlvM responsiveness during type 2 inflammation.

TGFβ-activation by dendritic cells drives Th17 induction and intestinal contractility and augments the expulsion of the parasite Trichinella spiralis in mice

Helminths are highly prevalent metazoan parasites that infect over a billion of the world's population. Hosts have evolved numerous mechanisms to drive the expulsion of these parasites via Th2-driven immunity, but these responses must be tightly controlled to prevent equally devastating immunopathology. However, mechanisms that regulate this balance are still unclear. Here we show that the vigorous Th2 immune response driven by the small intestinal helminth Trichinella spiralis, is associated with increased TGFβ signalling responses in CD4+ T-cells. Mechanistically, enhanced TGFβ signalling in CD4+ T-cells is dependent on dendritic cell-mediated TGFβ activation which requires expression of the integrin αvβ8. Importantly, mice lacking integrin αvβ8 on DCs had a delayed ability to expel a T. spiralis infection, indicating an important functional role for integrin αvβ8-mediated TGFβ activation in promoting parasite expulsion. In addition to maintaining regulatory T-cell responses, the CD4+ T-cell signalling of this pleiotropic cytokine induces a Th17 response which is crucial in promoting the intestinal muscle hypercontractility that drives worm expulsion. Collectively, these results provide novel insights into intestinal helminth expulsion beyond that of classical Th2 driven immunity, and highlight the importance of IL-17 in intestinal contraction which may aid therapeutics to numerous diseases of the intestine.

Experimental steering of electron microscopy studies using prior X-ray computed tomography

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Using microCT pre-scans to accurately steer serial block face SEM.

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High throughput screening and mapping samples to reduce time hunting for features of interest.

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Using microCT to optimise specimen preparation and staining.

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Using microCT to guide site-specific TEM sample preparation.

Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) can provide unrivalled high-resolution images of specific features and volumes of interest. However, the regions interrogated are typically very small, and sample preparation is both time-consuming and destructive. Here we consider how prior X-ray micro-computed tomography (microCT) presents an opportunity to increase the efficiency of electron microscopy in biology. We demonstrate how it can be used to; select the most promising samples and target site-specific locations; provide a wider context of the location being interrogated (multiscale correlative imaging); guide sample preparation and 3D imaging schemes; as well as quantify the effects of destructive sample preparation and staining procedures. We present a workflow utilising open source software in which microCT can be used either broadly, or precisely, to experimentally steer and inform subsequent electron microscopy studies. As automated sample registration procedures are developed to enable correlative microscopy, experimental steering by prior CT could be beneficially routinely incorporated into many experimental workflows.

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.

Trichuris muris whey acidic protein induces type 2 protective immunity against whipworm

Human whipworm (Trichuris trichiura) infects approximately 1 in 15 people worldwide, representing the leading infectious cause of colitis and subsequent, inflammatory bowel disease (IBD). Current control measures focused on mass deworming have had limited success due to low drug efficacies. Vaccination would be an ideal, cost-effective strategy to induce protective immunity, leading to control of infection and transmission. Here we report the identification of whey acidic protein, a whipworm secretory protein, as a strong immunogen for inducing protective efficacy in a surrogate mouse T. muris infection model. The recombinant WAP protein (rTm-WAP49), as well as a single, highly conserved repeat within WAP (fragment 8) expressed as an Na-GST-1 fusion protein (rTm-WAP-F8+Na-GST-1), generate a strong T helper type 2 (Th2) immune response when delivered as subcutaneous vaccines formulated with Montanide ISA 720. Oral challenge with T. muris infective eggs following vaccination led to a significant reduction in worm burden of 48% by rTm-WAP49 and 33% by rTm-WAP-F8+Na-GST-1. The cellular immune correlates of protection included significant antigen-specific production of Th2 cytokines IL-4, IL-9, and IL-13 by cells isolated from the vaccine-draining inguinal lymph nodes, parasite-draining mesenteric lymph nodes, and spleen in mice vaccinated with either rTm-WAP49 or rTm-WAP-F8+Na-GST-1. The humoral immune correlates included a high antigen-specific ratio of IgG1 to IgG2a, without eliciting an IgE-mediated allergic response. Immunofluorescent staining of adult T. muris with WAP antisera identified the worm's pathogenic stichosome organ as the site of secretion of native Tm-WAP protein into the colonic mucosa. Given the high sequence conservation for the WAP proteins from T. muris and T. trichiura, the results presented here support the WAP protein to be further evaluated as a potential human whipworm vaccine candidate.

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.

A sticky end for gastrointestinal helminths; the role of the mucus barrier

Gastrointestinal (GI) nematodes are a group of successful multicellular parasites that have evolved to coexist within the intestinal niche of multiple species. It is estimated that over 10% of the world's population are chronically infected by GI nematodes, making this group of parasitic nematodes a major burden to global health. Despite the large number of affected individuals, there are few effective treatments to eradicate these infections. Research into GI nematode infections has primarily focused on defining the immunological and pathological consequences on host protection. One important but neglected aspect of host protection is mucus, and the concept that mucus is just a simple barrier is no longer tenable. In fact, mucus is a highly regulated and dynamic-secreted matrix, underpinned by a physical hydrated network of highly glycosylated mucins, which is increasingly recognized to have a key protective role against GI nematode infections. Unravelling the complex interplay between mucins, the underlying epithelium and immune cells during infection are a major challenge and are required to fully define the protective role of the mucus barrier. This review summarizes the current state of knowledge on mucins and the mucus barrier during GI nematode infections, with particular focus on murine models of infection.

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.

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 autophagy gene Atg16l1 differentially regulates Treg and TH2 cells to control intestinal inflammation

A polymorphism in the autophagy gene Atg16l1 is associated with susceptibility to inflammatory bowel disease (IBD); however, it remains unclear how autophagy contributes to intestinal immune homeostasis. Here, we demonstrate that autophagy is essential for maintenance of balanced CD4⁺ T cell responses in the intestine. Selective deletion of Atg16l1 in T cells in mice resulted in spontaneous intestinal inflammation that was characterized by aberrant type 2 responses to dietary and microbiota antigens, and by a loss of Foxp3⁺ T_reg cells. Specific ablation of Atg16l1 in Foxp3⁺ T_reg cells in mice demonstrated that autophagy directly promotes their survival and metabolic adaptation in the intestine. Moreover, we also identify an unexpected role for autophagy in directly limiting mucosal T_H2 cell expansion. These findings provide new insights into the reciprocal control of distinct intestinal T_H cell responses by autophagy, with important implications for understanding and treatment of chronic inflammatory disorders.

DOI:http://dx.doi.org/10.7554/eLife.12444.001

The gut presents a puzzle to our immune system. Immune cells must rapidly respond to antigens produced by harmful bacteria, but food and the beneficial bacteria that inhabit the gut also produce antigens that our immune system must tolerate. Inappropriate immune responses in the gut can lead to inflammatory bowel disease, a debilitating disease with no current cure. We do not fully understand why these harmful inflammatory responses arise, but we know that genetic factors are important. Mutations in genes that affect a process known as autophagy – a pathway that breaks down and recycles unwanted material inside cells – make inflammatory bowel disease more likely to develop, but exactly how they do so remains unclear.

T helper cells are crucial controllers of intestinal immune responses and changes in their numbers and behaviour occur during inflammatory bowel disease. Kabat et al. explored how the autophagy pathway affects these key immune cells in mice. Blocking autophagy in T cells altered the balance of different types of T helper cells in the gut. A crucial population of regulatory T cells, which keep inflammatory responses in check, was lost. At the same time, another population of T cells expanded: the T helper 2 (T_H2) cells that are responsible for driving allergies. As a result, the mice developed intestinal inflammation and produced antibodies against gut bacteria and food.

Overall, Kabat et al.’s results show that autophagy defects can alter the balance of different types of T cells in the gut, leading to inflammation in the intestine. These observations contribute to our understanding of how genetic changes may influence susceptibility to inflammatory bowel disease. They also suggest that drugs that activate autophagy could help to treat diseases associated with changes in regulatory T cells or T_H2 cells, including inflammatory bowel disease and allergies. It will now be important to test this and to confirm whether similar changes in T cells are present in humans that have mutations in autophagy genes.

DOI:http://dx.doi.org/10.7554/eLife.12444.002

Differential alterations in the small intestine epithelial cell turnover during acute and chronic infection with Echinostoma caproni (Trematoda)

Background

The intestinal epithelium plays a multifactorial role in mucosal defense. In this sense, augmented epithelial cell turnover appears as a potential effector mechanism for the rejection of intestinal-dwelling helminths.

Methods

A BrdU pulse-chase experiment was conducted to investigate the infection-induced alterations on epithelial cell kinetics in hosts of high (mouse) and low (rat) compatibility with the intestinal trematode Echinostoma caproni.

Results

High levels of crypt-cell proliferation and tissue hyperplasia were observed in the ileum of infected mice, coinciding with the establishment of chronic infections. In contrast, the cell migration rate was about two times higher in the ileum of infected rats compared with controls, with no changes in tissue structure, indicating that an accelerated cell turnover is associated with worm expulsion.

Conclusion

Our results indicate that E. caproni infection induces a rapid renewal of the intestinal epithelium in the low compatible host that may impair the establishment of proper, stable host-parasite interactions, facilitating worm clearance.

Chronic Trichuris muris Infection in C57BL/6 Mice Causes Significant Changes in Host Microbiota and Metabolome: Effects Reversed by Pathogen Clearance

Trichuris species are a globally important and prevalent group of intestinal helminth parasites, in which Trichuris muris (mouse whipworm) is an ideal model for this disease. This paper describes the first ever highly controlled and comprehensive investigation into the effects of T. muris infection on the faecal microbiota of mice and the effects on the microbiota following successful clearance of the infection. Communities were profiled using DGGE, 454 pyrosequencing, and metabolomics. Changes in microbial composition occurred between 14 and 28 days post infection, resulting in significant changes in α and β- diversity. This impact was dominated by a reduction in the diversity and abundance of Bacteroidetes, specifically Prevotella and Parabacteroides. Metabolomic analysis of stool samples of infected mice at day 41 showed significant differences to uninfected controls with a significant increase in the levels of a number of essential amino acids and a reduction in breakdown of dietary plant derived carbohydrates. The significant reduction in weight gain by infected mice probably reflects these metabolic changes and the incomplete digestion of dietary polysaccharides. Following clearance of infection the intestinal microbiota underwent additional changes gradually transitioning by day 91 towards a microbiota of an uninfected animal. These data indicate that the changes in microbiota as a consequence of infection were transitory requiring the presence of the pathogen for maintenance. Interestingly this was not observed for all of the key immune cell populations associated with chronic T. muris infection. This reflects the highly regulated chronic response and potential lasting immunological consequences of dysbiosis in the microbiota. Thus infection of T. muris causes a significant and substantial impact on intestinal microbiota and digestive function of mice with affects in long term immune regulation.

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.

Sex-dependent genetic effects on immune responses to a parasitic nematode

BACKGROUND

Many disease aetiologies have sex specific effects, which have important implications for disease management. It is now becoming increasingly evident that such effects are the result of the differential expression of autosomal genes rather than sex-specific genes. Such sex-specific variation in the response to Trichuris muris, a murine parasitic nematode infection and model for the human parasitic nematode T. trichiura, has been well documented, however, the underlying genetic causes of these differences have been largely neglected. We used the BXD mouse set of recombinant inbred strains to identify sex-specific loci that contribute to immune phenotypes in T. muris infection.

RESULTS

Response phenotypes to T. muris infection were found to be highly variable between different lines of BXD mice. A significant QTL on chromosome 5 (TM5) associated with IFN-γ production was found in male mice but not in female mice. This QTL was in the same location as a suggestive QTL for TNF-α and IL-6 production in male mice suggesting a common control of these pro-inflammatory cytokines. A second QTL was identified on chromosome 4 (TM4) affecting worm burden in both male and female cohorts. We have identified several genes as potential candidates for modifying responses to T. muris infection.

CONCLUSIONS

We have used the largest mammalian genetic model system, the BXD mouse population, to identify candidate genes with sex-specific effects in immune responses to T. muris infection. Some of these genes may be differentially expressed in male and female mice leading to the difference in immune response between the sexes reported in previous studies. Our study further highlights the importance of considering sex as an important factor in investigations of immune response at the genome-wide level, in particular the bias that can be introduced when generalizing results obtained from only one sex or a mixed sex population. Rather, analyses of interaction effects between sex and genotype should be part of future studies.

A new role for mucins in immunity: insights from gastrointestinal nematode infection

The body's mucosal surfaces are protected from pathogens and physical and chemical attack by the gel-like extracellular matrix, mucus. The framework of this barrier is provided by polymeric, gel-forming mucins. These enormous O-linked glycoproteins are synthesised, stored and secreted by goblet cells that are also the source of other protective factors. Immune regulation of goblet cells during the course of infection impacts on mucin production and properties and ultimately upon barrier function. The barrier function of mucins in protection of the host is well accepted as an important aspect of innate defence. However, it is becoming increasingly clear that mucins have a much more direct role in combating pathogens and parasites and are an important part of the coordinated immune response to infection. Of particular relevance to this review is the finding that mucins are essential anti-parasitic effector molecules. The current understanding of the roles of these multifunctional glycoproteins, and other goblet cell products, in mucosal defence against intestinal dwelling nematodes is discussed.

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.

Thymic stromal lymphopoietin-dependent basophils promote Th2 cytokine responses following intestinal helminth infection

CD4(+) Th2 cytokine responses promote the development of allergic inflammation and are critical for immunity to parasitic helminth infection. Recent studies highlighted that basophils can promote Th2 cytokine-mediated inflammation and that phenotypic and functional heterogeneity exists between classical IL-3-elicited basophils and thymic stromal lymphopoietin (TSLP)-elicited basophils. However, whether distinct basophil populations develop after helminth infection and their relative contributions to anti-helminth immune responses remain to be defined. After Trichinella spiralis infection of mice, we show that basophil responses are rapidly induced in multiple tissue compartments, including intestinal-draining lymph nodes. Trichinella-induced basophil responses were IL-3-IL-3R independent but critically dependent on TSLP-TSLPR interactions. Selective depletion of basophils after Trichinella infection impaired infection-induced CD4(+) Th2 cytokine responses, suggesting that TSLP-dependent basophils augment Th2 cytokine responses after helminth infection. The identification and functional classification of TSLP-dependent basophils in a helminth infection model, coupled with their recently described role in promoting atopic dermatitis, suggests that these cells may be a critical population in promoting Th2 cytokine-associated inflammation in a variety of inflammatory or infectious settings. Collectively, these data suggest that the TSLP-basophil pathway may represent a new target in the design of therapeutic intervention strategies to promote or limit Th2 cytokine-dependent immunity and inflammation.

Concurrent bacterial stimulation alters the function of helminth-activated dendritic cells, resulting in IL-17 induction

Infection with schistosome helminths is associated with granulomatous inflammation that forms around parasite eggs trapped in host tissues. In severe cases, the resulting fibrosis can lead to organ failure, portal hypertension, and fatal bleeding. Murine studies identified IL-17 as a critical mediator of this immunopathology, and mouse strains that produce high levels of IL-17 in response to schistosome infection show increased mortality. In this article, we demonstrate that schistosome-specific IL-17 induction by dendritic cells from low-pathology C57BL/6 mice is normally regulated by their concomitant induction of IL-10. Simultaneous stimulation of schistosome-exposed C57BL/6 dendritic cells with a heat-killed bacterium enabled these cells to overcome IL-10 regulation and induce IL-17, even in wild-type C57BL/6 recipients. This schistosome-specific IL-17 was dependent on IL-6 production by the copulsed dendritic cells. Coimmunization of C57BL/6 animals with bacterial and schistosome Ags also resulted in schistosome-specific IL-17, and this response was enhanced in the absence of IL-10-mediated immune regulation. Together, our data suggest that the balance of pro- and anti-inflammatory cytokines that determines the severity of pathology during schistosome infection can be influenced not only by host and parasite, but also by concurrent bacterial stimulation.

Life on the edge: the balance between macrofauna, microflora and host immunity

Mammals, microflora and gut-dwelling macrofauna have co-evolved over many millions of years until relatively recently when the geographical prevalence of macrofauna in humans has become restricted to the developing world. Immune homeostasis relies on a balance in the composition of intestinal microflora; long-lived macrofauna have also been shown to regulate immune function, and their absence in Western lifestyles is suggested to be a factor for the increasing frequency of allergy and autoimmunity. The intestinal nematode Trichuris muris was recently demonstrated to utilise microflora to initiate its life cycle. The interdependence on one another of all three factors is such that when the balance is perturbed it must be realigned or the consequences may be detrimental to the mammalian host.

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.

Trichinella spiralis antigens prime mixed Th1/Th2 response but do not induce de novo generation of Foxp3+ T cells in vitro

Many parasitic helminth infections induce Th2-type immune responses and engage the regulatory network. In this study, we specifically investigated the influence of antigens derived from different life stages of the helminth Trichinella spiralis on the polarization of naive CD4(+) T cells by dendritic cells. Results obtained from C57BL/6 mice showed that T. spiralis derived antigens have the capacity to induce bone marrow-derived dendritic cells to acquire an incompletely mature phenotype that promotes a significant proliferation of naive CD4(+) T cells and a mixed Th1/Th2 cytokine profile with the predominance of Th2 cytokines. Increased production of IL-4, IL-9, IL-10 and IL-13 accompanied increased IFN-γ. Furthermore, dendritic cells pulsed with T. spiralis antigens did not induce an increase in the population of Foxp3(+) T regulatory cells. Although other helminth antigens have demonstrated the capacity to induce de novo generation of Foxp3(+) T regulatory cells, here our in vitro studies provide no evidence that T. spiralis antigens have this capacity.