Production and analysis of immunomodulatory excretory-secretory products from the mouse gastrointestinal nematode Heligmosomoides polygyrus bakeri

Maternal gastrointestinal nematode infection alters hippocampal neuroimmunity, promotes synaptic plasticity, and improves resistance to direct infection in offspring

The developing brain is vulnerable to maternal bacterial and viral infections which induce strong inflammatory responses in the mother that are mimicked in the offspring brain, resulting in irreversible neurodevelopmental defects, and associated cognitive and behavioural impairments. In contrast, infection during pregnancy and lactation with the immunoregulatory murine intestinal nematode, Heligmosomoides bakeri, upregulates expression of genes associated with long-term potentiation (LTP) of synaptic networks in the brain of neonatal uninfected offspring, and enhances spatial memory in uninfected juvenile offspring. As the hippocampus is involved in spatial navigation and sensitive to immune events during development, here we assessed hippocampal gene expression, LTP, and neuroimmunity in 3-week-old uninfected offspring born to H. bakeri infected mothers. Further, as maternal immunity shapes the developing immune system, we assessed the impact of maternal H. bakeri infection on the ability of offspring to resist direct infection. In response to maternal infection, we found an enhanced propensity to induce LTP at Schaffer collateral synapses, consistent with RNA-seq data indicating accelerated development of glutamatergic synapses in uninfected offspring, relative to those from uninfected mothers. Hippocampal RNA-seq analysis of offspring of infected mothers revealed increased expression of genes associated with neurogenesis, gliogenesis, and myelination. Furthermore, maternal infection improved resistance to direct infection of H. bakeri in offspring, correlated with transfer of parasite-specific IgG1 to their serum. Hippocampal immunohistochemistry and gene expression suggest Th2/Treg biased neuroimmunity in offspring, recapitulating peripheral immunoregulation of H. bakeri infected mothers. These findings indicate maternal H. bakeri infection during pregnancy and lactation alters peripheral and neural immunity in uninfected offspring, in a manner that accelerates neural maturation to promote hippocampal LTP, and upregulates the expression of genes associated with neurogenesis, gliogenesis, and myelination.

Gut microbiota-mediated polyphenol metabolism is restrained by parasitic whipworm infection and associated with altered immune function in mice

Polyphenols are phytochemicals commonly found in plant-based diets which have demonstrated immunomodulatory and anti-inflammatory properties. However, the interplay between polyphenols and pathogens at mucosal barrier surfaces has not yet been elucidated in detail. Here, we show that proanthocyanidin (PAC) polyphenols interact with gut parasites to influence immune function and gut microbial-derived metabolites in mice. PAC intake inhibited mastocytosis during infection with the small intestinal roundworm Heligmosomoides polygyrus, and altered the host tissue transcriptome at the site of infection with the large intestinal whipworm Trichuris muris, with a notable enhancement of type-1 inflammatory and interferon-driven gene pathways. In the absence of infection, PAC intake promoted the expansion of Turicibacter within the gut microbiota, increased fecal short chain fatty acids, and enriched phenolic metabolites such as phenyl-γ-valerolactones in the cecum. However, these putatively beneficial effects were reduced in PAC-fed mice infected with T. muris, suggesting concomitant parasite infection can attenuate gut microbial-mediated PAC catabolism. Collectively, our results suggest an inter-relationship between a phytonutrient and infection, whereby PAC may augment parasite-induced inflammation (most prominently with the cecum dwelling T. muris), and infection may abrogate the beneficial effects of health-promoting phytochemicals.

Bcl-6 expression by CD4+ T cells determines concomitant immunity and host resistance across distinct parasitic infections

Cluster of differentiation (CD4+) T cells consist of multiple subtypes, defined by expression of lineage-specific transcription factors, that contribute to the control of infectious diseases by providing help to immune and nonimmune target cells. In the current study, we examined the role of B cell lymphoma (Bcl)-6, a transcriptional repressor and master regulator of T follicular helper cell differentiation, in T cell-mediated host defense against intestinal and systemic parasitic infections. We demonstrate that while Bcl-6 expression by CD4+ T cells is critical for antibody-mediated protective immunity against secondary infection with the nematode Heligmosoides polygyrus bakeri, it paradoxically compromises worm expulsion during primary infection by limiting the generation of interleukin-10 (IL-10)-producing Gata3+ T helper 2 cells. Enhanced worm expulsion in the absence of Bcl-6 expressing T cells was associated with amplified intestinal goblet cell differentiation and increased generation of alternatively activated macrophages, effects that were reversed by neutralization of IL-10 signals. An increase in IL-10 production by Bcl-6-deficient CD4+ T cells was also evident in the context of systemic Leishmania donovani infection, but in contrast to Heligmosoides polygyrus bakeri infection, compromised T helper 1-mediated liver macrophage activation and increased susceptibility to this distinct parasitic challenge. Collectively, our studies suggest that host defense pathways that protect against parasite superinfection and lethal systemic protozoal infections can be engaged at the cost of compromised primary resistance to well-tolerated helminths.

Helminth-induced reprogramming of the stem cell compartment inhibits type 2 immunity

Enteric helminths form intimate physical connections with the intestinal epithelium, yet their ability to directly alter epithelial stem cell fate has not been resolved. Here we demonstrate that infection of mice with the parasite Heligmosomoides polygyrus bakeri (Hpb) reprograms the intestinal epithelium into a fetal-like state marked by the emergence of Clusterin-expressing revival stem cells (revSCs). Organoid-based studies using parasite-derived excretory-secretory products reveal that Hpb-mediated revSC generation occurs independently of host-derived immune signals and inhibits type 2 cytokine-driven differentiation of secretory epithelial lineages that promote their expulsion. Reciprocally, type 2 cytokine signals limit revSC differentiation and, consequently, Hpb fitness, indicating that helminths compete with their host for control of the intestinal stem cell compartment to promote continuation of their life cycle.

Characterization of a novel cysteine protease inhibitor in Baylisascaris schroederi migratory larvae and its role in regulating mice immune cell response

Baylisascaris schroederi (B. schroederi) is a severe threat to the survival of giant pandas. Currently, the immune regulation mechanism of B. schroederi is poorly understood. Cysteine protease inhibitors (CPI) play important roles in the regulation of host immune responses against certain nematodes. In this study, a recombinant CPI of B. schroederi migratory larvae (rBsCPI-1) was cloned and expressed, and the effects of rBsCPI-1 on the physiological activities and antigen presentation of monocyte-derived macrophages (MDMs) were analyzed. We also analyzed the regulatory effects of rBsCPI-1 on the proliferation and differentiation of CD4+ T cells. And further identified the signaling pathways which play important roles in this process. The results showed that rBsCPI-1 activated the TLR2/4-small Rho GTPases-PAK1 pathway. On the one hand, it increased the phagocytosis and migration of MDMs. On the other hand, it activated downstream MAPK and NF-κB signaling pathways to induce apoptosis of MDMs. rBsCPI-1 also induced MDMs to polarize to the M2 subtype, thereby exerting an immunosuppressive effect. Meanwhile, rBsCPI-1 inhibited the antigen presentation process by decreasing the expression of MHC-II molecules, further inhibiting the proliferation of CD4+ T cells and inducing a Th1/Th2 mixed immune response. Treg cells with immunosuppressive effects were increased. The PD-L2/PD-1 and CD80/CTLA-4 signaling pathways between MDMs and CD4+ T cells were also activated by rBsCPI-1. In conclusion, this study preliminarily confirmed that rBsCPI-1 affects the physiological activities and polarization of MDMs through the TLR2/4 signaling pathway, and further interferes with antigen presentation response, inducing CD4+ T cells to play an immunosuppressive cellular response during the migratory process of B. schroederi. Thus, this study will provide a reference for elucidating the immune evasion mechanism of B. schroederi and developing new drugs and protective vaccines against B. schroederi.

Maternal gastrointestinal nematode infection enhances spatial memory of uninfected juvenile mouse pups

The developing brain is particularly vulnerable to factors including maternal infection during pregnancy. Establishment of neural networks critical for memory and cognition begins during the perinatal period, when Heligmosomoides bakeri, a gastrointestinal (GI) nematode restricted to the maternal mouse intestine, has been shown to upregulate expression of long-term potentiation genes in the young rodent pup brain. We explored the impact of maternal infection during pregnancy and early lactation on the spatial behavior of uninfected male and female juvenile mice. Pre-weaned pups of H. bakeri infected dams exhibited less exploratory behaviour compared to pups of uninfected dams on postnatal day (PD) 16 but not PD 17, possibly reflecting a transient fear of an unfamiliar environment and/or a brief neurodevelopmental delay. Our two spatial memory tests show for the first time an enhancement of spatial memory in response to maternal nematode infection regardless of pup sex. At PD 17, pups of infected dams expressed object location memories after 3 h in the Object Location Test whereas offspring of uninfected mothers did not. In addition, at PD 34, juveniles of infected mothers retained their ability to find the escape hole in the Barnes Maze Test for one week whereas offspring from uninfected mothers did not. This finding is even more striking given that spatial memory was positively associated with pup length, yet this maternal infection impaired linear growth of pups. Thus, the positive impact of maternal infection on spatial memory countered any impairment associated with the shorter length of the pups. Overall, these novel findings indicate that a maternal GI nematode infection during pregnancy and lactation positively influences the spatial memory of uninfected juvenile offspring with potential fitness implications for the next generation.

Immunomodulatory action of excretory-secretory products of Angiostrongylus cantonensis in a mouse tumour model

Excretory-secretory products (ESPs) of parasitic helminths are well known to exert immunostimulation and immunomodulation in hosts. Immune regulation plays a key role in anti-tumour therapy. The present study explored the anti-tumour effect of ESPs released by Angiostrongylus cantonensis. In Hepa1-6 mouse tumour models, ESPs significantly reduced tumour growth. Tumour-bearing mice treated with ESPs had significantly higher CD3⁺, CD4⁺, and CD8⁺ T cell counts than those treated with Freund's adjuvant. In vitro, human hepatocarcinoma HepG2 cells, human lung cancer A549 cells, and normal human liver HL-7702 cells were co-incubated with ESPs for 24 h and 48 h. ESPs significantly accelerated HepG2 apoptosis but had no inhibitory effect on the proliferation of A549 and HL-7702 cells. Apoptotic HepG2 cells displayed condensed nuclei, apoptotic bodies, and swollen endoplasmic reticulum (ER). Expression of the endoplasmic reticulum stress (ERS)-related factors activating transcription factor 6 (ATF6) and C/EBP-homologous protein (CHOP) in HepG2 cells increased with increasing ESP concentration and treatment time. Calreticulin (CRT) is a key effector protein of ESPs, and recombinant calreticulin (rCRT) was produced in BL21 Escherichia coli (E. coli). In contrast to ESPs, rCRT markedly reduced the proliferation of HepG2 cells. The expression levels of ATF6 and CHOP in HepG2 cells treated with 30 μg/mL rCRT significantly increased at 48 h. Notably, these findings synergistically suggest that ESPs and rCRT are promising candidates for anti-tumour immunotherapy.

Proteomic analysis revealed T cell hyporesponsiveness induced by Haemonchus contortus excretory and secretory proteins

Haemonchus contortus has evolved highly integrated and sophisticated mechanisms to promote coexistence with hosts. The excretory-secretory (ES) products generated by this parasite contribute to the regulation of the host immune response to facilitate immune evasion and induce chronicity, but the proteins responsible for this process and the exact cellular mechanisms have yet to be defined. In this study, we identified 114 H. contortus ES proteins (HcESPs) interacting with host T cells and 15 T cell binding receptors via co-immunoprecipitation and shotgun liquid chromatography-tandem mass spectrometry analysis. Based on bioinformatics analysis, we demonstrated that HcESPs could inhibit T cell viability, induce cell apoptosis, suppress T cell proliferation and cause cell cycle arrest. Furthermore, the stimulation of HcESPs exerted critical control effects on T cell cytokine production profiles, predominantly promoting the secretion of interleukin (IL)-10, IL-17A and transforming growth factor-β1 and inhibiting IL-2, IL-4 and interferon-γ production. Collectively, these findings may provide insights into the interaction between ES proteins and key host effector cells, enhancing our understanding of the molecular mechanism underlying parasite immune evasion and providing new clues for novel vaccine development.

Age affects antibody levels and anthelmintic treatment efficacy in a wild rodent

The role of the host immune system in determining parasite burdens and mediating within-host parasite interactions has traditionally been studied in highly controlled laboratory conditions. This does, however, not reflect the diversity of individuals living in nature, which is often characterised by significant variation in host demography, such as host age, sex, and infection history. Whilst studies using wild hosts and parasites are beginning to give insights into the complex relationships between immunity, parasites and host demography, the cause-and-effect relationships often remain unknown due to a lack of high resolution, longitudinal data. We investigated the infection dynamics of two interacting gastrointestinal parasites of wild wood mice (Apodemus sylvaticus), the nematode Heligmosomoides polygyrus and the coccidian Eimeria hungaryensis, in order to assess the links between infection, coinfection, and the immunological dynamics of two antibodies (IgG1 and IgA). In an anthelmintic treatment experiment, mice were given a single oral dose of an anthelmintic treatment, or control dose, and then subsequently followed longitudinally over a period of 7–15 days to measure parasite burdens and antibody levels. Anthelmintic treatment successfully reduced burdens of H. polygyrus, but had no significant impact on E. hungaryensis. Treatment efficacy was driven by host age, with adult mice showing stronger reductions in burdens compared to younger mice. We also found that the relationship between H. polygyrus-specific IgG1 and nematode burden changed from positive in young mice to negative in adult mice. Our results highlight that a key host demographic factor like age could account for large parts of the variation in nematode burden and nematode-specific antibody levels observed in a naturally infected host population, possibly due to different immune responses in young vs. old animals. Given the variable success in community-wide de-worming programmes in animals and humans, accounting for the age-structure of a population could increase overall efficacy.

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Anthelmintic treatment reveals strong force of infection for H. polygyrus in wild wood mice.

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Anthelmintic treatment is more successful in younger compared to older mice.

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Relationship between IgG1 and H. polygyrus burden reverts with host age.

Heligmosomoides polygyrus bakeri Infection Decreases Smad7 Expression in Intestinal CD4+ T Cells, Which Allows TGF-β to Induce IL-10-Producing Regulatory T Cells That Block Colitis

Helminthic infections modulate host immunity and may protect their hosts from developing immunological diseases like inflammatory bowel disease. Induction of regulatory T cells (Tregs) may be an important part of this protective process. Heligmosomoides polygyrus bakeri infection also promotes the production of the regulatory cytokines TGF-β and IL-10 in the gut. In the intestines, TGF-β helps induce regulatory T cells. This study used Foxp3/IL-10 double reporter mice to investigate the effect of TGF-β on the differentiation of colon and mesenteric lymph node-derived murine Foxp3^- IL-10^- CD4⁺ T cells into their regulatory phenotypes. Foxp3^- IL-10^- CD4⁺ T cells from H. polygyrus bakeri-infected mice, as opposed to T cells from uninfected animals, cultured in vitro with TGF-β and anti-CD3/CD28 mAb differentiated into Foxp3⁺ and/or IL-10⁺ T cells. The IL-10-producing T cells nearly all displayed CD25. Smad7 is a natural inhibitor of TGF-β signaling. In contrast to gut T cells from uninfected mice, Foxp3^- IL10^- CD4⁺ T cells from H. polygyrus bakeri-infected mice displayed reduced Smad7 expression and responded to TGF-β with Smad2/3 phosphorylation. The TGF-β-induced Tregs that express IL-10 blocked colitis when transferred into the Rag/CD25^- CD4⁺ T cell transfer model of inflammatory bowel disease. TGF-β had a greatly diminished capacity to induce Tregs in H. polygyrus bakeri-infected transgenic mice with constitutively high T cell-specific Smad7 expression. Thus, infection with H. polygyrus bakeri causes down-modulation in Smad7 expression in intestinal CD4⁺ T cells, which allows the TGF-β produced in response to the infection to induce the Tregs that prevent colitis.

Analysis of the Trichuris suis excretory/secretory proteins as a function of life cycle stage and their immunomodulatory properties

Parasitic worms have a remarkable ability to modulate host immune responses through several mechanisms including excreted/secreted proteins (ESP), yet the exact nature of these proteins and their targets often remains elusive. Here, we performed mass spectrometry analyses of ESP (TsESP) from larval and adult stages of the pig whipworm Trichuris suis (Ts) and identified ~350 proteins. Transcriptomic analyses revealed large subsets of differentially expressed genes in the various life cycle stages of the parasite. Exposure of bone marrow-derived macrophages and dendritic cells to TsESP markedly diminished secretion of the pro-inflammatory cytokines TNFα and IL-12p70. Conversely, TsESP exposure strongly induced release of the anti-inflammatory cytokine IL-10, and also induced high levels of nitric oxide (NO) and upregulated arginase activity in macrophages. Interestingly, TsESP failed to directly induce CD4+ CD25+ FoxP3+ regulatory T cells (Treg cells), while OVA-pulsed TsESP-treated dendritic cells suppressed antigen-specific OT-II CD4+ T cell proliferation. Fractionation of TsESP identified a subset of proteins that promoted anti-inflammatory functions, an activity that was recapitulated using recombinant T. suis triosephosphate isomerase (TPI) and nucleoside diphosphate kinase (NDK). Our study helps illuminate the intricate balance that is characteristic of parasite-host interactions at the immunological interface, and further establishes the principle that specific parasite-derived proteins can modulate immune cell functions.

Host-Parasite Interactions Promote Disease Tolerance to Intestinal Helminth Infection

Parasitic helminths are among the most pervasive pathogens of the animal kingdom. To complete their life cycle, these intestinal worms migrate through host tissues causing significant damage in their wake. As a result, infection can lead to malnutrition, anemia and increased susceptibility to co-infection. Despite repeated deworming treatment, individuals living in endemic regions remain highly susceptible to re-infection by helminths, but rarely succumb to excessive tissue damage. The chronicity of infection and inability to resist numerous species of parasitic helminths that have co-evolved with their hosts over millenia suggests that mammals have developed mechanisms to tolerate this infectious disease. Distinct from resistance where the goal is to destroy and eliminate the pathogen, disease tolerance is an active process whereby immune and structural cells restrict tissue damage to maintain host fitness without directly affecting pathogen burden. Although disease tolerance is evolutionary conserved and has been well-described in plant systems, only recently has this mode of host defense, in its strictest sense, begun to be explored in mammals. In this review, we will examine the inter- and intracellular networks that support disease tolerance during enteric stages of parasitic helminth infection and why this alternative host defense strategy may have evolved to endure the presence of non-replicating pathogens and maintain the essential functions of the intestine.

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

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

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Pla2g1b expression correlated with resistance to intestinal helminth infection

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PLA₂g1B is essential for resistance to intestinal helminth infection in mice

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PLA₂g1B directly reduces phospholipid abundance in infective larvae

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

Of dogs and hookworms: man's best friend and his parasites as a model for translational biomedical research

We present evidence that the dog hookworm (Ancylostoma caninum) is underutilised in the study of host-parasite interactions, particularly as a proxy for the human-hookworm relationship. The inability to passage hookworms through all life stages in vitro means that adult stage hookworms have to be harvested from the gut of their definitive hosts for ex vivo research. This makes study of the human-hookworm interface difficult for technical and ethical reasons. The historical association of humans, dogs and hookworms presents a unique triad of positive evolutionary pressure to drive the A. caninum-canine interaction to reflect that of the human-hookworm relationship. Here we discuss A. caninum as a proxy for human hookworm infection and situate this hookworm model within the current research agenda, including the various 'omics' applications and the search for next generation biologics to treat a plethora of human diseases. Historically, the dog hookworm has been well described on a physiological and biochemical level, with an increasing understanding of its role as a human zoonosis. With its similarity to human hookworm, the recent publications of hookworm genomes and other omics databases, as well as the ready availability of these parasites for ex vivo culture, the dog hookworm presents itself as a valuable tool for discovery and translational research.

Life history adjustments to intestinal inflammation in a gut nematode

Many parasitic nematodes establish chronic infections. This implies a finely tuned interaction with the host immune response in order to avoid infection clearance. Although a number of immune interference mechanisms have been described in nematodes, how parasites adapt to the immune environment provided by their hosts remains largely unexplored. Here, we used the gastrointestinal nematode Heligmosomoides polygyrus to investigate the plasticity of life history traits and immunomodulatory mechanisms in response to intestinal inflammation. We adopted an experimental model of induced colitis and exposed worms to intestinal inflammation at two different developmental stages (larvae and adults). We found that H. polygyrus responded to intestinal inflammation by up-regulating the expression of a candidate gene involved in the interference with the host immune response. Worms infecting mice with colitis also had better infectivity (earlier adult emergence in the intestinal lumen and higher survival) compared with worms infecting control hosts, suggesting that H. polygyrus adjusted its life history schedule in response to intestinal inflammation.

IRF-8 regulates expansion of myeloid-derived suppressor cells and Foxp3+ regulatory T cells and modulates Th2 immune responses to gastrointestinal nematode infection

Interferon regulatory factor-8 (IRF-8) is critical for Th1 cell differentiation and negatively regulates myeloid cell development including myeloid-derived suppressor cells (MDSC). MDSC expand during infection with various pathogens including the gastrointestinal (GI) nematode Heligmosomoides polygyrus bakeri (Hpb). We investigated if IRF-8 contributes to Th2 immunity to Hpb infection. Irf8 expression was down-regulated in MDSC from Hpb-infected C57BL/6 (B6) mice. IRF-8 deficient Irf8^-/- and BXH-2 mice had significantly higher adult worm burdens than B6 mice after primary or challenge Hpb infection. During primary infection, MDSC expanded to a significantly greater extent in mesenteric lymph nodes (MLN) and spleens of Irf8^-/- and BXH-2 than B6 mice. CD4⁺GATA3⁺ T cells numbers were comparable in MLN of infected B6 and IRF-8 deficient mice, but MLN cells from infected IRF-8 deficient mice secreted significantly less parasite-specific IL-4 ex vivo. The numbers of alternatively activated macrophages in MLN and serum levels of Hpb-specific IgG1 and IgE were also significantly less in infected Irf8^-/- than B6 mice. The frequencies of antigen-experienced CD4⁺CD11a^hiCD49d^hi cells that were CD44^hiCD62L^- were similar in MLN of infected Irf8^-/- and B6 mice, but the proportions of CD4⁺GATA3⁺ and CD4⁺IL-4⁺ T cells were lower in infected Irf8^-/- mice. CD11b⁺Gr1⁺ cells from naïve or infected Irf8^-/- mice suppressed CD4⁺ T cell proliferation and parasite-specific IL-4 secretion in vitro albeit less efficiently than B6 mice. Surprisingly, there were significantly more CD4⁺ T cells in infected Irf8^-/- mice, with a higher frequency of CD4⁺CD25⁺Foxp3⁺ T (Tregs) cells and significantly higher numbers of Tregs than B6 mice. In vivo depletion of MDSC and/or Tregs in Irf8^-/- mice did not affect adult worm burdens, but Treg depletion resulted in higher egg production and enhanced parasite-specific IL-5, IL-13, and IL-6 secretion ex vivo. Our data thus provide a previously unrecognized role for IRF-8 in Th2 immunity to a GI nematode.

We investigated if IRF-8, which is critical for Th1 immunity and negatively regulates myeloid cell development including MDSC, contributes to Th2 immunity to the gastrointestinal nematode Heligmosomoides polygyrus bakeri (Hpb). Irf8 expression was down-regulated in MDSC from infected C57BL/6 (B6) mice. Hpb-infected IRF-8 deficient mice had significantly higher adult worm burdens than B6 mice. There were significantly more MDSC, fewer alternatively activated macrophages, lower serum levels of Hpb-specific antibodies in infected IRF-8 deficient than B6 mice, and MLN cells from infected IRF-8 deficient mice secreted less parasite-specific IL-4 ex vivo. There were similar frequencies of antigen-experienced CD4⁺CD11a^hiCD49d^hi T cells in MLN that were CD44^hiCD62L^- in infected Irf8^-/- and B6 mice, but lower proportions of CD4⁺GATA3⁺ and CD4⁺IL-4⁺ T cells in Irf8^-/- mice. Infected Irf8^-/- mice had a higher frequency of CD4⁺Foxp3⁺ T (Tregs) cells and significantly higher numbers of Tregs compared to infected B6 mice. MDSC from infected Irf8^-/- mice suppressed CD4⁺ T cell effector functions in vitro albeit less efficiently than B6 mice. Treg and/or MDSC depletion did not affect adult worm burdens in infected Irf8^-/- mice, but Treg depletion partially restored Th2 cytokine responses. These data highlight the importance of IRF-8 in Th2 immunity to Hpb infection.

Differential expression of genes in fetal brain as a consequence of maternal protein deficiency and nematode infection

Maternal dietary protein deficiency and gastrointestinal nematode infection during early pregnancy have negative impacts on both maternal placental gene expression and fetal growth in the mouse. Here we used next-generation RNA sequencing to test our hypothesis that maternal protein deficiency and/or nematode infection also alter the expression of genes in the developing fetal brain. Outbred pregnant CD1 mice were used in a 2×2 design with two levels of dietary protein (24% versus 6%) and two levels of infection (repeated sham versus Heligmosomoides bakeri beginning at gestation day 5). Pregnant dams were euthanized on gestation day 18 to harvest the whole fetal brain. Four fetal brains from each treatment group were analyzed using RNA Hi-Seq sequencing and the differential expression of genes was determined by the edgeR package using NetworkAnalyst. In response to maternal H. bakeri infection, 96 genes (88 up-regulated and eight down-regulated) were differentially expressed in the fetal brain. Differentially expressed genes were involved in metabolic processes, developmental processes and the immune system according to the PANTHER classification system. Among the important biological functions identified, several up-regulated genes have known neurological functions including neuro-development (Gdf15, Ing4), neural differentiation (miRNA let-7), synaptic plasticity (via suppression of NF-κβ), neuro-inflammation (S100A8, S100A9) and glucose metabolism (Tnnt1, Atf3). However, in response to maternal protein deficiency, brain-specific serine protease (Prss22) was the only up-regulated gene and only one gene (Dynlt1a) responded to the interaction of maternal nematode infection and protein deficiency. In conclusion, maternal exposure to GI nematode infection from day 5 to 18 of pregnancy may influence developmental programming of the fetal brain.

The Integrin LFA-1 Controls T Follicular Helper Cell Generation and Maintenance

T follicular helper (Tfh) cells are a CD4⁺ T cell subset critical for long-lived humoral immunity. We hypothesized that integrins play a decisive role in Tfh cell biology. Here we show that Tfh cells expressed a highly active form of leukocyte function-associated antigen-1 (LFA-1) that was required for their survival within the germinal center niche. In addition, LFA-1 promoted expression of Bcl-6, a transcriptional repressor critical for Tfh cell differentiation, and inhibition of LFA-1 abolished Tfh cell generation and prevented protective humoral immunity to intestinal helminth infection. Furthermore, we demonstrated that expression of Talin-1, an adaptor protein that regulates LFA-1 affinity, dictated Tfh versus Th2 effector cell differentiation. Collectively, our results define unique functions for LFA-1 in the Tfh cell effector program and suggest that integrin activity is important in lineage decision-making events in the adaptive immune system.

Plastic and micro-evolutionary responses of a nematode to the host immune environment

Parasitic organisms have to cope with the defences deployed by their hosts and this can be achieved adopting immune evasion strategies or optimal life history traits according to the prevailing pattern of immune-mediated mortality. Parasites often encounter variable immune environments both within and between hosts, promoting the evolution of plastic strategies instead of fixed responses. Here, we explored the plasticity and micro-evolutionary responses of immunomodulatory mechanisms and life history traits to the immune environment provided by the host, using the parasitic nematode Heligmosomoides polygyrus. To test if the parasite responds plastically to the immune environment, we stimulated the systemic inflammatory response of mice and we assessed i) the expression of two genes with candidate immunomodulatory functions (Hp-Tgh2 and Hp-CPI); ii) changes in the number of eggs shed in the faeces. To test if the immune environment induces a micro-evolutionary response in the parasite, we maintained the nematode in mice whose inflammatory response was up- or down-regulated during four generations. We found that H. polygyrus plastically responded to a sudden rise of pro-inflammatory cytokines, up-regulating the expression of two candidate genes involved in the process of immune modulation, and enhancing egg output. At the micro-evolutionary level, parasites maintained in hosts experiencing different levels of inflammation did not have differential expression of Hp-Tgh2 and Hp-CPI genes when infecting unmanipulated, control, mice. However, parasites maintained in mice with an up-regulated inflammation shed more eggs compared to the control line. Overall, our study shows that H. polygyrus can plastically adjust the expression of immunomodulatory genes and life history traits, and responds to selection exerted by the host immune system.

In vitro culture of Mesocestoides corti metacestodes and isolation of immunomodulatory excretory-secretory products

Cestode-mediated diseases hold the interesting feature of persisting metacestode larvae dwelling within the host tissues, in the midst of the immune response. Excretory-secretory (ES) products of the metacestode larval stage modulate the host immune response and modify the outcome of the disease. Therefore, isolation and analysis of axenic metacestode ES products are crucial to study their properties. Here, we report the development of a system for long-term in vitro cultivation of the metacestode of the parasitic cestode Mesocestoides corti (syn. Mesocestoides vogae). Although feeder cells and host serum supported the early growth of the parasite, long-term survival was not dependent on host serum or host-derived factors enabling the collection of parasite released products in serum-free medium. Functionally, these axenic ES products recapitulated M. corti tetrathyridia's ability to inhibit LPS-driven IL-12p70 secretion by dendritic cells. Thus, our new axenic culture system will simplify the identification and characterization of M. corti-derived immunomodulatory factors that will indirectly enable the identification and characterization of corresponding factors in the metacestode larvae of medically relevant cestodes such as Echinococcus multilocularis that are not yet amenable to serum-free cultivation.

Primary Heligmosomoides polygyrus bakeri infection induces myeloid-derived suppressor cells that suppress CD4+ Th2 responses and promote chronic infection

Primary infection with the gastrointestinal nematode Heligmosomoides polygyrus bakeri is chronic in C57BL/6 (B6) mice whereas challenge infection is rapidly eliminated. F4/80^-CD11b⁺Gr⁺ cells, presumed to be neutrophils, were reported to accumulate around encysting larvae in intestinal tissue during primary infection, but their exact identity and role remain unclear. We observed significant increases in F4/80^-CD11b^hiGr1^hi cells in mesenteric lymph nodes (MLNs) and spleen after primary but not challenge infection; a high proportion of these cells expressed Ly6G and Ly6C. These cells, which phenotypically resemble myeloid-derived suppressor cells (MDSC), increased in lamina propria (LP) early during primary infection. Increased MDSC were associated with low numbers of alternatively activated macrophages (AAMØ) in LP and CD4⁺GATA3⁺ T cells and AAMØ in MLN and spleen. Purified CD11c^-CD11b⁺Gr1⁺ cells from H. polygyrus bakeri-infected mice suppressed OVA-specific CD4⁺ T-cell proliferation via a nitric oxide-dependent mechanism and parasite-specific IL-4 secretion in vitro. Adoptive transfer of CD11c^-CD11b⁺Gr1⁺ cells from mice with primary infection resulted in significantly higher adult worm burdens and increased egg production in naïve B6 recipients infected with H. polygyrus bakeri. Altogether, these findings indicate that primary H. polygyrus bakeri infection induces a novel subset of MDSC that suppress CD4⁺ Th2 responses and promote chronic infection.

Downregulation of the Syk Signaling Pathway in Intestinal Dendritic Cells Is Sufficient To Induce Dendritic Cells That Inhibit Colitis

Helminthic infections modulate host immunity and may protect people in less-developed countries from developing immunological diseases. In a murine colitis model, the helminth Heligmosomoides polygyrus bakeri prevents colitis via induction of regulatory dendritic cells (DCs). The mechanism driving the development of these regulatory DCs is unexplored. There is decreased expression of the intracellular signaling pathway spleen tyrosine kinase (Syk) in intestinal DCs from H. polygyrus bakeri-infected mice. To explore the importance of this observation, it was shown that intestinal DCs from DC-specific Syk(-/-) mice were powerful inhibitors of murine colitis, suggesting that loss of Syk was sufficient to convert these cells into their regulatory phenotype. DCs sense gut flora and damaged epithelium via expression of C-type lectin receptors, many of which signal through the Syk signaling pathway. It was observed that gut DCs express mRNA encoding for C-type lectin (CLEC) 7A, CLEC9A, CLEC12A, and CLEC4N. H. polygyrus bakeri infection downmodulated CLEC mRNA expression in these cells. Focusing on CLEC7A, which encodes for the dectin-1 receptor, flow analysis showed that H. polygyrus bakeri decreases dectin-1 expression on the intestinal DC subsets that drive Th1/Th17 development. DCs become unresponsive to the dectin-1 agonist curdlan and fail to phosphorylate Syk after agonist stimulation. Soluble worm products can block CLEC7A and Syk mRNA expression in gut DCs from uninfected mice after a brief in vitro exposure. Thus, downmodulation of Syk expression and phosphorylation in intestinal DCs could be important mechanisms through which helminths induce regulatory DCs that limit colitis.