Characterization of the immuno-regulatory response to the tapeworm Hymenolepis diminuta in the non-permissive mouse host

The Tapeworm Hymenolepis diminuta as an Important Model Organism in the Experimental Parasitology of the 21st Century

The tapeworm Hymenolepis diminuta is a common parasite of the small intestine in rodents but it can also infect humans. Due to its characteristics and ease of maintenance in the laboratory, H. diminuta is also an important model species in studies of cestodiasis, including the search for new drugs, treatments, diagnostics and biochemical processes, as well as its host-parasite interrelationships. A great deal of attention has been devoted to the immune response caused by H. diminuta in the host, and several studies indicate that infection with H. diminuta can reduce the severity of concomitant disease. Here, we present a critical review of the experimental research conducted with the use of H. diminuta as a model organism for over more than two decades (in the 21st century). The present review evaluates the tapeworm H. diminuta as a model organism for studying the molecular biology, biochemistry and immunology aspects of parasitology, as well as certain clinical applications. It also systematizes the latest research on this species. Its findings may contribute to a better understanding of the biology of tapeworms and their adaptation to parasitism, including complex correlations between H. diminuta and invertebrate and vertebrate hosts. It places particular emphasis on its value for the further development of modern experimental parasitology.

Luna Virus and Helminths in Wild Mastomys natalensis in Two Contrasting Habitats in Zambia: Risk Factors and Evidence of Virus Dissemination in Semen

Transmission dynamics and the maintenance of mammarenaviruses in nature are poorly understood. Using metagenomic next-generation sequencing (mNGS) and RT-PCR, we investigated the presence of mammarenaviruses and co-infecting helminths in various tissues of 182 Mastomys natalensis rodents and 68 other small mammals in riverine and non-riverine habitats in Zambia. The Luna virus (LUAV) genome was the only mammarenavirus detected (7.7%; 14/182) from M. natalensis. Only one rodent from the non-riverine habitat was positive, while all six foetuses from one pregnant rodent carried LUAV. LUAV-specific mNGS reads were 24-fold higher in semen than in other tissues from males. Phylogenetically, the viruses were closely related to each other within the LUAV clade. Helminth infections were found in 11.5% (21/182) of M. natalensis. LUAV–helminth co-infections were observed in 50% (7/14) of virus-positive rodents. Juvenility (OR = 9.4; p = 0.018; 95% CI: 1.47–59.84), nematodes (OR = 15.5; p = 0.001; 95% CI: 3.11–76.70), cestodes (OR = 10.8; p = 0.025; 95% CI: 1.35–86.77), and being male (OR = 4.6; p = 0.036; 95% CI: 1.10–18.90) were associated with increased odds of LUAV RNA detection. The role of possible sexual and/or congenital transmission in the epidemiology of LUAV infections in rodents requires further study, along with the implications of possible helminth co-infection.

Infection with Hymenolepis diminuta Blocks Colitis and Hastens Recovery While Colitis Has Minimal Impact on Expulsion of the Cestode from the Mouse Host

Two experimental paradigms were adopted to explore host-helminth interactions involved in the regulation of colitis and to understand if colitis affects the outcome of helminth infection. First, male BALB/c mice infected with H. diminuta were challenged 4 days later with dinitrobenzene sulphonic acid (DNBS) and necropsied 3 days later. Second, mice were infected with H. diminuta 3 days after DNBS treatment and necropsied 11 or 14 days post-DNBS. Mice were assessed for colitic disease severity and infectivity with H. diminuta upon necropsy. Supporting the concept of helminth therapy, mice are protected from DNBS-colitis when infected with H. diminuta only 4 days previously, along with parallel increases in splenic production of Th2 cytokines. In the treatment regimen, H. diminuta infection produced a subtle, statistically significant, enhanced recovery from DNBS. Mice regained body weight quicker, had normalized colon lengths, and showed no overt signs of disease, in comparison to the DNBS-only mice, some of which displayed signs of mild disease at 14 days post-DNBS. Unexpectedly, colitis did not affect the hosts' anti-worm response. The impact of inflammatory disease on helminth infection is deserving of study in a variety of models as auto-inflammatory diseases emerge in world regions where parasitic helminths are endemic.

Helminth Interactions with Bacteria in the Host Gut Are Essential for Its Immunomodulatory Effect

Colonization by the benign tapeworm, Hymenolepis diminuta, has been associated with a reduction in intestinal inflammation and changes in bacterial microbiota. However, the role of microbiota in the tapeworm anti-inflammatory effect is not yet clear, and the aim of this study was to determine whether disruption of the microflora during worm colonization can affect the course of intestinal inflammation. We added a phase for disrupting the intestinal microbiota using antibiotics to the experimental design for which we previously demonstrated the protective effect of H. diminuta. We monitored the immunological markers, clinical parameters, bacterial microbiota, and histological changes in the colon of rats. After a combination of colonization, antibiotics, and colitis induction, we had four differently affected experimental groups. We observed a different course of the immune response in each group, but no protective effect was found. Rats treated with colonization and antibiotics showed a strong induction of the Th2 response as well as a significant change in microbial diversity. The microbial results also revealed differences in the richness and abundance of some bacterial taxa, influenced by various factors. Our data suggest that interactions between the tapeworm and bacteria may have a major impact on its protective effect.

Immunoproteomics and Surfaceomics of the Adult Tapeworm Hymenolepis diminuta

In cestodiasis, mechanical and molecular contact between the parasite and the host activates the immune response of the host and may result in inflammatory processes, leading to ulceration and intestinal dysfunctions. The aim of the present study was to identify antigenic proteins of the adult cestode Hymenolepis diminuta by subjecting the total protein extracts from adult tapeworms to 2DE immunoblotting (two-dimensional electrophoresis combined with immunoblotting) using sera collected from experimentally infected rats. A total of 36 protein spots cross-reacting with the rat sera were identified using LC-MS/MS. As a result, 68 proteins, including certain structural muscle proteins (actin, myosin, and paramyosin) and moonlighters (heat shock proteins, kinases, phosphatases, and glycolytic enzymes) were identified; most of these were predicted to possess binding and/or catalytic activity required in various metabolic and cellular processes, and reported here as potential antigens of the adult cestode for the first time. As several of these antigens can also be found at the cell surface, the surface-associated proteins were extracted and subjected to in-solution digestion for LC-MS/MS identification (surfaceomics). As a result, a total of 76 proteins were identified, from which 31 proteins, based on 2DE immunoblotting, were predicted to be immunogenic. These included structural proteins actin, myosin and tubulin as well as certain moonlighting proteins (heat-shock chaperones) while enzymes with diverse catalytic activities were found as the most dominating group of proteins. In conclusion, the present study shed new light into the complexity of the enteric cestodiasis by showing that the H. diminuta somatic proteins exposed to the host possess immunomodulatory functions, and that the immune response of the host could be stimulated by diverse mechanisms, involving also those triggering protein export via yet unknown pathways.

Helminth Antigen-Conditioned Dendritic Cells Generate Anti-Inflammatory Cd4 T Cells Independent of Antigen Presentation via Major Histocompatibility Complex Class II

A recently identified feature of the host response to infection with helminth parasites is suppression of concomitant disease. Dendritic cells (DCs) exposed to antigens from the tapeworm Hymenolepis diminuta significantly reduce the severity of dinitrobenzene sulfonic acid-induced colitis in mice. Here we elucidate mechanisms underlying this cellular immunotherapy. We show a requirement for Ccr7 expression on transferred H. diminuta antigen-treated (HD)-DCs, suggesting that homing to secondary lymphoid tissues is important for suppression of colitis. Furthermore, sodium metaperiodate-sensitive helminth-derived glycans are required to drive the anti-colitic response in recipient mice. Induction of Th2-type cytokines and Gata-3⁺Cd4⁺ cells in secondary lymphoid tissues is dependent on major histocompatibility complex class II (MHC II) protein expression on transferred DCs, although remarkably, transfer of MHC II^-/- HD-DCs still attenuated dinitrobenzene sulfonic acid-induced colitis in recipient mice. Moreover, transfer of Cd4⁺ splenic T cells retrieved from mice administered MHC II^-/- HD-DCs suppressed dinitrobenzene sulfonic acid-induced colitis in recipient mice. Our studies reveal that HD-DCs can suppress colitis via an alternative MHC II-independent pathway that involves, in part, mobilization of T-cell responses. These data support the utility of HD-DCs in blocking colitis, revealing a requirement for Ccr7 and providing for HD-DC autologous immunotherapy for disease in which MHC II expression and/or function is compromised.

The benign helminth Hymenolepis diminuta ameliorates chemically induced colitis in a rat model system

The tapeworm Hymenolepis diminuta is a model for the impact of helminth colonization on the mammalian immune system and a candidate therapeutic agent for immune mediated inflammatory diseases (IMIDs). In mice, H. diminuta protects against models of inflammatory colitis by inducing a strong type 2 immune response that is activated to expel the immature worm. Rats are the definitive host of H. diminuta, and are colonized stably and over long time periods without harming the host. Rats mount a mild type 2 immune response to H. diminuta colonization, but this response does not generally ameliorate colitis. Here we investigate the ability of different life cycle stages of H. diminuta to protect rats against a model of colitis induced through application of the haptenizing agent dinitrobenzene sulphonic acid (DNBS) directly to the colon, and monitor rat clinical health, systemic inflammation measured by TNFα and IL-1β, and the gut microbiota. We show that immature H. diminuta induces a type 2 response as measured by increased IL-4, IL-13 and IL-10 expression, but does not protect against colitis. In contrast, rats colonized with mature H. diminuta and challenged with severe colitis (two applications of DNBS) have lower inflammation and less severe clinical symptoms. This effect is not related the initial type 2 immune response. The gut microbiota is disrupted during colitis and does not appear to play an overt role in H. diminuta-mediated protection.

Helminths and intestinal barrier function

Approximately one-sixth of the worlds' population is infected with helminths and this class of parasite takes a major toll on domestic livestock. The majority of species of parasitic helminth that infect mammals live in the gut (the only niche for tapeworms) where they contact the hosts' epithelial cells. Here, the helminth-intestinal epithelial interface is reviewed in terms of the impact on, and regulation of epithelial barrier function, both intrinsic (epithelial permeability) and extrinsic (mucin, bacterial peptides, commensal bacteria) elements of the barrier. The data available on direct effects of helminths on epithelial permeability are scant, fragmentary and pales in comparison with knowledge of mobilization of immune reactions and effector cells in response to helminth parasites and how these impact intestinal barrier function. The interaction of helminth-host and helminth-host-bacteria is an important determinant of gut form and function and precisely defining these interactions will radically alter our understanding of normal gut physiology and pathophysiological reactions, revealing new approaches to infection with parasitic helminths, bacterial pathogens and idiopathic auto-inflammatory disease.

A benign helminth alters the host immune system and the gut microbiota in a rat model system

Helminths and bacteria are major players in the mammalian gut ecosystem and each influences the host immune system and health. Declines in helminth prevalence and bacterial diversity appear to play a role in the dramatic rise of immune mediated inflammatory diseases (IMIDs) in western populations. Helminths are potent modulators of immune system and their reintroduction is a promising therapeutic avenue for IMIDs. However, the introduction of helminths represents a disturbance for the host and it is important to understand the impact of helminth reintroduction on the host, including the immune system and gut microbiome. We tested the impact of a benign tapeworm, Hymenolepis diminuta, in a rat model system. We find that H. diminuta infection results in increased interleukin 10 gene expression in the beginning of the prepatent period, consistent with induction of a type 2 immune response. We also find induction of humoral immunity during the patent period, shown here by increased IgA in feces. Further, we see an immuno-modulatory effect in the small intestine and spleen in patent period, as measured by reductions in tissue immune cells. We observed shifts in microbiota community composition during the patent period (beta-diversity) in response to H. diminuta infection. However, these compositional changes appear to be minor; they occur within families and genera common to both treatment groups. There was no change in alpha diversity. Hymenolepis diminuta is a promising model for helminth therapy because it establishes long-term, stable colonization in rats and modulates the immune system without causing bacterial dysbiosis. These results suggest that the goal of engineering a therapeutic helminth that can safely manipulate the mammalian immune system without disrupting the rest of the gut ecosystem is in reach.

Soluble Egg Antigen Activates M2 Macrophages via the STAT6 and PI3K Pathways, and Schistosoma Japonicum Alternatively Activates Macrophage Polarization to Improve the Survival Rate of Septic Mice

Sepsis is one of the most challenging health problems worldwide. Our previous study showed that chronic schistosoma japonica (SJ) infection might increase serum anti-inflammatory factors to play a protective role, thus improving the survival rate of septic mice. Further research revealed that SJ infection promoted J774A.1 macrophage differentiation into M2 macrophages; suppressed LPS-induced activation of M1 macrophages; up-regulated CD163, IL-10, and TGF-β1 expression; inhibited TNF-α and iNOS expression; and blocked the effect of LPS-promoted TNF-α and iNOS expression. Furthermore, adoptive transfer of ex vivo programed M2 macrophages significantly increased the survival rate of septic mice. In vitro studies suggested that soluble egg antigen (SEA) from SJ played the same role as worm infection but had no impact on M1 macrophages. SEA reduced LPS-induced TNF-α and iNOS expression, decreased the inhibitory effect of LPS on IL-10 and TGF-β1 expression, increased STAT6 phosphorylation, and up-regulated PI3K and Akt expression but inhibited SOCS1 expression. When PI3K inhibitors were added, SEA-induced expression of CD163, IL-10, and arg1 might be reduced. Therefore, worm infection has a protective effect in septic mice in which SEA may play a key role via the STAT6 and PI3K pathways. This finding may provide a favorable solution for the treatment of sepsis, especially early cases. J. Cell. Biochem. 118: 4230-4239, 2017. © 2017 Wiley Periodicals, Inc.

Modulation of murine intestinal immunity by Moringa oleifera extract in experimental hymenolepiasis nana

The potential therapeutic value of Moringa oleifera extract (MOE), due to its anti-inflammatory and anti-oxidant effects, has been reported previously. In this study, Hymenolepis nana antigen (HNA) in combination with MOE was used in immunization against H. nana infection. Adult worm and egg counts were taken, while histological changes in the intestine were observed. Mucosal mast (MMCs) and goblet cells (GCs) were stained with specific stains, while serum and intestinal IgA were assayed using enzyme-linked immunosorbent assay (ELISA). Reduced glutathione (GSH) and lipid peroxidation (thiobarbituric acid reactive substances, TBARS) were assayed. Real-time polymerase chain reaction (PCR) was used for detection of mRNA expression in ileum tissue. The results demonstrated an improvement in the architecture of intestinal villi, decreased inducible nitric oxide synthase (iNOs) and TBARS, and increased GSH in HNA, MOE and MOE + HNA groups. In the same groups, an increase in GCs, mucin 2 (MUC2), interleukins (IL)-4, -5 and -9, and stem cell factor (SCF) versus a decrease in both interferon-gamma (IFN-γ) and transforming growth factor (TGF-β) expression appeared. HNA and MOE + HNA increased serum and intestinal IgA, respectively. MOE decreased MMCs and achieved the highest reductions in both adult worms and eggs. In conclusion, MOE could achieve protection against H. nana infections through decreased TGF-β, IFN-γ and MMC counts versus increased GC counts, T-helper cell type 2 (Th2) cytokines and IgA level.

Helminth Regulation of Immunity: A Three-pronged Approach to Treat Colitis

By reputation, the parasite is a pariah, an unwelcome guest. Infection with helminth parasites evokes stereotypic immune responses in humans and mice that are dominated by T helper (Th)-2 responses; thus, a hypothesis arises that infection with helminths would limit immunopathology in concomitant inflammatory disease. Although infection with some species of helminths can cause devastating disease and affect the course of microbial infections, analyses of rodent models of inflammatory disease reveal that infection with helminth parasites, or treatment with helminth extracts, can limit the severity of autoinflammatory disease, including colitis. Intriguing, but fewer, studies show that adoptive transfer of myeloid immune cells treated with helminth products/extracts in vitro can suppress inflammation. Herein, 3 facets of helminth therapy are reviewed and critiqued: treatment with viable ova or larvae, treatment with crude extracts of the worm or purified molecules, and cellular immunotherapy. The beneficial effect of helminth therapy often converges on the mobilization of IL-10 and regulatory/alternatively activated macrophages, while there are reports on transforming growth factor (TGF)-β, regulatory T cells and dendritic cells, and recent data suggest that helminth-evoked changes in the microbiota should be considered when defining anticolitic mechanisms. We speculate that if the data from animal models translate to humans, noting the heterogeneity therein, then the choice between use of viable helminth ova, helminth extracts/molecules or antigen-pulsed immune cells could be matched to disease management in defined cohorts of patients with inflammatory bowel disease.

IL-22 Restrains Tapeworm-Mediated Protection against Experimental Colitis via Regulation of IL-25 Expression

Interleukin (IL)-22, an immune cell-derived cytokine whose receptor expression is restricted to non-immune cells (e.g. epithelial cells), can be anti-inflammatory and pro-inflammatory. Mice infected with the tapeworm Hymenolepis diminuta are protected from dinitrobenzene sulphonic acid (DNBS)-induced colitis. Here we assessed expulsion of H. diminuta, the concomitant immune response and the outcome of DNBS-induced colitis in wild-type (WT) and IL-22 deficient mice (IL-22-/-) ± infection. Interleukin-22-/- mice had a mildly impaired ability to expel the worm and this correlated with reduced or delayed induction of TH2 immunity as measured by splenic and mesenteric lymph node production of IL-4, IL-5 and IL-13 and intestinal Muc-2 mRNA and goblet cell hyperplasia; in contrast, IL-25 increased in the small intestine of IL-22-/- mice 8 and 12 days post-infection compared to WT mice. In vitro experiments revealed that H. diminuta directly evoked epithelial production of IL-25 that was inhibited by recombinant IL-22. Also, IL-10 and markers of regulatory T cells were increased in IL-22-/- mice that displayed less DNBS (3 mg, ir. 72h)-induced colitis. Wild-type mice infected with H. diminuta were protected from colitis, as were infected IL-22-/- mice and the latter to a degree that they were almost indistinguishable from control, non-DNBS treated mice. Finally, treatment with anti-IL-25 antibodies exaggerated DNBS-induced colitis in IL-22-/- mice and blocked the anti-colitic effect of infection with H. diminuta. Thus, IL-22 is identified as an endogenous brake on helminth-elicited TH2 immunity, reducing the efficacy of expulsion of H. diminuta and limiting the effectiveness of the anti-colitic events mobilized following infection with H. diminuta in a non-permissive host.

Cytokine, antibody and proliferative cellular responses elicited by Taenia solium calreticulin upon experimental infection in hamsters

Taenia solium causes two diseases in humans, cysticercosis and taeniosis. Tapeworm carriers are the main risk factor for neurocysticercosis. Limited information is available about the immune response elicited by the adult parasite, particularly the induction of Th2 responses, frequently associated to helminth infections. Calreticulin is a ubiquitous, multifunctional protein involved in cellular calcium homeostasis, which has been suggested to play a role in the regulation of immune responses. In this work, we assessed the effect of recombinant T. solium calreticulin (rTsCRT) on the cytokine, humoral and cellular responses upon experimental infection in Syrian Golden hamsters (Mesocricetus auratus). Animals were infected with T. solium cysticerci and euthanized at different times after infection. Specific serum antibodies, proliferative responses in mesenteric lymph nodes and spleen cells, as well as cytokines messenger RNA (mRNA) were analyzed. The results showed that one third of the infected animals elicited anti-rTsCRT IgG antibodies. Interestingly, mesenteric lymph node (MLN) cells from either infected or non-infected animals did not proliferate upon in vitro stimulation with rTsCRT. Additionally, stimulation with a tapeworm crude extract resulted in increased expression of IL-4 and IL-5 mRNA. Upon stimulation, rTsCRT increased the expression levels of IL-10 in spleen and MLN cells from uninfected and infected hamsters. The results showed that rTsCRT favors a Th2-biased immune response characterized by the induction of IL-10 in mucosal and systemic lymphoid organs. Here we provide the first data on the cytokine, antibody and cellular responses to rTsCRT upon in vitro stimulation during taeniasis.

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

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

Resistin-like molecule alpha enhances the proliferation and migration of aortic vascular smooth muscle cells

OBJECTIVE

The mitogenic and chemotactic effects of resistin-like molecule alpha (RELMα) are thought to contribute to vascular remodeling in pulmonary arterial hypertension. Here we evaluate the expression of RELMα in atherosclerotic plaque and investigate its effects on the proliferation and migration of vascular smooth muscle cells (VSMCs).

METHODS

An atherosclerotic model was established by feeding 4-week-old C57BL/6J ApoE-/- mice (n = 9) with a high-fat diet. Wild-type 4-week-old C57BL/6J (n = 9) were fed the same diet and were used as controls. RELMα expression was evaluated by immunohistochemistry and quantified using real-time PCR (RT-PCR). A (3)H-thymidine incorporation assay and the Boyden chamber assay, respectively, were used to explore the effects of different concentrations of RELMα on the proliferation and migration of VSMCs.

RESULTS

Immunohistochemistry identified positively stained granules in atherosclerotic plaques. These results were confirmed by detection of RELMα mRNA using RT-PCR. We also demonstrated that in vitro exposure to RELMα significantly promoted the proliferation and migration of VSMCs in a dose-related manner (p < 0.01).

CONCLUSIONS

RELMα expressed in atherosclerotic plaque of ApoE-/- mice appears to enhance the proliferation and migration of aortic VSMCs in a dose-related manner.

Alternatively activated macrophages in types 1 and 2 diabetes

Macrophages are innate immune cells derived from monocytes, which, in turn, arise from myeloid precursor cells in the bone marrow. Macrophages have many important roles in the innate and adaptive immune response, as well as in tissue homeostasis. Two major populations have been defined: The classically activated macrophages that respond to intracellular pathogens by secreting proinflammatory cytokines and reactive oxygen species and alternatively activated macrophages which are induced during Th2 responses displaying anti-inflammatory activities. Both macrophage populations are central players in diabetes, the first one triggering inflammatory responses which initiates insulitis and pancreatic β cell death during type 1 diabetes, whereas the second population decreases hyperglycemia, insulitis, and inflammation in the pancreas, thereby negatively regulate type 1 diabetes. Obesity is an important factor in the development of type 2 diabetes; classically activated macrophages are a dominant cell population involved in the establishment of the inflammatory profile, insulin resistance, and activation of inflammatory signals during the development and progression of this disease. In contrast, alternatively activated macrophages regulate the release of proinflammatory cytokines, attenuating adipose tissue inflammation. Here, we review the advantages and disadvantages of these two macrophage populations with regard to their roles in types 1 and 2 diabetes.

Cestode regulation of inflammation and inflammatory diseases

Helminth parasites are masters of immune regulation; a likely prerequisite for long-term survival by circumventing their hosts' attempt to eradicate them. From a translational perspective, knowledge of immune events as a response to infection with a helminth parasite could be used to reduce the intensity of unwanted inflammatory reactions. Substantial data have accumulated showing that inflammatory reactions that promote a variety of auto-inflammatory diseases are dampened as a consequence of infection with helminth parasites, via either the mobilization of an anti-worm spectrum of immune events or by the direct effect of secretory/excretory bioactive immunomodulatory molecules released from the parasite. However, many issues are outstanding in the definition of the mechanism(s) by which infection with helminth parasites can affect the outcome, positively or negatively, of concomitant disease. We focus on a subgroup of this complex group of metazoan parasites, the cestodes, summarizing studies from rodent models that illustrate if, and by what mechanisms, infection with tapeworms ameliorate or exaggerate disease in their host. The ability of infection with cestodes, or other classes of helminth, to worsen a disease course or confer susceptibility to intracellular pathogens should be carefully considered in the context of 'helminth therapy'. In addition, poorly characterised cestode extracts can regulate murine and human immunocyte function, yet the impact of these in the context of autoimmune or allergic diseases is poorly understood. Thus, studies with cestodes, as representative helminths, have helped cement the concept that infection with parasitic helminths can inhibit concomitant disease; however, issues relating to long-term effects, potential side-effects, mixed pathogen infections and purification of immunomodulatory molecules from the parasite remain as challenges that need to be addressed in order to achieve the use of helminths as anti-inflammatory agents for human diseases.

The protective effect of the recombinant 53-kDa protein of Trichinella spiralis on experimental colitis in mice

BACKGROUND

Helminth infection has been proven to reduce the severity of experimental inflammatory bowel disease (IBD). The excretory-secretory proteins of helminths play an important role in the process of immunomodulation.

AIMS

In the present study, we aimed to investigate the protective potential of recombinant Trichinella spiralis (TS) 53-kDa protein (rTsP53), a component of excretory-secretory proteins, on experimental colitis in mice.

METHODS

BALB/c mice were treated subcutaneously with 50 μg rTsP53 three times at an interval of 5 days. Colitis was induced by intrarectal administration of 5 mg trinitrobenzene sulfonic acid (TNBS). Disease activities and macroscopic and microscopic scores were evaluated. To determine immune response provoked by rTsP53, we measured specific IgG1 and IgG2a values against rTsP53 in sera of mice. We also detected cytokine profiles as well as the markers of alternatively activated macrophages (M2) in mice.

RESULTS

RTsP53 ameliorated significantly the disease activity index (DAI) as well as the macroscopic and microscopic scores. IgG1 but not IgG2a was the predominant specific antibody detected in the sera of immunized mice, indicating the potential of stimulating T-helper (Th) 2 bias response by rTsP3. Pre-treatment with rTsP53 decreased serum Th1 cytokines (TNF-a, IFN-γ) and elevated serum levels of serum Th2 cytokines (IL-4, IL-13); it also decreased colonic Th1 cytokines (TNF-α, IL-6) and colonic regulatory cytokines (IL-10, TGF-β1). RTsP53 increased colonic M2 markers, arginase-1 (Arg-1), and found in inflammatory zone 1 (FIZZ1), compared to mice without rTsP53 pretreatment.

CONCLUSIONS

RTsP53 is a potential protective agent for IBD.

Infection with an intestinal helminth parasite reduces Freund's complete adjuvant-induced monoarthritis in mice

OBJECTIVE

Assessment of infection with helminth parasites in murine models of disease could identify antiinflammatory mechanisms that translate into treatments for arthritic disease. The aim of this study was to test the ability of infection with the tapeworm Hymenolepis diminuta to ameliorate Freund's complete adjuvant (CFA)-induced monoarthritis in mice.

METHODS

Mice received CFA with or without H diminuta, and knee swelling, pain, and measures of inflammation were assessed.

RESULTS

Injection of CFA resulted in rapid (within 24 hours) and sustained (lasting 20 days) knee swelling, a decreased pain threshold, increased blood flow to the knee, and increased production of tumor necrosis factor α and interleukin-12p40 (IL-12p40). In mice that were infected with H diminuta 8 days prior to receiving CFA, the severity of arthritis was reduced as assessed by these indices of inflammation and infection 2 days after CFA injection and resulted in more rapid resolution of knee swelling. This antiarthritic effect required a viable infection and was dependent on adaptive immunity, because infection with H diminuta did not protect mice lacking T cells and B cells or the IL-4 receptor α chain from CFA-induced inflammation. Interleukin-10 was of prime importance in the antiarthritic effect, because IL-10-knockout mice were not protected by infection, the antiarthritic effect was ablated by use of neutralizing IL-10 antibodies, and transfer of CD4+ cells from infected wild-type mice but not IL-10-knockout mice significantly reduced CFA-induced knee swelling.

CONCLUSION

In mice, the adaptive immune response to infection with H diminuta involves mobilization of IL-10, which has the concomitant advantage of dampening the innate immune responses that drive CFA-induced joint inflammation.

Exacerbation of oxazolone colitis by infection with the helminth Hymenolepis diminuta: involvement of IL-5 and eosinophils

Substantial data show that infection with helminth parasites ameliorates colitis; however, oxazolone-induced colitis is exaggerated in mice infected with the tapeworm, Hymenolepis diminuta. We tested the hypothesis that the IL-5 response to helminth infection enhances the severity of oxazolone-induced colitis. Mice were infected with H. diminuta and 8 days later were treated with oxazolone ± anti-IL-5 antibodies. Colitis was assessed 72 hours postoxazolone treatment by disease activity scores, myeloperoxidase activity, and histopathology. Other mice received injections of a replication-deficient adenovirus that carried the IL-5 (Ad.IL-5) gene or a control adenovirus (Ad.delete) ± oxazolone. The effect of H. diminuta+oxazolone in CCL11/CCL22 (eotaxin-1 and 2) knockout (KO) mice was determined. Helminth infection and Ad.IL-5 treatment increased IL-5 and eosinophil numbers. In vivo neutralization of IL-5 significantly reduced the severity of colitis in H. diminuta+oxazolone-treated mice, and H. diminuta did not exaggerate oxazolone-induced colitis in CCL11/CCL22 KO mice. Mice receiving Ad.IL-5 only had no colitis, while oxazolone-induced colitis was more severe in animals cotreated with Ad.IL-5 (Ad.delete + oxazolone was not significantly different from oxazolone only). Thus, while there is much to be gleaned about antiinflammatory mechanisms from rodent-helminth model systems, these data illustrate the caveat that infection with helminth parasites as a therapy could be contraindicated in patients with eosinophilia or elevated IL-5 unless coupled to appropriate measures to block IL-5 and/or eosinophil activity.

Hymenolepis diminuta: the effects of infection on transepithelial ion transport and tight junctions in rat intestines

In this study, we examine the effect of Hymenolepis diminuta on ion transport in the ileum and on tight junctions in the ileum and colon of rats. We also evaluate the effect of H. diminuta on C-fiber endings in the ileum, the direct habitat of H. diminuta, before and after mechanical stimulation and pharmacological modification by capsaicin (C-fiber irritant). Wistar rats were orally infected with five cysticercoids of H. diminuta. Using a modified Ussing chamber, electrophysiological parameters of the ileum were measured (transepithelial electrical potential difference and transepithelial electrical resistance) as well as the deposition of occludin (a tight junction protein) in the ileum and colon of the rats 8, 16, 25, 35, 40 and 60 days post infection. We observed a significant reduction in transepithelial electrical potential difference in the ileum of rats infected with H. diminuta. In both the ileum and colon of rats infected with H. diminuta we also observed a decrease in occludin deposition, which indicates leakage of tight junctions, correlating with the decrease in transepithelial electrical resistance of these tissues. The application of capsaicin confirmed the hypothesis that H. diminuta in rats affects the C-fiber sensory receptors, causing changes in ion transport in the ileum. The results of the performed electrophysiological and immunohistochemical examinations indicate hymenolepidosis-related changes in the active transport of ions and the passive movement of ions.

In vitro-derived alternatively activated macrophages reduce colonic inflammation in mice

BACKGROUND & AIMS

Infection with the rat tapeworm Hymenolepis diminuta reduces the severity of dinitrobenzene sulfonic acid (DNBS)-induced colitis in mice. Infection with H. diminuta increases colonic expression of arginase-1 and found in inflammatory zone 1 (FIZZ1), markers of alternatively activated macrophages (AAMs). We investigated whether AAMs have anticolitic effects.

METHODS

Normal or macrophage-depleted Balb/c mice were infected with H. diminuta; some mice were given DNBS, and the severity of colitis was assessed by disease activity scores, myeloperoxidase activity, and histologic examination. AAMs were also differentiated in vitro, given to mice by intraperitoneal or intravenous injection, and the effects on DNBS-induced colitis were determined. Numbers of AAMs were assessed in biopsy specimens from patients with Crohn's disease.

RESULTS

Depletion of intestinal macrophages using clodronate-liposomes prevented the anticolitic effect of infection with H. diminuta. Injection of AAMs, but not classically activated macrophages, significantly reduced the severity of DNBS-induced colitis. The AAM-induced, anticolitic effect was accompanied by increased interleukin (IL)-10 production from mitogen-stimulated spleen cells; in vivo neutralization of IL-10 partially reduced the effects of AAM transfer. Patients with active CD had reduced numbers of CD68(+)CD206(+) macrophages (which indicate AAM), whereas biopsy specimens from patients with inactive CD had increased numbers of these cells.

CONCLUSIONS

Analysis of the H. diminuta-murine DNBS system identified the AAM, which, when administered to mice, significantly reduced DNBS-induced colitis. The ability to derive AAMs from patients' blood suggests that adoptive transfer of these cells could be a novel approach to inflammatory bowel disease.

Infection with Hymenolepis diminuta is more effective than daily corticosteroids in blocking chemically induced colitis in mice

Purpose. To compare infection with the tapeworm, Hymenolepis diminuta, with steroid (dexamethasone) administration in the inhibition of dinitrobenzene sulfonic acid- (DNBS-) induced colitis in mice. Procedures. Mice were treated with DNBS ± infected with H. diminuta or treated with daily dexamethasone (2 mg/Kg, ip.) and were assessed 72 hours post-DNBS by the calculation of disease activity and histological damage scores, and spleen cell cytokine production. Results. H. diminuta-infected mice showed increased IL-4 and IL-10 production by spleen cells compared to other groups and were protected from DNBS-induced colitis. In contrast, there was little benefit of dexamethasone in the treatment of colitis. Collagen deposition in the colon was not different between the groups. Conclusions. H. diminuta was superior to dexamethasone in the prevention of DNBS-induced colitis and did not result in additional side effects (i.e., collagen deposition). Comparisons with current therapeutics and long-term followup to studies are essential if “helminth therapy” is to become a viable treatment for specific inflammatory diseases in the gut or other tissues.

Similarity and diversity in macrophage activation by nematodes, trematodes, and cestodes

This review summarizes current knowledge of macrophages in helminth infections, with a focus not only on delineating the striking similarities in macrophage phenotype between diverse infections but also on highlighting the differences. Findings from many different labs illustrate that macrophages in helminth infection can act as anti-parasite effectors but can also act as powerful immune suppressors. The specific role for their alternative (Th2-mediated) activation in helminth killing or expulsion versus immune regulation remains to be determined. Meanwhile, the rapid growth in knowledge of alternatively activated macrophages will require an even more expansive view of their potential functions to include repair of host tissue and regulation of host metabolism.

Early removal of alternatively activated macrophages leads to Taenia crassiceps cysticercosis clearance in vivo

To determine the role of alternatively activated macrophages in modulating the outcome of experimental cysticercosis caused by Taenia crassiceps, we investigated the effect of removal of alternatively activated macrophage by injecting clodronate-loaded liposomes into susceptible BALB/c mice. Following T. crassiceps infection, mice receiving PBS-loaded liposomes developed a dominant Th2-type response associated with the presence of alternatively activated macrophages together with antigen-specific hyporesponsiveness and high parasite burden. In contrast, similarly infected mice treated with clodronate-loaded liposomes mounted a mixed Th1/Th2-type response, reversed antigen-specific hyporesponsiveness and did not carry notable alternatively activated macrophage populations. These factors were associated with increased resistance to T. crassiceps cysticercosis. Interestingly, early AAM phi depletion was enough to limit parasite growth. However, if macrophages were depleted late in the infection, no effect on parasite burden was observed. These findings demonstrate that alternatively activated macrophages play a critical role in mediating susceptibility to experimental cysticercosis in which their early recruitment may favor parasite survival.

The immune response to and immunomodulation by Hymenolepis diminuta

Analyses of laboratory-based helminth-rodent model systems have been immensely useful in delineating the workings of the mammalian immune system. Investigations in the 1970s-1980s on the fate of the rat tapeworm, Hymenolepis diminuta, in rats and mice and the systemic and local responses evoked following infection have contributed directly to our knowledge of how permissive and non-permissive hosts respond to the challenge of infection with a helminth parasite. This convenient laboratory model system has, in the authors' opinion, regrettably received considerably less attention in recent years. With the goal of highlighting the utility of this model system, data is presented on: (1) the immune and enteric responses of rats and mice to infection with H. diminuta; (2) the ability of excretory or secretory products derived from H. diminuta to significantly reduce T cell and macrophage activation in vitro; and (3) how assessment of H. diminuta-rodent models can be used to identify immune effector or regulatory mechanisms that can be translated into novel treatments for inflammatory and autoimmune disorders.

Alternative activation of macrophages: an immunologic functional perspective

Macrophages are innate immune cells with well-established roles in the primary response to pathogens, but also in tissue homeostasis, coordination of the adaptive immune response, inflammation, resolution, and repair. These cells recognize danger signals through receptors capable of inducing specialized activation programs. The classically known macrophage activation is induced by IFN-gamma, which triggers a harsh proinflammatory response that is required to kill intracellular pathogens. Macrophages also undergo alternative activation by IL-4 and IL-13, which trigger a different phenotype that is important for the immune response to parasites. Here we review the cellular sources of these cytokines, receptor signaling pathways, and induced markers and gene signatures. We draw attention to discrepancies found between mouse and human models of alternative activation. The evidence for in vivo alternative activation of macrophages is also analyzed, with nematode infection as prototypic disease. Finally, we revisit the concept of macrophage activation in the context of the immune response.

Differential response of antigen presenting cells from susceptible and resistant strains of mice to Taenia crassiceps infection

Antigen presenting cells (APCs) are critically involved in the interaction between pathogens and the host immune system. Here, we examined two different populations of APCs in mice that are susceptible (BALB/c) or resistant (C57BL/6) to Taenia crassiceps cysticercosis. Bone marrow-derived dendritic cells (BMDCs) from both strains of mice were exposed to T. crassiceps excreted/secreted antigens (TcES) and, at the same time, to the Toll-like receptor (TLR) ligand LPS. BMDCs from BALB/c mice underwent a partial maturation when incubated with TcES and displayed decreased responses to TLR-dependent stimuli associated with low CD80, CD86, CD40 and CCR7 expression and impaired IL-15 production. These BMDCs-induced impaired allogenic responses. In contrast, BMDCs from C57BL/6 mice displayed normal maturation and induced strong allogenic responses. Moreover, the exposure to TcES resulted in a lower production of IL-12 and TNF-alpha by LPS-activated DCs from BALB/c mice compared to C57BL/6 DCs. Three parameters of macrophage activation were assessed during Taenia infection: LPS+IFN-gamma-induced production of IL-12, TNF-alpha and nitric oxide (NO) in vitro; infection-induced markers for alternatively activated macrophages (Arginase-1, RELM-alpha, Ym-1 and TREM-2 expression) and suppressive activity. The maximum response to LPS+IFN-gamma-induced TNF-alpha, IL-12 and NO production by macrophages from both strains of mice occurred 2 wk post-infection. However, as infection progressed, the production of these molecules by BALB/c macrophages declined. While the BALB/c macrophages displayed impaired pro-inflammatory responses, these macrophages showed strong Arginase-1, Ym-1, RELM-alpha and TREM-2 expression. By contrast, C57BL/6 macrophages maintained a pro-inflammatory profile and low transcripts for alternative activation markers. Macrophages from T. crassiceps-infected BALB/c mice showed stronger suppressive activity than those from C57BL/6 mice. These findings suggest that APC activation at both early and late time points during T. crassiceps infection is a possible mechanism that underlies the differential susceptibility to T. crassiceps infection displayed by these mouse strains.

Retnla (relmalpha/fizz1) suppresses helminth-induced Th2-type immunity

Retnla (Resistin-like molecule alpha/FIZZ1) is induced during Th2 cytokine immune responses. However, the role of Retnla in Th2-type immunity is unknown. Here, using Retnla^−/− mice and three distinct helminth models, we show that Retnla functions as a negative regulator of Th2 responses. Pulmonary granuloma formation induced by the eggs of the helminth parasite Schistosoma mansoni is dependent on IL-4 and IL-13 and associated with marked increases in Retnla expression. We found that both primary and secondary pulmonary granuloma formation were exacerbated in the absence of Retlna. The number of granuloma-associated eosinophils and serum IgE titers were also enhanced. Moreover, when chronically infected with S. mansoni cercariae, Retnla^−/− mice displayed significant increases in granulomatous inflammation in the liver and the development of fibrosis and progression to hepatosplenic disease was markedly augmented. Finally, Retnla^−/− mice infected with the gastrointestinal (GI) parasite Nippostrongylus brasiliensis had intensified lung pathology to migrating larvae, reduced fecundity, and accelerated expulsion of adult worms from the intestine, suggesting Th2 immunity was enhanced. When their immune responses were compared, helminth infected Retnla^−/− mice developed stronger Th2 responses, which could be reversed by exogenous rRelmα treatment. Studies with several cytokine knockout mice showed that expression of Retnla was dependent on IL-4 and IL-13 and inhibited by IFN-γ, while tissue localization and cell isolation experiments indicated that eosinophils and epithelial cells were the primary producers of Retnla in the liver and lung, respectively. Thus, the Th2-inducible gene Retnla suppresses resistance to GI nematode infection, pulmonary granulomatous inflammation, and fibrosis by negatively regulating Th2-dependent responses.

Retnla is a member of a family of cysteine-rich secreted proteins, referred to as ‘resistin-like molecules’ or ‘found in inflammatory zone’ that increase in expression during allergic reactions and following infection with a variety of metazoan parasites. Retnla was originally hypothesized to function as an effector molecule during helminth-induced Th2-type immune responses. Studies conducted here with Retnla-deficient mice, however, suggest that Retnla primarily functions as a regulatory molecule during helminth infection. Using three helminth model systems affecting three different organ systems, we show that Retlna is induced by IL-4 and IL-13 as a mechanism to suppress Th2-type immunity. Retnla deficiency increased inflammation in the lung following i.v. challenge with Schistosoma mansoni eggs. Retnla deficiency also accelerated the development of liver fibrosis following S. mansoni infection. This finding was particularly surprising since Retnla was previously shown to activate collagen-producing fibroblasts that induce fibrosis. Thus, Retnla may represent a novel target for the treatment of fibrotic diseases. Finally, resistance to the intestinal nematode parasite Nippostrongylus brasiliensis was significantly increased in the absence of Retnla. When viewed together, the combined results from all three models establish a critical role for the Th2-inducible gene Retnla (Fizz1/Relm-alpha) in the suppression of helminth-induced Th2-type immunity.

Parasitic helminths: a pharmacopeia of anti-inflammatory molecules

Infection with parasitic helminths takes a heavy toll on the health and well-being of humans and their domestic livestock, concomitantly resulting in major economic losses. Analyses have consistently revealed bioactive molecules in extracts of helminths or in their excretory/secretory products that modulate the immune response of the host. It is our view that parasitic helminths are an untapped source of immunomodulatory substances that, in pure form, could become new drugs (or models for drug design) to treat disease. Here, we illustrate the range of immunomodulatory molecules in selected parasitic trematodes, cestodes and nematodes, their impact on the immune cells in the host and how the host may recognize these molecules. There are many examples of the partial characterization of helminth-derived immunomodulatory molecules, but these have not yet translated into new drugs, reflecting the difficulty of isolating and fully characterizing proteins, glycoproteins and lipid-based molecules from small amounts of parasite material. However, this should not deter the investigator, since analytical techniques are now being used to accrue considerable structural information on parasite-derived molecules, even when only minute quantities of tissue are available. With the introduction of methodologies to purify and structurally-characterize molecules from small amounts of tissue and the application of high throughput immunological assays, one would predict that an assessment of parasitic helminths will yield a variety of novel drug candidates in the coming years.

The divergent roles of alternatively activated macrophages in helminthic infections

Macrophages play crucial roles in the immune response, as they can initiate, modulate and also be final effector cells during immune responses to infections. Macrophages are derived from myeloid precursor cells in bone marrow and are widely distributed in every tissue of the body. Over the past 10 years, the concepts about macrophage activation have clearly changed; macrophages are not called activated or inactivated as they used to be. These changes in the concept of macrophage response is the result of many in vitro and in vivo studies, but the major support for the current concept of alternatively activated macrophages (AAMphi) comes from parasitic helminth infections. Parasitic helminths have developed complex mechanisms to evade and modulate host immunity. Infections with these parasites induce strong polarized Th2-type immune responses frequently associated with impaired T-cell proliferative responses to parasitic or unrelated antigens. Given the recent advances in understanding the immunoregulatory capabilities of helminthic infections, it has been suggested that macrophages can be a target for immunomodulation. Furthermore, they become altered when a host experiences chronic exposure to helminth parasites or their by-products, which favour the induction of AAMphi. How AAMphi participate in modulating host immunity during helminth infections and what their roles are in clearing or favouring parasite survival remains elusive. Here we review the most recent advances in the literature on AAMphi at the host-parasite interface, including three classes of helminths: nematodes (Brugia, Nippostrongylus, Litomosoides, Heligmosomoides), trematodes (Schistosoma, Fasciola) and cestodes (Taenia, Echinococcus, Hymenolepis).

Intestinal cestodes

PURPOSE OF REVIEW

This review summarizes the biology, clinical aspects, diagnosis, treatment and epidemiology for the common and rarer (zoonotic) intestinal cestodes of humans.

RECENT FINDINGS

Mass drug application to eliminate Taenia solium carriers may have only temporary effects on cysticercosis transmission. At least two major world genotypes of T. solium have been identified and greater genetic heterogeneity may occur at the regional level. A new human taeniid T. asiatica has been confirmed which occurs sympatrically with T. saginata and T. solium in Southeast Asia. Coproantigen and PCR tests for Taenia spp. have greatly improved diagnostic efficacy and epidemiological studies. There appears to be an increase in human diphyllobothriasis in Europe, Japan and the Americas.

SUMMARY

Human intestinal cestode infections are globally primarily caused by species in three genera: Taenia, Hymenolepis or Diphyllobothrium. Sporadic zoonotic infections caused by nontaeniids are usually food-borne or due to accidental ingestion of invertebrate hosts. Intestinal cestode infections generally result in only mild symptoms characterized chiefly by abdominal discomfort and diarrhoea. Most human intestinal cestode infections can be treated with a single oral dose of praziquantel or niclosamide.

Helminth infection enhances disease in a murine TH2 model of colitis

BACKGROUND & AIMS

There is convincing evidence from animal and human studies that infection with parasitic helminths can alleviate the histopathology and symptoms of colitis. Here the ability of the rat tapeworm Hymenolepis diminuta to affect the course of oxazolone-induced colitis (a TH2 model) was assessed.

METHODS

Mice were infected with H diminuta and 8 days later they received oxazolone (3 mg in 50% EtOH, intrarectal). On autopsy (3 or 7 days postoxazolone), disease severity was assessed by macroscopic clinical scores, histologic damage scores, myeloperoxidase and eosinophil peroxidase activity, and cytokine synthesis.

RESULTS

As gauged by all markers of gut function, infection with H diminuta caused a significant exacerbation of oxazolone-induced colitis. Indeed, while mice receiving oxazolone only began to recover approximately 3-4 days posttreatment, the cotreated group continued to deteriorate. Helminth infection, independent of oxazolone administration, enhanced IL-4, IL-5, IL-10, and IL-13 production from in vitro stimulated immune cells and evoked increases in colonic eosinophil peroxidase of cotreated mice. Finally, while knockout of natural killer (NK) and NK-T cells by administration of a neutralizing NK1.1 antibody reduced the inflammation in oxazolone and oxazolone + H diminuta-treated animals, mice in the latter group still displayed significant colitis.

CONCLUSIONS

We have shown that H diminuta infection is beneficial in other models of colitis. The current data is presented as a caveat to the position that parasitic helminths in general can be considered as a therapy for heterogeneous inflammatory disorders without careful analysis of the immunologic basis of the condition.