Parasite-secreted products regulate the host response to larval Taenia crassiceps

Differential Protein Expression of Taenia crassiceps ORF Strain in the Murine Cysticercosis Model Using Resistant (C57BL/6) Mice

A cysticercosis model of Taenia crassiceps ORF strain in susceptible BALB/c mice revealed a Th2 response after 4 weeks, allowing for the growth of the parasite, whereas resistant C57BL/6 mice developed a sustained Th1 response, limiting parasitic growth. However, little is known about how cysticerci respond to an immunological environment in resistant mice. Here, we show that the Th1 response, during infection in resistant C57BL/6 mice, lasted up to 8 weeks and kept parasitemia low. Proteomics analysis of parasites during this Th1 environment showed an average of 128 expressed proteins; we chose 15 proteins whose differential expression varied between 70 and 100%. A total of 11 proteins were identified that formed a group whose expression increased at 4 weeks and decreased at 8 weeks, and another group with proteins whose expression was high at 2 weeks and decreased at 8 weeks. These identified proteins participate in tissue repair, immunoregulation and parasite establishment. This suggests that T. crassiceps cysticerci in mice resistant under the Th1 environment express proteins that control damage and help to establish a parasite in the host. These proteins could be targets for drugs or vaccine development.

Protein expression profile of Taenia crassiceps cysticerci related to Th1- and Th2-type responses in the mouse cysticercosis model

The intraperitoneal cysticercosis model with the Taenia crassiceps ORF strain in female BALB/cAnN mice has been widely used to study the immune response in cysticercosis. During early infection (2 weeks), the host develops a non-permissive Th1 response, whereas during late infection (8 weeks), molecules from the cysticerci induce a Th2 response that is permissive to parasite growth. The modulation of the Th2 response is induced by molecules excreted/secreted by the larval stage of the parasite. However, there is limited information regarding the response of cysticerci to the mouse immunological environment during infection. The proteomic profiles in T. crassiceps ORF cysticerci when faced with the mouse Th1 and Th2 responses were analyzed through two-dimensional gel electrophoresis (2DE), and the differential expression of proteins was evaluated. Thirteen proteins, whose differential expression varied between 70% and 100%, were selected randomly. Protein identification by MALDI-TOF MS and BLAST showed that the proteins were related to folding, signaling, enzymatic activities, cell-movement regulation, cell-cell interactions, motility, carbohydrate metabolism, detoxification, and redox regulation processes. Notably, some of the proteins can act as antigenic-protective molecules and elicit a weak Th1 response; however, most are involved in the avoidance of the immune system, which leads to a Th2 response, or apoptosis. The findings indicate the process by which T. crassiceps cysticerci responds based on the host environment and provides novel insights into the mechanism by which this facilitates its establishment and persistence in the mouse. Furthermore, these proteins could be used as targets for drug and vaccine development.

Suppression of inflammatory genes expression in the injured host intestinal wall during Mesocestoides vogae tetrathyridium larvae migration

Mesocestoides vogae is a cestode parasite of the family Mesocestoididae (order Cyclophyllidea). Its larvae, tetrathyridium, are approximately 1 mm long and 300 μm wide and infect a wide range of host species including humans. Tetrathyridium migrate through the intestinal wall to invade the peritoneal cavity. Despite intestinal penetration by such a large-sized parasite, symptomatic intestinal disorders are not common during the migration period. In this study, the dynamics of tetrathyridia migration and their pathogenicity towards intestinal tissues were examined in mice infected orally with these parasites. Most tetrathyridia were found to migrate through the intestinal wall, moving into the peritoneal cavity or liver 24 to 48 hours after the oral infections. Next, the pathogenicity of tetrathyridium in the intestinal wall was histopathologically evaluated, and tissue injury from tetrathyridium migration was confirmed. Inflammatory foci were observed as tetrathyridium migration tracks from 48 hours after oral infection; however, the number of inflammatory foci had decreased by half more than 48 hours later. Therefore, we examined the gene expression levels of the macrophage driving cytokine, IL-1β, and the eosinophil recruiting chemokine, CCL11, by quantitative reverse-transcriptase PCR. The expression levels of these genes in the infected group were significantly lower than those of the non-infected group at 48 hours post-infection. Although the immunomodulating ability of the excretory-secretory products released from tetrathyridium has been previously shown by in vitro assays, the significance of this ability in their lifecycle has remained unclear. In this study, we discovered that tetrathyridium causes temporal inflammation in the intestinal wall during penetration and large-scale migration in this organ, but tetrathyridium simultaneously suppresses the host’s inflammatory gene expression, might to be a strategy that reduces inflammatory responses and increases survival of the parasite.

Excretory-secretory (ES) products are released by parasitic helminths into their migration sites and/or the intestinal regions they inhabit where parasite and host immune responses interact. ES products are release by a wide range of parasitic helminths, some of which are known to modulate the host’s immune system. Some ES products from some cestode parasites are known to reduce the production of pro-inflammatory cytokines from artificially stimulated cells under in vitro conditions. However, the immunomodulatory properties of the ES products have only been observed with in vitro experimental models and the biological consequences of their potential ability to suppress the host’s immune system during the parasite’s lifecycle and how they affect host–parasite interactions await discovery. Our results show that tetrathyridium, the larval stage of the Mesocestoides vogae cestode, strongly inhibits the host’s inflammatory gene expression in the injured intestinal wall, and that the inflammatory hot-spots caused by larval migration disappear almost immediately after mice are orally infected with these parasites. The ability to suppress the host’s inflammatory gene expression when larvae migrate through and damage the host’s tissues is an effective survival strategy for M. vogae intestinal parasites.

Molecular cloning and characterization of leucine aminopeptidase gene from Taenia pisiformis

Leucine aminopeptidase (LAP, EC: 3.4.11.1) is an important metalloexopeptidase that catalyze the hydrolysis of amino-terminal leucine residues from polypeptides and proteins. In this study, a full length of cDNA encoding leucine aminopeptidase of Taenia pisiformis (TpLAP) was cloned by rapid amplification of cDNA-ends using the polymerase chain reaction (RACE-PCR) method. The full-length cDNA of the TpLAP gene is 1823 bp and contains a 1569 bp ORF encoding 533 amino acids with a putative mass of 56.4 kDa. TpLAP contains two characteristic motifs of the M17LAP family in the C-terminal sequence: the metal binding site 265-[VGKG]-271 and the catalytic domain motif 351-[NTDAEGRL]-357. The soluble GST-TpLAP protein was expressed in Escherichia coli Transetta (DE3) and four specific anti-TpLAP monoclonal antibodies (mAbs) were prepared. In enzymatic assays, the optimal activity was observed at pH 9.5 at 45 °C. GST-TpLAP displayed a hydrolyzing activity for the Leu-pNA substrate with a maximum activity of 46 U/ml. The enzymatic activity was significantly enhanced by Mn²⁺ and completely inhibited by 20 nM bestatin and 0.15 mM EDTA. The native TpLAP was detected specifically in ES components of adult T. pisiformis by western blotting using anti-TpLAP mAb as a probe. Quantitative real-time PCR revealed that the TpLAP gene was expressed at a high level in adult worm tissues, especially in the gravid proglottids (50.71-fold). Immunolocalization analysis showed that TpLAP was located primarily in the subtegumental parenchyma zone and the uterine wall of adult worms. Our results indicate that TpLAP is a new member of the M17LAP family and can be considered as a stage-differentially expressed protein. These findings might provide new insights into the study of the mechanisms of growth, development and survival of T. pisiformis in the final host and have potential value as an attractive target for drug therapy or vaccine intervention.

Immunity and immune modulation elicited by the larval cestode Mesocestoides vogae and its products

Larval cestodes (metacestodes) induce long-lasting infections leading to considerable pathology in humans and livestock. Their survival is typically associated with Th2-biased immune responses and immunosuppressive effects and depends on the parasite's ability to excrete/secrete antigens with immunoregulatory properties. Here, Mesocestoides vogae, a natural parasite of mice, is proposed as a new model species for the identification and characterization of cestode-derived immunomodulatory factors. We followed the kinetics of immune parameters after infection with M. vogae or exposure to their excretory/secretory (ES) products in a permissive strain of mice. Besides, a dominant IL-10 production and accumulation of macrophages and eosinophils expressing mRNA for Fizz-1, YM1 and Arg-1, mice showed minimal IFN-γ and transient IL-4 production at early time points with a complete loss at later stages of infection. We found that serum-free ES products without host contamination directly induced M2 macrophages and suppressed IFN-γ production in vivo and in vitro. This study highlights the use of the M. vogae as a cestode infection model and its ES products as a valuable tool for the identification of new therapeutic targets for the control of larval cestodiasis.

ATaenia crassicepsfactor induces apoptosis of spleen CD4+T cells and TFG-β andFoxp3gene expression in mice

This study was undertaken to determine whether a parasite substance produces structural pathology in the mouse spleen. A low-molecular-weightTaenia crassicepsmetacestode factor (MF) isolated from the peritoneal fluid of female mice infected withT. crassicepsmetacestodes induced pathological and immunological changes in mouse spleen cellsin vivo.Electron microscopy and confocal microscopy revealed severe changes in the spleen histoarchitecture ofT. crassiceps-infected and MF-treated mice. Apoptotic degenerated spleen cells were observed in the white and red pulps and were more conspicuous in the white pulp of the spleen from theT. crassiceps-infected mice than in that of the MF-treated mice. Flow cytometry analysis revealed that the numbers of spleen CD4+T cells were significantly lower in both experimental groups than in control mice. Theex vivoexpression of transforming growth factor (TGF)-β and factor Foxp3 were significantly higher in splenocytes of the experimental mice than the basal expression observed in the control cells. These findings may have potential applications for a better understanding of the host–parasite relationship in human neurocysticercosis.

Helminth infections predispose mice to pneumococcal pneumonia but not to other pneumonic pathogens

Pneumonia is the leading killer of children worldwide. Here, we report that helminth-infected mice develop fatal pneumonia when challenged with Streptococcus pneumoniae. Mice were chronically infected with either the flatworm Taenia crassiceps or the roundworm Heligmosomoides polygyrus. Upon challenge with a pneumonic type 3 strain of S. pneumoniae (A66.1), the worm-infected mice developed pneumonia at a rate and to a degree higher than age-matched control mice as measured by bioluminescent imaging and lung titers. This predisposition to pneumonia appears to be specific to S. pneumoniae, as worm-infected mice did not show evidence of increased morbidity when challenged with a lethal dose of influenza virus or sublethal doses of Staphylococcus aureus or Listeria monocytogenes. The defect was also present when worm-infected mice were challenged with a type 2 sepsis-causing strain (D39); an increased rate of pneumonia, decreased survival, and increased lung and blood titers were found. Pneumococcal colonization and immunity against acute otitis media were unaffected. Anti-helminthic treatment in the H. polygyrus model reversed this susceptibility. We conclude that helminth coinfection predisposes mice to fatal pneumococcal pneumonia by promoting increased outgrowth of bacteria in the lungs and blood. These data have broad implications for the prevention and treatment for pneumonia in the developing world, where helminth infections are endemic and pneumococcal pneumonia is common.

Microvesicles and intercellular communication in the context of parasitism

There is a rapidly growing body of evidence that production of microvesicles (MVs) is a universal feature of cellular life. MVs can incorporate microRNA (miRNA), mRNA, mtDNA, DNA and retrotransposons, camouflage viruses/viral components from immune surveillance, and transfer cargo between cells. These properties make MVs an essential player in intercellular communication. Increasing evidence supports the notion that MVs can also act as long-distance vehicles for RNA molecules and participate in metabolic synchronization and reprogramming eukaryotic cells including stem and germinal cells. MV ability to carry on DNA and their general distribution makes them attractive candidates for horizontal gene transfer, particularly between multi-cellular organisms and their parasites; this suggests important implications for the co-evolution of parasites and their hosts. In this review, we provide current understanding of the roles played by MVs in intracellular pathogens and parasitic infections. We also discuss the possible role of MVs in co-infection and host shifting.

A Taenia crassiceps metacestode factor enhances ovarian follicle atresia and oocyte degeneration in female mice

The histopathological effects of Taenia crassiceps infection or T. crassiceps metacestode factor inoculation on the mouse ovary were determined using six female mice in three groups: infected mice, mice inoculated with the metacestode factor and control mice. The control group was subcutaneously inoculated with healthy peritoneal fluid. The infected group was intraperitoneally inoculated with 40 T. crassiceps metacestodes, and the metacestode factor group was subcutaneously inoculated with T. crassiceps metacestode factor (MF). Light and electron microscopy and TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labelling) assays revealed a significant increase in ovarian follicular atresia (predominantly in antral/preovulatory stages of development), oocyte degeneration (P< 0.05), and a decrease in the amount of corpus luteum in follicles of mice infected and inoculated with MF compared with the control group. Significant abnormalities of the granulosa cells and oocytes of the primordial, primary and secondary ovarian follicles occurred in both treated mouse groups (P< 0.05) compared with no degeneration in the control group. These pathological changes in female mice either infected with T. crassiceps metacestodes or inoculated with T. crassiceps MF may have consequences for ovulation and fertility.

Taenia crassiceps infection abrogates experimental autoimmune encephalomyelitis

Helminth infections induce strong immunoregulation that can modulate subsequent pathogenic challenges. Taenia crassiceps causes a chronic infection that induces a Th2-biased response and modulates the host cellular immune response, including reduced lymphoproliferation in response to mitogens, impaired antigen presentation and the recruitment of suppressive alternatively activated macrophages (AAMФ). In this study, we aimed to evaluate the ability of T. crassiceps to reduce the severity of experimental autoimmune encephalomyelitis (EAE). Only 50% of T. crassiceps-infected mice displayed EAE symptoms, which were significantly less severe than uninfected mice. This effect was associated with both decreased MOG-specific splenocyte proliferation and IL-17 production and limited leukocyte infiltration into the spinal cord. Infection with T. crassiceps induced an anti-inflammatory cytokine microenvironment, including decreased TNF-α production and high MOG-specific production of IL-4 and IL-10. While the mRNA expression of TNF-α and iNOS was lower in the brain of T. crassiceps-infected mice with EAE, markers for AAMФ were highly expressed. Furthermore, in these mice, there was reduced entry of CD3(+)Foxp3(-) cells into the brain. The T. crassiceps-induced immune regulation decreased EAE severity by dampening T cell activation, proliferation and migration to the CNS.

Taenia crassiceps infection attenuates multiple low-dose streptozotocin-induced diabetes

Taenia crassiceps, like other helminths, can exert regulatory effects on the immune system of its host. This study investigates the effect of chronic T. crassiceps infection on the outcome of Multiple Low Dose Streptozotocin-Induced Diabetes (MLDS). Healthy or previously T. crassiceps-infected mice received MLDS and type 1 diabetes (T1D) symptoms were evaluated for 6 weeks following the induction of MLDS. T. crassiceps-infected mice displayed lower blood glucose levels throughout the study. A significantly lower percentage of T. crassiceps-infected mice (40%) developed T1D compared to the uninfected group (100%). Insulitis was remarkably absent in T. crassiceps-infected mice, which had normal pancreatic insulin content, whereas uninfected mice showed a dramatic reduction in pancreatic insulin. Infected mice that received MLDS did not show an increase in their regulatory T cell population, however, they had a greater number of alternatively activated macrophages, higher levels of the cytokine IL-4, and lower levels of TNF-α. Therefore, infection with T. crassiceps causes an immunomodulation that modifies the incidence and development of MLDS-induced autoimmune diabetes.

Helminth immunoregulation: the role of parasite secreted proteins in modulating host immunity

Helminths are masterful immunoregulators. A characteristic feature of helminth infection is a Th2-dominated immune response, but stimulation of immunoregulatory cell populations, such as regulatory T cells and alternatively activated macrophages, is equally common. Typically, Th1/17 immunity is blocked and productive effector responses are muted, allowing survival of the parasite in a "modified Th2" environment. Drug treatment to clear the worms reverses the immunoregulatory effects, indicating that a state of active suppression is maintained by the parasite. Hence, research has focussed on "excretory-secretory" products released by live parasites, which can interfere with every aspect of host immunity from initial recognition to end-stage effector mechanisms. In this review, we survey our knowledge of helminth secreted molecules, and summarise current understanding of the growing number of individual helminth mediators that have been shown to target key receptors or pathways in the mammalian immune system.

Trichinella spiralis: Effect of thymus factor X on apoptosis and necrosis in mice

The aim of the study was to determine the effect of thymus factor X (TFX-Jelfa) on the percentage of apoptotic and necrotic lymphocytes in the spleen, mesenteric lymph nodes, and muscle tissue of mice infected with 200 larvae of Trichinella spiralis. TFX was administered subcutaneously at a dose of 15mg/kg. On days 7, 14, 21, 28, 35, 42, and 60 after infection, apoptotic and necrotic cells were detected by flow cytometry after staining with the Annexin V-Fluos Staining Kit. TFX increased the percentage of apoptotic lymphocytes in the spleen, mesenteric lymph nodes, and muscle tissue of mice infected with T. spiralis. The effect of TFX on the percentage of necrotic lymphocytes was weaker and less clear. Parasite load was lower in infected mice treated with TFX than in the untreated control mice. The effect of TFX on the host immune response and the survival of parasite larvae was therefore probably affected by the extent of inflammatory infiltrates, and not by the percentage of lymphocytes undergoing apoptosis.

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.

Role of the programmed Death-1 pathway in the suppressive activity of alternatively activated macrophages in experimental cysticercosis

We characterised a population of macrophages potentially involved in the immunoregulation induced by experimental cysticercosis. Following Taenia crassiceps infection, macrophages recruited in the peritoneal cavity were isolated and co-cultured at different ratios with T cells from naïve mice previously stimulated with anti-CD3/CD28 antibodies; these macrophages inhibited naïve T cell proliferation. This suppressive effect was Interleukin (IL)-10, Interferon-gamma (IFN-gamma), and nitric oxide (NO) independent. In contrast, macrophage-T cell contact was necessary to maintain anergy of T cells. Reverse transcriptase-PCR analysis of these macrophages showed higher transcripts of IL-10, chitinases Fizz1 and Ym1, and arginase-1 compared with naïve macrophages; by contrast, IL-12p40, and inducible nitric oxide synthase (iNOS) transcripts were undetected, whereas C-C chemokine ligand 5 (CCL5) was unchanged. Analysis of the membrane molecules expressed on Taenia-induced macrophages showed an up-regulation of several markers, mainly programmed death ligand 1 (PD-L1) and PD-L2. Blockade of PD-L1, PD-L2 or their receptor PD-1, but not of another marker, eliminated their ability to inhibit T-cell proliferation. Parallel experiments using ovalbumin (OVA)-peptide as a model antigen displayed similar results. Additionally, the same mechanism appears to be functional in splenocytes of T. crassiceps-infected mice given that blockade of PD-1, PD-L1 or PD-L2 re-established their ability to proliferate in response to parasite antigens. Moreover, Taenia-induced macrophages were able to suppress a mixed lymphocyte reaction in a PD-1-dependent manner. Thus, cestode infections induce macrophages alternatively activated with strong suppressive activity involving the PD-1/PD-L's pathway.

Resistance to reinfection in rats induced by irradiated metacercariae of Clonorchis sinensis

A study was made to observe the association between the resistance to reinfection induced by irradiated metacercariae (MC) of Clonorchis sinensis and antigen specific Th1- and Th2-type cytokine productions in rats. Rats were infected with 20 MC of C. sinensis, previously exposed to a single dose of gamma irradiation, which varied from 0 to 100 Gy. All of them, single dose of 12 Gy showed higher IgG antibody titer with lowest worm recovery. Thus, 50 MC were used to challenge infection in rats previously infected with 20 MC irradiated at 12 Gy and the highest resistance to challenge infection was observed. The results of lymphocyte proliferation with specific antigen, ES Ag were shown no difference of proliferative responses as compared with primary and challenge infection at 12 Gy irradiation dose. In the case of cytokines production were observed that interferon (IFN-gamma) and interlukin (IL-2) were significantly enhanced, while IL-4 and IL-10 was almost unchanged to make comparison between primary and secondary infection at 12 Gy irradiation dose. In conclusion, the single dose of 12 Gy could be adopted for induction of the highest resistance to challenge infection. Up-regulation of Th1 type cytokines, IFN-gamma and IL-2 may be affected to develop vaccine by irradiated MC.

Trichuris suis excretory secretory products (ESP) elicit interleukin-6 (IL-6) and IL-10 secretion from intestinal epithelial cells (IPEC-1)

Immune responses to gastrointestinal helminth infections have received increasing attention due to similarities to allergen-induced responses. In fact, the whipworm parasite of swine, Trichuris suis, has been used in beginning clinical trials as an antidote to inflammatory bowel disease. This strategy was based on this similarity and the recognition that other worms have been documented to induce anti-inflammatory responses in the host. In an effort to understand the basis for this response, we hypothesized that the proteins and peptides secreted by T. suis stimulate local intestinal epithelial cells to produce anti-inflammatory cytokines. To test this hypothesis in a correlate system of the natural swine host, T. suis excretory secretory products (ESP) were used to treat both differentiated and undifferentiated intestinal pig epithelial cells (IPEC-1) in vitro as a model for the effect on villus tip and crypt epithelial cells in the vicinity of the worms. IPEC-1 were exposed to low-level doses (0.3mg/ml) of T. suis ESP, and IL-4, IL-6 and IL-10 cytokine responses were measured by an enzyme-linked immunosorbant assay (ELISA). IL-6 was the predominant cytokine produced, accompanied by moderate IL-10 secretion from both differentiated and undifferentiated cells. As expected, IL-4 was not produced by IPEC-1. Additionally, IL-6 and IL-10 cytokines were produced within 24h, suggesting that these two cytokines form part of the primary host response to T. suis infections. These data suggest that T. suis ESP could enhance host immune responses and modulation through the induction of enteric IL-6 and IL-10.

Reactive oxygen species and 12/15-lipoxygenase contribute to the antiproliferative capacity of alternatively activated myeloid cells elicited during helminth infection

Understanding the role of CD11b(+)GR-1(+) myeloid suppressor cells in the immune suppression and immunoregulation associated with a variety of diseases may provide therapeutic opportunities. In this article, we show, in a model of helminth infection, that CD11b(+)GR-1(+) myeloid suppressor cells but not CD11b(+)F4/80(high) mature macrophages expanded in the peritoneal cavity of BALB/c mice implanted with Taenia crassiceps. Peritoneal cell populations from early stage-infected animals impaired T cell proliferation by secreting NO. Yet, they lost their ability to secrete NO in the late stage of infection. Concomitantly, their capacity to exert arginase activity and to express mRNAs coding for FIZZ1 (found in inflammatory zone 1), Ym, and macrophage galactose-type C-type lectin increased. Furthermore, cells from early stage-infected mice triggered T cells to secrete IFN-gamma and IL-4, whereas in the late stage of infection, they only induced IL-4 production. These data suggest that CD11b(+)GR-1(+) myeloid suppressor cells displaying an alternative activation phenotype emerged gradually as T. crassiceps infection progressed. Corroborating the alternative activation status in the late stage of infection, the suppressive activity relied on arginase activity, which facilitated the production of reactive oxygen species including H(2)O(2) and superoxide. We also document that the suppressive activity of alternative myeloid suppressor cells depended on 12/15-lipoxygenase activation generating lipid mediators, which triggered peroxisome proliferator-activated receptor-gamma. IL-4 and IL-13 signaling contributed to the expansion of myeloid suppressor cells in the peritoneal cavity of T. crassiceps-infected animals and to their antiproliferative activity by allowing arginase and 12/15-lipoxygenase gene expression.

The implantation of Taenia solium metacestodes in mice induces down-modulation of T-cell proliferation and cytokine production

The purpose of this study was to determine the effect of the implantation of Taenia solium metacestodes and the treatment with suppressive metacestode factor (F1) on the ability of spleen cells from Balb/c mice to produce cytokines. Cytokine production was estimated 12 days following the implantation or 4 days after the last dose of F1 (five doses) by RT-PCR and flow cytometry analyses. Spleen cells were obtained from metacestode-implanted, F1-treated and control mice. They were stimulated with concanavalin A (ConA) ex vivo and used for RT-PCR studies and for CD25 expression and intracellular cytokine production estimations using specific monoclonal antibodies labeled with phycoerithrin or fluorescein. Results of the RT-PCR showed that all cells expressed IFN-gamma, IL-2 and IL-4 mRNAs. IL-10 mRNA was not expressed in any case. Flow cytometry analyses showed that both spleen CD4+ and CD8+ cells from metacestode-implanted or treated-F1 mice expressed significantly diminished percentages of CD25 when compared with control cells (P<0.05). The estimation of intracellular cytokines showed that the production of IL-2 and IL-4 in CD8+ cells, and of IFN-gamma in CD4+ cells from mice implanted with metacestodes was significantly impaired when compared with the values from control cells (P<0.05).

Host gender in parasitic infections of mammals: an evaluation of the female host supremacy paradigm

A review of current literature on mammalian hosts' sexual dimorphism (SD) in parasitic infections revealed that (1) it is a scarcely and superficially studied biological phenomenon of considerable significance for individual health, behavior, and lifestyles and for the evolution of species; (2) there are many notable exceptions to the rule of a favorable female bias in susceptibility to infection; (3) a complex network of molecular and cellular reactions connecting the host's immuno-neuroendocrine systems with those of the parasite is responsible for the host-parasite relationship rather than just an adaptive immune response and sex hormones; (4) a lack of gender-specific immune profiles in response to different infections; (5) the direct effects of the host hormones on parasite physiology may significantly contribute to SD in parasitism; and (6) the need to enrich the reductionist approach to complex biological issues, like SD, with more penetrating approaches to the study of cause-effect relationships, i.e., network theory. The review concludes by advising against generalization regarding SD and parasitism and by pointing to some of the most promising lines of research.

Immunohistochemical localisation of 3beta-hydroxysteroid dehydrogenase in Sarcocystis spp

3Beta-hydroxysteroid-dehydrogenase (3beta-HSD) is an isoenzyme that catalyses an essential step in the synthesis of all classes of active steroid hormones. The presence of steroid hormones of the vertebrate type in invertebrates is acknowledged in addition to a group of steroid-like hormones called ecdysteroids that were present in arthropods and helminths. In the present study, 3beta-HSD was detected in the bradyzoites enclosed in sarcocysts of Sarcocystis spp. with immunohistochemistry. The results suggest that self-originating steroid hormones may play important roles in the development of Sarcocystis spp., and possibly in the regulation of the reciprocal immune interaction between the host and these parasites.

Isolation and characterization of a secretory component of Echinococcus multilocularis metacestodes potentially involved in modulating the host-parasite interface

Echinococcus multilocularis metacestodes are fluid-filled, vesicle-like organisms, which are characterized by continuous asexual proliferation via external budding of daughter vesicles, predominantly in the livers of infected individuals. Tumor-like growth eventually leads to the disease alveolar echinococcosis (AE). We employed the monoclonal antibody (MAb) E492/G1, previously shown to be directed against a carbohydrate-rich, immunomodulatory fraction of Echinococcus granulosus, to characterize potentially related components in E. multilocularis. Immunofluorescence studies demonstrated that MAb E492/G1-reactive epitopes were found predominantly on the laminated layer and in the periphery of developing brood capsules. The respective molecules were continuously released into the exterior medium and were also found in the parasite vesicle fluid. The MAb E492/G1-reactive fraction in E. multilocularis, named Em492 antigen, was isolated by immunoaffinity chromatography. Em492 antigen had a protein/carbohydrate ratio of 0.25, reacted with a series of lectins, and is related to the laminated layer-associated Em2(G11) antigen. The epitope recognized by MAb E492/G1 was sensitive to sodium periodate but was not affected by protease treatment. Anti-Em492 immunoglobulin G1 (IgG1) and IgG2 and, at lower levels, IgG3 were found in sera of mice suffering from experimentally induced secondary, but not primary, AE. However, with regard to cellular immunity, a suppressive effect on concanavalin A- or crude parasite extract-induced splenocyte proliferation in these mice was observed upon addition of Em492 antigen, but trypan blue exclusion tests and transmission electron microscopy failed to reveal any cytotoxic effect in Em492 antigen-treated spleen cells. This indicated that Em492 antigen could be modulating the periparasitic cellular environment during E. multilocularis infection through as yet unidentified mechanisms and could be one of the factors contributing to immunosuppressive events that occur at the host-parasite interface.

INFRAPOPULATION DYNAMICS OF A WILD STRAIN OF TAENIA CRASSICEPS (WFU) (CESTODA: TAENIIDAE) IN BALB/cJ MICE

Taenia crassiceps cysticerci form large infrapopulations that persist in the tissues of their rodent hosts. Early infrapopulation growth appears inhibited and is followed by rapid increases that appear not to be controlled by the host immune response. This investigation was undertaken to examine the infrapopulation growth dynamics of a normally developing strain (WFU) of T. crassiceps during a 60-day primary intraperitoneal (i.p.) infection. Three, 6, 9, 14, 28, and 60 days after i.p. inoculation of 5 cysticerci, mice were killed, and the numbers of larvae, developmental stage, and buds per larva were recorded. Larval infrapopulation abundance increased exponentially beginning on day 6 postinoculation (PI), indicating an initial lag in reproduction. A stage-structured exponential growth model, assuming no mortality, fits the larval infrapopulation dynamics in terms of the numbers of larvae in reproductive and nonreproductive stages, indicating that cysticerci evade or suppress (or both) host immune mechanisms that are parasite restrictive after the first week of infection.

Review article: helminths as therapeutic agents for inflammatory bowel disease

Over the last decade major advances have been made in our understanding of the mechanisms and mediators of inflammation that hold the promise of the development of new therapies for inflammatory disease. While much is to be gleaned from the application of new technologies, assessment of the age-old host-parasite relationship may also provide insights on how to counter pathological inflammatory events. In the case of inflammatory bowel disease [particularly Crohn's disease, which is associated with T helper 1 (Th1) events] it is proposed that infection with parasitic helminths would be beneficial: the paradigm being that of immune deviation, where Th2 cytokines mobilized in response to the helminth will prevent or antagonize the disease-promoting Th1 events in the gut. The situation is unlikely to be this simple. Here we review and critique the data in support of helminth therapy for inflammatory bowel disease, drawing attention to the gaps in knowledge and presenting a view on how the field may be advanced. While the concept of helminth therapy may be superficially unappealing, this review may convince the reader of the value of more extensive analyses of the impact of helminth infection on enteric inflammation.

Steroid hormone production by parasites: the case of Taenia crassiceps and Taenia solium cysticerci

Many examples of reciprocal endocrine interactions between parasites and hosts have been found in insects, arthropods and mammals. Cysticercosis produced by Taenia solium metacestodes is a widely distributed parasite infection that affects the human and the pig. Taenia crassiceps experimental murine cysticercosis has been used to explore the role of biological factors involved in host-parasite interactions. We had shown that T. crassiceps cysticercosis affects the serum concentration of steroid hormones and the reproduction behavior of the male mice host. In an effort to understand the biology of the parasite, we had investigated the parasite capacity to produce sex steroids. For this purpose, T. crassiceps cysticerci were incubated in the presence of different steroid precursors. TLC and recrystallization procedures showed that testosterone is produced from 3H-androstenedione in cysticerci. The conversion of 3H-testosterone to androstenedione, although present is much less significant. In addition, we had studied the production of testosterone by T. solium cysticerci. For this purpose, cysticerci were dissected from pork meat and incubated as above described. The results showed that T. solium cysticerci also produce testosterone. We have speculated about the importance of androgens in the growth of T. crassiceps cysticerci and found that the addition of the antiandrogen flutamide to the culture media of the parasites significantly decreased 3H-thymidine incorporation. We therefore hypothesized, that the ability of cysticerci to produce testosterone from steroid precursors might be important for the parasite growth and development.

CD4+ and CD19+ splenocytes undergo apoptosis during an experimental murine infection with Taenia crassiceps

The Taenia crassiceps cysticercus is a cestode that naturally and experimentally infects rodents in which it reproduces by budding. In the laboratory, a persistent cellular immunosuppression with a concomitant increasing load of parasites has been observed in experimentally infected BALB/cAnN mice. In this study, enhanced apoptosis was found in spleen cells from 30-day infected mice with a typical "ladder-patterned" DNA fragmentation and an increase in phosphatidylserine expression. A characteristic poly-(ADP-ribose) polymerase cleavage indicates that this cell death is caspase-mediated. Apoptosis was detected in the CD4(+) and CD19(+) splenocytes of infected mice after in vitro stimulation with cysticercal antigens. Considering previous results on the crucial role that CD4(+) T cells play in controlling the extent of infection, apoptosis in this T-lymphocyte subpopulation induced by T. crassiceps cysticerci could be responsible for the immunosuppression that underlies parasite success.

Taenia crassiceps cysticercosis: immune response in susceptible and resistant BALB/c mouse substrains

Taenia crassiceps can naturally and experimentally infect rodents in which they reproduce by budding. Differences in the susceptibility to T. crassiceps cysticercosis were found between two BALB/c substrains: BALB/cAnN (susceptible) and BALB/cJ (resistant). In chimeric mice, resistance was transferred to susceptible mice with bone marrow cells from the resistant mice, which argues in favor of an immune mediation of the resistant phenotype. To further explore the immune response that could underlie these differences in susceptibility, the specific cellular immune response elicited by the parasite was explored in both substrains. An increased proliferative response and IL-2 levels were induced by cysticercal antigens only in splenocytes from resistant mice. A decrease in the percentage of CD4(+) (11.1%), CD8(+) (17.5%) was found in splenocytes from susceptible BALB/cAnN mice. A study of the TCRV beta repertoire revealed a significant decrease in V beta 2 in both CD4(+) and CD8(+) splenocytes only in the susceptible BALB/cAnN strain.

The initial immune response during experimental cysticercosis is of the mixed Th1/Th2 type

The immunological events that occur during the initial stages of experimental cysticercosis are not known. The studies presented here examined the cytokines produced by peritoneal exudate cells (PECs), splenocytes and mesenteric lymph node (MLN) cells during the first week of infection with larval Taenia crassiceps in BALB/cJ mice. Proliferation assays determined that the earliest time when antigen-specific responses could be measured was 5 days post-infection. Concanavalin A (ConA) stimulation of host cells elicited an initial burst of IL-4 production at 24 h of infection and ConA-stimulated Th2-type cytokine production is predominant by 7 days post-infection. Thus, there are responses at day 1 of infection that seem to promote a Th2-type response. Stimulation of MLN cells, splenocytes and PECs with larval antigens supported previous reports of mixed Th1/Th2-type cytokine production with increases in interleukin (IL)-4, IL-10 and interferon (IFN)-gamma. Ex vivo IFN-gamma production by PECs from infected mice was increased at 3, 5 and 7 days post-infection, whereas at these times reduced ex vivo IL-10 production was observed. This ex vivo IFN-gamma response preceded an increasing IL-10 production by PECs between 3 and 7 days post-infection in parasite-specific and ConA-induced proliferation assays. Thus, infection with larval T. crassiceps results in an initial response mediated by IFN-gamma that is quickly followed by an increase in IL-10 production and subsequent reduction in the amount of IFN-gamma being produced.

Suppressed cytotoxic T lymphocyte responses in experimental cysticercosis

Mitogen-induced T cell responses are suppressed in mice infected with larvae of Taenia crassiceps. The effects of experimental infection on specific T cell responses, however, have not been examined. In the present study, we demonstrate that larval-infected mice exhibit suppressed ability to develop anti-virus specific cytotoxic T lymphocyte (CTL) responses while maintaining apparently normal natural killer (NK) cell responsiveness.

The schistosome oligosaccharide lacto-N-neotetraose expands Gr1(+) cells that secrete anti-inflammatory cytokines and inhibit proliferation of naive CD4(+) cells: a potential mechanism for immune polarization in helminth infections

Immunomodulatory oligosaccharides found on helminths also are found in human milk, and both helminths and milk have been shown to be immunosuppressive. We have been examining the immunomodulatory capabilities of two oligosaccharides expressed in milk and on helminth parasites, lacto-N-fucopentaose III and lacto-N-neotetraose (LNnT). In an attempt to dissect mechanisms that lead to Th2 polarization and immune suppression, we examined the early response in mice to the glycoconjugate LNnT-Dextran (LNnT-Dex). We found that injection of LNnT-Dex expanded a cell population, phenotypically defined as Gr1(+)/CD11b(+)/F4/80(+), as early as 2 h after injection. Examination of spontaneous cytokine production showed that this Gr1(+)/F4/80(+) population of cells spontaneously produced low levels of proinflammatory cytokines, but higher levels of IL-10 and TGF-beta ex vivo, compared to peritoneal cells from mice injected with Dex. Gr1(+) cells adoptively suppressed naive CD4(+) T cell proliferation in vitro in response to anti-CD3/CD28 Ab stimulation. Suppression of naive CD4(+) cells involved cell contact and was dependent on IFN-gamma and NO, with a discrete role played by IL-10. Coculture of naive CD4(+)T cells with Gr1(+) suppressor cells did not lead to CD4(+) T cell apoptosis, although it did imprint on naive CD4(+) T cells a response characterized by lower levels of IFN-gamma, coincident with increased IL-13 production. Our results suggest that both human milk and helminth parasites may share a ligand-specific mechanism involved in the generation of anti-inflammatory mediators that suppress Th1-type and inflammatory responses.