Echinostoma Caproni Research Articles

Order and timing of infection with different parasite life stages impacts host and parasite life histories.

Co-exposure to multiple parasites can alter parasite success and host life history when compared to single infections. These infection outcomes can be affected by the order of parasite arrival, the host immune response, and the interspecific interactions among co-infecting parasites. In this study, we examined how the arrival order of two trematode parasites, Schistosoma mansoni and Echinostoma caproni, influenced parasite ecology and the life history of their snail host, Biomphalaria glabrata. Snail hosts were exposed to E. caproni cercariae before, with, and after their exposure to S. mansoni miracidia. We then measured the effects of this timing on infection prevalence, infection intensity of E. caproni metacercariae, and cercarial output of S. mansoni, as well as on snail reproduction and survival. Snails infected only with S. mansoni and snails exposed to E. caproni after S. mansoni both shed more cercariae than simultaneously exposed snails. Additionally, S. mansoni prevalence was lower in snails that were first exposed to E. caproni compared to snails that were exposed to E. caproni after S. mansoni. Moreover, snails exposed to E. caproni before S. mansoni did not differ in their survival compared to control snails, whereas simultaneously exposed snails and snails exposed to E. caproni after S. mansoni had lower survival than control snails. Combined, this prevalence and survival data suggest a potential protective role of early E. caproni exposure. The timing of E. caproni exposure impacts S. mansoni establishment and reproduction, but host survival patterns are likely driven by S. mansoni prevalence alone.

Trichinella spiralis-derived extracellular vesicles induce a protective immunity against larval challenge in mice.

Human trichinellosis is a serious disease with no effective treatment till now. Recently, the protective immunity induced by parasite-derived extracellular vesicles (EVs) are studied for some parasites such as Echinostoma caproni. The current study aimed to investigate the novel Trichinella spiralis-derived EVs as a potential vaccine candidate for the first time in a mouse model. Trichinella spiralis EVs were isolated and identified using transmission electron microscopy, gel electrophoresis, protein content measurements, and beads-based flow cytometry. Vaccination was done by subcutaneous injection of two doses of 3.5μg T. spiralis-derived EVs. We observed a significant reduction in T. spiralis adult worm and muscle larval counts in mice immunized with T. spiralis-derived EVs (EVs-Ts group) and controlled inflammatory changes in the intestine and muscles. The EVs-Ts group showed a higher level of IFN- γ, whereas the IL-4 secretion was elevated more in the EVs group (EVs group) and showed a lower level after challenge with T. spiralis infection (EVs-Ts group). This implies a mixed Th1/Th2 immune response with obvious Th1 polarization. Moreover, elevation of serum T. spiralis-specific IgG was reported. In conclusion, this preliminary study provides T. spiralis EVs as a promising candidate for future development of anti-Trichinella vaccine.

Changes in resident microbiota associated with mice susceptibility or resistance to the intestinal trematode Echinostoma caproni.

Echinostoma caproni (Trematoda: Echinostomatidae) is an intestinal trematode with no tissue phases in the definitive host that has been extensively used as an experimental model to study the factors that determine resistance against intestinal helminths. In E. caproni infections in mice, interleukin-25 (IL-25) plays a critical role and it is required for the resistance to infection. However, little is known on the factors that determine its production. Primary E. caproni infection in mice is characterized by the development of chronic infections and elevated worm recovery, in relation to a local Th1 response with elevated production of interferon-γ. However, partial resistance against secondary E. caproni infections in ICR (Institute of Cancer Research) mice is developed after the chemotherapeutic cure of a primary infection and the innately produced IL-25 after pharmacological treatment. In this paper, we analyse the potential role of intestinal microbiota in the production of IL-25, and the subsequent resistance to infection. For this purpose, we analysed the production of IL-25 under conditions of experimental dysbiosis and also the changes in the resident microbiota in primary infections, pharmacological curation and secondary infections. The results obtained showed that resident microbiota play a major role in the production of IL-25 and the appearance of members of the phylum Verrucomicrobia as a consequence of the curation of the primary infection could be related to the partial resistance to secondary infection.

Mitophylogenomics of the zoonotic fluke Echinostoma malayanum confirms it as a member of the genus Artyfechinostomum Lane, 1915 and illustrates the complexity of Echinostomatidae systematics.

The complete mitochondrial genome (mitogenome or mtDNA) of the trematode Echinostoma malayanum Leiper, 1911was fully determined and annotated. The circular mtDNA molecule comprised 12 protein-coding genes (PCGs) (cox1 - 3, cob, nad1 - 6, nad4L, atp6), two mitoribosomal RNAs (MRGs) (16S or rrnL and 12S or rrnS), and 22 transfer RNAs (tRNAs or trn), and a non-coding region (NCR) rich in long and short tandem repeats (5.5 LRUs/336bp/each and 7.5 SRUs/207bp/each). The atp8 gene is absent and the 3' end of nad4L overlaps the 5' end of nad4 by 40bp. Special DHU-arm missing tRNAs for Serine were found for both tRNASer1(AGN) and tRNASer2(UCN). Codons of TTT (for phenylalanine), TTG (for leucine), and GTT (for valine) were the most, and CGC (for Arginine) was the least frequently used. A similar usage pattern was seen in base composition, AT and GC skewness for PCGs, MRGs, and mtDNA* (coding cox3 to nad5) in E. malayanum and Echinostomatidae. The nucleotide use is characterized by (T > G > A > C) for PCGs/mtDNA*, and by (T > G ≈ A > C) for MRGs. E. malayanum exhibited the lowest genetic distance (0.53%) to Artyfechinostomum sufrartyfex, relatively high to the Echinostoma congeners (13.20-13.99%), higher toHypoderaeum conoideum (16.18%), and the highest to interfamilial Echinochasmidae (26.62%); Cyclocoelidae (30.24%); and Himasthlidae (25.36%). Topology indicated the monophyletic position between E. malayanum/A. sufrartyfex and the group of Echinostoma caproni, Echinostoma paraensei, Echinostoma miyagawai, and Echinostoma revolutum, rendering Hypoderaeum conoideum and unidentified Echinostoma species paraphyletic. The strictly closed genomic/taxonomic/phylogenetic features (including base composition, skewness, codon usage/bias, genetic distance, and topo-position) reinforced Echinostoma malayanum to retake its generic validity within the Artyfechinostomum genus.

Morphological and molecular characterization of larval trematodes infecting the assassin snail genus Anentome in Thailand.

The assassin snail genus Anentome is widespread in Southeast Asia, and is distributed all over the world via the aquarium trade. One species of genus Anentome, Anentome helena, is known to act as intermediate host of parasitic trematodes. This study investigates the taxonomic diversity of larval trematodes infecting A. helena and Anentome wykoffi in Thailand. Larval trematodes were identified by combining morphological and DNA sequence data (cytochrome c oxidase I and internal transcribed spacer 2). Species delimitation methods were used to explore larval trematode species boundaries. A total of 1107 specimens of Anentome sp. were collected from 25 localities in Thailand. Sixty-two specimens of A. helena (n = 33) and A. wykoffi (n = 29) were infected by zoogonid cercariae, heterophyid metacercariae and echinostome metacercariae, with an overall prevalence of 5.6% (62/1107) and population-level prevalences in the range of 0.0-22.3%. DNA sequence data confirmed that the larval trematodes belong to the families Echinostomatidae, Heterophyidae and Zoogonidae. As such, this is the first report of zoogonid cercariae and heterophyid metacercariae in A. helena, and echinostome metacercariae in A. wykoffi. Moreover, this study provides evidence of tentative species-level differentiation between Thai Echinostoma sp. and Cambodian Echinostoma mekongi, as well as within Echinostoma caproni, Echinostoma trivolvis and Echinostoma revolutum.

Host exposure history and priority effects impact the development and reproduction of a dominant parasite

Within a single organism, numerous parasites often compete for space and resources. This competition, together with a parasite’s ability to locate and successfully establish in a host, can contribute to the distribution and prevalence of parasites. Coinfection with trematodes in snail intermediate hosts is rarely observed in nature, partly due to varying competitive abilities among parasite taxa. Using a freshwater snail host (Biomphalaria glabrata), we studied the ability of a competitively dominant trematode, Echinostoma caproni, to establish and reproduce in a host previously infected with a less competitive trematode species, Schistosoma mansoni. Snails were exposed to S. mansoni and co-exposed to E. caproni either simultaneously or 1 week, 4 weeks, or 6 weeks post S. mansoni exposure. Over the course of infection, we monitored the competitive success of the dominant trematode through infection prevalence, parasite development time, and parasite reproductive output. Infection prevalence of E. caproni did not differ among co-exposed groups or between co-exposed and single exposed groups. However, E. caproni infections in co-exposed hosts took longer to reach maturity when the timing between co-exposures increased. All co-exposed groups had higher E. caproni reproductive output than single exposures. We show that although timing of co-exposure affects the development time of parasite transmission stages, it is not important for successful establishment. Additionally, co-exposure, but not priority effects, increases the reproductive output of the dominant parasite.

Effect of Echinostoma caproni on Presumptive Lactic Acid Bacteria Abundance and Salmonella enterica Serovar Typhimurium Colonization in the Mouse Gut.

Co-infections of mammalian hosts with intestinal helminths and bacterial pathogens are common, especially in areas with inadequate sanitation. Interactions between co-infecting species and host microbiota can cause significant changes in host immunity, disease severity, and pathogen transmission, requiring unique treatment for each case. A greater understanding of the influences of parasite-bacteria co-infections will improve diagnosis and therapeutic approaches to control infectious diseases. To study the influence of the trematode parasite Echinostoma caproni on commensal and pathogenic bacteria in the mouse gut, we examined the abundance of intestinal lactic acid bacteria and Salmonella enterica serovar Typhimurium in control mice not exposed to E. caproni (P-) or S. Typhimurium (S-), E. caproni-infected (P+S-), S. Typhimurium-infected (P-S+), and E. caproni-S. Typhimurium co-infected (P+S+) mice, and determined bacterial burdens in the livers and spleens of the P-S+ and P+S+ mice. We also examined a subset of P+S- and P+S+ mice for survival and the relative location of E. caproni in the small intestine. The numbers of presumptive lactic acid bacteria were significantly higher in the P+S+ and P-S+ mice compared to the uninfected mice, and S. Typhimurium colonization in the liver and spleen was significantly reduced in the P+S+ mice compared to the P-S+ mice. Echinostoma caproni were located anteriorly in the intestine of P+S- mice, while in the P+S+ mice, the parasites were distributed more posteriorly. Survival of E. caproni was unaffected in either group. The results of our study suggest that E. caproni facilitates a higher abundance of presumptive lactic acid bacteria in the mouse intestine and reduces colonization of S. Typhimurium in the liver and spleen of the co-infected host.

Interleukin-25-mediated resistance against intestinal trematodes does not depend on the generation of Th2 responses

BackgroundThe cytokine interleukin-25 (IL-25) is recognized as the most relevant initiator of protective T helper 2 (Th2) responses in intestinal helminth infections. This cytokine induces resistance against several species of intestinal helminths, including the trematode Echinostoma caproni. E. caproni has been extensively used as an experimental model to study the factors determining resistance to intestinal infections. In the study reported here, we assessed the role of IL-25 in the generation of resistance in mice infected with E. caproni.MethodsThe factors that determine the production of IL-25 in mice experimentally infected with E. caproni were determined, as were the consequences of IL-25 production in terms of polarization of the immune response and resistance to infection.ResultsOur results show that the role of IL-25 in the polarization of the immune response differs between the primary and secondary immune responses. IL-25 is required for the development of a Th2 phenotype in primary E. caproni infections, but it can also promote the differentiation to Th2 memory cell subsets that enhance type-2 immunity in memory responses. However, the development of Th2 responses does not induce resistance to infection. The Th2 phenotype does not elicit resistance, and IL-25 is responsible for the resistance regardless of its type-2 cytokine activity and activation of signal transducer and activator of transcription (STAT6). Alternative activation of macrophages induced by IL-25 can be implicated in the resistance to infection.ConclusionsIn contrast to primary infection, secondary infection elicits a type-2 immune response even in the absence of IL-25 expression. Despite the development of a type-2 response, mice are susceptible to secondary infection associated with the lack of IL-25. Resistance to infection is due to the production of IL-25, which acts autonomously from Th2 response in terms of parasite clearance.Graphical

Molecular characterisation and vaccine efficacy of two novel developmentally regulated surface tegument proteins of Fasciola hepatica

The surface tegument of Fasciola hepatica is a crucial tissue due to its key role at the host-parasite interface. We characterised three novel proteins, termed Fhteg1, Fhteg5 and Fhteg8, that are found in the tegument membrane fraction of adult F. hepatica. Bioinformatic analysis of proteomic datasets identified Fhteg5 and Fhteg8 as tegumental glycoproteins and revealed that Fhteg1, Fhteg5 and Fhteg8 are associated with exosomes of adult F. hepatica. Fhteg1, Fhteg5 and Fhteg8 appear to be related to uncharacterised sequences in F. gigantica, Fasciolopsis buski, Echinostoma caproni, Clonorchis sinensis, Opisthorchis viverrini, Schistosoma japonicum and S. mansoni, although F. hepatica appears to have expanded this family. Fhteg1 and Fhteg5 were characterised in detail. The Fhteg1 and Fhteg5 gene transcripts each demonstrate significant upregulation in juvenile fluke 2–4 days post-excystment, with transcript levels maintained during development over 3 weeks in vitro. RNAseq data showed that both Fhtegs are expressed in the adult life stage, although the transcript levels were about 8 fold lower than those in juveniles (3 week post infection). Using immunocytochemistry, Fhteg1 and Fhteg5 were each shown to be expressed in cells adjacent to the muscle layer as well as on the surface of 1 week old juveniles, whilst Fhteg5 was also present in cells at the base of the pharynx. RNAi mediated knockdown of Fhteg1 and Fhteg5 transcripts in 4–10 day old juveniles had no effect on parasite survival, movement or growth in vitro. Although no IgG responses were observed for Fhteg1 or Fhteg5 during infection in sheep and cattle, both proteins elicited a low IgG response in a proportion of infected rats. Rats vaccinated with Fhteg1 and Fhteg5 showed good IgG responses to both proteins and a mean 48.2 % reduction in worm burden following parasite challenge. Although vaccination of cattle with both proteins induced a range of IgG responses, no protection was observed against parasite challenge. This is the first study to provide insights into the molecular properties of two novel, developmentally regulated surface tegument proteins in F. hepatica.

The Road Not Taken: Host Infection Status Influences Parasite Host-Choice

The manipulation of host organisms by their parasites has captured the attention of ecologists, parasitologists, and the public. However, our knowledge of parasite behavior independent of a host is limited despite the far-reaching implications of parasite behavior. Parasite behaviors can help explain trematode community structure, the aggregation of parasites within host populations, and can potentially be harnessed in biocontrol measures. In this study, we used a simple choice chamber design to examine whether trematode parasites can detect the infection status of a potential host and avoid hosts infected with a competitively dominant species. Our results show that Schistosoma mansoni, a competitively subordinate species, can detect and avoid hosts infected with a competitively dominant parasite, Echinostoma caproni. However, E. caproni, despite showing a significant preference for snails infected with S. mansoni over uninfected snails, showed little ability to detect the infection status of the host or even the host's presence. We propose subordinate species may be under stronger selection to avoid dominant competitors whereas dominant competitors may be more strongly selected to find any suitable host, regardless of infection status. Previous research has focused on parasites distinguishing between 'host' and 'non-host', which does not fully capture the complexity of these interactions. However, the ability of subordinate parasites to determine the infection status of a host results in a consistent evolutionary advantage.

Secreted cathepsin L-like peptidases are involved in the degradation of trapped antibodies on the surface of Echinostoma caproni.

Antibody trapping is a recently described strategy for immune evasion observed in the intestinal trematode Echinostoma caproni, which may aid to avoiding the host humoral response, thus facilitating parasite survival in the presence of high levels of local-specific antibodies. Parasite-derived peptidases carry out the degradation of trapped antibodies, being essential for this mechanism. Herein, we show that cathepsin-like cysteine endopeptidases are active in the excretory/secretory products (ESPs) of E. caproni and play an important role in the context of antibody trapping. Cysteine endopeptidase activity was detected in the ESPs of E. caproni adults. The affinity probe DCG-04 distinguished a cysteine peptidase band in ESPs, which was specifically recognized by an anti-cathepsin L heterologous antibody. The same antibody localized this protein in the gut and syncytial tegument of adult worms. Studies with cultured parasites showed that in vivo-bound antibodies are removed from the parasite surface in the absence of peptidase inhibitors, while addition of cathepsin L inhibitor prevented their degradation. These results indicate that cathepsin L-like peptidases are involved in the degradation of surface-trapped antibodies and suggest that cysteine peptidases are not only crucial for tissue-invading trematodes, but they can be equally relevant at the parasite-host interface in gut-dwelling flukes.

Mini-FLOTAC as an alternative, non-invasive diagnostic tool for Schistosoma mansoni and other trematode infections in wildlife reservoirs

BackgroundSchistosomiasis and food-borne trematodiases are not only of major public health concern, but can also have profound implications for livestock production and wildlife conservation. The zoonotic, multi-host nature of many digenean trematodes is a significant challenge for disease control programmes in endemic areas. However, our understanding of the epidemiological role that animal reservoirs, particularly wild hosts, may play in the transmission of zoonotic trematodiases suffers a dearth of information, with few, if any, standardised, reliable diagnostic tests available. We combined qualitative and quantitative data derived from post-mortem examinations, coprological analyses using the Mini-FLOTAC technique, and molecular tools to assess parasite community composition and the validity of non-invasive methods to detect trematode infections in 89 wild Hubert’s multimammate mice (Mastomys huberti) from northern Senegal.ResultsParasites isolated at post-mortem examination were identified as Plagiorchis sp., Anchitrema sp., Echinostoma caproni, Schistosoma mansoni, and a hybrid between Schistosoma haematobium and Schistosoma bovis. The reports of E. caproni and Anchitrema sp. represent the first molecularly confirmed identifications for these trematodes in definitive hosts of sub-Saharan Africa. Comparison of prevalence estimates derived from parasitological analysis at post-mortem examination and Mini-FLOTAC analysis showed non-significant differences indicating comparable results between the two techniques (P = 1.00 for S. mansoni; P = 0.85 for E. caproni; P = 0.83 for Plagiorchis sp.). A Bayesian model, applied to estimate the sensitivities of the two tests for the diagnosis of Schistosoma infections, indicated similar median posterior probabilities of 83.1% for Mini-FLOTAC technique and 82.9% for post-mortem examination (95% Bayesian credible intervals of 64.0–94.6% and 63.7–94.7%, respectively).ConclusionsOur results showed that the Mini-FLOTAC could be applied as an alternative diagnostic technique for the detection of the zoonotic S. mansoni and other trematodes in rodent reservoirs. The implementation of non-invasive diagnostics in wildlife would offer numerous advantages over lethal sampling methodologies, with potential impact on control strategies of zoonotic helminthiases in endemic areas of sub-Saharan Africa and on fostering a framework of animal use reduction in scientific practice.

The complete mitochondrial genome of Echinostoma miyagawai: Comparisons with closely related species and phylogenetic implications

Echinostoma miyagawai (Trematoda: Echinostomatidae) is a common parasite of poultry that also infects humans. Es. miyagawai belongs to the “37 collar-spined” or “revolutum” group, which is very difficult to identify and classify based only on morphological characters. Molecular techniques can resolve this problem. The present study, for the first time, determined, and presented the complete Es. miyagawai mitochondrial genome. A comparative analysis of closely related species, and a reconstruction of Echinostomatidae phylogeny among the trematodes, is also presented. The Es. miyagawai mitochondrial genome is 14,416 bp in size, and contains 12 protein-coding genes (cox1–3, nad1–6, nad4L, cytb, and atp6), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rRNAs), and one non-coding region (NCR). All Es. miyagawai genes are transcribed in the same direction, and gene arrangement in Es. miyagawai is identical to six other Echinostomatidae and Echinochasmidae species. The complete Es. miyagawai mitochondrial genome A + T content is 65.3%, and full-length, pair-wise nucleotide sequence identity between the six species within the two families range from 64.2–84.6%. The Es. miyagawai sequences is most similar to Echinostoma caproni. Sequence difference are 15.0–33.5% at the nucleotide level, and 8.6–44.2% at the amino acid level, among the six species, for the 12 protein-coding genes. ATG and TAG are the most common initiation and termination codons, respectively. Twenty of the Es. miyagawai transfer RNA genes transcribe products of the conventional cloverleaf structure, while two of the transfer RNA genes, namely trnS1(AGC) and trnS2(UGA), have unpaired D-arms. Phylogenetic analyses using our mitochondrial data indicate that Es. miyagawai is closely related to other Echinostomatidae species, except for Echinostoma hortense, which forms a distinct paraphyletic branch, and Echinochasmus japonicus, which is outside the clade containing all other Echinostomatidae species. These phylogenetic results support the elevation of subfamily Echinostomatidae. Our dataset also provides a significant resource of molecular markers to study the taxonomy, population genetics, and systematics of the echinostomatids.

Reproduction of Echinostoma caproni mother sporocysts (Trematoda).

The localisation and the composition of germinal material in miracidia and mother sporocysts of Echinostoma caproni were studied with the use of histological and electron microscopic methods. Germinal material in miracidia was localised in the posterior body half and was represented by 3-4 undifferentiated cells and 5-7 germinal cells. Taken together, these cells are referred to as the primordium of the germinal mass. In the mother sporocyst, germinal elements also form and develop in the germinal mass, which is located caudally. It comprises undifferentiated cells and germinal cells as well as embryos of various ages (up to the stage of 30-50 blastomeres). Germinal cells divide only by cleavage. New germinal cells are formed only from undifferentiated cells, which can proliferate in the germinal mass and nowhere else. This indicates that the germinal mass is the reproductive organ of E. caproni mother sporocyst.

Adaptation of the secretome of Echinostoma caproni may contribute to parasite survival in a Th1 milieu.

Echinostoma caproni (Trematoda: Echinostomatidae) is an intestinal trematode, broadly employed to study the host-dependent mechanisms that govern the evolution of intestinal helminth infections. Resistance against E. caproni homologous secondary infections has been reported in mice and appears to be related to the generation of a local Th2 response, whereas Th1 responses promote the development of chronic primary infections. Herein, the ability of E. caproni to modulate its secretome according to the host environment is investigated. A two-dimensional differential in gel electrophoresis (2D-DIGE) analysis was performed to elucidate changes in the excretory/secretory products of E. caproni adults after primary and secondary infections in mice. A total of 16 protein spots showed significant differences between groups, and 7 of them were successfully identified by mass spectrometry. Adult worms exposed to a primary infection appear to upregulate proteins involved in detoxification (aldo-keto reductase), stress response (GroEL), and enhancement of parasite survival (acetyl-CoA A-acetyltransferase and UTP-glucose-1-phosphate urydyltransferase). In contrast, any protein was found to be significantly upregulated after secondary infection. Upregulation of such proteins may serve to withstand the hostile Th1 environment generated in primary infections in mice. These results provide new insights into the resistance mechanisms developed by the parasites to ensure their long-term survival.

Nutrient availability modulates both host and parasite life histories in a snail-trematode interaction.

Host nutrient availability can have important life history consequences for hosts and their parasites. The responses of each participant within the association can vary extensively across host-parasite systems. In this paper, we outline the life history responses of the aquatic snail Biomphalaria glabrata and its trematode parasite Echinostoma caproni during host nutrient restriction. The onset of host starvation had rapid and strong effects on snail reproduction, significantly reducing egg output in control snails and eliminating egg production in infected individuals. The combination of E. caproni infection and nutrient restriction also had a dramatic effect on B. glabrata survival, with starved infected snails dying at a faster rate than hosts from any other treatment. In terms of parasite reproduction, host nutrient restriction did not influence the quantity of parasite larvae produced after starvation onset but did influence parasite quality, reducing both larval swimming time and overall longevity. Together these results demonstrate that nutrient restriction can strongly influence both host and parasite life histories, and therefore should be considered in future studies attempting to understand patterns of disease in host populations.

Specific Pathogen Recognition by Multiple Innate Immune Sensors in an Invertebrate.

Detection of pathogens by all living organisms is the primary step needed to implement a coherent and efficient immune response. This implies a mediation by different soluble and/or membrane-anchored proteins related to innate immune receptors called PRRs (pattern-recognition receptors) to trigger immune signaling pathways. In most invertebrates, their roles have been inferred by analogy to those already characterized in vertebrate homologs. Despite the induction of their gene expression upon challenge and the presence of structural domains associated with the detection of pathogen-associated molecular patterns in their sequence, their exact role in the induction of immune response and their binding capacity still remain to be demonstrated. To this purpose, we developed a fast interactome approach, usable on any host–pathogen couple, to identify soluble proteins capable of directly or indirectly detecting the presence of pathogens. To investigate the molecular basis of immune recognition specificity, different pathogens (Gram-positive bacterium, Micrococcus luteus; Gram-negative, Escherichia coli; yeast, Saccharomyces cerevisiae; and metazoan parasites, Echinostoma caproni or Schistosoma mansoni) were exposed to hemocyte-free hemolymph from the gastropod Biomphalaria glabrata. Twenty-three different proteins bound to pathogens were identified and grouped into three different categories based on their primary function. Each pathogen was recognized by a specific but overlapping set of circulating proteins in mollusk’s hemolymph. While known PRRs such as C-type lectins were identified, other proteins not known to be primarily involved in pathogen recognition were found, including actin, tubulin, collagen, and hemoglobin. Confocal microscopy and specific fluorescent labeling revealed that extracellular actin present in snail hemolymph was able to bind to yeasts and induce their clotting, a preliminary step for their elimination by the snail immune system. Aerolysin-like proteins (named biomphalysins) were the only ones involved in the recognition of all the five pathogens tested, suggesting a sentinel role of these horizontally acquired toxins. These findings highlight the diversity and complexity of a highly specific innate immune sensing system. It paves the way for the use of such approach on a wide range of host–pathogen systems to provide new insights into the specificity and diversity of immune recognition by innate immune systems.

Antibody trapping: A novel mechanism of parasite immune evasion by the trematode Echinostoma caproni.

BackgroundHelminth infections are among the most prevalent neglected tropical diseases, causing an enormous impact in global health and the socioeconomic growth of developing countries. In this context, the study of helminth biology, with emphasis on host-parasite interactions, appears as a promising approach for developing new tools to prevent and control these infections.Methods/Principal findingsThe role that antibody responses have on helminth infections is still not well understood. To go in depth into this issue, work on the intestinal helminth Echinostoma caproni (Trematoda: Echinostomatidae) has been undertaken. Adult parasites were recovered from infected mice and cultured in vitro. Double indirect immunofluorescence at increasing culture times was done to show that in vivo-bound surface antibodies become trapped within a layer of excretory/secretory products that covers the parasite. Entrapped antibodies are then degraded by parasite-derived proteases, since protease inhibitors prevent for antibody loss in culture. Electron microscopy and immunogold-labelling of secreted proteins provide evidence that this mechanism is consistent with tegument dynamics and ultrastructure, hence it is feasible to occur in vivo. Secretory vesicles discharge their content to the outside and released products are deposited over the parasite surface enabling antibody trapping.Conclusion/SignificanceAt the site of infection, both parasite secretion and antibody binding occur simultaneously and constantly. The continuous entrapment of bound antibodies with newly secreted products may serve to minimize the deleterious effects of the antibody-mediated attack. This mechanism of immune evasion may aid to understand the limited effect that antibody responses have in helminth infections, and may contribute to the basis for vaccine development against these highly prevalent diseases.

Subcutaneous injection of exosomes reduces symptom severity and mortality induced by Echinostoma caproni infection in BALB/c mice

Recent studies have shown the importance of exosomes in the host-parasite relationship. These vesicles are an important part of the excretory/secretory pathway for proteins with the potential to alter immune responses. Therefore, in the present study, we examined the immunomodulatory role of exosomes in BALB/c mice using Echinostoma caproni as an experimental model of intestinal helminth infection. For this purpose, BALB/c mice were injected twice s.c. with purified exosomes of E. caproni, followed by experimental infection. We report a delay in the development of the parasite in mice immunised with exosomes, a concomitant reduced symptom severity and increased survival upon infection. Immunisations with exosomes evoked systemic antibody responses with high levels of IgM and IgG. IgG1, IgG2b and IgG3 are the subtypes responsible for the IgG increase. These antibodies showed specific recognition of exosomal proteins, indicating that these vesicles carry specific antigens that are involved in the humoral response. The administration of exosomes induced an increase of IFN-γ, IL-4 and TGF-β levels in the spleen of mice prior to infection. The subsequent infection with E. caproni resulted in a further increase of IL-4 and TGF-β, together with an abrupt overproduction of IL-10, suggesting the development of a Th2/Treg immune response. Our results show that the administration of exosomes primes the immune response in the host, which in turn can contribute to tolerance of the invader, reducing the severity of clinical signs in E. caproni infection.

The Role of Light and Dark on the Dispersal and Transmission ofEchinostoma caproni(Digenea: Echinostomatidae) Cercariae

ABSTRACT: Abiotic stimuli are critical in the dispersal and transmission of trematode cercariae from the first intermediate host to the next host in the life cycle. The role of 2 abiotic stimuli, light and gravity, were examined in the dispersal and transmission of the cercariae of Echinostoma caproni in a laboratory setting. Nearly 100% of cercariae placed in a vertical chamber that permitted upward migration with a marginal probability of return swam to the surface in both light and dark conditions, suggesting that a positive phototaxis is not involved in dispersal and that a negative geotaxis may be the critical component in the vertical migration. The presence of a sentinel snail (Biomphalaria glabrata) in the bottom portion of the transmission chamber resulted in a significant reduction of cercariae dispersing upward and a significantly higher intensity of metacercariae in snails under lighted conditions than in the dark. In a light/dark choice experiment the prevalence and intensity of metacercaria...