Fasciola gigantica: Ultrastructural cytochemistry of the tegumental surface in newly- excysted metacercariae and in vitro-penetrated juvenile flukes informs a concept of parasite defence at the interface with the host

Cytochemical staining techniques were carried out en bloc with in vitro excysted and gut-penetrated Fasciola gigantica larvae in order to visualise the glycocalyx of the tegument, a structure which comprises the parasite component of the host-parasite interface, yet is incompletely preserved by conventional fixation and preparation techniques for electron microscopy. Positive reactivity with ruthenium red and periodic acid-thiocarbohydrazine-osmium (PATCO) techniques revealed that the glycocalyx is polyanionic and carbohydrate-rich throughout its depth. It comprises a trilaminate arrangement, with a thin dense zone and fibrillar layer closely apposed to the outer aspect of the apical plasma membrane, invested by an irregular thick mucopolysaccharide capsule. The latter, not recorded in adult flukes, may represent a specific adaptation to facilitate invasion in the face of host immunity, and may also protect the parasite surface from the action of host- and parasite-derived proteases. Early in the invasion of a naïve host, the glycocalyx may be partly responsible for triggering the responses of innate immunity, while later in infection, or when an anamnestic response is initiated in an immunocompetent host, the antibodies and activated lymphocytes of specific acquired immunity are invoked to interact with the parasite surface. The cytochemical properties of the glycocalyx, together with its potential for dynamic turnover due to exocytosis of the T0 tegumental secretory bodies, are likely to aid neutralisation of potentially damaging immune effectors and ensure their removal from the vicinity of the parasite by sloughing in complex with glycocalyx components.

In-plate recapturing of a dual-tagged recombinant Fasciola antigen (FhLAP) by a monoclonal antibody (US9) prevents non-specific binding in ELISA

Recombinant proteins expressed in E. coli are frequently purified by immobilized metal affinity chromatography (IMAC). By means of this technique, tagged proteins containing a polyhistidine sequence can be obtained up to 95% pure in a single step, but some host proteins also bind with great affinity to metal ions and contaminate the sample. A way to overcome this problem is to include a second tag that is recognized by a preexistent monoclonal antibody (mAb) in the gene encoding the target protein, allowing further purification. With this strategy, the recombinant protein can be directly used as target in capture ELISA using plates sensitized with the corresponding mAb. As a proof of concept, in this study we engineered a Trichinella-derived tag (MTFSVPIS, recognized by mAb US9) into a His-tagged recombinant Fasciola antigen (rFhLAP) to make a new chimeric recombinant protein (rUS9-FhLAP), and tested its specificity in capture and indirect ELISAs with sera from sheep and cattle. FhLAP was selected since it was previously reported to be immunogenic in ruminants and is expressed in soluble form in E. coli, which anticipates a higher contamination by host proteins than proteins expressed in inclusion bodies. Our results showed that a large number of sera from non-infected ruminants (mainly cattle) reacted in indirect ELISA with rUS9-FhLAP after single-step purification by IMAC, but that this reactivity disappeared testing the same antigen in capture ELISA with mAb US9. These results demonstrate that the 6XHis and US9 tags can be combined when double purification of recombinant proteins is required.

Functional analysis of novel aquaporins from Fasciola gigantica

Fascioliasis, caused by liver flukes of the genus Fasciola, is an important disease of ruminants. In order to identify a potential new drug target we have studied aquaporin (AQP) in Fasciola gigantica. AQPs facilitate the transport of water, glycerol and other small solutes across biological membranes. The structure, function, and pathology of AQPs have been extensively studied in mammals but data for AQPs from trematodes is still limited. In the present study, we have functionally characterized two closely related AQP isoforms, FgAQP-1 and FgAQP-2, from the trematode F. gigantica. Immunohistochemical analysis located the FgAQPs in the tegumental cells, their processes and the tegument itself. In addition, they were present in the epithelial linings of testes and ovary. Expression in Xenopus oocytes of these FgAQPs increased osmotic water permeability 3-4-fold but failed to increase glycerol and urea permeability. AQPs have two highly conserved NPA motifs that are important for the function of the channel pore. In FgAQP-1 and FgAQP-2 the first NPA motif is changed to TAA. Substitution of Thr with Asn in the TAA motif of FgAQP-1 increased its water permeability twofold but did not affect urea and glycerol impermeability while the substitution at the pore mouth of Cys204 by Tyr caused loss of water permeability. In addition, the FgAQPs did not increase methylamine and ammonia permeability after expression in yeast. In comparison to rat AQP-1 the described FgAQPs showed low water permeability and further in vivo analyses are necessary to determine their contribution to osmoregulation in Fasciola.

Evaluation of the diagnostic potential of different immunological techniques using polyclonal antibodies against Fasciola gigantica excretory/secretory antigens in sheep

The early detection of Fasciola antigens (Ags) in serum or stool could be more valuable in diagnosis as early treatment would be applied before irreparable damage occurs. In this study, fresh adult Fasciola gigantica (F. gigantica) worms were cultivated for 16 hrs. Excretory/secretory (E/S) Ags were extracted from the culturemedium and used to raise rabbit antibodies (Abs) to Fasciola. The purified Abs were then used in sandwich ELISA (S-ELISA) to detect Fasciola Ags in serum and stool samples from a total of 152 sheep, and sandwich-Dot-ELISA (S-D-ELISA) for the serum samples. Gross inspection of liver for flukes or other parasites was performed and results of parasitological stool examination were recorded. Accordingly, sheep were divided into healthy control group (25 sheep), Fasciola positive group (97 sheep) and other helminthic infection groups (30 sheep). S-ELISA for serum samples showed 91.9% sensitivity and 89% specificity. Fasciola Ags, detected in serum of sheep by S-D-ELISA, showed 97.2% sensitivity and 95% specificity and coproantigens detected by S-ELISA, showed 95.8% sensitivity and 92.7% specificity. Although, the specificity of stool examination was higher than that recorded for serum, the sensitivity of ELISA techniques to diagnose Fasciola Ags was higher than that recorded for parasitological examination. It is concluded that, S-D-ELISA has better sensitivity and specificity than S-ELISA for both stool and serum, and may prove useful for field applications.

Immunolocalization of cytoskeletal components in the tegument of the 3-week-old juvenile and adult Fasciola gigantica

Components of three cytoskeletal elements, namely, microtubule, intermediate and actin filaments have been localised in the tegument of the 3-week-old juvenile and adult Fasciola gigantica by means of immunofluorescence and immunoperoxidase techniques, using mouse monoclonal anti-alpha-tubulin, anti-cytokeratin antibodies and biotinylated-phalloidin, respectively. The immunostaining with the above probes were also performed in adult Schistosoma mansoni for comparison. The presence of tubulin, indicative of microtubules, was demonstrated in the tegumental cell bodies, their cytoplasmic processes, and the basal layer of the tegumental syncytium of F. gigantica. While in S. mansoni, tubulin appeared as vertical lines stretching across the whole thickness of the syncytium. Cytokeratin, representing one type of intermediate filaments, was detected in the tegumental cell bodies, their cytoplasmic processes, tegumental syncytium and spines of F. gigantica. In contrast, cytokeratin was evident only in the syncytium of S. mansoni, but not in the spines. Phalloidin, which could bind to actin, a subunit of microfilament, was detected in the tegumental cell bodies, their processes, and the microtrabecular network which form the scaffold of the tegumental syncytium of F. gigantica. In S. mansoni, actin was localized in similar tissues except the syncytium was not stained while spines exhibited intense staining. In F. gigantica, the presence of microtubules and actin filaments in the tegumental cells, their processes and in the syncytium could mediate the movement of secretory granules from the cell bodies towards the basal as well as the apical layer of the tegument. Cytokeratin filaments may serve to reinforce the integrity of the tegumental syncytium as well as the spines.

Molecular and immunological characterisation of Fasciola species

Fasciola hepatica and F. gigantica are polymorphic liver flukes that show considerable overlap between species, and various protein separation techniques have been used as alternative means of differentiation. Acid and alkaline polyacrylamide gel electrophoresis (PAGE) show differences between F. hepatica and F. gigantica. Following SDS-PAGE, F. hepatica proteins are characterised by the presence of eight major peptide bands, with molecular weights estimated as 48, 45, 43.5, 37, 33, 29, 27 and 25.5 kDa. In contrast, F. gigantica shows only five major protein bands of 57.6, 54, 48, 29 and 27 kDa. Isoelectric focusing (IEF) demonstrates 17 bands from F. hepatica and 22 bands from F. gigantica between pH 3.5 and pH 10. Although many bands appear common to both species, some are species-specific. Six cases of human acute fascioliasis diagnosed clinically, haematologically and immunologically are also studied. Gel immunodiffusion and immunoelectrophoresis, using adult F. hepatica and F. gigantica antigens, are used to determine the species, and indicate that the antisera are more specific for F. hepatica.

Identification of the Egyptian species of Fasciola

Reports on the species of Fasciola present in the Nile Delta, Egypt, appear controversial. Some authors reported the presence of both Fasciola gigantica and Fasciola hepatica, others reported F. gigantica only and mentioned that F. hepatica was found only in imported animals. This study was an attempt to identify the species of Fasciola flukes collected from locally bred animals. Morphologic, morphoanatomic, morphometric, and chemotaxonomic criteria of the fluke isolates were studied. Speciation based on morphologic and morphometric data was not decisive due to overlap in the values of most measurements. Morphoanatomic data proved the presence of both the species, and isoelectric focusing (IEF) of fluke soluble protein confirmed the presence of both F. gigantica and F. hepatica in Egypt.

The liver flukes Fasciola gigantica and Fasciola hepatica express the leucocyte cluster of differentiation marker CD77 (globotriaosylceramide) in their tegument

Glycosphingolipids from the parasitic liver flukes Fasciola gigantica and Fasciola hepatica were isolated and their carbohydrate moieties were structurally analysed by methylation analysis, exoglycosidase treatment, on-target exoglycosidase cleavage and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. For both liver fluke species, the ceramide monohexosides Gal1-ceramide and Glc1-ceramide were found in relative amounts of 1.0 to 0.1, respectively. From F. gigantica, the ceramide dihexoside was isolated in sufficient amounts to be structurally determined as lactosylceramide, Gal beta4-Glc1-ceramide, while for both liver fluke species the ceramide trihexoside was shown to be Gal alpha4Gal beta4-Glc1-ceramide, which is designated as either globotriaosylceramide, Pk-blood group antigen or CD77 leucocyte cluster of differentiation antigen. To our knowledge, this is the first report on the expression of globo-series glycosphingolipids in non-mammalian species. Ceramide analysis of ceramide monohexosides yielded as major components octadecanoic and 2-hydroxyoctadecanoic fatty acids together with C18- and C20-phytosphingosines. By the use of an anti-CD77 monoclonal antibody and the Escherichia coli Shiga toxin B1 subunit, globotriaosylceramide could be immunolocalised to the tegument of F. hepatica cryosections. The sharing of CD77 between liver flukes and their mammalian hosts fits in with the concept of molecular mimicry, which is closely parallel to the established imitation of host CD15 (Lewis X) displayed by the blood fluke Schistosoma mansoni.

Banding patterns of Fasciola hepatica and Fasciola gigantica (Trematoda) by isoelectric focusing

Liver flukes Fasciola hepatica and Fasciola gigantica are polymorphic and vary morphologically depending upon the host being parasitized. It is known also that mixed infection occurs where both species are present. A technique involving protein separation was used to distinguish the 2 species. Isoelectric focusing of soluble proteins was performed on polyacrylamide gels using whole-body proteins from adult flukes. Although many bands appeared common to both species and some were shared with host tissues, the banding patterns could be used to distinguish 1 species from the other. Soluble protein isoelectric focusing is simple, reproducible, and has very good resolution. It seems well suited to the differentiation of the 2 fluke species.

Glycogen, protein and lipid content of adult Fasciola gigantica (Trematoda)

The concentration of carbohydrates, proteins, and lipids in the whole worm, gut, and body musculature of Fasciola gigantica was investigated from worms collected from cattle slaughtered in the Jos abattoir. Protein accounted for the highest concentration of the constituents constituting 62.59 +/- 0.86% of the dry weight of the fluke. This was followed by lipid with 28.15 +/- 0.86% of the dry weight while carbohydrate (glycogen) was 6.29 +/- 0.11% of the dry weight. Thin-layer chromatography revealed the presence of six distinct bands of neutral lipids, namely: monoglycerides, 1,2-diglycerides, 1,3-diglycerides, free fatty acids, triglycerides and sterol esters from both whole worm homogenate and fractions of the gut and muscle tissues. In the case of phospholipids, lysophosphatidyl choline, sphingomyeline, phosphatidyl choline and phosphatidyl-ethanol amine were recovered. When the free fatty acids were subjected to further fractionation, palmitic, stearic, as well as oleic acids were recovered in appreciable quantities indicating that lipids are being catabolized in these trematodes.