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PubMed1990

A technique for identification of cercariae of Schistosoma haematobium, S. curassoni, S. bovis and S. intercalatum.

The chaetotaxy of 84 samples or isolates of Schistosoma spp. from western or central Africa has been studied. Three indices were calculated for cercariae of each sample; their average value, the skewness and kurtosis of each indice was established. Each species (S. haematobium, S. curassoni, S. bovis and S. intercalatum) was discriminated with nine variables. The present work gives information to assess, specific diagnosis with simple calculations easily achieved on a small computer.

Animals↗
PubMed2005

DC-SIGN mediates binding of dendritic cells to authentic pseudo-LewisY glycolipids of Schistosoma mansoni cercariae, the first parasite-specific ligand of DC-SIGN.

During schistosomiasis, parasite-derived glycoconjugates play a key role in manipulation of the host immune response, associated with persistence of the parasite. Among the candidate host receptors that are triggered by glycoconjugates are C-type lectins (CLRs) on dendritic cells (DCs), which in concerted action with Toll-like receptors determine the balance in DCs between induction of immunity versus tolerance. Here we report that the CLR DC-SIGN mediates adhesion of DCs to authentic glycolipids derived from Schistosoma mansoni cercariae and their excretory/secretory products. Structural characterization of the glycolipids, in combination with solid phase and cellular binding studies revealed that DC-SIGN binds to the carbohydrate moieties of both glycosphingolipid species with Galbeta1-4(Fucalpha1-3)GlcNAc (Lewis(X)) and Fucalpha1-3Galbeta1-4(Fucalpha1-3)GlcNAc (pseudo-Lewis(Y)) determinants. Importantly, these data indicate that surveying DCs in the skin may encounter schistosome-derived glycolipids immediately after infection. Recent analysis of crystals of the carbohydrate binding domain of DC-SIGN bound to Lewis(X) provided insight into the ability of DC-SIGN to bind fucosylated ligands. Using molecular modeling we showed that the observed binding of the schistosome-specific pseudo-Lewis(Y) to DC-SIGN is not directly compatible with the model described. To fit pseudo-Lewis(Y) into the model, the orientation of the side chain of Phe(313) in the secondary binding site of DC-SIGN was slightly changed, which results in a perfect stacking of Phe(313) with the hydrophobic side of the galactose-linked fucose of pseudo-Lewis(Y). We propose that pathogens such as S. mansoni may use the observed flexibility in the secondary binding site of DC-SIGN to target DCs, which may contribute to immune escape.

Animals↗
PubMed2001

Fasciola hepatica: surfaces involved in movement of miracidia and cercariae.

Rapid freezing and substitution with fixative prior to scanning electron microscopy was used to demonstrate the pattern of beat and recovery of the cilia of free swimming miracidia of Fasciola hepatica. There were stages of dexioplectic metachronal co-ordination and the power stroke was approximately 15 degrees anticlockwise from the anterior-posterior axis. Around the circumference of the body of the miracidia there were approximately 12 metachronal waves of power and recovery. Free-swimming cercariae were recorded by time-lapse photography and, after conventional fixation, by scanning electron microscopy. Cercarial tail-beats were to the posterior of the body in the lateral plane at a rate of 8 Hz. The tail has paired lateral ridges positioned to act as leading edges. There is an array of 32 sensory papillae on the mid-ventral surface of the tail. The tegument of the most distal part of the tail is described: it is free of sensory endings and the surface shows a spiral pattern.

Animals↗
PubMed1984

A field-evolved differential filtration method for recovery of schistosome cercariae.

Modifications to Theron 's (1979) differential filtration technique are described which improve both sensitivity and reliability. Following pre-filtration to remove larger debris and some plankton, the sample is formalized; constant stirring prevents losses due to the cercarial stickiness normally caused by the fixation process. Once fixed, Schistosoma mansoni cercariae are reliably retained and well displayed on nylon monofilament cloth of 50 micrometers pore size. Such a coarse recovery filter permits very large samples to be processed and results in filters which are easy to read. Field comparison showed the method improved sensitivity by a factor of more than 20 times and laboratory evaluation indicated a recovery rate of over 80%.

Animals↗
PubMed1993

Immunity to Schistosoma mansoni in mice vaccinated with irradiated cercariae: cytokine interactions in the pulmonary protective response.

In C57BL/6 strain mice vaccinated with attenuated cercariae of Schistosoma mansoni, the major site of immune elimination of challenge parasites is the lungs. We have monitored pulmonary events after both vaccination and challenge by bronchoalveolar lavage, and examined the profile of cytokines released by recovered cells upon stimulation with larval antigens in vitro. From 14 days post-vaccination, lavage samples contain infiltrating lymphocytes which produce abundant interferon-gamma (IFN-gamma) and interleukin-3 (IL-3). We suggest that the lymphocytes recruited to the lungs are effector/memory cells of the Th1 subset. Challenge of vaccinated mice results in a second influx of IFN-gamma- and IL-3-secreting cells into the airways, earlier than after vaccination alone, or in appropriate controls. Ablation studies reveal that CD4+ T cells are the source of the IFN-gamma. The timing of cytokine production after both vaccination and challenge coincides with phases of macrophage activation already recorded, and with the presence of parasites in the lungs. Administration of monoclonal antibody directed against IFN-gamma, over the period of challenge elimination, almost completely abrogates protection in vaccinated mice, but does not affect the ratio of Th1:Th2 cells in the lungs. Immunity in this model is not, however, affected by inhibition of nitric oxide production, or neutralization of TNF. We suggest that the effector mechanism may operate by blocking parasite migration, and that loss of protection following neutralization of IFN-gamma may be attributed to changes in composition, density and cohesiveness of pulmonary foci.

Animals↗
PubMed1994

Identification and characterization of a UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalactosaminyltransferase from cercariae of the schistosome Trichobilharzia ocellata. Catalysis of a key step in the synthesis of N,N'-diacetyllactosediamino (lacdiNAc)-type glycans.

Three different stages of the avian schistosome Trichobilharzia ocellata appeared to contain a novel N-acetylgalactosaminyltransferase activity. To investigate its function in the biosynthesis of schistosome glycoconjugates, the enzyme was partially purified from cercariae, a free-living stage of the parasite, by affinity chromatography on UDP-Sepharose. Acceptor specificity studies showed that the enzyme catalyses the transfer of N-acetylgalactosamine (GalNAc) from UDP-GalNAc to oligosaccharides, glycopeptides and glycoproteins carrying a terminally beta-linked N-acetylglucosamine (GlcNAc) residue, regardless of the underlying structure. Analysis of the products obtained with GlcNAc and a desialylated and degalactosylated diantennary glycopeptide by 400 MHz 1H-NMR spectroscopy revealed that a GalNAc beta 1-->4GlcNAc (N,N'-diacetyllactosediamine,lacdiNAc) unit was formed. The enzyme can therefore be described as a UDP-GalNAc:GlcNAc beta-R beta 1-->4-N-acetylgalactosaminytransferase (beta 4-GalNAcT). Using specific acceptors, the enzyme could be distinguished from all other beta 4-GalNAcTs described to date, including the one from pituitary gland that is involved in the specific glycosylation of pituitary glycohormones. By contrast, the enzymatic properties of the schistosome beta 4-GalNAcT (except for the sugar-donor specificity) strongly resemble those of the beta 4-galactosyltransferase of higher animals, an enzyme which is known to control the synthesis of Gal1-->4GlcNAc (lacNAc)-type oligosaccharide chains. By analogy, the beta 4-GalNAcT is concluded to control the key step in the synthesis of lacdiNAc-type chains. LacdiNAc-type glycans are also common to the mollusc Lymnaea stagnalis, which is the intermediate host of T.ocellata. It is proposed that the schistosome beta 4-GalNAcT functions in the expression of specific carbohydrate structures that contribute to a molecular mimicry, enabling the schistosome to evade the defence system of the snail host.

Animals↗
PubMed1983

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae III. Identification of a mouse strain, P/N, that fails to respond to vaccination.

Eleven strains of inbred mice were examined for their ability to develop resistance to challenge Schistosoma mansoni infection as a result of previous exposure to homologous cercariae that had been attenuated by high-dose irradiation. Two strains, C57B1/6J and BALB/c, demonstrated consistently high levels of vaccine-induced immunity (means of 64% and 58% resistance, respectively, when compared to control groups of the same strain) and were designated as 'high responder' strains to vaccination. Six other strains fell into an intermediate category, demonstrating moderate, yet statistically significant, levels of immunity resulting from vaccination (means of 30-50% resistance). Only one of the strains examined consistently failed to respond to vaccination by the development of significant levels of immunity to challenge infection. Animals of the P/N strain demonstrated a mean of only 15% resistance to challenge in five experiments and have been classified as 'low responders' to vaccination. P/N mice have previously been characterized as deficient in their ability to mount delayed hypersensitivity reactions, produce lymphokine and display macrophage activation for cytolysis of extracellular and intracellular targets in other experimental systems, suggesting that these immune responses may be critical to the establishment of vaccine-induced resistance to S. mansoni infection. The availability of high and low responder mouse strains should facilitate a genetic approach to characterization of the immune effector mechanism(s) of vaccine-induced resistance to S. mansoni infection.

Animals↗
PubMed1985

Site potential for challenge attrition in mice, rats and guinea pigs vaccinated with irradiated cercariae of Schistosoma mansoni.

The potential sites of attrition of a challenge population of schistosomes have been investigated in mice, rats and guinea pigs vaccinated with irradiated cercariae of Schistosoma mansoni, by the use of challenge regimens that permit sequential site elimination. Vaccinated mice showed significant immunity to a percutaneous cercarial challenge, but were only marginally resistant to an i.v. challenge with healthy lung stage worms. Vaccinated rats and guinea pigs differed from mice, in that they were able to mediate significant challenge attrition at post-skin sites. Healthy lung worms were subject to immune elimination by rats in the lungs, or perhaps en route to the liver, but not in the liver itself. In contrast, guinea pigs had the capacity to kill challenge lung worms injected into either the lungs or the liver. Interestingly, lung worms harvested by extended incubation were shown to be sub-optimal in terms of viability, since they were eliminated in significant numbers when injected i.v. into vaccinated mice. These data show that different hosts vaccinated in essentially the same manner differ in terms of their site potential for challenge attrition. It is emphasised however, that sites implicated by these experiments as having the capacity to mediate immune elimination are not necessarily the sites at which challenge attrition occurs under normal circumstances.

Animals↗
PubMed1986

Schistosoma mansoni: liver phase challenge attrition is a stage-dependent phenomenon in guinea-pigs vaccinated with highly irradiated cercariae.

Guinea-pigs vaccinated with highly irradiated cercariae of Schistosoma mansoni have been examined for their ability to kill challenge parasites at the level of the liver. Skin and lung phase attrition were eliminated by surgical introduction of 4/5 day old schistosomula, or 2, 3 or 6 week schistosomes into the mesenteric vasculature of vaccinated and naive animals. These experiments showed consistently that lung schistosomula and 2 week old parasites were killed preferentially by sensitized animals, but that older worms were refractory. Liver phase immune elimination would therefore seem to be a stage-dependent phenomenon in the vaccinated guinea pig model of schistosomiasis.

Animals↗
PubMed1986

Inhibition of human peripheral blood mononuclear cell proliferative responses by released materials from Schistosoma mansoni cercariae.

During in vitro transformation of Schistosoma mansoni cercariae into schistosomula, surface and glandular materials are released into the culture medium. Extracts of these materials, termed cercarial released extracts 1 and 2 (CRE-1 and CRE-2), were analysed and found to consist primarily of protein and carbohydrate at ratios of 5:1 (CRE-1) and 7:1 (CRE-2). It was observed that inclusion of either CRE-1 or CRE-2 in cultures of human peripheral blood mononuclear cells (PBMN) led to decreased cell proliferation. This was true whether the cells were resting, control cultures or were stimulated with either phytohaemagglutinin or an antigenic preparation from adult S. mansoni worms. The inhibition was equally effective with PBMN of patients with active schistosomal infection or PBMN from uninfected individuals. Since these materials are released spontaneously during cercarial-to-schistosomular transformation they may have a putative immunosuppressive effect in decreasing antischistosomular activities early after cercarial penetration.

Animals↗
PubMed1990

Evidence for enhancement of IgG1 subclass expression in mice polyvaccinated with radiation-attenuated cercariae of Schistosoma mansoni and the role of this isotype in serum-transferred immunity.

Serum or immunoglobulin fractions of serum from CBA/Ca mice vaccinated three or four times with radiation-attenuated cercariae of Schistosoma mansoni have been investigated for their capacity to confer protection upon naive mice. The data confirm that around 35% protection can be transferred with polyvaccine mouse serum administered in 0.5-ml aliquots 1 h before challenge (intravenously) and 24 h post-challenge (intraperitoneally). We show in addition, however, that polyvaccine serum is also protective when injected into the skin site of challenge as a single 0.05-ml aliquot. In contrast, lymphocytes obtained from the donors of protective serum conferred only 13% protection upon recipient mice. The passive cutaneous anaphylaxis assay showed that IgG1 is incremented by polyvaccination, while passive transfer experiments revealed that of the different isotypes fractionated from whole protective serum, only IgG1 has the capacity to protect naive recipients against challenge. The resistance transferred by IgG1 represents more than 60% of that obtained with whole serum and can be achieved using either the intravenous/intraperitoneal or the subcutaneous administration regimen. Recipients of serum given via the subcutaneous route exhibit cutaneous inflammatory focal reactions which comprise 20% eosinophils and 80% mononuclear cells; these foci entrap challenge larvae. The importance of IgG1 subclass expression to the success of serum-transferred resistance is discussed.

Animals↗
PubMed1990

Schistosoma mansoni: localization of the 28 kDa secreted protease in cercaria.

Monospecific rabbit antibodies were utilized to localize the 28 kDa serine protease which is released from transforming schistosomula of Schistosoma mansoni in cercariae and freshly transformed schistosomula. This protease exerts two postulated activities, degradation of connective tissue proteins thus promoting skin penetration and release of the cercarial glycocalyx leading to accelerated schistosomular transformation. Upon immunogold labelling of cercarial cryosections, the 28 kDa protease was found stored in both the preacetabular and postacetabular glands. This enzyme was also detected in the cercarial glycocalyx by immunogold and immunofluorescence labelling and by its proteolytic activity. Following transformation and shedding of the glycocalyx, the same 28 kDa protease was found on the surface membrane of transformed schistosomula which are resistant to immune damage. It is suggested that the 28 kDa membrane protease which cleaves in vitro the complement proteins C3, C3b and C9, may promote in vivo immunoresistance of S. mansoni.

Animals↗
PubMed1998

Accelerated influx of dendritic cells into the lymph nodes draining skin sites exposed to attenuated cercariae of Schistosoma mansoni in guinea-pigs.

We compared temporal changes in the cell composition of the skin-draining lymph nodes (SLN) in guinea-pigs exposed percutaneously to normal or attenuated cercariae of Schistosoma mansoni. Different populations were analysed by flow cytometry of double-stained cells by monoclonal antibodies to the major histocompatibility complex class II molecule and lymph node cells of guinea-pigs. Exposure to S. mansoni caused a marked increase in the proportion of B cells and dendritic cells (DC) on day 2, reaching a peak number on day 4. These changes were comparable in both infected and vaccinated animals exposed to normal or attenuated parasites, respectively. Total number of DC, however, showed different kinetics; in infected animals, the number peaked on day 2 and then gradually declined, whereas it reached a higher peak on day 4 in vaccinated animal. Daily injection of bromo-deoxyuridine after exposure to the parasite reduced the total number of DC in the SLN on day 4. A reduction in DC counts in the contralateral side SLN was also evident in vaccinated animals. Our results indicate that a significant number of newly formed DC are recruited to the skin by 4th day of vaccination, followed by increased efflux to the SLN. It is possible that retention of attenuated S. mansoni in the skin may cause accelerated recruitment of newly formed DC from the bone marrow, and facilitate transport and processing of antigens highly expressed on attenuated parasites.

Animals↗
PubMed1983

Identification of surface antigens of schistosomula of Schistosoma mansoni recognized by antibodies from mice immunized by chronic infection and by exposure to highly irradiated cercariae.

Surface components of mechanically transformed schistosomula of Schistosoma mansoni were labeled by lactoperoxidase-catalyzed iodination. After solubilization with Triton X-100, antigens were identified by immunoprecipitation. Serum from chronically infected Swiss mice reproducibly precipitated seven major polypeptides with approximate molecular weights (X 10(3] of 94, 68, 45, 40 to 32, 22, and 16. The antigens of molecular weights (X 10(3] of 94, 40 to 32, 22, and 16 were shown to be exposed on the parasite surface by interaction of the antibodies with intact labeled schistosomula. Sera from several strains of infected inbred mice precipitated the same polypeptides. The antibodies produced during chronic infection were found to be stimulated by adult worms since sera from 6-week-infected animals precipitated none of the surface antigens, and the pattern produced by precipitation with antibodies from a mouse infected with male worms only was indistinguishable from the pattern obtained with sera from mice with bisexual infections. Antibodies from mice immunized with highly irradiated cercariae reproducibly precipitated major polypeptides of approximately (X 10(3] 94, 68, 45, 32, 22, 19, and 15 daltons. The antigens of (X 10(3] 94, 43, 32, 22, and 15 daltons were shown to be exposed on the parasite surface by interaction of the antibodies with intact labeled schistosomula. The 15 X 10(3)-dalton surface protein was recognized by sera from vaccinated, but not chronically infected, mice, suggesting that it represents a stage-specific immunogen present on schistosomula but not on adult worms. Sera from two inbred strains of mice which develop different degrees of immunity recognized the same antigens.

Animals↗
PubMed1998

Inducible nitric oxide synthase-deficient mice develop enhanced type 1 cytokine-associated cellular and humoral immune responses after vaccination with attenuated Schistosoma mansoni cercariae but display partially reduced resistance.

High levels of nitric oxide (NO) are produced by inducible nitric oxide synthase (iNOS) in response to activating signals from Th1-associated cytokines and play an important role in cytotoxicity and cytostasis against many pathogenic microorganisms. In addition to its direct effector function, NO serves as a potent immunoregulatory factor. NO produced by gamma interferon-activated macrophages immobilizes and kills Schistosoma mansoni larvae, and several studies have indicated a role for this pathway in protective immunity against this parasite. The potential regulatory influence of NO in immunity to S. mansoni is less well understood. In this study, we have used iNOS-deficient mice to determine the role of NO in mice vaccinated with irradiated cercariae of S. mansoni. We show by enzyme-linked immunosorbent assay and reverse transcriptase PCR analysis that vaccinated iNOS-deficient mice develop exacerbated type 1 cytokine responses in the lungs, the site where resistance to infection is primarily manifested. In addition, parasite-specific immunoglobulin G2a (IgG2a) and IgG2b antibody responses were significantly increased in vaccinated iNOS-deficient animals and total IgE antibody levels in serum were decreased relative to those in wild-type controls. Surprisingly, since resistance in this vaccine model is largely Th1 dependent and since Th1-related cellular and humoral immune responses were found to be exacerbated in vaccinated iNOS-deficient mice, vaccine-elicited protective immunity against challenge infection was found to be reduced. These findings demonstrate that iNOS plays a paradoxical role in immunity to S. mansoni, both in the effector mechanism of resistance and in the down regulation of the type 1 cytokine response, which is ultimately required for NO production.

Animals↗
PubMed1979

Immunoglobulin E, mast cells, and eosinophils in the skin of rhesus monkeys immunized with x-irradiated cercariae of Schistosoma japonicum.

Immunoglobulin E (IgE), mast cells, and eosinophils in the skin of rhesus monkeys immunized with highly X-irradiated cercariae of Schistosoma japonicum were studied. IgE was stained by the unlabeled antibody enzyme method and was found on mast cells. Before challenge, mast cells were found only in the dermis. Immediately after the challenge, mast cells were found in both the dermis and epidermis and many of them were degranulated. Soon after, margination and emigration of granulocytes, predominantly eosinophils, occurred along the blood capillaries in the dermis. Gradulally, preivascular infiltration of eosinophils was seen in the dermis and migration of eosinophils from the dermis into the epidermis appeared, resulting in the formation of minute eosinophilic abscesses in the epidermis. In addition, the IgE was found as a thin coat on the integument of the schistosomula. Deteriorated schistosomula were seen amid the eosinophilic abscesses in the epidermis and in eosinophilic infiltrations in the dermis. The present findings suggest the possibility that the reaction of IgE, mast cells, and eosinophils were integrated into one immunological effect, namely the schistosomulicidal action.

Animals↗
PubMedDate not supplied

Involvement of regional lymph nodes after penetration of Schistosoma mansoni cercariae in naive and infected mice.

The parotid lymph nodes of naive and previously infected Balb/c mice were studied after, respectively, infection and re-infection with cercariae of Schistosoma mansoni via the ears. Schistosomula were able to pass through the lymph node by following the lymph flow or by penetrating the veins of the medullary cords. The number of nodal mast cells was higher from day 2 to 6 of primary infection; and from day 5 to 11 of re-infection. The amount of degranulating mast cells was significantly higher at day 4 of infection and at day 1 of re-infection. Eosinophils characterized the nodal inflammatory processes observed after day 5 in both primarily-infected and re-infected mice. However, only in the latter the eosinophils were able to adhere to the larval surface. In primarily-infected mice, no intranodal larva presented signs of degeneration. In contrast, in re-infected animals, some degenerating larvae were found inside eosinophilic infiltrates. The eosinophils reached the nodal tissue by migrating through the high endothelial venules and their collecting veins.

Animals↗
PubMed2001

Ultrastructure and chaetotaxy of sensory receptors in the cercariae of a species of Crepidostomum Braun, 1900 and Bunodera Railliet, 1896 (Digenea: Allocreadiidae).

Previous investigations of cercarial sensory systems have focused on chaetotaxy and ultrastructure of sensory receptors and have revealed chaetotaxic patterns within families, genera, and species as well as different types of sensory receptors. However, chaetotaxic and ultrastructural observations have rarely been combined. We investigated the ultrastructure of cercarial sensory receptors in conjunction with the chaetotaxy and neuromorphology in 2 allocreadiid species belonging to the genera Crepidostomum and Bunodera. Cercariae were treated with acetylthiocholine iodide and silver nitrate, and for scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Similar cholinergic nerve networks were revealed. Chaetotaxy was consistent with that of other allocreadiids. Seven and 6 types of receptors were distinguished with SEM in Crepidostomum sp. and Bunodera sp., respectively. Types differed in number of cilia (1 or 2), cilium length (short, moderately long, or long), presence or absence of a tegumentary collar and a domelike base, and tegumentary collar length (low, moderately low, or high), TEM of some types revealed unsheathed cilia, basal body, and thickened nerve collars. Some receptor types were site specific. Thus, long uniciliated receptors were concentrated on the dorsal surface. Other types, such as short uniciliated receptors, were widespread throughout most regions. Ultrastructure and site-specificity observations suggest that most receptors are mechanoreceptors.

Acetylthiocholine↗