Schistosoma mansoni: topochemical features of cercariae, schistosomula, and adults

Triethylene glycol-modified iridium(iii) complexes for fluorescence imaging of Schistosoma japonicum

Schistosomiasis, an infectious disease caused by the Schistosoma parasitic worm, presents a serious public health issue. To date, investigation of anti-Schistosomiasis drug mechanisms through fluorescence imaging remains challenging due to the lack of appropriate dyes as fluorescent probes. Phosphorescent Ir(iii) complexes have been attracting substantial attention among various classes of fluorophores given their excellent photophysical properties. Herein, four phosphorescent Ir(iii) complexes were synthesized, two of which contained a triethylene glycol (TEG) hydrophilic group. The phosphorescent emission range of the four complexes lay between 500 and 750 nm, and their quantum yields ranged from 0.031 to 0.146. Furthermore, under the experimental concentration conditions, the TEG-modified complexes had low cytotoxicity. Cell fluorescence labeling experiments indicated that the TEG-modified complexes had good membrane permeability. Finally, the TEG-modified complexes showed remarkable labeling effects in adult Schistosoma fluorescence imaging. Thus, TEG-modified Ir(iii) complexes could be used as a new class of bilharzial fluorescent probes.

Miltefosine lipid nanocapsules: Intersection of drug repurposing and nanotechnology for single dose oral treatment of pre-patent schistosomiasis mansoni

A dual drug repurposing/nanotechnological approach was used to develop an alternative oral treatment for schistosomiasis mansoni using miltefosine (MFS), an anticancer alkylphosphocholine, and lipid nanocapsules (LNCs) as oral nanovectors. We demonstrated earlier that MFS possesses significant activity against different developmental stages of Schistosoma mansoni in the mouse model using 5 successive 20mg/kg/day oral doses. Moreover, an effective single dose (20mg/kg) oral treatment against the adult stage of S. mansoni in mice was developed using LNCs, particularly modified with CTAB, a positive charge imparting agent (MFS-LNC-CTAB(+)), or oleic acid as membrane permeabilizer (MFS-LNC-OA). Efficacy enhancement involved, at least in part, targeting of the worm tegument with MFS-LNCs as a new therapeutic entity. As the tegument surface charge and composition may differ in pre-patent stages of the parasite, it was of importance in the present study to assess the efficacy of a single oral dose of the two MFS-LNC formulations against invasive and immature stages for potential advantage relative to praziquantel. Results indicated potent schistosomicidal effects against both invasive and immature stages of S. mansoni in infected mice, efficacy being both formulation and developmental stage dependent. This was indicated by the significant reduction in the total worm burden of the invasive stage by 91.6% and 76.8% and the immature stage by 82.7% and 96.7% for MFS-LNC-CTAB+ and MFS-LNC-OA, respectively. Histopathological findings indicated amelioration of hepatic pathology with regression of the granulomatous inflammatory reaction and reduction in granulomas number and size, verifying marked improvement in architecture of hepatic lobules. From a clinical perspective, MFS-LNCs offer potential as an alternative single oral dose nanomedicine with a wide therapeutic profile for the mass chemotherapy of schistosomiasis mansoni.

Interference with the host haemostatic system by schistosomes

Schistosomes, parasitic flatworms that cause the tropical disease schistosomiasis, are still a threat. They are responsible for 200 million infections worldwide and an estimated 280,000 deaths annually in sub-Saharan Africa alone. The adult parasites reside as pairs in the mesenteric or perivesicular veins of their human host, where they can survive for up to 30 years. The parasite is a potential activator of blood coagulation according to Virchow's triad, because it is expected to alter blood flow and endothelial function, leading to hypercoagulability. In contrast, hepatosplenic schistosomiasis patients are in a hypocoagulable and hyperfibrinolytic state, indicating that schistosomes interfere with the haemostatic system of their host. In this review, the interactions of schistosomes with primary haemostasis, secondary haemostasis, fibrinolysis, and the vascular tone will be discussed to provide insight into the reduction in coagulation observed in schistosomiasis patients.

Interference with the haemostatic system by pathogens is a common mechanism and has been described for other parasitic worms, bacteria, and fungi as a mechanism to support survival and spread or enhance virulence. Insight into the mechanisms used by schistosomes to interfere with the haemostatic system will provide important insight into the maintenance of the parasitic life cycle within the host. This knowledge may reveal new potential anti-schistosome drug and vaccine targets. In addition, some of the survival mechanisms employed by schistosomes might be used by other pathogens, and therefore, these mechanisms that interfere with host haemostasis might be a broad target for drug development against blood-dwelling pathogens. Also, schistosome antithrombotic or thrombolytic molecules could form potential new drugs in the treatment of haemostatic disorders.

Three-dimensional structure of a schistosome serpin revealing an unusual configuration of the helical subdomain

Parasitic organisms are constantly challenged by the defence mechanisms of their respective hosts, which often depend on serine protease activities. Consequently, protease inhibitors such as those belonging to the serpin superfamily have emerged as protective elements that support the survival of the parasites. This report describes the crystal structure of ShSPI, a serpin from the trematode Schistosoma haematobium. The protein is exposed on the surface of invading cercaria as well as of adult worms, suggesting its involvement in the parasite-host interaction. While generally conforming to the well established serpin fold, the structure reveals several distinctive features, mostly concerning the helical subdomain of the protein. It is proposed that these peculiarities are related to the unique biological properties of a small serpin subfamily which is conserved among pathogenic schistosomes.

Opisthorchis viverrini: ultrastructure and cytochemistry of the glycocalyx of the tegument

The ultrastructure and cytochemistry of the glycocalyx of the tegument of Opisthorchis viverrini during maturation from newly excysted juvenile to adult stages were investigated using colloidal iron, ruthenium red and lectin stainings. The results showed that the glycocalyx was intensely stained by the first two dyes, thus indicating the presence of relatively high amounts of negative charges. However, the thickness and intensity of the staining decreased during the fluke's maturation. Binding studies using lectin probes on the surface of adult parasites showed that binding sites for Canavaliaensiformis (Con A), Triticum vulgaris (WGA) and Ricinus communis I(RCA I) were present in relative large amounts on the glycocalyx of the adult tegument, whereas those for Dolichos biflorus (DBA) were relatively fewer in number, and those for Ulex europaeus I (UEA I) were absent. The binding patterns of Con A, WGA, RCA I and DBA were generally similar, and the reaction product was uniformly distributed over the dorsal and ventral surfaces of the parasite's body. These bindings, therefore, indicate the presence of D-mannose/D-glucose, N-acetyl-D-glucosamine/sialic acid, D-galactose and N-acetyl-D-galactosamine residues on the glycocalyx of the adult tegument.

Early liver dysfunction in schistosomiasis

BACKGROUND/AIMS

Liver dysfunction is said to occur only late in the course of schistosomiasis. As albumin levels tend to be normal, the observed prolonged prothrombin time is thought to arise from subclinical consumption coagulopathy. The aim of this study was to further evaluate this matter by studying the role of Schistosoma mansoni and liver function in the genesis of the compromised haemostasis tests in chronic "pure" schistosomiasis patients.

METHODS

Twenty-five adults with chronic "pure" schistosomiasis were selected: 12 with the hepatointestinal form (group 2) and 13 with the compensated hepatosplenic form (group 3), as well as 10 matched control individuals (group 1). Alcoholism, viral hepatitis B and C, malnutrition (BMI<20 kg/m2), use of anticoagulant or anti-aggregant drugs and chronic diseases apart from schistosomiasis were carefully excluded. All patients were submitted to abdominal ultrasound and upper digestive endoscopy. Blood samples were used for routine hepatic tests and for transthyretin, prothrombin, antithrombin and protein C antigen determinations by immunodiffusion. Laboratory markers of coagulation activation (prothrombin fragment1+2(F1+2), serine esterases-antithrombin complexes (ATM) and plasminogen activator, tissue type activity (t-PA) were also assayed by ELISA and photometric determination, respectively.

RESULTS

Decreased plasma levels of transthyretin (p<0.001), protein C (p:0.006), prothrombin (p:0.022) and antithrombin (p:0.008) contrasted with normal albuminaemia (p:0.094), F1+2 (p:0.061) and ATM (p:0.714) plasma levels in group 3 patients; t-PA activity (p:0.001) on the other hand, were increased in this group.

CONCLUSIONS

These results suggest impairment of liver clearance and protein synthesis capacity rather than consumption coagulopathy. They also indicate that changes in liver function are not a late event in the course of schistosomiasis.

Altered behaviour of carbohydrate-bound molecules and lipids in areas of the tegument of adult Schistosoma mansoni worms damaged by praziquantel

By using fluorescent probes the distribution and fluid properties of lipid and saccharide-bound molecules was assessed in the tegument of praziquantel (-) treated Schistosoma mansoni adult male worms. Our results show that higher amounts of glycoproteins and/or glycolipids are exposed in damaged areas of the membrane compared with undamaged ones. At damaged regions these molecules present high lateral diffusion coefficient and mobile fraction values which suggests that after praziquantel(-) treatment they are being shed by the worm into the medium. The lateral diffusion coefficient of the lipid analogue 5'-octadecanoyl aminofluorescein is unchanged in damaged or undamaged areas but the mobile fraction is significantly reduced at damaged areas. The immunological significance of these altered surface properties is discussed.

Ultrastructure and histochemistry of the tegument of juvenile paramphistomes during migration in Indian ruminants

The tegument of juvenile Paramphistomum epiclitum and Fischoederius elongatus (Paramphistomidae: Digenea) resembles those of other digeneans. Seven types of papillae were observed, mostly on the oral and acetabular surfaces, and increase in number during migration. Also evident are two types of secretory body (T1 and T2) which are synthesized separately in tegumental cytons underlying the syncytium. Exocytosis of T2 bodies occurs at the apical membrane and appears to contribute to a fibrous glycocalyx. The tegumental syncytium lining the pharynx and acetabulum is thinner and has a higher capacity for vacuolation than the general tegument. These may represent important sites for osmoregulation. The absence of mitochondria from the tegument in migrating juveniles suggests limited involvement in energy demanding processes. Pigmentation of the subtegument is first evident in mature cercariae and is progressively eliminated during migration.

Schistosoma mansoni: patch-clamp study of a nonselective cation channel in the outer tegumental membrane of females

An apparent ion channel with a conductance of 295 pS is present in isolated inside-out patches of outer tegumental membrane taken from female Schistosoma mansoni. With positive voltages applied to the intracellular face of the patch, percentage open time for the channel was 0 to 50; with negative voltages applied, percentage open time was greater than 99. Step changes in applied voltage characteristically induced opening-closing activity. However, there was no maintained applied voltage at which there was a high level of sustained opening-closing activity. The 295 pS conductance was by far the most commonly occurring conductance but it appears to result from cooperativity among several channels, the unitary conductance for the channel averaging 95 pS. Alterations in the Na+ or K+ concentration ratios changed the reversal potential for this conductance but alterations in the Cl- concentration did not. From this it is concluded that this channel is selective for Na+ or K+ over Cl- and it appears to be a nonselective cation channel.

Paragonimus ohirai: immunobiochemical characterization on the tegumental glycocalyx of excysted juvenile recognized by a monoclonal antibody

The tegumental glycocalyx of excysted juvenile (EJ) of Paragonimus ohirai was immunobiochemically characterized using a monoclonal antibody (MS-Mab). HPLC gel filtration showed that the antigens detected by two-site ELISA had a molecular weight of greater than or equal to 2 x 10(6) Da (dextran marker). On reduced SDS-PAGE, the glycocalyx antigen retained in the stacking gel was cleaved into several much smaller antigens after pronase treatment. The antigenic activity of the glycocalyx was stable in two-site ELISA to heat and acid treatments, but sensitive to alkali, periodate, base/borohydride, and pronase treatments. Precipitin formation in immunodouble diffusion between MS-Mab and EJ crude antigen was inhibited only by two monosaccharides: galactose and N-acetylgalactosamine. The purified glycocalyx bound strongly to PNA lectin, fairly well to RCA120 lectin, and slightly to SBA lectin, but not to Con A, WGA, UEA-1, DBA, or LFA lectins. Exo-beta-galactosidase treatment increased SBA binding, whereas it decreased PNA binding. PNA was observed to strongly bind to the body surface of living EJ. The antigenic activity of the glycocalyx was remarkably lost by incubation with exo-beta-galactosidase and O-glycanase. The glycocalyx was reactive with sera of P. ohirai-infected rats, and its reactivity was remarkably reduced by O-glycanase treatment. The ELISA level was higher in sera at an early stage of infection than in a late one. These studies show that the EJ tegumental glycocalyx is antigenic in infection, a marked, high molecular weight glycoprotein containing antigenic O-linked sugars, and that the sugar epitope is at the nonreducing terminal of the O-linked sugars and is composed of galactose and N-acetylgalactosamine.

Schistosoma mansoni: ultrastructural demonstration of a miracidial glycocalyx that cross-reacts with antibodies raised against the cercarial glycocalyx

Cercariae are covered by a glycocalyx that is highly antigenic. Here, we have examined the surface of miracidia for a similar structure. The miracidia are covered by epithelial plates and syncytial ridges. By transmission electron microscopy, the plates and ridges were covered by a 0.5-micron-thick glycocalyx composed of a mesh of 9- to 10-nm fibrils that were stained by ruthenium red delivered in the aldehydes or ferrocyanide-reduced osmium tetroxide. Rabbit antibodies prepared against phenol extracted and chromatographed cercarial glycocalyx were detected by immunoelectron microscopy with secondary antibodies conjugated to horseradish peroxidase. Reaction product bound to both the miracidial and cercarial glycocalyx. In addition, the outer leaflets of the cercarial tegumental membrane and membranes of the miracidial surface structures, including plates, ridges, terebratorium, and sensory papillae, had reaction product. Controls incubated with nonspecific rabbit serum had no reaction product. By indirect immunofluorescence, antibodies against the cercarial glycocalyx stained both plates and ridges. As the miracidia transformed to sporocysts, the glycocalyx remained associated with the plates as they were sloughed. These studies demonstrate that miracidia possess a glycocalyx similar in structure and antigenicity to the cercarial glycocalyx.

Schistosoma mansoni: development of the cercarial glycocalyx

The development of the cercarial glycocalyx of Schistosoma mansoni was studied by transmission electron microscopy and immunofluorescence light microscopy employing antibodies raised against extracted and chromatographed glycocalyx. By electron microscopy, cercariae present in the brood chamber of daughter sporocysts were surrounded by an electron-dense granular and fibrillar matrix. This material appeared structurally distinct from the glycocalyx which was coarsely fibrillar and located only on the surface of organisms that had developed a final tegument. The thickness of the glycocalyx apparently increased with the maturation of the tegument, since teguments that had many spines also had the thickest glycocalyx. Immunofluorescent staining of frozen sections of infected snail hepatopancreas showed that glycocalyx antigens were present on the surface of the cercariae and not in the matrix within the brood chamber or in snail tissues. Immunofluorescent staining of isolated larval cercariae showed staining of some but not all parasites with partially elongated tails. These studies suggest that the glycocalyx develops late in cercarial development (late in Stage 6 or in Stage 7 of Cheng and Bier), is made by the cercariae themselves, and is not a product of either the sporocyst wall cells or snail hepatopancreas.

Identification and characterization of a polysaccharide-containing antigen from Schistosoma mansoni eggs which cross-reacts with the surface of schistosomula

Antisera were produced by immunizing rabbits with either a trichloroacetic acid-soluble fraction, or a high molecular weight (Mr) fraction of Schistosoma mansoni SEA (a saline-soluble fraction of homogenized egg). Both of these sera reacted monospecifically in immunoelectrophoresis against unfractionated SEA, recognizing a cathodally migrating antigen. This antigen had been identified previously as being responded to by S. mansoni-infected mouse sera, and has been designated K3 (Kappa 3). The rabbit antisera were used to partially characterize antigen K3 as having Mr in the range greater than 750-70 K, and being resistant to boiling, resistant to the action of proteases, but sensitive to periodate. It partially binds to Concanavalin A. In addition to SEA, the antigen was present in homogenized cercariae and schistosomula, but not adult worms, and it was also present in detergent extracts of intact cercariae and schistosomula. Using an antibody-dependent cell adherence assay, anti-K3 serum was found to react with the surface of live cercariae and with the surface of schistosomula recovered from the skin of mice infected up to 48 h previously. Anti-K3 serum also reacted with the surface of S. bovis, S. haematobium and to a lesser extent S. japonicum schistosomula.

Surface proteins and antigens of adult Schistosoma mansoni tegumental membranes detached onto poly-lysine coated beads

Poly-lysine coated beads attached readily onto Schistosoma mansoni. On detachment, the beads removed membranes from the surface of the tegument. Analysis of the proteins of the detached membranes showed that three major proteins of 94, 73 and 62 kDa were present in contrast to a more complex range of proteins present in the phosphate-buffered saline released membranes. The membranes attached to beads were radio-iodinated and the antigens examined in immunoprecipitates by sodium dodecyl sulphate-polyacrylamide gel electrophoresis using various antisera. In addition to the well-established 32 and 20 kDa antigens of the tegument, other major antigens of 200, 25 and 11-12 kDa were iodinated in the membranes attached to the beads. The results suggest that the major antigens studied in the tegument may not correspond to the major proteins identified. The present approach shows promise for deducing the topography of the surface antigens and proteins of schistosomes.

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.

Ion fluxes changes during early stages of Schistosoma mansoni. Evaluation of complement effect

The relationship between the average membrane potential (delta psi av) and sensitivity to complement action of the Schistosoma mansoni parasite was explored. The average membrane potential was estimated by measuring the uptake of [3H]tetraphenyl phosphonium ([3H]Ph4P+). The parasites take up Ph4P+ indicating the existence of a negative internal plasma potential which is in part dependent on the transmembrane K+ gradient, maintained by an active Na+/K+-ATPase. Values for Ph4P+ uptake could be corrected for mitochondrial accumulation by employing the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP), which collapses the mitochondrial potential. The plasma membrane potential derived by this technique was in the range of -60 mV. Transformation of this parasite, from its early cercaria stage to the adult worm, was associated with changes in the average membrane potential. The apparent hyperpolarization, which accompanies transformation, may be related to changes in ionic permeability and morphology which occur concomitantly. Complement acting through both the classical and alternative pathways was found to affect the potential of the parasite in its early development stages. The correlation between effects on delta psi av and sensitivity to complement action, indicates that the complement-induced changes in delta psi av are indeed tightly associated with its mode of action. Treatment of the parasite with complement resulted in net hyperpolarization of the membrane indicating that hyperpolarization rather than depolarization of the membrane is linked to the primary non-lethal action of complement.

The cercarial glycocalyx of Schistosoma mansoni

Cercariae, the freshwater stage of Schistosoma mansoni infectious to man, are covered by a single unit membrane and an immunogenic glycocalyx. When cercariae penetrate the host skin, they transform to schistosomula by shedding tails, secreting mucous and enzymes, and forming microvilli over their surface. Here the loss of the glycocalyx from cercariae transforming in vitro was studied morphologically and biochemically. By scanning electron microscopy, the glycocalyx was a dense mesh composed of 15-30 nm fibrils that obscured spines on the cercarial surface. The glycocalyx was absent on organisms fixed without osmium and was partially lost when parasites aggregated in their own secretions before fixation. By transmission electron microscopy, a 1-2 microns thick mesh of 8-15-nm fibrils was seen on parasites incubated with anti-schistosomal antibodies or fixed in aldehydes containing tannic acid or ruthenium red. Cercariae transformed to schistosomula when tails were removed mechanically and parasites were incubated in saline. Within 5 min of transformation, organisms synchronously formed microvilli which elongated to 3-5 microns by 20 min and then were shed. However, considerable fibrillar material remained adherent to the double unit membrane surface of schistosomula. For biochemical labeling, parasites were treated with eserine sulfate, which blocked cercarial swimming, secretion, infectivity, and transformation to schistosomula. Material labeled by periodate oxidation and NaB3H4 was on the surface as shown by autoradiography and had an apparent molecular weight of greater than 10(6) by chromatography. Periodate-NaB3H4 glycocalyx had an isoelectric point of 5.0 +/- 0.4 and was precipitable with anti-schistosomal antibodies. More than 60% of the radiolabeled glycocalyx was released into the medium by transforming parasites in 3 h and was recovered as high molecular weight material. Parasites labeled with periodate and fluorescein-thiosemicarbazide and then transformed had a corona of fluorescence containing microvilli, much of which was shed onto the slide. Material on cercariae labeled by lodogen-catalyzed iodination was also of high molecular weight and was antigenic. In conclusion, the cercarial glycocalyx appears to be composed of acidic high molecular weight fibrils which are antigenic and incompletely cleared during transformation.

Isolation and characterization of glycosaminoglycans from Schistosoma mansoni

Tegumental tissues of paired adult Schistosoma mansoni were removed by treatment with Triton X-100 and recovered by centrifugation. The chloroform-methanol insoluble residues of this isolated tegumental fraction and of the denuded carcasses were analysed for glycosaminoglycan (GAG) and sialic acid contents. Treatment with GAG-specific enzymes followed by electrophoretic analysis showed that both the carcass and tegument contained heparin and/or heparan sulfate, chondroitin sulfate and hyaluronic acid. All these except hyaluronic acid were present in the tegumental fraction. Based on uronic acid content, about 73% of the total GAG was in the tegumental membrane, 15% in the tegmental matrix and the remaining 12% was in the carcass. The presence of heparin-like polysaccharide may present entrapment of the schistosoma by the hosts' blood-clotting process.

Fasciola hepatica: tegumental alterations as a consequence of lectin binding

Adult flukes, Fasciola hepatica, incubated in Hedon - Fleig saline containing concanavalin A (Con A) for 10 and 45 min, respectively, exhibited severe alterations to tegumental morphology involving increased secretory activity, blebbing of the apical plasma membrane, increased total surface area, and swelling of the basal infolds . The effects of Con A were prevented by the addition of alpha-methyl-D-mannoside to the incubating medium. Similar, but less pronounced, effects were caused by wheat germ agglutinin (WGA) binding. Con A and WGA binding indicate the presence of mannose, glucosamine, or glucose moieties and of N-acetylglucosamine. The effects of lectin binding were similar to the early effects of antibody attachment, and it was considered that accelerated membrane turnover was occurring in both cases. Swelling of the basal infolds was thought to be a result of increased apical surface membrane and/or increased permeability due to lectin binding.

Identification of a sialic acid containing glycocalyx on the surface of Schistosoma mansoni

Ruthenium red fixation of adult Schistosoma mansoni revealed the existence of a negatively charged layer external to the outer bilayer, which was morphologically similar to the glycocalyx of other cell types. Regional and sexual differences were found in the extent and organisation of the surface coat, which can be correlated with interfacial free energy, adhesiveness and protection from immune effectors. Neuraminidase treatment confirmed the presence of surface sialic acid. Mechanical or skin penetrated schistosomula, maintained in vitro for 24 h were found not to have a glycocalyx and this may relate to their increased susceptibility to immune killing. Lung stage schistosomula however, did bind ruthenium red to their surface.

Schistosoma mansoni: surface membrane isolation by polycationic beads

The Schistosoma mansoni surface membrane complex was isolated by binding polycationic beads to the worm surface in a sucrose- or sorbitol-acetate buffer, pH 5.0, at 4 C. The ratio of incorporation [3H]cholesterol/[14C]arachidonic acid was measured as well as the specific activities of the alkaline phosphatase (EC 3.1.3.1), Type I phosphodiesterase (EC 3.1.4.1), and Ca2+-adenosine triphosphatase (EC 3.6.1.3). The results indicated that membranes isolated on beads were of comparable or greater purity than membranes isolated by sucrose gradient centrifugation. The isolation procedure was rapid (30 min) and produced membrane fractions whose cytoplasmic surfaces were probably exposed.

The exposed carbohydrates of schistosomula of Schistosoma mansoni and their modification during maturation in vivo

Lectins labeled with 125I or conjugated with fluorescein were employed to study the carbohydrates on the surface of different stages of schistosomula of Schistosoma mansoni. Newly transformed schistosomula were shown to bind concanavalin A; the 60 000 and 120 000 dalton agglutinins from Ricinus communis; the fucose-binding protein from Lotus tetragonolobus; wheat germ agglutinin and peanut agglutinin. Soybean agglutinin, Ulex europaeus agglutinin and Dolichos biflorus agglutinin, on the other hand, failed to bind to the schistosomulum surface. The binding of peanut and soybean agglutinin was unaffected by pretreatment of the parasites with neuraminidase. Binding of concanavalin A, the 120 000 dalton agglutinin from Ricinus communis, wheat germ agglutinin and peanut agglutinin to the surface of 5-day schistosomula, recovered from the lungs of mice, was also demonstrated. In each case, however, the level of binding was approximately 70% less than that observed with newly transformed schistosomula and the binding of the fucose-binding protein from L. tetragonolobus practically disappeared. In contrast with newly transformed schistosomula, lung stage schistosomula, pretreated with neuraminidase, displayed a significant increase in the binding of peanut and soybean agglutinin. The results indicate that a significant alteration in the surface carbohydrates of S. mansoni occurs during in vivo maturation of the parasite. This change may contribute to the organism's ability to survive in the vertebrate host.

The occurrence of proteolipid antigens in Schistosoma mansoni

Adult Schistosoma mansoni were shown to synthesize a peptide containing lipid against which an antiserum could be raised in rabbits. The proteolipid purified by silicic acid chromatography was soluble in chloroform/methanol mixtures, it was very hydrophobic and contained fatty acids in its molecule, as well as other unidentified neutral lipids.

Distribution of exposed and hidden carbohydrates of Schistosoma mansoni adult worms demonstrated by selective binding of fluorochrome-conjugated lectins

The distribution of exposed and hidden lectin-binding glycoconjugates in adult Schistosoma mansoni worms was studied. Fluorochrome-conjugated lectins were allowed to react both with intact worms and with frozen sections of worms. The results show a selective reactivity of lectins with tegumental surface structures, the intestine, eggs and basement membranes. Strong binding of wheat germ agglutinin (WGA) was seen to the exposed surface of intact worms. Peanut agglutinin (PNA), Ricinus communis agglutinin (RCA) and concanavalin A (Con A) gave a weaker reaction. There was a preferential affinity of PNA and RCA to the spikes covering the tubercles of male worms whereas Con A gave a more uniform staining pattern. Internal structures exposed in frozen sections of worms gave distinct staining reactions. Binding sites for Con A were widely distributed throughout the worm. PNA produced a more selective binding and was the only lectin staining basement membranes as distinct structures. There was a strong selective staining of the gut with soybean agglutinin (SBA) and RCA. Eggs seen in large quantitites inside female parasites reacted strongly with SBA and PNA and less intensely with RCA and WGA. The observed selectivity of lectin binding may reflect physiological function. The results may be important as a basis for using lectin affinity-chromatography for purification and characterization of worm constituents.

Schistosomula of Schistosoma mansoni clear concanavalin A from their surface by sloughing

The lectin concanavalin A (Con A) was used as a model probe to study the behavior of molecules bound to the surface of recently transformed schistosomula of Schistosoma mansoni. Con A binding was saturable (150-180 pg/organism) and specifically competed by alpha-methyl mannoside. Both FITC-Con A and 125-I-Con A were lost from the surface of schistosomula with a halftime of 8-10 h in culture in defined medium. A comparable decrease in the binding of Con A to schistosomula cultured and then labeled with the lectin indicated that the labeling procedure itself was not inducing the observed change. Internalization of Con A was not seen by either fluorescence microscopy or electron microscope radioautography. In addition, 70-80% of the radioactivity lost from the parasite was recoverable by TCA precipitation from the culture medium as intact Con A (27,000 mol wt on SDS PAGE). Thus, the mechanism of clearance of bound Con A from the surface of cultured schistosomula is apparently by sloughing of Con A molecules intact into the culture media and not by endocytosis and degradation. Con A binding sites, visualized with hemocyanin by scanning electron microscopy, appeared homogeneously distributed over the surface of schistosomula when organisms were labeled at 4 degree C or after fixation with glutaraldehyde. However, Con A and hemocyanin formed aggregates on the surface of schistosomula when labeling was performed at 37 degrees C, which suggests that lectin binding sites have lateral mobility within the plane of the membrane. These aggregates are likely independent of metabolism by the parasite because aggregation also occurs on the surface of organisms killed with azide.

Loss of covalently labeled glycoproteins and glycolipids from the surface of newly transformed schistosomula of Schistosoma mansoni

Schistosomula of Schistosoma mansoni were labeled by oxidation with galactose oxidase or with periodate followed by reduction with NaB3H4 to study the loss of the surface membrane of these parasites in vitro. Grain counts of light microscope autoradiographs (LMARG) of radiolabeled schistosomula show that both galactose oxidase and periodate specifically label the surface of the organisms. Galactose oxidase labels 11 glycoproteins on the surface of skin and mechanical schistosomula, ranging in apparent molecular weight from 17,000 to greater than 105,000. These glycoproteins are lost from the surface of schistosomula with a halftime of 10-15 h in culture in defined medium. Most of these glycoproteins appear to be shed intact from the surface of the schistosomula rather than endocytosed and degraded, because greater than 50% of each of the lost proteins can be recovered by trichloroacetic acid precipitation of the culture medium and because there is no internalization of the radiolabels into cultured schistosomula examined by LMARG. In addition to glycoproteins, periodate labels at least seven glycolipids on the surface of mechanical schistosomula. After culture for 15 h, more than half of each of these periodate-labeled proteins and lipids are lost from the schistosomula, and their abundance relative to each other remains similar to that of freshly labeled organisms. Since both proteins and lipids are lost from the surface of the schistosomula at the same rate, we believe that we are observing a general loss of the parasite surface membrane.

Characterization of chemical stimuli for the penetration of Schistosoma mansoni cercariae. II. Conditions and mode of action

The mode of action of chemical substances which trigger the penetration of S. mansoni cercariae into agar substrata is studied. The effectiveness of these substances is largely independent on their polarity and water solubility. Thus, they do not seem to act by a passive membrane permeation process, but they may interact with specific receptor sites, which are characterized. The receptor sites seem to respond to the following chemical characteristics of the stimulating aliphatic hydrocarbon chain: Carboxylic end group, lipophilic end group, chain length, cis-double bond. The penetration stimulating substances cause, even in cercariae in free water, a transformation of the tegument, manifested as a reduction of the Cercarienhüllen-Reaktion and a loss of osmotic protection.

KCl-Extractable surface antigens of Schistosoma mansoni: immunological characterization and applicability in immunodiagnosis

A Schistosoma mansoni antigen preparation was obtained by extraction of adult worms with a 3 M KCl solution. An indirect immunofluorescence reaction on cryostat sections of adult worms showed that the extracted antigens mainly originated from the tegument. The complex antigenic composition of the tegument extract was shown by immunoelectrophoresis against serum from infected mice and immunized rabbits, which gave up to 9 and 17 precipitation lines, respectively. When we compared the use of adult worm antigens and the tegument antigen preparation in the DASS and ELISA tests for immunodiagnosis of human schistosomiasis, the average sensitivity of the tests with the two preparations was about equal, although considerable differences between individual sera occurred. Analysis of tegument antigens, fractionated by gel filtration, showed that the main serological activity of the tegument antigen preparation was due to high molecular weight antigens.

Glycosyl transferase activities are associated with the surface membrane in adult Schistosoma mansoni

Incubation of live adult Schistosoma mansoni in a variety of media released tegumental material containing membrane bound alkaline phosphatase, mannosyl transferase and galactosyl transferase activities. Centrifugation of the tegumental material released by incubation of worms in phosphate-buffered saline in sucrose density gradients yielded a pellet and four fractions, two of which consisted mainly of surface membranes. The distribution of the enzymes in the gradient, espeically in the two surface membrane-containing subfractions was similar. Application of the "digitonin shift" technique showed that the membranes containing the enzyme reactivities were moved to an equal extent into a denser part of the sucrose gradient. Thus the enzymes are located on the same or similar cholesterol-containing membranes. It is concluded that the transferases, like the alkaline phosphatases, are located in the surface membranes of S. mansoni and the consequences of this location for the host-parasite interaction are discussed.

Characterization of the exposed carbohydrates on the surface membrane of adult Schistosoma mansoni by analysis of lectin binding

The surface architecture of adult male Schistosoma mansoni was explored using a range of lectins with differing carbohydrate specificites. Highest specific binding was achieved with concanavalin A and the agglutinin of molecular weight 60000 from Ricinus communis; the binding of wheat germ agglutinin was mostly non-specific. Small amounts of peanut agglutinin and soybean agglutinin binding were observed and the binding of these lectins was increased by pre-treating the parasite with neuraminidase. The fucose binding protein of Lotus tetragonolobus failed to bind. These results indicate that mannose and/or glucose, galactose, N-acetylglucosamine, N-acetyl-galactosamine and sialic acid are exposed on the surface of the adult male schistosome.

Factors affecting surface changes in intact cercariae and cercarial bodies of Schistosoma mansoni

The effect of different incubation media and of temperature on the induction of water sensitivity has been investigated in intact and tailless Schistosoma mansoni cercariae. Removal of the cercarial tail by vortex stirring and elevation of the temperature of the medium from 27 to 37 degrees C resulted in the rapid onset of permeability changes in the larvae. The rate of change was greater in water than in TC-199 or Hanks' BSS media. Lowering the pH of the medium or increasing the concentration of Ca2+ ions decreased the rate of permeability change: raising the pH of the medium or the addition of 10(-5) M EDTA enhanced the rate. Raising the temperature of the medium also increased the rate of permeability change in intact cercariae although the rates obtained varied with the different media tested, being greatest in TC-199. It is concluded that both temperature elevation and loss of the cercarial tail influence the onset and rate of permeability changes in cercarial bodies during the transformation to schistosomula.