Analysis of tegumental surface proteins of Schistosoma mansoni primary sporocysts

Axenically transformed primary sporocysts of Schistosoma mansoni (NMRI strain) were labeled with 125I in an effort to identify sporocyst proteins exposed at the tegumental surface. Using the 125I activating reagent, 1,3,4,6-tetrachloro-3 alpha,6 alpha-diphenylglycoluril, in conjunction with SDS-PAGE and autoradiography, up to 12 bands were radiolabeled out of 60 components visualized by silver staining. Labeled proteins ranged in apparent Mr from greater than 200 to less than 12 kDa. Pronase treatment of living sporocysts after radioiodination removed all labeled material, suggesting that only surface proteins were being iodinated. Western blot analysis employing 5 monoclonal antibodies (MAB's) to sporocyst surface antigens revealed a wide range of reactivities which produced banding patterns closely reflecting autoradiograms of identical samples. The concomitant removal by Pronase of immunoreactive and radiolabeled surface proteins with identical Mr in the range of 90-130 kDa suggests that epitopes recognized by these antibodies are associated with these higher molecular weight surface proteins. However, although Pronase removes all labeled surface proteins, substantial nonradiolabeled, immunoreactive material with Mr less than 90 kDa still remains on enzyme-treated parasites. This indicates that MAB-reactive epitopes, in addition to their occurrence with surface proteins, are also associated with either unlabeled, protease-resistant surface components or internal antigens. The immunohistochemical localization of antibody-reactive material in gland-like structures within sporocysts supports an internal source for nonradiolabeled, immunoreactive components. Finally, the periodate sensitivity of the epitopes recognized by all tested MAB's suggests that carbohydrate moieties may represent a common and extremely immunogenic constituent of the sporocyst surface.(ABSTRACT TRUNCATED AT 250 WORDS)     

Schistosoma mansoni: origin and expression of a tegumental surface antigen on the miracidium and primary sporocyst

A monoclonal antibody, recognizing a carbohydrate epitope associated with several tegumental surface components on Schistosoma mansoni primary sporocysts, was used to follow tegumental formation during transformation of the miracidium to sporocyst and its subsequent development in vitro and in vivo. Indirect fluorescent antibody and direct immunogold labeling methods confirm a structural connection between the intercellular ridges and a submuscular, multinucleate syncytium in the miracidium. Immunoreactive vesicles within this latter system directly contribute to elaboration of the tegumental surface membrane, through the process of membrane fusion. Lateral expansion of intercellular ridges by vesicular fusion ultimately result in fully transformed sporocysts exhibiting vesicular membrane epitopes as prominent tegumental surface components. Light microscopical and ultrastructural observations, together with Western immunoblot analyses, suggest a gradual depletion of intracellular and surface immunoreactive material of vesicular origin in primary sporocysts grown in culture for up to 12 days. In contrast, similar immunoreactive vesicles appear to be continuously synthesized throughout in vivo primary sporocyst development. Monoclonal antibody reactive epitopes appear to be uniquely expressed in the miracidium/primary sporocyst since similar molecules are absent from daughter sporocysts, cercariae, adults, and snail tissues.     

Morpho-anatomic and functional sectorization of Schistosoma mansoni daughter sporocysts

During the larval development of S. mansoni in the snail host, morpho-anatomic changes occur in the daughter sporocyst by a sectorization of this larval stage. Three sectors can be distinguished: an anterior zone with a well-differentiated birth pore; dilated zones containing the developing cercariae; constricted zones without cercarial embryo. The photonic and electronic microscopical study shows variations in the tegumental structure of these sectors. This evolution of the daughter sporocysts is discussed in relation with the dynamics of larval stages and the replication process of sporocysts.     

Glycodelin and amniotic fluid transferrin as inhibitors of E-selectin-mediated cell adhesion

Human amniotic fluid contains a variety of glycoproteins. Several of these substances have been shown to exert immunomodulatory effects. Glycodelin, previously known as placental protein 14, is one of these glycoproteins. It has a unique carbohydrate configuration, consistent with fucosylated LacdiNAc structures that are very unusual for mammals. Oligosaccharides with fucosylated LacdiNAc antennae have previously been shown to block selectin-mediated cell adhesion. Another glycoprotein, human transferrin, is also present in amniotic fluid in relatively high concentrations. This transferrin shows a different glycosylation compared with serum transferrin. Amniotic fluid transferrin carries sialylated Lewis X antigens. Glycodelin and transferrin were isolated from amniotic fluid and for comparison from serum of pregnant women by chromatographic methods. The purified proteins were used as ligands to block E-selectin-mediated HepG2 cell adhesion. Two types of binding assays with distinct receptor accommodations (immobilised E-selectin and activated HUVECs) were used to quantify inhibition efficiencies of the different proteins. We found that glycodelin is a strong inhibitor with a 10(3)-fold potency compared to the monovalent tetrasaccharide sialyl Lewis X whereas the potency of transferrin is rather low.     

Biochemical and immunological characterization of excretory-secretory products of Vesicocoelium solenophagum and plasma proteins of its bivalve host, Sinonovacula constricta

In this study, the excretory-secretory products (ESP) of the daughter sporocysts of Vesicocoelium solenophagum (Trematoda) and plasma proteins of its host, Sinonovacula constricta were characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and gelatin-substrate gel analyses, and the relationships between them were analysed using immunoblotting. Proteinase activity was detected in the ESP from daughter sporocysts of V. solenophagum. Some polypeptides of the ESP were found to be recognized by antiserum, raised against plasma from non-infected S. constricta, suggesting that the ESP may mimic host molecules (molecular mimicry). In contrast, neither the obvious proteinase activity nor the binding to the antisera was observed for the soluble proteins of daughter sporocyst, indicating that the ESP may play a important role in the parasite-host relationship. Although the plasma of infected S. constricta contained polypeptides that were similar to the plasma of non-infected bivalves, increased quantities of proteins at >170 kDa, 15 kDa and decreased quantities at 60 kDa were observed in the plasma of infected bivalves. Immunoblotting analysis revealed that the plasma of infected bivalves had a faint reaction with both anti-non-infected plasma antisera and anti-sporocyst antisera. These results indicated that the structure and quantity of some polypeptides from the plasma of infected bivalves had changed because of the infection with V. solenophagum. The polypeptides between the plasma of bivalves from a non-epidemic area and that from an epidemic area were similar, but the former had more polypeptides of 170-220 kDa and much greater proteinase activity than the latter, suggesting that the increased polypeptides of 170-220 kDa and the high proteinase activity in plasma may be favourable for protecting the host from being invaded by the parasites.     

Differential binding of hemolymph proteins from schistosome-resistant and -susceptible Biomphalaria glabrata to Schistosoma mansoni sporocysts

Humoral factors have been associated with resistance of Biomphalaria glabrata to infection by Schistosoma mansoni. The goal of this study was to determine which serum (cell-free hemolymph) proteins bind to the surface of S. mansoni sporocysts. For this, 125I-labeled serum from schistosome-resistant (10-R2) and -susceptible (M-line) B. glabrata was incubated with sporocysts, washed, and then subjected to SDS-PAGE and autoradiography. Other samples examined included radiolabeled 10-R2 and M-line serum, sporocysts incubated with unlabeled serum followed by incubation with radiolabeled serum, and radiolabeled sporocysts. Results indicated that many polypeptides in the serum from both strains of B. glabrata were radiolabeled. Dominating both profiles were bands in the 90-210-kDa range. However, some differences between the serum of the 2 snail strains were observed with M-line serum having several radiolabeled polypeptides in the 31-40- and 66-85-kDa range that were absent in serum from 10-R2 B. glabrata. When sporocysts were incubated with radiolabeled serum, 3 polypeptides (116, 180, 210 kDa) from both snail strains bound to the surface of the parasite. Further, a 55-kDa polypeptide bound to sporocysts incubated with 10-R2 serum but did not bind to those parasites incubated with M-line serum. Preincubation of sporocysts with unlabeled serum prior to incubation with radiolabeled serum significantly inhibited the uptake of radiolabeled proteins. This differential binding of serum polypeptides from different strains of B. glabrata may be important in determining resistance or susceptibility of the snail to larval schistosome infection.     

Characterization of excretory-secretory proteins synthesized in vitro by Schistosoma mansoni primary sporocysts

Excretory-secretory (E-S) products released by larval schistosomes have been implicated in the interference of host snail defense systems. Because of the potentially important role that E-S products play in the parasite-host relationship, total and newly synthesized E-S proteins from in vitro-cultured Schistosoma mansoni primary sporocysts were characterized using incorporation of [35S]methionine followed by sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. Total E-S protein decreased more than 5-fold from day 1 to day 3 of culture and remained constant until day 8 when protein concentrations began to increase. Release of newly synthesized protein, however, increased from day 1 through day 8. Both silver staining and fluorography of SDS-PAGE-separated E-S products revealed a wide variety of polypeptides ranging in Mr from 13 to greater than 200 kDa. The dynamics of the release of individual polypeptides, both total and newly synthesized, varied over time. Although certain polypeptides decreased in concentration, others remained constant or increased with time in culture. Culture conditions were found to be important for sporocyst viability and growth, and for release of newly synthesized proteins. Sporocysts cultured in medium containing fetal bovine serum (complete) grew significantly larger and had a significantly greater viability than did sporocysts cultured in medium lacking serum (incomplete). Also, sporocysts cultured in complete medium synthesized and released significantly more protein than did sporocysts cultured in incomplete medium. These sporocysts continued to produce a 54-kDa polypeptide, whereas sporocysts in incomplete medium stopped producing this protein by day 3 of culture. The present study has shown that S. mansoni primary sporocysts, cultured in vitro, synthesize and secrete a wide variety of glycoproteins and that the type and quantity of glycoproteins released are dependent on culture conditions.     

Glycotope sharing between snail hemolymph and larval schistosomes: larval transformation products alter shared glycan patterns of plasma proteins

Recent evidence supports the involvement of inducible, highly diverse lectin-like recognition molecules in snail hemocyte-mediated responses to larval Schistosoma mansoni. Because host lectins likely are involved in initial parasite recognition, we sought to identify specific carbohydrate structures (glycans) shared between larval S. mansoni and its host Biomphalaria glabrata to address possible mechanisms of immune avoidance through mimicry of elements associated with the host immunoreactivity. A panel of monoclonal antibodies (mABs) to specific S. mansoni glycans was used to identify the distribution and abundance of shared glycan epitopes (glycotopes) on plasma glycoproteins from B. glabrata strains that differ in their susceptibilities to infection by S. mansoni. In addition, a major aim of this study was to determine if larval transformation products (LTPs) could bind to plasma proteins, and thereby alter the glycotopes exposed on plasma proteins in a snail strain-specific fashion. Plasma fractions (< 100 kDa/> 100 kDa) from susceptible (NMRI) and resistant (BS-90) snail strains were subjected to SDS-PAGE and immunoblot analyses using mAB to LacdiNAc (LDN), fucosylated LDN variants, Lewis X and trimannosyl core glycans. Results confirmed a high degree of glycan sharing, with NMRI plasma exhibiting a greater distribution/abundance of LDN, F-LDN and F-LDN-F than BS-90 plasma (< 100 kDa fraction). Pretreatment of blotted proteins with LTPs significantly altered the reactivity of specific mABs to shared glycotopes on blots, mainly through the binding of LTPs to plasma proteins resulting in either glycotope blocking or increased glycotope attachment to plasma. Many LTP-mediated changes in shared glycans were snail-strain specific, especially those in the < 100 kDa fraction for NMRI plasma proteins, and for BS-90, mainly those in the > 100 kDa fraction. Our data suggest that differential binding of S. mansoni LTPs to plasma proteins of susceptible and resistant B. glabrata strains may significantly impact early anti-larval immune reactivity, and in turn, compatibility, in this parasite-host system.     

Lectin and human blood group determinants of Schistosoma mansoni: alteration following in vitro transformation of miracidium to mother sporocyst.

A mixed agglutination assay method was employed to detect the presence of surface determinants for various lectins and human blood group antibodies on Schistosoma mansoni miracidia and cultured mother sporocysts. Miracidia were found to possess surface receptors for the lectins Con A (concanavalin A), anti-Heel (eel serum agglutinin), and anti-ADb (Dolichos seed extract), as well as human anti-A antibodies. Following in vitro transformation of the miracidium to mother sporocyst, anti-Heel and human anti-A receptors were no longer detectable on the sporocyst surface, while determinants for Con A and anti-ADb remained essentially unaltered. It is concluded that transition of the miracidium to the sporocyst results in the alteration of surface molecular structures on schistosome larve. Furthermore, since determinants for Con A, anti-Heel, anti ADb, and human anti-A have been found associated with macromolecules in the hemolymph of the snail Biomphalaria glabrata (Stnislawski et al., 1976), there is now evidence that miracidia and mother sporocysts of S. mansoni and their snail host share molecules with common lectin and human blood group determinants.     

Serotonin-induced muscular activity in Schistosoma mansoni larval stages: importance of 5-HT transport and role in daughter sporocyst production

Mother sporocysts of Schistosoma mansoni transport exogenously supplied serotonin (5-hydroxytrypamine; 5-HT), and respond to it with increases in motility. In the present study, we investigated the importance of 5-HT transporter activity in the manifestation of these 5-HT-induced motility changes, and further examined the role of 5-HT in the development of daughter sporocysts in vitro. Serotonin-induced motility of in vitro-derived sporocysts is not inhibited by antidepressant compounds, e.g., fluoxetine, that block 5-HT transport, suggesting that the receptors responsible for motility responses to 5-HT are surface exposed. Using a sporocyst in vitro culture system, we show that depletion of larval stores of 5-HT reduces production of daughter sporocysts, the second intramolluscan larval stage. Moreover, we demonstrate a strong correlation between endogenous 5-HT levels and basal mother sporocyst muscle activity. Overall, these data suggest that larval stages of S. mansoni can detect exogenous 5-HT via surface-exposed receptors, and they are consistent with the hypothesis that endogenous stores of 5-HT are important for the proper regulation of muscular contractions in mother sporocysts, and for the successful emergence of daughter sporocysts.     

Differential expression of LacdiNAc,fucosylated LacdiNAc,and Lewis x glycan antigens in intramolluscan stages of Schistosoma mansoni

We report the expression of 3 well-characterized adult Schistosoma mansoni glycan antigens among molluscan stages of the parasite. These antigens are LacdiNAc (LDN; GalNAcbeta1-4GlcNAc-R), fucosylated LacdiNAc (LDNF; GalNAc[Fucal-3]beta1-4GlcNAc-R), and Lewis x (Le(x); Gal[Fucalpha1-3]beta1-4GlcNAc-R). The presence of the glycans was determined by both immunoblot and immunohistological methods using monoclonal antibodies that specifically recognize each glycan epitope. Immunoblot analyses reveal that LDN and LDNF epitopes are expressed on many different glycoproteins, including eggs, mother sporocysts, daughter sporocysts, and cercariae, although LDN expression among daughter sporocysts is greatly reduced. LDN and LDNF epitopes are localized on the tegument and in the intrasporocyst cell masses of both in vitro-derived and in vivo-derived mother sporocysts and in the daughter sporocysts derived on day 16 after infection. Unexpectedly, high levels of LDN and LDNF glycans were detected in the infected, but not in the uninfected, snail hemolymph, suggesting that the infecting larvae secrete LDN and LDNF glycoconjugates into the snail hosts. In contrast, the expression of Le(x) antigen among the molluscan stages is highly restricted. Le(x) is present on a few high-molecular weight glycoproteins in eggs and cercariae but is undetectable in mother and daughter sporocysts. Taken together with our earlier studies on vertebrate stages of S. mansoni, these results show that LDN and LDNF glycans are conserved during schistosome development. The study further extends the evidence that Le(x) is a developmentally regulated antigen in schistosomes.     

The destruction of Schistosoma mansoni mother sporocysts in vitro by amoebae isolated from Biomphalaria glabrata: an ultrastructural study

Some of the ultrastructural features of the in vitro destruction of the mother sporocyst of Schistosoma mansoni by amoebae (Nuclearia sp.) isolated from the pericardial sacs of Biomphalaria glabrata are described. The interaction involves (1) the attachment of the amoeba plasma membrane to the tegumental membrane of the sporocyst, (2) penetration of the tegument by a single cell process containing only a finely granular cytoplasm, (3) the lytic destruction of the sporocyst tissues, and (4) their removal by phagocytosis. Since the amoebae retain their lysosomal complement, the mechanisms of sporocyst penetration and lysis are unknown. Myelin figures and multivesiculate and residual bodies are frequently seen in amoebal secondary lysosomes. Cell organelles and body components of the sporocysts are phagocytosed by amoebae attached to their surfaces, located inside the body or elsewhere in the vicinity of the disintegrating sporocyst.     

Axenic culture of Schistosoma mansoni sporocysts in low O2 environments.

Recent successes in culturing intramolluscan larval stages of Schistosoma mansoni have relied on synxenic culture with a cell line (Bge) developed from embryos of a molluscan host Biomphalaria glabrata. To further facilitate progress toward control of schistosomiasis, a system for axenic in vitro culture of the parasite has now been developed. When culture media were preconditioned by Bge cells, sporocysts lived longer in vitro and produced more offspring. Because Bge-derived components could be protecting sporocysts from oxidative stress, axenic sporocysts were cultured at lowered O2 levels. In an hypoxic environment, S. mansoni sporocysts grew well and produced daughter sporocysts continuously under axenic conditions and in a medium completely lacking host molecules. Sporocyst production occurs independently of host influence.     

Encapsulation response of the marine prosobranch Cerithidea californica to natural infections of Renicola buchanani sporocysts (Trematoda: Renicolidae)

A hyalinocyte-mediated encapsulation reaction is elicited by sporocysts of Renicola buchanani infecting the anterior mantle region of Cerithidea californica. Three phases of capsule formation are recognized: (1) an initial aggregating of hyalinocytes around each sporocyst in which pseudopodia from encapsulating cells loosely interdigitate with the parasite's tegumental microvilli, (2) the infiltrating of numerous hyalinocytes to form a dense matrix of cells which lies in close contact with the sporocyst's tegument, and (3) the horizontal flattening of hyalinocytes against the sporocyst's surface to form a tightly adhering capsule four to eight cell layers deep. Sporocysts are not harmed as a consequence of encapsulation. Capsule formation in response to R. buchanani sporocysts is considered a type of leucocytic encapsulation, specifically designated hyalinocytic encapsulation.     

Secretory protein biosynthesis in snail hemocytes: in vitro modulation by larval schistosome excretory-secretory products

Circulating hemocytes of the snail, Biomphalaria glabrata, synthesize and secrete a variety of polypeptides when maintained in vitro in serum-free medium containing [35S] methionine. SDS-PAGE/fluorographic analysis of supernatants from resistant snail (10-R2-OK strain) hemocyte cultures revealed the presence of numerous labeled polypeptides ranging in Mr from 220 to 14 kDa. Most of these same proteins were also produced by hemocytes of a susceptible B. glabrata strain (M-line), but the overall rate of secretory protein synthesis was reduced from that of resistant snail cells. In addition, excretory-secretory (ES) products contained in supernatants from Schistosoma mansoni miracidial transformation and 1-day primary sporocyst cultures stimulated increases in the synthesis of various polypeptides. Particularly striking was a 3-fold increase in the synthesis of a 66-kDa secretory polypeptide by hemocytes of both snail strains, and a concomitant increase in M-line hemocytes and decrease in 10-R2-OK cells of a 63-kDa polypeptide. Overall, however, the level of ES product-induced secretory protein synthesis was greater in 10-R2-OK snail hemocytes than in those of the M-line strain. Exposure of a nonhemocytic B. glabrata cell line to parasite culture supernatants had no stimulatory/inhibitory effect on labeled protein ouput, suggesting that the observed hemocyte response may be snail cell-type specific. Finally, the larval ES components responsible for modulating hemocyte protein metabolism are mainly concentrated in a heat-stable fraction composed of molecules of greater than 30 kDa. However, the loss of the ability of heated parasite products to stimulate synthesis of certain hemocyte proteins and the presence of minor stimulating activity in a low molecular weight fraction (less than 10 kDa) implies the possible existence of multiple larval components affecting formation of specific hemocyte secretory polypeptides. It is concluded that snail hemocytes are capable of in vitro synthesis and secretion of a variety of methionine-containing polypeptides, and that ES products of early larval schistosomes can modulate (i.e., stimulate or inhibit) this metabolic process. A differential response of susceptible vs. resistant hemocytes to larval products suggests that the degree to which these cells can be metabolically activated may determine their cytotoxic effectiveness.     

Depletion interactions in polymer solutions promote red blood cell adhesion to albumin-coated surfaces

The effects of concentration and molecular weight of neutral dextrans on the adhesion of human red blood cells (RBC) to albumin-coated glass have been investigated using a parallel-plate flow chamber. Results indicate that the adhesion is markedly increased in the presence of 70 kDa and 500 kDa dextran, with this increase reflected by both the number of cells adhering and the strength of the adhesion. This increased adhesiveness is attributed to reduced surface concentrations of the large polymers and hence attractive forces due to depletion interaction. Depletion interaction brings the adjacent surfaces closer, leading to an increased number of binding sites available to the cell and thus more efficient and stronger adhesion of single cells. Our results suggest that depletion might play a role in other specific cell-cell or cell-surface interactions via initiating close contacts to allow specific binding.     

Purification and binding properties of hemagglutinin from Biomphalaria glabrata.

A hemagglutinin has been purified from Biomphalaria glabrata (PR-B) hemolymph, albumin glands, and egg masses using affinity chromatography with Sephadex gels. The purified material from any of the sources above demonstrated identical immunological properties during immunoelectrophoresis or immunodiffusion, and similar serological specificity for human A₁ erythrocytes and to a lesser extent A₂ erythrocytes. Hemagglutinin was able to bind in vitro to the tegumental surface of cultured Schistosoma mansoni sporocysts, cercariae, and miracidia. Sporocysts dissected from infected snails and shed cercariae were already found to have hemagglutinin on their tegumental surface as demonstrated by immunofluorescence. It is postulated that hemagglutinin binding to the surface of larval helminths may “mask” them from being recognized by the snail host's cellular defense system.     

Sulfated glycoconjugates are powerful modulators of bovine sperm adhesion and release from the oviductal epithelium in vitro

The mechanisms of sperm adhesion and release within the mammalian oviduct are still poorly understood. In this in vitro study, a previously developed adhesion assay was used to analyze the effects of heparin, N-desulfated heparin, fucoidan, dextran sulfate, and dextran on bovine sperm-oviductal cell adhesion and release. Results showed that 1) all sulfated glycoconjugates were powerful inhibitors of sperm binding to oviductal monolayers in a dose-dependent manner, whereas N-desulfated heparin and dextran had no effect; 2) sperm pretreatment with heparin and fucoidan markedly inhibited adhesion; 3) treatment of oviductal monolayers with heparinase I, II, or sodium chlorate (an inhibitor of sulfation) had no effect on sperm adhesion; 4) sulfated glycoconjugates were also powerful and quick inducers of sperm release from oviductal monolayers; and 5) addition of sulfated glycoconjugates to the cocultures caused a sudden increase of bound-sperm flagellar beat frequencies, followed by a release of highly motile sperm. In conclusion, these data support the hypothesis that sulfated glycoconjugates may act as signals that induce sperm release and migration from the oviductal reservoir.     

Glycoconjugates and cell adhesion: the adhesive proteins laminin, thrombospondin and von Willebrand's factor bind specifically to sulfated glycolipids

The adhesive glycoproteins laminin, thrombospondin and von Willebrand's factor bind specifically and with high affinity to sulfated glycolipids, and it is this binding that probably accounts for their ability to agglutinate glutaraldehyde-fixed erythrocytes. The 3 proteins differ, however, in the effect of sulfated polysaccharides on their binding to sulfatides. Fucoidan strongly inhibits binding of both laminin and thrombospondin, but not of von Willebrand's factor, suggesting the involvement of laminin or thrombospondin or other unknown sulfatide-binding proteins in specific cell interactions that are also inhibited by fucoidan. Thrombospondin adsorbed onto plastic promotes the attachment and spreading of G361 melanoma cells. Interestingly, fucoidan and an antibody directed against the sulfatide-binding domain of thrombospondin selectively inhibit spreading but not attachment. Sulfatides, but not neutral glycolipids or gangliosides, when adsorbed onto plastic also promote attachment and spreading of G361 melanoma cells. Direct adhesion of G361 cells requires high densities of sulfatide. In the presence of laminin, however, specific adhesion of G361 cells to sulfatide is strongly stimulated and requires only low densities of adsorbed lipid, suggesting that laminin mediates adhesion by cross-linking receptors on the melanoma cell surface to sulfatide adsorbed onto the plastic. Although thrombospondin binds to sulfatide and to G361 cells, it does not enhance but rather inhibits direct and laminin-dependent G361 cell adhesion to sulfatide, presumably because it is unable to bind simultaneously to ligands on opposing surfaces. Thus, sulfated glycoconjugates participate in both laminin- and thrombospondin-mediated cell adhesion, but their mechanisms of interaction are different.     

Sequence of reconversion of the sporocysts of Schistosoma mansoni producing cercariae, to the production of new generations of sporocysts (author's transl)

During the life cycle of Schistosoma mansoni the production of sporocysts of a higher order than secondary is a normal mode of larval multiplication which intervenes in asexual reproduction of the parasite. The sequence of reconversion of sporocysts producing cercariae to those producing sporocysts III, IV, etc... can be divided into three principal steps: (1) cessation of cercariae production; (2) degeneration of cercariae contained in the sporocyst, and (3) production of the new generation of sporocysts. Degeneration of intrasporocystic larval material seems to be an indispensable step for the new orientation of production. The signifance of this method os multiplication in the ecology of transmission is discussed.