Cytochemical characterization of tegument membrane-associated carbohydrates in Taenia crassiceps larvae.

The tegument of larval Taenia crassiceps possesses a surface coat rich in both neutral and acidic carbohydrates. Neutral glycans were detected in Golgi vesicles of the tegument perikarya, vesicles of the distal tegument, and on the surface of the plasma membrane. Autoradiographs indicated the tegument perikarya as major sites of 3H-galactose incorporation into acid-insoluble macromolecules. The labeled material is subsequently translocated to more superficial regions of the tegument, then concentrated in the brush border. Loss of radioactivity is appreciable within 6 hr of the synthesis of this material, indicating continual replacement of this tegument surface component.     

Taenia crassiceps: Regional variations in ultrastructure and evidence of endocytosis in the cysticercus' tegument

Regional variations in the thickness of the tegument, in the morphology of microtriches and mitochondria, in the distribution of dense bodies, smooth micropinocytotic vesicles (SMVs), and coated micropinocytotic vesicles (CMVs) have been shown for the cysticercus of Taenia crassiceps. The number of SMVs and CMVs present in the syncytial layer are in inverse proportion to each other, the former being more numerous in the bladder wall and upper part of the invagination canal and the latter in the lower part of the canal and the rostellar region. Tegumental cells contain numerous granular endoplasmic reticulum-Golgi complexes involved in the synthesis of both primary lysosomes and dense bodies. Vesicles characteristic of various stages of heterolysosomes are present and show regional variations in numbers and size. Acid phosphatase activity (EC 3.1.3.2) is present on the tegumental surface, and within the Golgi complex, primary lysosomes, and heterophagosomes of the tegumental cells. CMVs are reported for the first time in the tegument of any helminth and have characteristics similar to CMVs in other tissues. T. crassiceps, therefore, because of the presence of both SMVs and CMVs, is a unique model system for the study of basic mechanisms of endocytosis.     

Protective immunity against Taenia crassiceps murine cysticercosis induced by DNA vaccination with a Taenia saginata tegument antigen

This study investigated the protective capacity of the recombinant Taenia saginata Tso18 antigen administered as a DNA vaccine in the Taenia crassiceps murine model of cysticercosis. This Tso18 DNA sequence, isolated from a T. saginata oncosphere cDNA library, has homologies with Taenia solium and Echinococcus sp. It was cloned in the pcDNA3.1 plasmid and injected once intramuscularly into mice. Compared to saline-vaccinated control mice, immunization reduced the parasite burden by 57.3-81.4%, while lower levels of non-specific protection were induced in control mice injected with the plasmid pcDNA3.1 (18.8-33.1%) or a plasmid with irrelevant construct, pcDNA3.1/3D15 (33.4-38.8%). Importantly, significant levels of protection were observed between the pcDNA3.1/Tso18 plasmid and pcDNA3.1/3D15 plasmid immunized mice. Mice immunized with pTso18 synthesized low levels of, primarily IgG1 sub-class, antibodies. These antibodies were shown to recognize a 66 kDa antigen fraction of T. crassiceps and T. solium. Splenocytes enriched in both CD4+CD8- and CD4-CD8+ T cells from these vaccinated mice proliferated in vitro when exposed to antigens from both T. solium and T. crassiceps cestodes. Immunolocalization studies revealed the Tso18 antigen in oncospheres of T. saginata and T. solium, in the adult tapeworm and in the tegument of T. solium cysticerci. The protective capacity of this antigen and its extensive distribution in different stages, species and genera of cestodes points to the potential of Tso18 antigen for the possible design of a vaccine against cestodes.     

Mechanisms and specificity of amino acid transport in Taenia crassiceps larvae (Cestoda)

The absorption of lysine, arginine, phenylalanine and methionine by Taenia crassiceps larvae is linear with respect to time for at least 2 min. Arginine uptake occurs by a mediated system and diffusion, and arginine, lysine and ornithine (in order of decreasing affinity) are completely competitive inhibitors of arginine uptake. The basic amino acid transport system has a higher affinity for l-amino acids than d-amino acids, and blocking the α-amino group of an amino acid destroys its inhibitory action. Phenylalanine uptake by T. crassiceps larvae is inhibited in a completely competitive fashion by serine, leucine, alanine, methionine, histidine, phenylalanine, tyrosine and tryptophan (in order of increasing affinity). Methionine apparently binds non-productively to the phenylalanine (aromatic amino acid-preferring) transport system. l-methionine uptake by larvae is inhibited more by d-alanine and d-valine than by their respective l-isomers, while d- and l-methionine inhibit l-methionine uptake equally well. The presence of an unsubstituted α-amino group is essential for an inhibitor to have a high affinity for the methionine transport system. Uptake of arginine, phenylalanine and methionine is Na⁺-insensitive, and both phenylalanine and methionine are accumulated by larvae against a concentration difference in the presence or absence of Na⁺. Arginine accumulation is precluded by its rapid metabolism to proline, ornithine and an unidentified compound.     

Taenia crassiceps organic acids detected in cysticerci

Taenia crassiceps cysticerci is used as an experimental model to cysticercosis studies; however there are subcutaneous cases of cysticercosis caused by these cysticerci. It remains unclear in the literature the energetic and fatty acid metabolism in cestodes. Its metabolic study may provide knowledge of pathways that may serve as potential anti-helminthic drugs sites of action. In this work we studied the citric acid cycle organic acids and the fatty acid oxidation in cysticerci removed from mice with 21 and 42 days of infection in two different evolutive stages: growing and final. The organic acids were extracted using perchloric acid and analyzed by HPLC methodology. We found significant statistically differences in oxalate, malate, lactate, and beta-hydroxybutirate concentrations between cysticerci. These results indicate the aerobic metabolism in vivo in spite of the low oxygen concentration of its habitat, and also indicate the presence of fatty acid oxidation as an alternative energetic source.     

Metabolism of steroid hormones by Taenia solium and Taenia crassiceps cysticerci

Previous in vitro experiments showed that both, Taenia crassiceps and Taenia solium cysticerci have the ability to metabolize exogenous androstenedione to testosterone. Here we evaluate on the capacity of both cysticerci to synthesize several sex steroid hormones, using different hormonal precursors. Experiments using thin layer chromatography (TLC) showed that both cysticerci were able to produce ³H-hydroxyprogesterone, ³H-androstenedione and ³H-testosterone when ³H-progesterone was used as the precursor. They also synthesized ³H-androstenediol and ³H-testosterone when ³H-dehydroepiandrosterone was the precursor. In addition, both cysticerci interconverted ³H-estradiol and ³H-estrone. These results, strongly suggest the presence and activity of the Δ4 and Δ5 steroid pathway enzymes, 3β-hydroxysteroid dehydrogenase/Δ^5-4 isomerase-like enzyme (3β-HSD), that converts androstenediol into testosterone; and the 17β-hydroxysteroid dehydrogenase that interconverts estradiol and estrone, in both types of cysticerci.     

Taenia crassiceps: absorption of hexoses and partial characterization of Na + -dependent glucose absorption by larvae

The uptake of ¹⁴C-fructose by T. crassiceps larvae was linear with respect to concentration. Uptake of 0.05 mM¹⁴C-fructose was not inhibited by 5.0 mM unlabeled fructose, tagatose, or sorbose. Fructose appears to enter larvae by diffusion only. The uptake of radioglucose and radiogalactose was not linear with respect to concentration at low substrate concentrations; at high substrate concentrations, the uptake of both hexoses was linear with respect to concentration. Inhibitor studies indicated that both glucose and galactose enter larvae by a combination of diffusion and a mediated process, and that these hexoses are mutually competitive inhibitors of one another. The uptake of glucose and galactose was also inhibited by α-and β-methyl glucoside, fucose, and phlorizin, but not by several amino acids, certain sugar analogs, nor ouabain. Glucose transport is Na⁺ sensitive; K⁺ was demonstrated to be a competitive inhibitor of Na⁺ activation of glucose uptake. After a 90-min incubation in 5 mM unlabeled glucose, larvae accumulated glucose against an apparent concentration difference. Although larvae appear freely permeable to ouabain, this compound had no apparent effect on glucose accumulation. The results of this study are compared with previous studies on Hymenolepis diminuta, Calliobothrium verticillatum, Hydatigera (Taenia) taeniaeformis, and mammalian systems.     

Taenia crassiceps: experimental model of intraocular cysticercosis

An experimental model of Taenia crassiceps intraocular cysticercosis was developed in rabbits. The objectives of this study were to analyze the pathophysiology of this parasitic infection and to evaluate the humoral immune response. Cysticerci, inoculated in the anterior chamber of the eye, were able to grow; no inflammatory changes in the eye or anticysticercus antibodies in serum or in aqueous humor were detected during the 12-day period. In contrast, rabbits that had previously been either infected intraperitoneally with living T. crassiceps cysts or immunized intramuscularly with T. crassiceps antigenic extract developed an intense inflammatory reaction in the eye and high levels of antibodies were detected in serum and aqueous humor even before the intraocular inoculation of parasites. Furthermore, intraocular cysticerci showed minimal growth and some were eliminated. These findings support the concept that the eye is an immunologically privileged site in the nonimmunized host and the importance of the immune response in the elimination of this parasitic infection.     

Steroid hormone production by parasites: the case of Taenia crassiceps and Taenia solium cysticerci

Many examples of reciprocal endocrine interactions between parasites and hosts have been found in insects, arthropods and mammals. Cysticercosis produced by Taenia solium metacestodes is a widely distributed parasite infection that affects the human and the pig. Taenia crassiceps experimental murine cysticercosis has been used to explore the role of biological factors involved in host–parasite interactions. We had shown that T. crassiceps cysticercosis affects the serum concentration of steroid hormones and the reproduction behavior of the male mice host. In an effort to understand the biology of the parasite, we had investigated the parasite capacity to produce sex steroids. For this purpose, T. crassiceps cysticerci were incubated in the presence of different steroid precursors. TLC and recrystallization procedures showed that testosterone is produced from ³H-androstenedione in cysticerci. The conversion of ³H-testosterone to androstenedione, although present is much less significant. In addition, we had studied the production of testosterone by T. solium cysticerci. For this purpose, cysticerci were dissected from pork meat and incubated as above described. The results showed that T. solium cysticerci also produce testosterone. We have speculated about the importance of androgens in the growth of T. crassiceps cysticerci and found that the addition of the antiandrogen flutamide to the culture media of the parasites significantly decreased ³H-thymidine incorporation. We therefore hypothesized, that the ability of cysticerci to produce testosterone from steroid precursors might be important for the parasite growth and development.     

Evagination and infectivity of Taenia crassiceps cysticerci in experimental animals

Cysticerci of Taenia crassiceps reproduce asexually by exogenous budding in the rodent intermediate host, and can experimentally develop to the adult stage within the small intestine of golden hamsters. In the present study, we report the loss of cysticercus infectivity for hamsters after maintaining the strain for 4 yr by consecutive peritoneal passage in mice. Larval infectivity was restored after a cysticercus from the WFU strain developed into a gravid tapeworm after being passaged through a dog. The eggs of this tapeworm were infective for mice, which subsequently developed cysticerci with renewed capability for infecting experimental hamsters. An in vitro evagination assay was also conducted using eleventh-generation WFU strain cysticerci, as well as second- and fourth-generation dog-derived cysticerci. Significantly higher (P < 0.0001) evagination was observed for 5-mo-old dog-derived and WFU infrapopulations when compared with respective evagination values for 9- and 12-mo-old infrapopulations. The extent of evagination was linked to the capacity of cysticerci to infect hamsters, so that greater evagination resulted in a higher infectivity for hamsters and vice versa.     

Translation of Taenia crassiceps mRNA in cell-free heterologous systems.

1. mRNA isolated from larval Taenia crassiceps directs efficiently the synthesis of proteins in cell-free heterologous systems. 2. Part of the newly synthesized proteins in a reticulocyte system are precipitable by a rabbit antiserum against T. crassiceps proteins. 3. Analysis of the antiserum-protein dissociated complex by sodium dodecyl sulfate polyacrylamide gel electrophoresis indicates that most of the proteins synthesized are of low molecular weight (13,000-22,000) although a protein of mol. wt. 260,000 is also produced. 4. Whether the newly synthesized proteins which are precipitable by specific antisera correspond to parasite antigens or to proteins with closely antigenic similarities remains to be established.     

Different effects of chorionic gonadotropin on Taenia crassiceps and Taenia solium cysticerci cultured in vitro

Hormones play a significant role in murine Taenia crassiceps cysticercosis, and they may also participate in the susceptibility to Taenia solium cysticercosis. In the present study, in vitro effects are reported for human chorionic gonadotropin (hCG) on the larval stages of T. crassiceps (WFU strain) and T. solium. hCG effectively promotes parasite reproduction, i.e., it increases the number of buds on T. crassiceps cysticerci and the percentage of evagination and parasite length in T. solium. This is the first report in which a direct effect of hCG is reported for a parasite. hCG or mouse luteinizing hormone could be recognized by the cysticerci as mitogenic factors and contribute to the female and pregnancy bias toward susceptibility to T. crassiceps and T. solium cysticercosis, respectively.