Ultrastructural damage of Trypanosoma cruzi epimastigotes exposed to decomplemented immune sera

The susceptibility of Trypanosoma cruzi epimastigotes to lysis by normal or immune sera in a complement-dependent reaction has been reported, but the effects induced directly by immune serum depleted of complement remain unstudied. The aim of this work was to study the ultrastructural alterations induced in T. cruzi epimastigotes by immune mouse or rabbit sera with or without complement. A local isolate of T. cruzi (Queretaro) was used in all experiments. Immune sera were raised in both mouse and rabbit by immunization with T. cruzi epimastigote antigens. Light microscopy showed intense agglutination of epimastigotes when incubated with decomplemented mouse or rabbit immune sera. A distinctive ultrastructural feature of this agglutination pattern was the fusion of plasma membranes and a pattern of intercrossing between subpellicular microtubules. Agglutination was associated with fragmentation of nuclear membranes and swelling of cytoplasm, Golgi cisternae, endoplasmic reticulum, mitochondria and kinetoplast membranes. Agglutinated parasites also incorporated trypan blue stain. Results of [3H]-thymidine incorporation confirmed that epimastigotes exposed to specific antibodies in the absence of complement were incapable of proliferating. Ultrastructural changes observed in epimastigote micrographs incubated with decomplemented immune mouse sera were statistically significant (P<0.001) when compared with results obtained from images after incubation with decomplemented normal mouse sera.

Taenia solium: germinal cell precursors in tapeworms grown in hamster intestine

BACKGROUND

In a previous study, it was shown that growth of evaginated metacestodes occurs in the germinative tissue of the neck by duplication of somatic stem cells. In these specimens, it was not possible to find the mitotic figures required to demonstrate duplication of germ cell lines.

METHODS

Taenia solium strobilae were collected from the intestinal lumen of outbred hamsters infected orally with 10 metacestodes dissected from naturally infected pigs. Animals were anesthetized 1-10 days postinfection, the small intestine excised, submerged in PBS, and cut open longitudinally. Live Taenias were incubated for 6-8 h in medium containing colchicine or 3H-thymidine, washed, and embedded for electron microscopy. For light microscopy and autoradiography, longitudinal sections were cut from whole blocks and mounted on glass slides. A population of large cells without nuclear membranes and containing discrete aggregates of chromatin were observed apposed to myofibrils in the germinative tissue of the neck. These cells were confirmed by electron microscopy as metaphase mitotic figures, with chromosomes attached to a microtubular spindle, embedded in cytoplasm, without a nuclear membrane, and with characteristic centrioles.

RESULTS

Only tapeworms in which 3H-thymidine was injected directly into the worm tissue by microsyringe were positive by autoradiography, demonstrating that in contrast to evaginated metacestodes, intestinal worms do not transport thymidine across the tegument.

CONCLUSIONS

The results show that differentiating T. solium worms have a subset of stem cells that require passage through a mammalian host to go into mitosis, and that tapeworms grown in an experimental animal do not take up 3H-thymidine in vitro.

Characterization of a monoclonal antibody directed to the surface of MA104 cells that blocks the infectivity of rotaviruses

Rhesus rotavirus (RRV) binds to sialic acid residues on the surface of target cells, and treatment of these cells with neuraminidase greatly reduces virus binding with the consequent reduction of infectivity. Variants that can efficiently infect neuraminidase-treated cells have been isolated, indicating that attachment to sialic acid is not an essential step for animal rotaviruses to infect cells. To identify and characterize the neuraminidase-resistant receptor for rotaviruses, we have isolated a hybridoma that secrets a monoclonal antibody (MAb) (2D9) that specifically blocks the infectivity of wild-type (wt) RRV and of its sialic acid-independent variant nar3, in untreated as well as in neuraminidase-treated cells. The infectivity of a human rotavirus was also inhibited, although to a lesser extent. MAb 2D9 blocks the binding of the variant to MA104 cells, while not affecting the binding of wt RRV; in addition, this MAb blocked the attachment of a recombinant glutathione S-transferase (GST)-VP5 fusion protein, but did not affect the binding of GST-VP8. Altogether these results suggest that MAb 2D9 is directed to the neuraminidase-resistant receptor. This receptor seems to mediate the direct attachment of the variant to the cell, through VP5, while the receptor is used by wt RRV for a secondary interaction, after its initial binding to sialic acid, through VP8. MAb 2D9 interacts specifically with the cell surface by indirect immunofluorescence, immunoelectron microscopy, and FACS. By a solid-phase immunoisolation technique, MAb 2D9 was found to react with three proteins of ca. 47, 55, and 220 kDa, which might form a complex.

Characterization of glutathione S-transferase of Taenia solium

A Taenia solium glutathione-S-transferase fraction (SGSTF) was isolated from a metacestode crude extract by affinity chromatography on reduced glutathione (GSH)-sepharose. The purified fraction displayed a specific glutathione S-transferase (GST) activity of 2.8 micromol/min/mg and glutathione peroxidase selenium-independent activity of 0.22 micromol/min/mg. Enzymatic characterization of the fraction suggested that the activity was closer to the mammalian mu-class GSTs. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel filtration, and enzyme activity analysis showed that the fraction was composed of a major band of Mr = 26 kd and that the active enzyme was dimeric. Immunohistochemical studies using specific antibodies against the major 26-kd band of the SGSTF indicated that GST protein was present in the tegument, parenchyma, protonephridial, and tegumentary cytons of the T. solium metacestode. Antibodies generated against the SGSTF tested in western blot showed cross-reactivity against GSTs purified from Taenia saginata, T. taeniaeformis, and T. crassiceps, but did not react with GSTs from Schistosoma mansoni, or mice, rabbit, and pig liver tissue. Furthermore, immunization of mice with SGSTF reduced the metacestode burden up to 74.2%. Our findings argue in favor of GST having an important role in the survival of T. solium in its hosts.

Formation of calcareous corpuscles in the lumen of excretory canals of Taenia solium cysticerci

Platyhelminths, like many other organisms, are capable of producing mineral concretions. In cestodes these are referred to as calcareous corpuscles. Studies on these concretions in different cestodes both in vivo and in vitro have resulted in a number of hypotheses on their origin, formation, and structure. Calcareous corpuscles are believed to be of cellular origin, although the kind of cell involved and the mechanisms of mineralization remain under discussion. In the present paper we show that formation of calcareous corpuscles in cysticerci of Taenia solium is not of intracellular origin, as described for other cestodes, but occurs extracellularly in the lumen of protonephridial ducts in a way similar to that proposed for trematodes. This finding enhances the function of the protonephridial ducts, at least in the larvae of T. solium, to the roles formerly ascribed to the calcareous corpuscles.

Taenia solium: description of the intestinal implantation sites in experimental hamster infections

Experimental infections in golden hamsters with viable Taenia solium metacestodes were used to study by light and electron microscopy the implantation site of the adult tapeworm in the intestinal wall. Implantation sites from 3-, 4-, 10-, and 40-day infections were located in the upper third of the duodenum, excised and fixed in Zenker's or Karnovsky's solution, embedded in Polybed resin, and sectioned longitudinally to observe the position of the worm on the intestinal wall. The scolex of the tapeworm was situated between host villi, with the rostellum penetrating the intestinal wall and the suckers entrapping adjacent villi. Serial sections through several whole implantation sites revealed that the worm was anchored to the host by all 4 suckers simultaneously, each of which was located at a different level and had entrapped intestinal villi in its cavity. Host tissue within the suckers was damaged, exhibiting various degrees of cell lysis and necrosis of epithelial and submucosal cells. The tegumentary surface and microtriches of the scolex were well preserved, with occasional coalescence of tegumentary microvesicles in 10- and 40-day-old infections; microtriches were in direct contact with the damaged host tissue. This study is the first morphological and ultrastructural description of the attachment of T. solium to the intestinal wall employing an experimental model, the results of which may contribute to a better understanding of the biology of human tapeworm infections.

Host cells in the spiral canal of Taenia solium (Cestoda) cysticerci

The presence of host inflammatory cells inside the spiral canal of all viable Taenia solium cysts obtained from naturally infected pigs is described. Cells can penetrate into the vicinity of suckers and rostellum, although most appear damaged, suggesting that conditions in the canal are deleterious for them. These observations extend the localization of host inflammatory infiltrate to this intricate microniche, which may offer new approaches for the treatment of cysticercosis, based on a scolex-targeted action. The presence of host cells in the canal of cysts also poses the problem of the resulting contamination with host materials in studies using cysts extracts. As an example, host DNA contamination is readily detectable in genomic DNA isolated from T. solium and Taenia taeniaeformis cysts, as demonstrated by polymerase chain reaction amplification and subsequent sequencing of a segment of the 18S ribosomal gene.

Autoradiographic analysis of the germinative tissue in evaginated Taenia solium metacestodes

Evaginated Taenia solium metacestodes dissected from infected pork meat were incubated in vitro in RPMI 1640 medium with tritiated thymidine, washed, and further incubated for various chase periods. Worms were fixed and embedded in Poly/Bed and sections were processed for autoradiography. Results showed that all longitudinal sections had a germinative region located 500-700 mm posterior to the apex of the scolex with tegumentary cytons arranged in staggered columns perpendicular to the tegument. After 6-hr pulse and 0-12-hr chase periods, a large number of labeled cells were found in the parenchyma and tegumentary wall, included were myocytons, calcareous corpuscle cells, flame cells, osmoregulatory channel cells, and, in the medullary parenchyma, labeled undifferentiated round cells with a large nucleus, prominent nucleolus, abundant ribosomes, and no cytoplasmic organelles. These undifferentiated cells were not labeled after 24-hr and 48-hr chase periods, an observation that strongly suggests these cells divide and migrate toward the tegument in a pattern similar to that described for other cestodes. The morphology and localization of these cells support the view that they are stem cells that give rise to the various cell types of the tegumentary wall. The results indicate that T. solium contains a germinative tissue similar to that described in other cestodes, in which stem cells proliferate continuously, differentiate, and migrate to the tegument, constituting the main process by which these worms develop from metacestode to the adult stage.

In vitro culture of Taenia crassiceps larval cells and cyst regeneration after injection into mice

Taenia crassiceps cysticerci were disrupted through trypsinization to isolate cells which can be maintained in culture for up to 15 days. When injected intraperitoneally into susceptible BALB/cAnN mice, complete cysticerci were recovered in a number that is proportional to the quantity of injected cells. Thus, cysticerci contain cells which can reconstitute complete cysts, suggesting that individual cells play a role, independent to budding, during asexual multiplication of T. crassiceps cysticerci in the peritoneal cavity of mice. In contrast, injection of the cells into resistant C57BL/6J mice does not result in the recovery of complete cysts. These findings provide a new experimental model to identify resistance factors in the hosts, for the in vitro screening of anti-cysticerci drugs and for the genetic manipulation of cysticerci through recombinant DNA techniques.

Purification and ultrastructural localization of surface glycoproteins of Taenia solium (Cestoda) cysticerci

A glycoprotein-enriched fraction was obtained by Concanavalin A-Sepharose 4B affinity chromatography from a crude extract of T. solium cysticerci. The six most prominent glycoproteins with molecular sizes of 180, 103, 96, 68, 55 and 45 kDa were purified by electro-elution from polyacrylamide gel slices. Ultrastructural localization assays using hyperimmune rabbit sera to each glycoprotein, demonstrated their presence on the tegumentary surface of the bladder wall of T. solium cysticerci. Similar studies showed that the 180 kDa glycoprotein is also present on the surface of the T. solium and T. saginata adult worms, as well as in T. saginata, T. pisiformis and T. crassiceps cysticerci. The 55 kDa glycoprotein, which is one of the most abundant on the cyst surface, was found to correspond to the heavy chain of pig IgG by Western blotting.

Crystals of virus-like particles in the metacestodes of Taenia solium and T. crassiceps

Crystals of virus-like particles (VLP) are described as occurring in the nuclei of damaged tegumentary cytons from carcasses of Taenia solium metacestodes that had been stripped of their teguments. The VLP are grouped as parallel lines of round particles in an hexagonal packaging of spheroids forming small or large crystals. The individual particles have an external diameter of 36-37 nm and a wall of 5-6 nm thick, which surround a cavity of lower electron density. As identical crystals were also observed in normal tissues of T. solium and of T. crassiceps, it is suggested that both species of cysticerci are normal carriers of a similar species of virus. The possible biological implications of this condition are discussed.

Ultrastructural changes associated with the inhibition of monocyte chemotaxis caused by products of axenically grown Entamoeba histolytica

The supernatant fluid of axenically grown Entamoeba histolytica-HM1 significantly modifies the ultrastructural features associated with monocyte chemotaxis as assayed in Boyden chambers. This morphological evidence supports the existence of a factor, monocyte locomotion inhibitory factor (MLIF), produced by E. histolytica that inhibits the in vitro locomotion of human monocytes. None of the leucocyte-locomotion modifying drugs included in this study (i.e., cytochalasin-B, colchicine, vinblastine, and hydrocortisone) caused changes totally comparable with those induced by MLIF. The most striking feature was the increase of centriole-associated microtubules induced by MLIF and by cytochalasin-B. MLIF may inhibit monocyte locomotion by directly inducing excessive microtubule assembly, although a direct, if somewhat weak effect upon microfilaments cannot be excluded. The increase in microtubules could then represent a perhaps futile attempt of the microtubule organizing center to overcome the locomotion blockade that has occurred elsewhere in the cell. If active in vivo, MLIF may contribute to the paucity of inflammation in the advanced stages of invasive amebiasis, and consequently to the lack of scar tissue formation upon recovery from such lesions, as monocytes constitute an essential link to the healing process.

Histological and ultrastructural localization of antigen B in the metacestode of Taenia solium

The morphological localization of antigen B (AgB) in the tissues of the Taenia solium metacestode was studied by immunological and biochemical methods. Indirect immunofluorescence carried out on vibratome sections showed that AgB is widely distributed throughout the tissue. A more intense fluorescence was observed in the tegumentary cytons of the bladder wall and in the lumen of the spiral canal of the invaginated scolex. Ultrastructural analysis of larvae washed in PBS after dissection from meat and then incubated with rabbit antibodies against AgB, followed by peroxidase-labeled goat anti-rabbit IgG, did not exhibit electron-dense material on the external surface. Larvae fixed in glutaraldehyde immediately after dissection and exposed to the immunoperoxidase reagents did exhibit electron-dense material on microtriches, indicating that AgB is only loosely bound to the external surface. Crude extracts of surface-radioiodinated cysticerci analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) contained no labeled proteins with the molecular weight of AgB. Autoradiography of the immunoelectrophoretograms in which the crude extract was confronted with antibodies to AgB demonstrated that this antigen was not labeled, and therefore is not exposed on the tegumentary surface. The results suggest that AgB is synthesized by the tegumentary cytons of the parasite and secreted through the tegumental membrane into the host tissues and the lumen of the spiral canal.

The inflammatory reaction surrounding Taenia solium larvae in pig muscle: ultrastructural and light microscopic observations

An inflammatory reaction with the general characteristics of a chronic granuloma surrounding Taenia solium larvae in pig muscle is described. Larvae with an inflammatory capsule were obtained at slaughter from pigs 6-8 months-of-age and were processed for light and electron microscopy. Eosinophils (granulocytes with orange staining and peroxidase-positive granules) were found to be degranulated and in close contact with the parasite surface. Histiocyte, epithelioid cells, macrophages and lymphocytes were also evident, as well as large numbers of plasma cells in the outer areas of the wall-circumscribed reaction. The parasites were ultrastructurally intact, with a normal tegument and only occasional changes in the microvesicles. The results are discussed with reference to parasite survival in the host.