Intravacuolar Tubules Research Articles

Ultrastructural Study of Host-Parasite Relationship and Pathogenicity of Eimeria Sp. Infecting Libyan Jird ( Meriones Libycus ) ( Lichtenstein , 1828 )

The relationship of Eimeria sp. and its host fat LibyanJird (Meriones libycus) was studied on an ultrastructural level. The host cellular organelles (nucleus, mitochondria, endoplasmic reticulum and golgi apparatus) and the changes of its infected intestinal epithelial cells during the development of parasitic stages (schizogony and gamogony) were studied and compared with those non-infected cells. The ultrastructures of intravacuolar tubules and folds in the parasitophorous vacuole (P.V.) were described. These fine structures may involve in the transporttation of materials from the host cell to across the parasitovorous vacuole (P.V.).

Characterization of a murine monoclonal antibody generated against Neospora caninum tachyzoites by use of western blot analysis and immunoelectron microscopy

Summary A murine monoclonal antibody (mab) 6G7 generated against tachyzoites of Neospora caninum recognized 8 major and several minor antigens, as observed by western blot analysis. Relative rate of migration of the 8 major antigens ranged from 31 to 97.4 kd. In addition, mab 6G7 recognized a Toxoplasma gondii tachyzoite antigen with a relative rate of migration of 107 kd. Immunogold labeling of N caninum tachyzoites grown in human foreskin fibroblast cells indicated that mab 6G7 binds to micronemes, dense granules, basal portions of rhoptries, and intravacuolar tubules within the parasitophorous vacuole. Monoclonal antibody 6G7 also bound to micronemes and basal portions of rhoptries within tachyzoites of T gondii. Monoclonal antibody 6G7 did not significantly inhibit development of tachyzoites in vitro.

Use of infected cultured cells to compare ultrastructural features of Neospora caninum from dogs and Toxoplasma gondii

SUMMARY The ultrastructure of tachyzoites of 3 isolates of Neospora caninum from dogs was examined, using transmission electron microscopy of infected cultured cells. Ultrastructure of the 3 isolates was similar. Tachyzoites had a pellicle, 22 subpellicular microtubules, a conoid, anterior and posterior polar rings, 8 to 12 electron-dense rhoptries, numerous micronemes, a single vesicular nucleus, tubular mitochondria, Golgi complexes, ribosomes, endoplasmic reticula, an inactive micropore, electron-dense bodies, lipid bodies, and amylopectin bodies. Most tachyzoites were located adjacent to the host cell nucleus in a parasitophorous vacuole that contained numerous intravacuolar tubules. Tachyzoites divided by endodyogeny. Neospora caninum tissue cysts were not seen. Comparison of N caninum with Toxoplasma gondii tachyzoites indicated that the 2 species can be differentiated on the basis of structure and numbers of rhoptries and numbers and location of micronemes and electron-dense bodies.

Immuno‐histochemical and ultrastructural characteristics of a cyst‐forming sporozoon associated with encephalomyelitis and myositis in dogs

Light-microscopy, including immuno-histochemical staining, and transmission and scanning electron microscopy were applied for the characterization of a Toxoplasma-like parasite associated with encephalomyelitis and myositis in dogs of the boxer breed. Most parasites were tachyzoites, occurring in clusters, up to 60 micron in diameter, in parasitophorous vacuoles of host cells. Cyst stages with a definite cyst wall were few, but could be demonstrated in all cases. Immunostaining with antiserum against Toxoplasma gondii was negative, while both tachyzoites and bradyzoites were stained with serum from affected dogs. Ultrastructurally, the parasite was characterized by a great number of rhoptries, few amylopectin granules, lack of micropores in the tachyzoites, and the occurrence of numerous dense bodies in the bradyzoites. Numerous intravacuolar tubules were present in the space of the parasitophorous vacuole. The cyst wall resembled that of T. gondii. Until a definite host is found, the parasite may be regarded as an "orphan", cyst-forming sporozoon that is ultrastructurally different from other known protozoan parasites. It has a light-microscopical similarity to T. gondii but is antigenically different.

Ultrastructure of Cryptosporidium muris (strain RN 66) parasitizing the murine stomach.

The ultrastructure of Cryptosporidium muris, which parasitizes the stomach of mice, was studied by transmission electron microscopy. The entire development of the parasite occurred in the microvilli of the surface mucus cells in the gastric glands. The ultrastructural features of the attachment site of C. muris to the host cell differed remarkably from those of C. parvum and its closely related species, which parasitize the intestine of various animals. The size of C. muris was greater at almost every developmental stage than that of C. parvum. These findings confirmed that C. muris and C. parvum are distinct species. The mitochondria, subpellicular microtubules, and Golgi complex were demonstrated in detail. A small invagination in the meront and intravacuolar tubules were found in Cryptosporidium. The wall of each developing oocyst in the parasitophorous vacuole was composed of three layers: the outermost layer was considered to be a true oocyst wall, whereas the middle and innermost layers were assumed to develop into the sporocyst wall. The outermost layer was fragile and disintegrated as the oocyst matured. In excystation in vitro, a suture was seen in a thick layer of the two-layered sporocyst wall of an oocyst (sporocyst wall; see Discussion) that enveloped four sporozoites. The fine structure of the attachment site of the present species to the host cell appears to reveal a unique mode of host-parasite interaction in Cryptosporidium infection.

Ultrastructure of the macrogamont ofGoussia cichlidarumLandsberg and Paperna, 1985, a Coccidian parasite in the swimbladder of Cichlid fish

Ultrastructural features of the macrogamont of Goussia cichlidarum , a coccidian parasite of cichlid fish are described. Host cells derived from the swimbladder lining epithelium are reduced to membranous sacs in early gamogony. These are displaced to the surface of the epithelium, but maintain their attachment until an early stage of oogony. An elaborate junction zone between the host cell and the epithelial cells suggests a nutritive function. Immature macrogamonts are bound by a double unit membrane with only a few micropores. Intravacuolar tubules are absent. Mature macrogamonts are bound by a single unit membrane and are surrounded by an additional two envelopes. Round organelles resembling wall-forming bodies of other coccidia, reach their maximum number and differentiation in mature macrogamonts.

Ultrastructure of the macrogamont of Eimeria funduli, a coccidium parasitizing killifishes

Abstract. The ultrastructurc of the macrogamont of Eimeria funduli was studied in hepatocytcs of the killifish Funldulus grandis and F. similis. The macrogamont developed in a parasitophorous vacuole (PV) that was bounded by two unit membranes probably derived from an envelope of modified host rough cndoplasmic reticulum (RER). The membrane adjacent to the host‐cell cytoplasm was lined with ribosomes. whereas the membrane facing the PV was smooth and blebbed into the PV. Intravacuolar tubules were not observed in the PV. The macrogamonts had a single limiting membrane with lew micropores. Developing macrogamonts had abundant RER. few Golgi bodies, and a few small polysaccharide granules. Nuclei of developing macrogamonts had dispersed chromatin and compact nucleoli. Polysaccharide granules in developing and mature macrogamonts were identified with the periodic acid‐thiocarbohydrazide‐silver proteinate technique. In mature macrogamonts, polysaccharide granules as large as 1 –2 μm in diameter nearly filled the cytoplasm. The cytoplasm contained three kinds of inclusions that were associated with either the RER or Golgi apparatus. Inclusions identified as type I wall‐forming (WF) bodies were small, dense, membrane‐bound granules that developed from the Golgi apparatus. Inclusions identified as type II WF bodies were usually dense, irregularly shaped bodies that occupied RER cisternae. Some type II WF bodies had a heterogeneous content but most were homogeneous. A third type of inclusion was related to the cytoplasmic aspect of RER cisternae and consisted of tubules and vacuoles enclosed in a membrane.

Ultrastructural changes in the macrogamete and early oocyst of Eimeria maxima resulting from drug treatment.

The ultrastructure of the macrogamete and developing oocyst of Eimeria maxima (Weybridge strain) was examined in the intestinal cells of chicks fed 3 different anticoccidial drugs. Amprolium at 125 p.p.m., arprinocid at 35 p.p.m. and dinitolmide at 250 p.p.m. caused considerable morphological abnormality and incomplete development of the wall-forming bodies of Type 2 (WFB II), which did not appear able to participate in oocyst wall formation. The wall-forming bodies of Type 1 (WFB I) were able in each case to participate in oocyst wall formation although amprolium and dinitolmide produced morphological abnormalities in them. In birds medicated with dinitolmide, the outer layer of the oocyst wall was formed initially at opposite poles of the macrogametes rather than as a uniform layer. Other abnormalities resulting from drug treatment are reported and some evidence that intravacuolar tubules may be formed by the parasite pellicle is presented.

Ultrastructure of Developing Gamonts of Eimeria contorta Haberkorn, 1971 (Protozoa, Sporozoa) with Emphasis on the Host-Parasite Interface

Gamonts of Eimeria contorta were observed in intestinal epithelial cells of rats on days 6 and 7 postinfection. Early gamonts of both sexes were bound by a single limiting membrane, underlain locally by additional membranes. Mature microgamonts were limited by a single membrane as well, whereas macrogametes had a three-membrane pellicle. Amylopectin was found in gamonts of both sexes. Microgametes developed while connected to the microgamont's surface by a reinforced stalk. Flagellar basal bodies contained microtubules arranged in triplets. Macrogamonts contained labyrinthine wall-forming bodies (type 2) within cisternae of the rough endoplasmic reticulum before homogeneous wall-forming bodies (type 1) were found in the cytoplasm. In both sexes, the host cell membrane of the parasitophorous vacuole showed numerous blebs and intravacuolar folds; the latter appeared to branch occasionally. Intravacuolar tubules (IT) were connected to the surface of macrogametes and also interconnected with each other. The IT may have functions other than nutrient uptake. A third type of intravacuolar structure found within macrogametes resembled coils of longitudinally striated tubules. In cross section, these coils consisted of a series of microtubules interconnected by membranous bridges. In advanced stages, the coils were arranged parallel to the macrogamete's surface, thus forming an "exterior layer." They may have a role in oocyst wall formation.

The fine structure of the developing macrogamete of Eimeria maxima.

The fine structure of the developing macrogamete of Eimeria maxima was studied from chicks killed at intervals from 138 to 147 h after inoculation. The macrogamete developed within a parasitophorous vacuole. Lying within the vacuole and extending for some distance around the periphery of the macrogamete were intravacuolar tubules, grouped in certain areas, and in some cases they were seen to make direct connexions with the cytoplasm of the parasite. During development, electron-pale vesicles were pinched off externally from the surface of the macrogamete. There appeared to be 2 forms of wall-forming bodies of the Type I during development, one form being less osmiophilic than the other. Other organelles present, such as wall-forming bodies of Type II, granular endoplasmic reticulum, mitochondria, canaliculi, lipid inclusions and intravacuolar folds, were similar in structure to those of other Eimeria species.

Ultrastructural studies on the endogenous development of eimeria brunetti. III. Macrogametogony and the macrogamete.

The ultrastructural changes occurring during macrogametogony in Eimeria brunetti were studied in tissue from the small intestine of infected young domestic fowls. As the macrogametocyte developed, an increase in the volume of the cytoplasm and the nucleus occurred. At this early stage of development the organism was limited by a single unit membrane which possessed a number of micropores. The organism was situated in a parasitophorous vacuole which contained intra-vacuolar folds and intra-vacuolar tubules. The wall forming bodies of type II (WFB II) started to appear before the wall forming bodies of Type I (WFB I). The WFB I developed in the cytoplasmic matric whereas the WFB II were formed within the cisternae of the rough endoplasmic reticulum apparently in association with Golgi bodies. The mature WFB I were homogeneous, limited by a unit membrane, and larger than WFB II which had no limiting membrane but remained surrounded by a membrane of the rough endoplasmic reticulum. Polysaccharide granules were formed in the cytoplasm between strands of the rough endoplasmic reticulum. During maturation the WFB I & II and the polysaccharide granules increased in size and number, and as this occurred a number of electron translucent vacuoles were ejected from the surface of the macrogametocyte. The mature macrogamete possessed a large nucleus with a nucleolus, a number of multi-membranous vacuoles, mitochondria, and canaliculi. The WFB I & II were located at the cell periphery and the polysaccharide granules further towards the interior of the organism. The organism was limited by a unit membrane but during macrogametogony a homogeneous layer had developed which extensively coated the macrog...

An electron-microscopic study of the development of virulent and avirulent strains of Semliki Forest Virus in mouse brain

Two strains of Semliki Forest Virus (SFV), the avirulent and virulent, were used to study the development of virus in both baby and adult mouse brain. The development of SFV in the brain was similar in baby and adult brain using the virulent strain and in the baby mouse brain using the avirulent strain. Mature virus could not be found in adult mouse brain using the avirulent strain. This paper shows that extracellular virus particles near the cell membrane stimulate the formation of coated vesicles and thus absorption of virus particles by the cell. It is suggested that these coated vesicles with contained virus particles are stimulated to develop nucleoid cores on their membrane forming cytopathic vacuoles, Type II (CPV-II). Excessive membrane growth takes place and the membrane of the CPV-II with the nucleoid cores invaginates to form intravacuolar tubules. It is suggested that these tubules become responsible for the formation of mature virus particles. Thus the membrane of the CPV-II appears to be responsible for the development of both the inner core and outer coat of the virus.

The fine structure of the endogenous stages of Eimeria labbeana. 3. Feeding Organelles.

The fine structure of the feeding organelles of the endogenous developmental stages of Eimeria labbeana from the ileal mucosa of the common Pigeon, Columba livia, is described and compared with similar structures of other species of Eimeria. Intra-cytoplasmic, membrane-bound vesicles of varying shapes and dimensions, and pinocytotic vesicle, were seen in association with cup-shaped or v-shaped invaginations in early schizonts, early macrogamonts, and macrogametes. Deep invaginations, averaging 1.7 x 0.5 mu in size, and found on the surface of early schizonts, early and young macrogamonts, and developing microgamonts, apparently function as organelles of ingestion and breakdown of host-cell cytoplasm. Micropores were rarely seen in schizonts and never in microgametes. The merozoite had one typical micropore (850 x 680 A) and a number of micropore-like invaginations. Micropores of the microgamonts averaged 610 x 580A, and those of macrogamonts and macrogametes averaged 1,220 x 780 A. A typical micropore was observed in an early oocyst. Intravacuolar tubules, each 580 A in diameter and composed of nine microtubule-like subunits, were observed only in about 1 per cent of the more than 4,000 macrogametes studied. This paper establishes that E. labbeana is a species that possesses all the known organelles associated with feeding, expect the intravacuolar folds.

The fine structure of the endogenous stages of Eimeria labbeana: 2. Mature macrogamonts and young oocysts.

The fine structure of the mature macrogamonts and intracellular oocysts of Eimeria labbeana from the ileal mucosa of experimentally infected Pigeons (Columbia livia) was investigated and described. The macrogamont reached a maximum size of 12.0 x 9.5 mum (average equals 10.8 x 8.8 mum), and was located within a narrow parasitophorus vacuole. Most of the macrogamonts were limited by two membranes. Intravacuolar tubules, 1.2 mum long and 58 nm in diameter, established direct connections between the parasite and the host cell. Each tabule was composed of 9 subunits arranged around the central lumen. Cytoplasmic canaliculi were composed of bundles of microtubule-like structures (8-10 nm wide). Type 1 wall-forming bodies reached a maximum size of 1.8 x 1.5 mum, and many had centric or eccentric electron transparent portions within them. They were frequently seen lodged within peripherally-located mitochondria. Type 2 wall-forming bodies averaged 1.5 mum in diameter. The role of the two types of wall-forming bodies in forming the outer and inner layers of the wall of the oocyst was similar to that in other species of Eimeria. The oocyst wall was 0.2 mum thick and composed of a limiting membrane (20 nm thick), an outer layer (75 nm thick), and an inner layer (100 nm thick).

Structure and mode of function of the organelles associated with nutrition of the macrogametes of Eimeria acervulina.

The macrogamete of Eimeria acervulina, lay and developed within the host cell in a parasitophorous vacuole. The cytoplasmic membrane of the host cell bordering the vacuole was not smooth, but it had numerous folds extending into the vacuole. These "intravacuolar folds" varied in depth and number in different sections. In some, the majority of the folds were disconnected from the host cell. Once disconnected, they evidently disintegrated forming the amorphous, particulate material present in the parasitophorous vacuole. The pellicle of the young macrogamete consisted of a single unit membrane with an osmiophilic material representing the second membrane. Two unit membranes were apparent at a later stage of development when the wall-forming bodies had been formed and amylopectin granules deposited. Two kinds of organelles were present on the surface of the macrogamete, typical micropores and invaginations of the pellicle. The micropores arose from an invagination of the outer membrane, which continued through the invagination without interruption. Irrespective of whether an inner membrane was present in the pellicle or not, a thickened cylindrical wall around the inner portion of the invagination was always present. Micropores appeared in large numbers in both micro- and macrogametocytes. As many as three micropores were seen in a surface area of 2 mu2. Invaginations arose in a similar manner by infolding of the pellicle. They differed from micropores in that the thickened cylindrical wall present around the inner portion of the micropore was absent, and also in that invaginations had no uniform appearance. They were of varying shapes, and lengths, varying from very short V-shaped to long and narrow. Micropores and invaginations take in nutrients in the form of particulate matter present in the parasitophorous vacuole, this material having been derived from the host-cell membranous "intravacuolar folds". The micropores function as cytostomes and the invaginations take in material by means of pinocytosis. Large numbers of intravacuolar tubules were seen at the surface of the macrogamete. They were present only at certain areas of the macrogamete and in groups and were connecting the parasite with the host cell. They were about 80-110 nm in diameter, and were seen to attain a length of up to 6 mu. Evidence was obtained indicating that the tubules transport free ribosomes from the host cell to the parasite. The ribosomes were seen to accumulate in "pockets" within the cytoplasm of the host cell, at the area where the tubules were connected.