Ultrastructure of tachyzoites, bradyzoites and tissue cysts of Neospora caninum

Dividing tachyzoites of Neospora caninum were 4 x 3 microns and had ultrastructural characteristics typical for the cyst-forming coccidia. Unusual ultrastructural characteristics of fully-formed tachyzoites included no micropores, 8-12 anterior and 4-6 posterior rhoptries, and a few posterior micronemes. Most tachyzoites were located free in the host cell cytoplasm; only a few occurred within a parasitophorous vacuole. Parasite multiplication appeared to be rapid because most organisms were in various stages of endodyogeny. Neural tissue cysts of N. caninum were 24.3 x 19.2 microns and contained 50-200 bradyzoites (7.3 x 1.5 microns), which lacked micropores. The cyst wall was 0.74-1.12 microns thick and consisted of the primary cyst wall (the parasitophorous vacuole membrane) and a thick granular layer with electron-dense vesicles.     

Ultrastructure of Tachyzoites, Bradyzoites and Tissue Cysts of Neospora caninum

. Dividing tachyzoites of Neospora caninum were 4x3 μm and had ultrastructural characteristics typical for the cyst-forming coccidia. Unusual ultrastructural characteristics of fully-formed tachyzoites included no micropores, 8–12 anterior and 4–6 posterior rhoptries, and a few posterior micronemes. Most tachyzoites were located free in the host cell cytoplasm; only a few occurred within a parasitophorous vacuole. Parasite multiplication appeared to be rapid because most organisms were in various stages of endodyogeny. Neural tissue cysts of N. caninum were 24.3 × 19.2 μm and contained 50–200 bradyzoites (7.3 × 1.5 μm), which lacked micropores. The cyst wall was 0.74–1.12 μm thick and consisted of the primary cyst wall (the parasitophorous vacuole membrane) and a thick granular layer with electron-dense vesicles.     

Monoclonal antibodies to Hammondia hammondi allowing immunological differentiation from Toxoplasma gondii

Five murine monoclonal antibodies (MAbs) were developed against purified sporozoites of Hammondia hammondi. Despite a large antigenic similarity between the 2 closely related coccidia, H. hammondi and Toxoplasma gondii, these MAbs only reacted with H. hammondi. Three MAbs, ID3, 3F2, and 4C9-7, recognized antigens of 38 kDa localized in rhoptries (1D3), in rhoptries and in oocyst and cyst walls (3F2), and in rhoptries and the apical region (4C9-7). Another MAb, 4C9-10, reacted with a 27-kDa antigen in dense granules of sporozoites and tachyzoites, and MAB 11B3 labeled an antigen of >94 kDa located in the pellicular membrane of the 3 stages of the parasite. These MAbs could be used for a rapid discrimination of the 2 coccidia in epidemiological studies or for diagnostic purposes in tissues.     

The cathepsin B of Toxoplasma gondii,toxopain-1, is critical for parasite invasion and rhoptry protein processing

Cysteine proteinases play a major role in invasion and intracellular survival of a number of pathogenic parasites. We cloned a single copy gene, tgcp1, from Toxoplasma gondii and refolded recombinant enzyme to yield active proteinase. Substrate specificity of the enzyme and homology modeling identified the proteinase as a cathepsin B. Specific cysteine proteinase inhibitors interrupted invasion by tachyzoites. The T. gondii cathepsin B localized to rhoptries, secretory organelles required for parasite invasion into cells. Processing of the pro-rhoptry protein 2 to mature rhoptry proteins was delayed by incubation of extracellular parasites with a cathepsin B inhibitor prior to pulse-chase immunoprecipitation. Delivery of cathepsin B to mature rhoptries was impaired in organisms with disruptions in rhoptry formation by expression of a dominant negative micro1-adaptin. Similar disruption of rhoptry formation was observed when infected fibroblasts were treated with a specific inhibitor of cathepsin B, generating small and poorly developed rhoptries. This first evidence for localization of a cysteine proteinase to the unusual rhoptry secretory organelle of an apicomplexan parasite suggests that the rhoptries may be a prototype of a lysosome-related organelle and provides a critical link between cysteine proteinases and parasite invasion for this class of organism.     

Lectin cytochemistry in the gastrointestinal tract with special reference to glycosylation in the Golgi apparatus of Brunner's gland cells.

Two hydrophilic, low temperature-embedding resins, Lowicryl K4M and LR White, were compared in lectin cytochemistry. Post-embedding staining of colloidal gold-labeled Griffonia symplicifolia agglutinin II (GSA-II) resulted in staining of the Golgi apparatus and mucous granules of mucous neck cells in the gastric fundic gland, pylorocytes, and Brunner's gland cells embedded in either resin, although it was much easier to make ultra-thin sections with LR White-embedded material than with the other. Post-fixation with uranyl acetate followed by LR White embedding improved general ultrastructure so that lectin binding sites were identified precisely. All examined lectins, soybean agglutinin (SBA), Maclura pomifera agglutinin (MPA), GSA-II, and Ulex europaeus agglutinin I (UEA-I), stained mucous granules and the Golgi apparatus, in which the staining pattern was characteristic of each lectin: cis cisternae were labeled with SBA and MPA, intermediate cisternae with GSA-II, and trans cisternae and mucous granules with SBA, GSA-II, UEA-I, and lightly with MPA. No labeling was observed in the rough endoplasmic reticulum with any lectin. These findings suggest that the Golgi apparatus is the site of O-linked glycosylation and can be divided into at least three distinct compartments with regard to the glycosylation.     

Immunocytochemical localization of enterobacterial common antigen in Escherichia coli and Yersinia enterocolitica cells.

Enterobacterial common antigen (ECA) was localized on Lowicryl K4M sections and on ultrathin cryosections by using either a mouse monoclonal antibody or an absorbed rabbit polyclonal immune serum with the corresponding gold-labeled secondary antibodies. Comparable results were obtained with both monoclonal antibody and polyclonal immune serum. Controls with two ECA-negative mutants revealed the ECA specificity of both labeling systems. On Lowicryl K4M sections, good labeling of the outer membrane and of membrane-associated areas in the cytoplasm was obtained. Unexpectedly, however, the ribosome-containing areas of the cytoplasm also showed significant labeling. On ultrathin cryosections, labeling of the cytoplasmic areas was much weaker, although the density of label in the outer membrane was comparable to that obtained with the Lowicryl K4M sections. With the techniques used, it cannot be completely excluded that the appearance of ECA in the cytoplasm is due to displacement of ECA-reactive sites during the preparation procedure.     

Toxoplasma gondii: isolation of tachyzoites rhoptries and incorporation into Iscom

Rhoptries have been isolated from Toxoplasma gondii tachyzoites by subcellular fractionation in isopynic density sucrose gradient. Five bands were observed, and transmission electron microscopy of these indicated that rhoptries were in band 3. This band had a density of 1.17 g/cm(3). Fraction 1 had membrane structures of the parasite. Fraction 2 contained membranes and mitochondria. Fraction 4 had mostly conoid structure and fraction 5 showed ghosts. The electrophoretic and Western blotting analysis of the fractions indicated the presence of a number of proteins. Iscoms were constructed from band 3, which contained the rhoptry structures. Iscom showed a only protein incorporated of 55 kDa. Isolation of the parasite organelles has got in this work is necessary to identification, characterization, and function elucidation of the organelle proteins.     

Electron microscopic detection of RNA sequences by non-radioactive in situ hybridization in the mollusk Lymnaea stagnalis.

The subcellular localization of mRNA sequences encoding neuropeptides in neuropeptidergic cells of the pond snail Lymnaea stagnalis was investigated at the electron microscopic (EM) level by non-radioactive in situ hybridization. Various classes of probes specific for 28S rRNA and for the ovulation hormone (caudodorsal cell hormone; CDCH) mRNA were labeled with biotin or digoxigenin and were detected after hybridization with gold-labeled antibodies. Hybridizations were performed on ultra-thin sections of both Lowicryl-embedded and frozen cerebral ganglia, and a comparison demonstrated that most intense hybridization signals with an acceptable preservation of morphology were obtained with ultra-thin cryosections. Addition of 0.1% glutaraldehyde to the formaldehyde fixative improved the morphology, but on Lowicryl sections this added fixative resulted in a decrease of label intensity. A variety of probes, including plasmids, PCR products, and oligonucleotides, were used and all provided good results, although the use of oligonucleotides on Lowicryl sections resulted in decreased gold labeling. The gold particles were found mainly associated with rough endoplasmic reticulum (RER) but were also observed in lysosomal structures. Finally, the in situ hybridization method presented in this study proved to be compatible with the immunocytochemical detection of the caudodorsal cell hormone, as demonstrated by double labeling experiments.     

Location of B- and Z-DNA in the chromosomes of a primitive eukaryote dinoflagellate

The usual conformation of DNA is a right-handed double helix (B-DNA). DNA with stretches of alternating purine-pyrimidine (G-C or A-T) can form a left-handed helix (Z-DNA). The transition B----Z, facilitated by the presence of divalent cations, cytosine methylation, or constraints on DNA such as superhelicity may play a role in the regulation of gene expression and/or in DNA compaction (Zarling, D. A., D. J. Arndt-Jovin, M. Robert-Nicoud, L. P. McIntosh, R. Tomae, and T. M. Jovin. 1984. J. Mol. Biol. 176:369-415). Divalent cations are also important in the structure of the quasi-permanently condensed chromosomes of dinoflagellate protists (Herzog, M., and M.-O. Soyer. 1983. Eur. J. Cell Biol. 30:33-41) which also have superhelicity in their DNA. The absence of histones in dinoflagellate chromosomes suggest that the search for Z-DNA sequences might be fruitful and could provide one indication of the physiological role of this particular DNA conformation. We report a complete immunofluorescent and immunogold analysis of the nuclei of the dinoflagellate Prorocentrum micans E. using monoclonal and polyclonal anti-B and anti-Z-DNA antibodies. Positive labeling was obtained with immunofluorescence using squash preparations and cryosections, both of which showed the intranuclear presence of the two DNA conformations. In ultrathin sections of aldehyde-prefixed, osmium-fixed, and epoxy-embedded cells, we have localized B-DNA and Z-DNA either with single or double immunolabeling using IgG labeled with 5- and 7-nm gold particles, respectively. Chromosomal nucleofilaments of dividing or nondividing chromosomes, as seen in ultrathin sections in their arch-shaped configuration, are abundantly labeled with anti-B-DNA antibody. Extrachromosomal anti-B-DNA labeling is also detected on the nucleoplasm that corresponds to DNA loops; we confirm the presence of these loops previously described external to the chromosomes (Soyer, M.-O., and O. K. Haapala. 1974. Chromosoma (Berl.). 47:179-192). B labeling is also visible in the nucleolus organizer region (NOR) and in the fibrillo-granular area (containing transcribing rDNA) of the nucleolus. Z-DNA was localized in limited areas inside the chromosomes, often at the periphery and near the segregation fork of dividing chromosomes. In the nucleolus, Z-DNA is observed only in the NOR area and never in the fibrillo-granular area. For both types of antibody experiments, controls using gold-labeled IgG without primary antibody were negative. A quantitative evaluation of the distribution of the gold-labeled IgG and a parametric test support the validity of these experiments.(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantitative immunolocalization of four immunodominant antigens of Toxoplasma gondii

Ultrastructural localization of four immunodominant antigens of Toxoplasma gondii was investigated quantitatively on thin sections and replicas by an immunogold technique using four monoclonal antibodies (Mab). On immunoblot Mab IV47, GII9, II38 and IE10 identified proteins of 28, 30, 45 and 66-70 kDa, respectively. Use of digital image analyzer and a semi-automatic procedure developed by us, the patterns of label distribution were compared in three cell structures: cell surface, submembrane area and rhoptries. On the whole cell surface, protein P28 and P30 were 2.5 and 4 times more abundant than P66-70 respectively. The protein P28 was essentially concentrated in the submembrane area with a labeling of 195.4 +/- 46.7 gold particles/microns 2 that follows a decreasing gradient from this area to the cell centre. In the rhoptries, all four antigens were detected, P45 and P66-70 being major with a labeling of 97.1 +/- 31.1 gold particles/microns 2 and 155.1 +/- 39.3 gold particles/microns 2 respectively. The results support the hypothesis that rhoptries are the essential site for antigen storage.     

Morphometric analysis of gold particles in low-label cell compartments.

Quantitative estimation of the binding of gold-conjugated ligands to various cell organelles has become a commonly used method to quantify the amount of ligand-binding sites associated with those organelles. However, often a small percentage of organelles is labeled or the density of gold labeling is low. We have defined the "gold-labeled region" as a zone that has a boundary defined by the localization of the outermost gold particles. Such a phenomenon was recently observed in a study of the internalization of gold-labeled native surfactant into lamellar bodies of cultured pulmonary type II cells. We estimated the size and density of gold-labeled regions in lamelar bodies using a simple stereological approach and demonstrated that the low percentage of gold-labeled organelles can be explained as a result of the probability of random selecting through the labeled areas. Our method, which permits use of transmission electron microscopy to calculate the true parameters of gold-labeled regions, can significantly facilitate analyses of ligand binding to various cell compartments.     

Neospora caninum protein disulfide isomerase is involved in tachyzoite-host cell interaction

We have previously shown that treatment of Neospora caninum tachyzoites with the aspartyl protease inhibitor pepstatin A reduces host cell invasion [Naguleswaran, A., Muller, N., Hemphill, A., 2003. Neospora caninum and Toxoplasma gondii: a novel adhesion/invasion assay reveals distinct differences in tachyzoite-host cell interactions. Exp. Parasitol. 104, 149-158]. Pepstatin A-affinity-chromatography led to the isolation of a major band of approximately 52 kDa which was identified as a homologue of a previously described Toxoplasma gondii putative protein disulfide isomerase (TgPDI) through tandem mass spectrometry. A BLAST search against N. caninum expressed sequence tags (ESTs) on the ApiDots server using TgPDI cDNA as query sequence revealed a 2251 bp PDI-like consensus (NcPDI), which shows 94% identity to the T. gondii homologue. In N. caninum tachyzoites, NcPDI was found mainly in the soluble hydrophilic fraction. Immunofluorescence showed that expression of NcPDI was dramatically down-regulated in the bradyzoite stage, and immunogold-EM on tachyzoites localised the protein to the cytoplasm, mostly in close vicinity to the nuclear membrane, to the micronemes, and to the parasite cell surface. However, NcPDI was absent in rhoptries and dense granules. Preincubation of tachyzoites with the sulfhydryl blocker 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), p-chloromercuribenzoic acid (pCMBA), and with the PDI inhibitor bacitracin reduced adhesion of parasites to host cells. In addition, incubation of N. caninum tachyzoites with affinity-purified anti-NcPDI antibodies reduced host cell adhesion. PDIs catalyse the formation, reduction or isomerisation of disulfide bonds. Many major components of the adhesion and invasion machinery of apicomplexan parasites are cysteine-rich and dependent on correct folding via disulfide bond formation. Thus, our data points towards an important role for surface-associated NcPDI in Neospora-host cell interaction.     

Localization of mitochondrial DNA encoded cytochrome <Emphasis Type="Italic">c</Emphasis> oxidase subunits I and II in rat pancreatic zymogen granules and pituitary growth hormone granules

Cytochrome c oxidase (COX) complex is an integral part of the electron transport chain. Three subunits of this complex (COX I, COX II and COX III) are encoded by mitochondrial (mit-) DNA. High-resolution immunogold electron microscopy has been used to study the subcellular localization of COX I and COX II in rat tissue sections, embedded in LR Gold resin, using monoclonal antibodies for these proteins. Immunofluorescence labeling of BS-C-1 monkey kidney cells with these antibodies showed characteristic mitochondrial labeling. In immunogold labeling studies, the COX I and COX II antibodies showed strong and specific mitochondrial labeling in the liver, kidney, heart and pancreas. However, in rat pancreatic acinar tissue, in addition to mitochondrial labeling, strong and specific labeling was also observed in the zymogen granules (ZGs). In the anterior pituitary, strong labeling with these antibodies was seen in the growth hormone secretory granules. In contrast to these compartments, the COX I or COX II antibodies showed only minimal labeling (five- to tenfold lower) of the cytoplasm, endoplasmic reticulum and the nucleus. Strong labeling with the COX I or COX II antibodies was also observed in highly purified ZGs from bovine pancreas. The observed labeling, in all cases, was completely abolished upon omission of the primary antibodies. These results provide evidence that, similar to a number of other recently studied mit-proteins, COX I and COX II are also present outside the mitochondria. The presence of mit-DNA encoded COX I and COX II in extramitochondrial compartments, provides strong evidence that proteins can exit, or are exported, from the mitochondria. Although the mechanisms responsible for protein exit/export remain to be elucidated, these results raise fundamental questions concerning the roles of mitochondria and mitochondrial proteins in diverse cellular processes in different compartments.     

Colloidal gold labeling of intracellular ligands in dorsal root sensory neurons, visualized by scanning electron microscopy

We report a novel technique that combines high-resolution scanning electron microscopy (SEM) of intracellular structures with backscattered electron imaging (BEI) of colloidal gold-labeled intracellular ligands. Murine dorsal root ganglia were immersion-fixed, freeze-cleaved, labeled with gold complexes, and critical point-dried. Specimens were carbon-coated and viewed by BEI. They were then minimally sputter-coated with gold and previously identified cells relocated by secondary electron imaging (SEI). This permitted increased resolution of intracellular detail while gold particles remained detectable by BEI. Incubation with RNAse-gold and DNAse-gold complexes resulted in specific labeling of cytoplasm and nucleus, respectively. Immunolabeling of neurofilament (NF) and small nuclear ribonucleoproteins (snRNP) resulted in selective labeling of intracellular antigens. Nonspecific binding was abolished by use of 1% skin milk. Specifically, incubation with monoclonal anti-NF68 resulted in labeling of cytoplasm in 66% of neurons, notably of the large cells known to contain large amounts of NF. Satellite cells, which lack NF, showed low levels of background label. Human autoimmune anti-Sm serum recognizes snRNP particles, with the exception of the nucleolar U3 snRNP. Labeling with this serum resulted in specific labeling of 92% of nuclei, with only background labeling over nucleoli and cytoplasm. The results show that it is feasible to employ high-resolution SEM in conjunction with colloidal gold labeling to localize intracellular ligands in situ.     

Dynamics and 3D organization of secretory organelles of Toxoplasma gondii

Micronemes, rhoptries and dense granules are secretory organelles of Toxoplasma gondii crucial for host cell invasion and formation of the parasitophorous vacuole (PV). We examined whether their relative volumes change during the intracellular cycle. Stereological analysis of random ultrathin sections taken at 5min of interaction, 7 and 24h post-infection demonstrated that the relative volume of each type of organelle decreases just after the respective peak of secretion. Micronemes are radially arranged below the polar ring, while rhoptries converge to but only a few reach the inside of the conoid. In contrast to the apical and polarized organelles, dense granules were found scattered throughout the cytoplasm, with no preferential location in the parasite cell body. Extensive observation of random sections indicated that each organelle probably secretes in a different region. Micronemes secrete just below the posterior ring and probably require that the conoid is extruded. The rhoptries passing through the conoid secrete at a porosome-like point at the most apical region. Dense granules secrete laterally, probably at fenestrations in the inner membrane complex. Immunocytochemistry showed that there are no subpopulations of rhoptries or dense granules, as a single organelle can contain more than one kind of its specific proteins. The vacuolar-like profiles observed at the apical portion of parasites just after invasion were confirmed to be empty rhoptries, as they were positively labeled for rhoptry proteins. These findings contribute for a better understanding of the essential behavior of secretory organelles.     

Immunocytochemical localization of antigens recognized by human antisera in infective larvae of Wuchereria bancrofti

Ultrathin sections of L3 of Wuchereria bancrofti embedded in hydrophilic resin were incubated with antisera pools from individuals (1) asymptomatic microfilaremic with different microfilaria (mf) densities (1-100, 101-500, and >1,000 mf/ml); (2) chronic with hydrocele or lymphedema; and (3) with no evidence of microfilaremia or clinical filariasis but residing in an endemic area. The groups of microfilaremic subjects studied presented differences relative to the intensity of labeling, with the density of gold particles per square micrometer proportional to microfilaremia. Incubation of ultrathin sections of W. bancrofti L3 larvae in the presence of antisera from patients exhibiting chronic obstructive lymphatic pathology of hydrocele and from individuals with clear clinical evidence of lymphedema exhibited a strong reaction in the same tissues. Except for the endemic normal group, all groups studied showed reactivity against epitopes in all tissues of infective larvae of W. bancrofti. The cuticle presented an intense labeling, suggesting a possible target structure for immune response.     

Regulation of DNA synthesis in human fetal hepatocytes by placental lactogen, growth hormone, and insulin-like growth factor I/somatomedin-C

Hepatocytes were isolated by gentle collagenase digestion of liver fragments from human fetuses of 8-16 weeks gestation obtained following prostaglandin-induced pregnancy terminations. They were maintained on collagen-coated tissue culture dishes in selective arginine-free medium for up to 72 hr, and the action of hormones and growth factors on DNA synthesis was studied by autoradiography following incubation with 3H-thymidine. The labeling index of hepatocytes was consistently enhanced by 25-250 ng/ml human placental lactogen (HPL), 25-250 ng/ml human growth hormone (HGH), 10-50 ng/ml insulin-like growth factor I/somatomedin-C (IGF I/Sm-C), and 10% dialyzed fetal calf serum, reaching a maximum of three- to four-fold greater than in basal medium alone. Under basal conditions, 30% of hepatocytes stained positively for the presence of IGF peptides using a monoclonal antibody raised against purified human IGF I/Sm-C. Although this proportion did not change following treatment with HGH and HPL, IGF I/Sm-C released by cells into culture medium was considerably increased in the presence of both hormones. Incubation with the SmC 1.2 monoclonal antibody abolished the increase in labeling index in response to IGF I/Sm-C and partially blocked the response to both HPL and HGH. These results indicate that both HPL and HGH stimulate DNA synthesis in human fetal hepatocytes and suggest that this effect is at least partly indirect through the release and paracrine action of IGF I/Sm-C.     

Acute toxoplasma infection of mice induces spleen NK cells that are cytotoxic for T. gondii in vitro

Murine spleen natural killer (NK) cells from normal and Toxoplasma-infected BALB/c mice were examined for their reactivity against RH strain tachyzoites in vitro. First, the effect of suspending medium on survival of extracellular RH tachyzoites was determined. Optimal parasite viability (by ethidium bromide-acridine orange staining) was observed when tachyzoites were incubated in phosphate-buffered saline (PBS) containing 10% horse serum (HS) for as long as 5 hr. In addition, parasite viability in PBS-HS correlated with subsequent infectivity, because freshly harvested and PBS-HS-incubated tachyzoites were equivalent in their ability to cause lethal infections in normal mice and to survive within normal mouse macrophages. Furthermore, viability and tumoricidal capacity of murine spleen NK cells incubated in PBS-HS was comparable to that of NK cells incubated in a standard cytotoxicity medium. Incubation of effector NK cells and target tachyzoites in PBS-HS in vitro revealed that spleen NK cells from 3-day Toxoplasma-infected mice had significantly greater cytotoxicity for extracellular RH tachyzoites than did control cells from uninfected mice. Moreover, Toxoplasma gondii-induced spleen NK cell toxoplasmacidal activity was significant at all effector to target cell ratios tested, and appeared to be mediated by direct contact between the host cell and the parasite. These in vitro results suggest that NK cells may be important in host defense against T. gondii.     

Toxoplasma gondii: immunocytochemistry of four immunodominant antigens with monoclonal antibodies

Four monoclonal antibodies in which diagnostic usefulness has been observed, concerning congenital, acquired, and reactivated toxoplasmosis, were raised against Toxoplasma gondii tachyzo?tes in order to localize immunodominant antigens. On immunoblots, it appears that McAb IV47, McAB GII9, McAb II38, and McAb IE10 identify families of proteins with estimated molecular weights of 28-30 kDa, 30 kDa, 45-50 kDa, and 66-70 kDa, respectively. By immunogold preembedding techniques one can observe an homogeneous labeling of the outer pellicle of the tachyzo?tes with the McAb GII9 and IV47 and a light labeling with the McAb II38 and IE10. The three-dimensional observation of cell surface antigens is performed by applying a modified metal extraction replica method, i.e., A plasma polymerization method of glow discharge by Tanaka (1979). By immunogold preembedding techniques [with saponin permeabilization (0.1%)], and by immunogold postembedding techniques, a labeling of the rhoptries is observed with McAb GII9 and McAb IV47 but essentially all label is found with McAb II38 and IE10. With McAb GII9 a uniform labeling is observed on the cell surface. By immunoenzymatic techniques (peroxidase) a cell surface labeling is observed with the four McAb. Intracellular Toxoplasma, the outer pellicle, and the vesicles of the network (elaborated by Toxoplasma in parasitophorous vacuole) are also labeled with McAb IE10. These results indicate that McAb GII9 recognizes antigens of the antigen family (P 30) located on the cell surface and in the rhoptries. The antigen recognized by McAb IV47 is essentially located on and beneath the Toxoplasma cell surface membrane, and McAb II38 and IE10 identify preferentially rhoptry proteins.     

Three-dimensional immunogold labeling of nuclear matrix proteins in permeabilized cells.

A preembedment labeling procedure is described for the three-dimensional (3D) labeling of nuclear matrix proteins in permeabilized cells. The procedure is based on the use of ultra-small (1 nm) gold particles as a marker system. This marker penetrates the nucleus more efficiently than the conventionally used 5-10 nm colloidal gold probes. Dehydration is performed by freeze-substitution to preserve the ultrastructure of the cell as optimally as possible. During freeze-substitution the samples are stained by uranyl ions to stain the cellular material throughout the resin section. The 3D gold-labeled and uranyl-stained specimen is embedded in Epon resin and semi-thin (0.2-0.5 microns) sections are made for stereo electron microscopy. The applicability of this method is illustrated by the localization of nuclear matrix-associated nuclear bodies in permeabilized interphase and mitotic HeLa cells.