Minimizing false negatives in electron microscope searches for virus or other specific features of cancer cells.

Electron microscopic searches for virus particles and other specific features of cancer cells involve exceptionally poor sampling statistics. It is probable that most searches conducted in the past were of limited value in establishing whether such viruses or special features are associated with one or more tumor types. On the other hand, in a few cases, the electron microscope has provided the first, or even the only, evidence of virus particles. A radical change in the way the electron microscope is applied to this problem is suggested whereby a high-voltage microscope is used to examine thicker sections and an image-processing arrangement is used to focus and select images and to search the images for virus particles. It is suggested that it is important to distinguish virus producers amongst oncogenic viral genome carriers since these may be in a more advanced state of tumor induction and may be capable of transmitting the virus to others.     

Further Studies on the Effect of 5-Iododeoxyuridine on Polyoma Virus Multiplication in Mouse Cells

5-Iododeoxyuridine (IUDR) inhibited production of infectious polyoma virus in mouse embryo cells and mouse kidney cells in culture. Deoxythymidine reversed its effect. IUDR did not inactivate infectivity of free virus particles. IUDR did not prevent adsorption and penetration of polyoma virus to cells. The events sensitive to IUDR treatment occurred at around 20 hours after infection. The cytopathic effects of polyoma virus, including emergence of DNA containing-inclusions in the nucleus, were observable in infected cells in which viral replication was completely arrested by IUDR. It was shown by fluorescent antibody technique in infected mouse embryo cells and by complement fixation test in infected mouse kidney cells that IUDR inhibited completely the synthesis of viral antigen. No virus-like particles were demonstrated in the IUDR-treated infected-mouse kidney cells by electron microscope examinations.     

STRUCTURE AND DEVELOPMENT OF VIRUSES OBSERVED IN THE ELECTRON MICROSCOPE : IV. VIRUSES OF THE RI-APC GROUP

Representative viruses of the RI-APC group were observed with the electron microscope in thin sections of infected HeLa cells. The viral particles varied in density, were approximately 60 mµ in diameter and had a center to center spacing when close packed of about 65 mµ. Many of the less dense particles exhibited an internal body averaging 24 mµ in diameter. It was suggested that within the nucleus the virus differentiated from dense granular and reticular material and formed crystals. Disintegration of the crystals and disruption of the nuclear membrane with release of virus into the cytoplasm appeared to occur at any stage. No evidence to suggest development of the virus in the cytoplasm was obtained. It was possible to deduce the structure of the viral crystal from the electron micrographs. The viral particles are packed in a cubic body—centered lattice. Correlative histochemical observations in the light microscope which are now in progress revealed that the crystals and non-crystalline aggregates of virus were strongly Feulgen-positive.     

A CORRELATED HISTOCHEMICAL AND ELECTRON MICROSCOPIC STUDY OF THE INTRANUCLEAR CRYSTALLINE AGGREGATES OF ADENOVIRUS (RI-APC VIRUS) IN HELA CELLS

HeLa cells in tissue cultures infected with types 3, 4, or 7 of adenovirus (RI-APC virus) were studied in order to correlate certain histochemical and electron microscopic findings. Adjacent thin (ca. 0.05 µ) and thick (2–4 µ) sections of osmium-fixed, methacrylate-embedded cells were cut; by mapping the sections the same cells could be identified with both the electron and the light microscope. Intranuclear crystalline aggregates seen with the electron microscope to be composed of ordered arrays of viral particles were found by means of the Feulgen reaction to contain DNA. DNA is therefore assumed to be a constituent of the viral particle. The virus appeared to develop from an osmiophilic Feulgen-negative matrix. Displacement of nuclear chromatin occurred during this process. A Feulgen-azure staining method was found to permit clear distinction between viral and nuclear (host) DNA in thick sections.     

Cryo X-ray nano-tomography of vaccinia virus infected cells

We have performed full-field cryo X-ray microscopy in the water window photon energy range on vaccinia virus (VACV) infected cells to produce tomographic reconstructions. PtK2 cells were infected with a GFP-expressing VACV strain and frozen by plunge fast freezing. The infected cells were selected by light fluorescence microscopy of the GFP marker and subsequently imaged in the X-ray microscope under cryogenic conditions. Tomographic tilt series of X-ray images were used to yield three-dimensional reconstructions showing different cell organelles (nuclei, mitochondria, filaments), together with other structures derived from the virus infection. Among them, it was possible to detect viral factories and two types of viral particles related to different maturation steps of VACV (immature and mature particles), which were compared to images obtained by standard electron microscopy of the same type of cells. In addition, the effect of radiation damage during X-ray tomographic acquisition was analyzed. Thin sections studied by electron microscopy revealed that the morphological features of the cells do not present noticeable changes after irradiation. Our findings show that cryo X-ray nano-tomography is a powerful tool for collecting three-dimensional structural information from frozen, unfixed, unstained whole cells with sufficient resolution to detect different virus particles exhibiting distinct maturation levels.     

C-type virus-lymphocyte interactions in developing mouse thymus.

The appearance of C-type virus particles in thymus cells of Swiss mouse embryos, 11.5 to 15.5 days post-conception age (PCA), was studied with the electron microscope. In thymic rudiments of all specimens examined, virus particles were seen in epithelial cytoplasm, budding from epithelial cell surfaces and in extracellular spaces. Lymphoid cells were first seen in thymic rudiments of 13.5 days PCA, and did not display virus particles at this stage. At 14.5 days PCA, thymic lymphocytes had localized plasmalemmal thickenings of high electron-density which were adjacent to extracellular virus particles. Viruses appeared to be penetrating thymic lymphocytes by viropexis in embryos of 15.5 days PCA. At this stage, many lymphocytes also had cytoplasmic virus-containing vesicles and viral buds at their surfaces. These observations suggest the possibility that, in embryos, C-type viruses are transmitted horizontally from thymic epithelium to early populations of thymic lymphocytes.     

登革病毒对人树突状细胞感染性的研究

探讨登革病毒对人树突状细胞(DC)的感染性。人外周新鲜血常规分离单核细胞,经细胞因子GMCSF、IL4诱导培养成DC,通过形态学特征、细胞表型和淋巴细胞刺激能力鉴定。用登革病毒2型(DV2)感染DC,于作用后6h、24h、48h、72h、96h分别收集上清液和细胞,甲基纤维素微量空斑试验测定病毒滴度,间接免疫荧光法检测细胞上病毒抗原表达,透射电镜观察病毒在细胞内的定位。病毒感染后6h即可在培养上清中测出病毒,病毒滴度在48h达到高峰,以后逐渐下降。间接免疫荧光法证明感染的DC胞浆及胞膜上携带病毒抗原。透射电镜下在病毒感染48h后DC胞浆内可见大量病毒颗粒。树突状细胞是登革病毒感染的靶细胞,病毒可感染DC并产生大量病毒颗粒,可能在其发病机制中起重要作用。     

Studies on the budding process of a temperature-sensitive mutant of murine leukemia virus with a scanning electron microscope.

The scanning electron microscope was used to study the budding process of the wild-type Moloney murine leukemia virus and one of its temperature-sensitive mutants, designated ts 3. A considerably larger number of budding particles was observed on TB cells infected with ts 3 at the nonpermissive temperature (39 C) than at the permissive temperature (34 C). No apparent difference was noted between the number of particles on ts 3-infected cells at (34 C) and wild-type-infected cells at 34 or 39 C. Virions were detected at the cell membrane of ts 3-infected cells at 39 C as early as 8 h postinfection. Virion density increased progressively up to 48 h after which no increase was observed. An average of 1,600 virus particles was observed at the cell surface at the peak of virus production. The distribution of these on the cell membrane appeared to be random. The maximum proportion of the cell surface occupied by the viral particles did not exceed 10%. After temperature shift from 39 to 34 C, approximately 90% of the particles had dissociated from the cell membrane within 1 h.     

RELATION OF TOBACCO MOSAIC VIRUS TO THE HOST CELLS

The relation of tobacco mosaic virus (TMV) to host cells was studied in leaves of Nicotiana tabacum L. systemically infected with the virus. The typical TMV inclusions, striate or crystalline material and ameboid or X-bodies, which are discernible with the light microscope, and/or particles of virus, which are identifiable with the electron microscope, were observed in epidermal cells, mesophyll cells, parenchyma cells of the vascular bundles, differentiating and mature tracheary elements, and immature and mature sieve elements. Virus particles were observed in the nuclei and the chloroplasts of parenchyma cells as well as in the ground cytoplasm, the vacuole, and between the plasma membrane and the cell wall. The nature of the conformations of the particle aggregates in the chloroplasts was compatible with the concept that some virus particles may be assembled in these organelles. The virus particles in the nuclei appeared to be complete particles. Under the electron microscope the X-body constitutes a membraneless assemblage of endoplasmic reticulum, ribosomes, virus particles, and of virus-related material in the form of wide filaments indistinctly resolvable as bundles of tubules. Some parenchyma cells contained aggregates of discrete tubules in parallel arrangement. These groups of tubules were relatively free from components of host protoplasts.     

呼肠孤病毒与SARS相关的形态学依据

SARS患者病理尸检肺组织样品分离病毒出现细胞病变的Hep2 培养细胞,按常规制作超薄切片,透射电镜下观察。电镜下,检出在感染细胞内复制、组装的呼肠孤病毒及其包涵体。病毒粒子衣壳立体对称、无包膜、直径在60~80nm。成熟病毒粒子核心致密常排列呈晶格状,不成熟病毒粒子核心空亮。数目不等的上述两种病毒粒子、长短不等的微管样结构和病毒浆常在核旁胞质内组成大小不等、无定形的病毒包涵体。此发现进一步提供了呼肠孤病毒感染有可能与SARS相关的形态学依据。     

Comparison of protein A-gold and ferritin immunoelectron microscopy of Semliki Forest virus in mouse brain using a rapid processing technique

Processing tissue for transmission electron microscopy by standard laboratory methods can take two to three days. This makes the development of new techniques time consuming and generally restricts the use of the electron microscope in routine diagnostic work. The possibility of viewing tissue with the electron microscope five hours after sampling using rapid processing techniques is presented. The morphology of the tissue appears undamaged with cell and organelle ultrastructures being readily recognized, as is the presence of virus and its replicating stages. When combined with immunoelectron microscopy a rapid labeling protocol is possible. We have used the technique to develop protein A-gold (6 and 16 nm particles) and ferritin immunoelectron microscopic techniques to demonstrate viral antigens in brain cell cultures and brain tissue from mice infected with Semliki Forest virus.     

Study of neutralizing monoclonal antibodies to bovine herpes virus Type-1 (Cooper strain) by immunoperoxidase and immunoelectron microscopy

Abstract Three neutralizing monoclonal antibodies (mAbs) that are specific against bovine herpes virus Type-1 (BHV-1) were studied as to their viral specificity by immunoperoxidase and immunoelectron microscopy. Microscopic examination of GBK BHV-1 infected cells revealed peroxidase activity represented by red-brown granular deposits in the nucleus and cytoplasm. No immunoperoxidase activity was observed in negative controls. For the ultrastructural observations, two approaches were used. Firstly we tested a pre-embedding technique using GBK infected cells, mAbs and gold conjugated-protein A. Gold particles were observed linked to the viral envelopes and to the host cell membrane. Alternatively, a second technique employed BHV-1 purified by potassium tartrate gradients, mAbs and gold conjugated-protein A. After performing the immune reaction, the samples were adsorbed to formvar-coated grids, stained with phosphotungstic acid and observed in a transmission electron microscope. Gold particles were mainly attached to the virion envelope.     

Role of cytoplasmic vacuoles in varicella-zoster virus glycoprotein trafficking and virion envelopment.

Varicella-zoster virus (VZV) encodes several glycoproteins which are present on both mature viral envelopes and the surfaces of infected cell membranes. Mechanisms of VZV glycoprotein transport and virion envelopment were investigated by both continuous radiolabeling and pulse-chase analyses with tritiated fucose in VZV-infected cells. We studied in detail the large cytoplasmic vacuoles which were present in infected cells but absent from uninfected cells. The specific activity in each subcellular compartment was defined by quantitative electron microscope autoradiography, using a cross-fire probability matrix analysis to more accurately assess the individual compartment demarcated by the silver grains. By these techniques, we documented a progression of activity originating in the Golgi apparatus and traveling through the post-Golgi region into virus-induced cytoplasmic vacuoles and finally to areas of the cellular membrane associated with the egress of viral particles. Significant amounts of radiolabel were not observed in the nucleus, and only low levels of radiolabel were associated with the cellular membrane not involved with the egress of viral particles. In addition, immunolabeling of Lowicryl-embedded VZV-infected cells demonstrated the presence of VZV glycoproteins within cytoplasmic vacuole membranes as well as on virion envelopes. These observations suggested that cytoplasmic vacuoles harbored VZV-specified glycoproteins and were also the predominant site of VZV virion envelopment within the infected cell. Neither enveloped nor unenveloped viral particles were observed within the Golgi apparatus itself.     

Evidence for multiple vegetative DNA replication origins and alternative replication mechanisms of bovine papillomavirus type 1

By following up the chance detection in the electron microscope of a DNA replication intermediate within a preparation of bovine papillomavirus (BPV-1) DNA isolated from purified virus particles, information was obtained about the mechanism of BPV-1 genome replication during the final stages of virus multiplication in naturally infected bovine wart tissue. The structure of viral replication intermediates was investigated by electron microscopic analysis of viral DNA linearized by digestion with restriction endonucleases which cleave the circular BPV-1 chromosome at defined sites. Both Cairns and rolling circle-type molecules were identified. Furthermore, replication eyes were widely distributed within the viral genome, indicating that vegetative BPV-1 DNA replication origins are largely uncoupled from previously described plasmid maintenance sequence elements.     

登革病毒对人血管内皮细胞感染性的研究

用登革病毒Ⅱ型（DV2）感染体外培养和传代的人脐静脉内皮细胞（HUVEC）,研究发现,HUVEC是登革病毒的允许性细胞。病毒感染后12h即可在培养上清中用微量蚀斑法测出病毒,病毒滴度48h达高峰,以后迅速下降。并发现在一定范围内病毒产量随病毒感染复数（MOI）的增加而增高。间接免疫荧光法证明感染的HUVEC胞浆及胞膜上携带DV2抗原。电镜和光镜下,感染细胞未见明显的形态和结构改变。     

Electron microscopy of cells showing viral cytopathic effects in Papanicolaou smears

A technique is described whereby cells showing cytologic changes suggestive of virus infection by light microscopy can be processed further for examination in the electron microscope so that virus particles present in the cell can be visualized directly. We present the results of electron microscopy of over 100 Papanicolaou-stained smears processed this way. The morphologic changes in the cells and the ultrastructural appearances of the virus particles are demonstrated. This technique is particularly valuable for retrospective studies of mounted cytologic or histologic material. It has also proven to be a valuable research tool in the study of human polyomavirus and human wart virus infection.     

Colloidal gold probes for the identification of virus particles: An appraisal

Electron microscope examination of negatively stained preparations continues to be the method of choice for the diagnosis of virus particles although in some instances an immunological test is necessary. Colloidal gold immunocytochemical probes are becoming increasingly popular for electron microscopy and their suitability for the identification of virus particles is assessed.Virus particles were immunolabelled in situ on plastic/carbon coated electron microscope grids with specific antibody and colloidal gold probes. The labelling obtained was specific, definite and with very little background. The technique is very sensitive, very quick, and since a minimum of preparation is needed it appears to possess considerable potential for virus diagnosis.     

Viral basophilic inclusions in the digestive gland of razor clams Ensis arcuatus (Pharidae) in Galicia (NW Spain)

During a histological survey of razor clam Ensis arcuatus (Jeffreys, 1865) from Galicia (NW Spain), basophilic inclusion bodies were observed in epithelial cells of the digestive gland. Transmission electron microscopy revealed the intranuclear position of these inclusions containing viral particles with icosahedral symmetry. Size and symmetry of these unenveloped virus particles suggest similarities to the families Papillomaviridae and Polyomaviridae which have been described as causing a viral gametocytic hypertrophy in oysters Crassostrea virginica and C. gigas. This is the first report of viral particles in E. arcuatus.