Electron microscopy of viruses of human papilloma, molluscum contagiosum, and vaccinia, including observations on the formation of virus within the cell

Deep-etch EM reveals that the early poxvirus envelope is a single membrane bilayer stabilized by a geodetic "honeycomb" surface coat

Three-dimensional "deep-etch" electron microscopy (DEEM) resolves a longstanding controversy concerning poxvirus morphogenesis. By avoiding fixative-induced membrane distortions that confounded earlier studies, DEEM shows that the primary poxvirus envelope is a single membrane bilayer coated on its external surface by a continuous honeycomb lattice. Freeze fracture of quick-frozen poxvirus-infected cells further shows that there is only one fracture plane through this primary envelope, confirming that it consists of a single lipid bilayer. DEEM also illustrates that the honeycomb coating on this envelope is completely replaced by a different paracrystalline coat as the poxvirus matures. Correlative thin section images of infected cells freeze substituted after quick-freezing, plus DEEM imaging of Tokuyasu-type cryo-thin sections of infected cells (a new application introduced here) all indicate that the honeycomb network on immature poxvirus virions is sufficiently continuous and organized, and tightly associated with the envelope throughout development, to explain how its single lipid bilayer could remain stable in the cytoplasm even before it closes into a complete sphere.

Recognition and quantitation of herpesvirus particles in human vesicular lesions

Herpesvirus particles from crude vesicular fluid of a patient were stained with uranyl acetate and potassium phosphotungstate, and then were identified and counted by electron microscopy. Virus was seen and quantitated in all the samples taken from five vesicles. Specimens from human lesions can be prepared and examined within 3 hours, permitting rapid presumptive identification of herpesvirus.

An electron microscope study of molluscum contagiosum

The development of the molluscum body and of the molluscum contagiosum virus is described. All cells of the molluscum lesion do not form molluscum bodies, but those which do probably show cytoplasmic abnormality prior to the appearance of virus particles within the cytoplasm. Such abnormal cells may reflect the activity of some infective precursor of the morphologically observable virus particle; they may alternatively represent cells which have successfully resisted invasion by the infective precursor.

Cells which have failed to resist invasion gradually become filled with virus particles and the nucleus becomes eccentric. The molluscum body thus formed is virtually a bag of virus particles, the wall of the bag being the peripheral cytoplasm, which seems to resist invasion and in which the nucleus remnant can readily be detected.

There appear to be two kinds of viruses. Development of the commoner virus is compared and contrasted with studies by Morgan and his colleagues of vaccinia and fowl pox. It is akin to fowl pox in its origin from foci of finely dispersed cytoplasm, here called cytoplasmic clouds; it is akin to vaccinia in that no evidence can be found of a denser, finely granular, pre-nucleoid material; it is like both in that the virus does not observably develop within the nucleus; and it is unlike both in that a nuclear change—the appearance of rather unspecific dense bodies—is seen. The structural changes seen in the virus particles during development are similar to those described by Morgan et al., but a slightly different interpretation is given of the behaviour of the transient ‘nucleoid’: they believe that it expands to form a central viroplasm, whereas in this paper it is believed to disperse through an already present central viroplasm.

The second type of virus is of uncertain origin. It may develop from, or at least it seems to be related to, a double-membrane structure seen in abnormal lesion cells.

Recent advances in molluscum contagiosum virus research

Molluscum contagiosum virus (MCV) and variola virus (VAR) are the only two poxviruses that are specific for man. MCV causes skin tumors in humans and primarily in children and immunocompromised individuals. MCV is unable to replicate in tissue culture cells or animals. Recently, the DNA sequence of the 190 kbp MCV genome was reported by Senkevich et al. MCV was predicted to encode 163 proteins of which 103 were clearly related to those of smallpox virus. In contrast, it was found that MCV lacks 83 genes of VAR, including those involved in the suppression of the host response to infection, nucleotide biosynthesis, and cell proliferation. However, MCV possesses 59 genes predicted to code for novel proteins including MHC-class I, chemokine and glutathione peroxidase homologs not found in other poxviruses. The MCV genomic data allow the investigation of novel host defense mechanisms and provide new possibilities for the development of therapeutics for treatment and prevention of the MCV infection.

Detection of human papovavirus antigen in oral papillary lesions

The papillary lesions of oral verruca vulgaris, condyloma acuminatum, and verrucous carcinoma were examined for the presence of papovavirus antigens by the peroxidase-antiperoxidase immunohistochemical methods. The antigens could be detected in the nuclei of cells only in the stratum granulosum and stratum corneum in some cases of verruca vulgaris and condyloma acuminatum but in no case of verrucous carcinoma.

Diagnostic virology using electron microscopic techniques

This chapter illustrates the development of the use of electron microscopy in viral diagnosis. The field covered is confined to medical viral diagnosis, but parallel developments have taken place in both veterinary and botanical fields and techniques derived from both these sources are also included where relevant. It is reported that the scanning transmission mode of operation, which can induce image contrast changes electronically, may enhance studies with unstained sections and perhaps facilitate thin section immune electron microscopy (IEM). The application of negative stain IEM has been particularly useful for the study of the antigenic nature of some of the newly discovered noncultivable viruses. Viral antigens can also be detected in thin sections of infected cells by IEM with suitably labeled specific antibodies. Confirmation of viral infection by electron microscopy on tissues originally processed for light microscopy is also frequently useful.

Ultrastructural studies of intraoral verruca vulgaris

The literature offers conflicting views regarding the existence of verruca vulgaris in the oral cavity. In an attempt to clarify this issue, a series of ten oral lesions which had been diagnosed as verruca vulgaris and ten oral lesions diagnosed as squamous-cell papilloma were examined ultrastructurally. Six of the lesions diagnosed as verruca vulgaris contained the characteristic intranuclear viral particles which are normally found in that lesion. None of the lesions diagnosed as squamous-cell papilloma exhibited this type of intranuclear viral inclusions.

[Comparison of the epidermodysplasia verruciformis Lewandowsky-Lutz with the other Papova virus acanthomas by light and electron microscopy (author's transl)]

Based on histology and electron microscopy, a series of Papova virus acanthomas consisting of 300 common warts and Condylomata acuminata as well as primary efflorescences of 7 typical and 7 questionable cases of Epidermodysplasia verruciformis have been classified. Four cytological types expressing different cytopathogenic viral actions were established. Typ 4 ("basophilic foamy giant keratinocytes") seems to be specific for Epidermodysplasia verruciformis which thus can be differentiated histologically against ordinary warts (type 1-3).

Intracellular herpesvirus aggregate in the form of a pentagonal dipyramidal crystal-like structure

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Human papova (wart) virus

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Human Wart Virus: In vitro Cultivation

Inoculation of cell cultures of fetal skin of human and murine origin with virus extracted from human wart tissue resulted in the appearance of intracellular wart virus specific antigen, as demonstrated by fluorescent antibody techniques. Appearance of antigen was accompanied by cytopathogenicity and the accumulation of large numbers of characteristic virus particles.

Papova virus group

The papilloma, polyoma, and vacuolating agents seem to form a natural group of tumor viruses, for which the name papova virus group is proposed. Members of the group have the following properties: 45 mmicro diameter, deoxyribonucleic acid core, 42 capsomeres, absence of essential lipids, thermal resistance, slow growth cycle with multiplication within the cell nucleus, and tumorigenicity.

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 micro) and thick (2-4 micro) 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.

Electron microscope observations on intracellular virus-like particles associated with the cells of the Lucké renal adenocarcinoma

The common renal adenocarcinoma of the leopard frog was studied in thin sections with the electron microscope. Approximately a third of the tumors examined were found to contain spheroidal bodies of uniform size and distinctive morphology that are believed to be virus particles. These consist of hollow spheres (90 to 100 mmicro) having a thick capsule and a dense inner body (35 to 40 mmicro) that is eccentrically placed within the central cavity (70 to 80 mmicro). Virus particles of this kind occur principally in the cytoplasm but occasionally they are also found in the nucleus and in the extracellular spaces of the tumor. The intranuclear inclusion bodies that are visible with the light microscope are largely comprised of hollow, spherical vesicles with thin limiting membranes. These are embedded in a finely granular matrix. A few of the thin walled vesicles contain a dense inner body like that of the cytoplasmic virus particles. This suggests that they may be immature virus particles. The inclusion bodies are believed to be formed in the course of virus multiplication but they usually contain very few mature virus particles. Bundles of dense filaments and peculiar vacuolar inclusions also occur in the cytoplasm of the tumor cells. These seem to be related in some way to the presence of virus but their origin and significance remain obscure. These findings are discussed in relation to previous work suggesting that the Lucké adenocarcinoma is caused by an organ-specific filtrable agent. It is concluded that the "virus particles" found in electron micrographs of the tumor cells may be the postulated tumor agent. On the other hand, the possibility remains that the particles described here are not those that are causally related to the tumors.

Studies by electron microscopy of thin sections of infectious myxomatosis in rabbits

Rabbits were inoculated with the C.P.M. strain of myxoma virus and the resulting subcutaneous tumors were fixed, embedded, and sectioned for observation with the electron microscope. Both round cells and the typical stellate myxomatous cells were observed in addition to changes in the collagen pattern at the intercellular spaces. The cytoplasm of the cells showed a great number of bodies of varying size and density, the largest of them having the size and other characteristics of the elementary bodies of the virus. Some of the bodies showed an internal structure, being formed by the tight clumping of small dense particles. Distribution curves of the diameter of the elementary bodies and of the smaller internal particles are presented. The morphological problems involved in the virus-host cell relationship are discussed in the case of the myxoma virus.