Electron microscopy of herpes simplex virus. IV. Studies with ferritin-conjugated antibodies

Super-resolution proximity labeling reveals anti-viral protein network and its structural changes against SARS-CoV-2 viral proteins

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replicates in human cells by interacting with host factors following infection. To understand the virus and host interactome proximity, we introduce a super-resolution proximity labeling (SR-PL) method with a "plug-and-playable" PL enzyme, TurboID-GBP (GFP-binding nanobody protein), and we apply it for interactome mapping of SARS-CoV-2 ORF3a and membrane protein (M), which generates highly perturbed endoplasmic reticulum (ER) structures. Through SR-PL analysis of the biotinylated interactome, 224 and 272 peptides are robustly identified as ORF3a and M interactomes, respectively. Within the ORF3a interactome, RNF5 co-localizes with ORF3a and generates ubiquitin modifications of ORF3a that can be involved in protein degradation. We also observe that the SARS-CoV-2 infection rate is efficiently reduced by the overexpression of RNF5 in host cells. The interactome data obtained using the SR-PL method are presented at https://sarscov2.spatiomics.org. We hope that our method will contribute to revealing virus-host interactions of other viruses in an efficient manner.

Easy and reliable double-immunogold labelling of herpes simplex virus type-1 infected cells using primary monoclonal antibodies and studied by cryosection electron microscopy

Cell biology concerns the interactions between different cellular compartments and between the cell and the environment. The mechanisms of herpes simplex virus type-1 (HSV-1) envelopment and the transport of virus particles and HSV-1 glycoproteins have not been completely investigated. It is of interest to examine the formation of complete virus particles and the cellular distribution of viral glycoproteins correlated with microtubules. The illustration of these conditions by immunocytochemistry is best done by multiple labelling techniques in the same cell. Single-staining of neighbouring serial sections or two-face double-immunolabelling methods are not technically compatible with ultrathin cryosections. The results are reported here of a simultaneous, simple and reliable immunogold double-staining technique using primary antibodies of the same species in ultrathin cryosections. Compared to other inactivation procedures, phosphate-buffered 3% paraformaldehyde plus 2% glutaraldehyde for 2 h at room temperature is an excellent and gentle method to destroy free anti-IgG binding sites on the antibodies and to prevent cross-labelling, which has proven necessary for obtaining reproducible results on cellular distribution of tubulin and viral glycoproteins gD-1 and gC-1.

Herpes simplex virus type 1-infected human embryonic lung cells studied by optimized immunogold cryosection electron microscopy

Herpes simplex virus type 1 (HSV-1) is a common human pathogen of skin and mucous membranes and is potentially dangerous when the infection is disseminated. Viral morphogenesis, especially the mechanism of viral envelopment and the exact pathway for processing and transport of HSV-1 glycoproteins, is still unclear. We report the results of optimized immunogold-labeled cryosection electron microscopy of HSV-1-infected cultured human fibroblasts (MRC-5). The simplified method presented has proved necessary to obtain reproducible results on cellular distribution of viral glycoproteins. It is now possible to demonstrate the viral glycoprotein gD-1, but not gC-1, in the nuclear membranes and to demonstrate gD-1- and gC-1-labeled viral particles in the perinuclear space, and to show the fate of the viral particles in the endoplasmic reticulum and Golgi area in infected cells.

Intra-nuclear localization of two envelope proteins, gB and gD, of herpes simplex virus

The envelopes of herpes simplex virus (HSV) particles are acquired from the inner nuclear membrane (INM) of the infected cell and virus-coded glycoproteins are present in the envelope of mature virions. Our ultrastructural study examined the process of virus envelopment and the targeting of two major viral glycoproteins, gB and gD, to the INM in HSV-infected human embryonic fibroblasts. It was shown that envelopment and transport of virus particles from the nucleus is facilitated by the formation of a dynamic tubulo-reticulum arising from the INM. Capsids were assembled in the nucleus and collected within INM tubules which protruded into the perinuclear space and thence into the cisternae of the endoplasmic reticulum (ER). Envelopment occurred by constriction and fusion of the tubular channel walls, releasing enveloped virions into the ER. Transport to the cell surface took place in membrane-bound compartments and probably followed the normal secretory pathway through the Golgi apparatus. Immunogold probes, tagged with specific monoclonal antibodies, were used to localize gB and gD during the process of virus maturation. Cytoplasmic membranes were not labelled, but probes bound inside the nucleus, mainly at sites of virus assembly. Labelling occurred on the nucleoplasmic side of the INM which surrounded capsids in the process of envelopment, but not on the outside of that membrane, although characteristic gB glycoprotein spikes were labelled on the envelopes of extracellular virus particles and on virions in trans-Golgi transport vesicles just prior to their release from the infected cell. gB was not detected on the surface of enveloped virions in the perinuclear space, or the cisternae of the ER or cis-Golgi, which suggests that the specific epitope was masked during that stage of intracellular processing. gD probes bound to virion envelopes and also to the tegument region of some particles found in both perinuclear and extracellular sites. We postulate the precursor core proteins for both gB and gD are transported first to the nucleus, and then, together with maturing capsids, are targeted to the INM, and later inserted into viral envelopes at the site of budding. Post-translational glycosylation of envelope proteins could occur as virus particles exit the nucleus and travel through the ER and Golgi compartments.

A type-specific conformational epitope on the nucleocapsid of equid herpesvirus-1 and its use in diagnosis

A type-specific monoclonal antibody was produced by immunizing mice with purified equid herpesvirus-1 (EHV-1). The EHV-1 specific mAb reacted with all the EHV-1 strains tested so far by indirect ELISA, immunofluorescence, and immunoperoxidase tests. No reactions were detected with the EHV-4, EHV-2, or EHV-3 strains tested. The indirect immunofluorescence and immunoperoxidase tests showed that the nuclei of infected cells were predominantly stained by this mAb. Triton treatment of the virus and immunogold labeling experiments indicated that the nucleocapsid of EHV-1 was the target antigen of the mAb. Preliminary results indicated that this mAb might be a useful tool in detecting specific antibody in horses that have been exposed to EHV-1. In a blocking ELISA, antibodies in sera from hamsters, mice and a foal which had been exposed to EHV-1 were differentiated from those in sera of animals exposed to EHV-4.

Intracellular maturation and sorting of two herpes simplex virus type 1 glycoproteins. Immunogold staining of ultrathin cryosections

Simultaneous immunocytochemical triple staining of ultrathin cryosections of herpes simplex virus type 1-infected cells was carried out using monoclonal antibodies specific for glycoprotein C, glycoprotein D and alpha + beta tubulin. The viral glycoproteins were identified in the cytoplasm, in the Golgi sacs, on the plasma membrane and on the surface of intra- and extracellular virus particles, but not on the nuclear membrane. The glycoproteins identified in the cytoplasm outside the Golgi region were not always confined to the membranes of vesicles, but were often located in close proximity to the tubulin-labelled structures. The glycoproteins C and D were usually codistributed in the cytoplasm, and both accumulated in the Golgi sacs in the same membrane domains. As the glycoproteins occur in close proximity to the microtubular structures, we speculate that these might be directly involved in the intracellular transport of viral glycoproteins.

Role of the Golgi apparatus in cellular pathology

The Golgi apparatus response to pathological disorders is predominantly as an intermediary component of membrane biogenesis where it is involved in processing, sorting and secretion of materials via secretory granules, and in the formation of lysosomes. A common initial response of the Golgi apparatus to any stress is an alteration or cessation of secretory activity. In the transformed cell, the Golgi apparatus is altered both morphologically and biochemically, suggesting a shift from a secretory to a membrane-generating mode of functioning. However, since fewer or less well-developed Golgi apparatus are frequently found in transformed cells, analytical methods of membrane isolation developed for normal tissues may not always yield equivalent results when applied to tumors. Cell surface alterations characteristic of malignant cells may result from modifications occurring at the level of the Golgi apparatus. Some lysosomal dysfunctions may result from underglycosylation of acid hydrolases by the Golgi apparatus. The use of cell-free systems between endoplasmic reticulum and Golgi apparatus or within Golgi apparatus cisterane is providing a new approach to the elucidation of the role of the Golgi apparatus in normal as well as pathological states.

Ultrastructural immunocytochemical localization of herpes simplex virus (type 1) in trigeminal ganglion neurons

Four days after corneal inoculation of mice with herpes simplex (type 1) virus (HSV), infected trigeminal ganglion cells with and without calcitonin gene-related peptide (CGRP) antigenicity were examined by electron microscopy in sections treated with colloidal gold labeled antibodies. Cells that contain CGRP were identified by the dense gold labeling of small vesicles about 100 nm in diameter. Adjacent thin sections were stained using an indirect colloidal gold immunocytochemical technique to reveal HSV-1 antigens. In CGRP-positive neurons, HSV antigens were located over both nuclear and cytoplasmic compartments. HSV label was found over cytoplasmic vesicles that were significantly larger than those labeled with anti-CGRP antisera; the HSV-containing vesicles ranged in profile diameter from less than 170 to greater than 400 nm. There was no overlap in the distribution of the two labels. Thus, for this time period, the organelles involved in transport of the endogenous neuropeptide and HSV appear to remain discrete. Furthermore, there was no significant difference in the distribution of HSV in CGRP-reactive and CGRP-negative trigeminal ganglion cells. Thus, there is no indication of a preferential distribution or limited replication of HSV in CGRP-positive neurons.

Visualization of glycoproteins after tunicamycin and monensin treatment of herpes simplex virus infected cells

The effects of tunicamycin and monensin on the morphogenesis of herpes simplex virus type 1 and on the ultrastructure and function of host cell membranes was investigated by conventional technics of electron microscopy and cytochemical localization of glycoproteins with thiocarbohydrazide-SO2. Infected RS 537 rabbit fibroblasts were treated with tunicamycin, which inhibits the glycosylation of many glycoproteins, or monensin, which inhibits the transport of proteins to the cell surface, and were compared with untreated infected cells. Tunicamycin treatment almost entirely suppresses the perinuclear envelopment of viral capsids, induces the nuclear export of unusually numerous naked viral capsids, and prevents the proliferation of the Golgi apparatus. On the other hand, perinuclear envelopment of viral capsids still occurs following a monensin treatment; however, enveloped viral capsids are not released into the extracellular space; in addition this treatment induces the proliferation of the rough endoplasmic reticulum (RER). The number of structures stained for glycoproteins in tunicamycin-treated cells is markedly lower than that in nontreated infected cells, whereas an unusual additional staining of the entire outer nuclear membrane and of the RER occurs following monensin treatment.

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.

Ultrastructural localization of viral antigen in nuclear inclusions of cytomegalovirus infected guinea pig cells

Intranuclear localization of viral antigens in guinea pig cytomegalovirus (GPCMV) infected guinea pig embryo (GPE) cells was investigated by cross-reactive indirect immunoperoxidase and immunoferritin techniques utilizing guinea pig antisera to GPCMV. Following primary fixation with 4 percent paraformaldehyde, a brief treatment of infected cells with 0.25 percent trypsin was found to enhance penetration of antibodies and the conjugates. Ferritin or horseradish peroxidase conjugated goat anti-rabbit IgG was used as a secondary antibody that cross reacted with guinea pig immunoglobulins in order to reduce non-specific immunochemical reactions. Using light microscopy following immunoperoxidase staining, GPCMV antigens in an intranuclear location were not discernable when the infected cells were stained without pretreatment with trypsin, however intranuclear GPCMV antigens could be visualized after the fixed cells were treated with trypsin for 2-4 minutes prior to addition of the antiserum. Electron microscopic examination following indirect immunoferritin staining revealed viral antigens localized on viral capsids and on scattered electrondense amorphous matrices but not on the surrounding tubular structures on fibrils. The possibility that tubular structures may be a host cell product produced in response to GPCMV infection is discussed.

Ultraviolet induced lysosome activity in corneal epithelium

A 5,000 W Xe-Hg high pressure lamp and a double monochromator were used to produce a 3.3 nm half-bandpass ultraviolet radiation at 295 nm. Pigmented rabbit eyes were irradiated with radiant exposures from 140 Jm-2 to 10,000 Jm-2 and evaluated by slit-lamp biomicroscopy, light and electron microscopy. Corneal threshold (Hc) was 200 Jm-2 and lens threshold (HL) was 7,500 Jm-2. The most repeatable and reliable corneal response to these levels of UV was the development of corneal epithelial granules. Histological changes included a loss of superficial epithelial cells and selective UV induced autolysis of the wing cells. It is suggested that the biomicroscopically observed granules are the clinical manifestation of the secondary lysosomes revealed by light and electron microscopy. It is proposed that UV breaks down the primary lysosome membranes to release hydrolytic enzymes which in turn form the secondary lysosomes during autolysis. Extreme levels of radiant exposure at 295 nm result in indiscriminate destruction of all layers of the corneal epithelium, but the posterior cornea was spared.

Electron microscopic studies of tumor viruses. II. Entry and uncoating of Epstein-Barr virus

Entry of Epstein-Barr virus into human lymphoblastoid cells (Daudi cells) was studied by electron microscopy. At the site of viral attachment, two distinct interactions conducive to penetration of the virus occurred between the viral envelope and cell membrane, namely, (i) simultaneous dissolution of both the envelope and cell membrane, presumably resulting in passage of viral capsids into the cytoplasm and (ii) dissolution confined to the cell membrane with resulting penetration of enveloped virus. In the latter case envelope dissolution appears to occur subsequently in the cytoplasm with release of capsids. Fusion of the viral envelope with the cell membrane was not observed. The capsids exhibited two distinct structural forms--one dense, the other translucent or light in appearance. The former disrupted near the cell membrane with release of viral cores into the cytoplasm whereas the light capsids containing dense cores migrated toward the nucleus and accumulated in the perinuclear region. Apparently the process of releasing deoxyribonucleic acid (DNA) from the light capsid is slowed down or prevented in Daudi cells. A hypothesis is presented concerning the manner in which these two types of capsids initiate infection.

Intramembrane changes occurring during maturation of herpes simplex virus type 1: freeze-fracture study

During the maturation of two strains of herpes simplex virus type 1 (VR3 and Patton), intramembrane changes were detected with the freeze-fracture technique in the viral envelope and the infected cell plasma membrane, and these changes were compared with data obtained from thin sections. Regardless of the strain, the inner leaflet of the viral envelope of extracellular virions was characterized by a density of intramembrane particles (IMP) three times larger than the host nuclear and plasma membrane. Addition of IMP, which probably represent virus-coded proteins, was detected in the viral envelope only after budding from the nuclear membrane, whereas it occurred during envelopment of capsids at cytoplasmic vacuoles. Fused membranes also showed one of their fracture faces covered with a high density of IMP similar to that of the mature virion envelope. The internal side of the membrane leaflet bearing these numerous particles was always characterized by the presence of an electron-dense material in thin sections. In addition, the plasma membrane of fibroblasts and Vero cells showed strain-specific changes: patches of closely packed IMP were observed with the VR3 strain, whereas ridges almost devoid of IMP characterized the plasmalemma of cells infected with the Patton strain. These intramembrane changes, however, were not observed as early as herpes membrane antigens. Thus, application of the freeze-fracture technique to herpes simplex virus type 1-infected cells revealed striking structural differences between viral and uninfected cell membranes. These differences are probably related to insertion and clustering of virus-coded proteins in the hydrophobic part of the membrane bilayer.

Inhibition of adsorption of West-Nile and herpes simplex viruses by procaine

The effect of the local anaesthetic drug procaine on the adsorption of two enveloped viruses was studied. Physiological concentrations of the drug (7 X 10(-3)--7 X 10(-2) M) strongly inhibited the adsorption of both West-Nile and herpes viruses as determined by plaque assay and the infective center assay.

Biologic and antigenic characteristics of Epstein-Barr virus-related Herpesviruses of chimpanzees and baboons

Leukocyte-transforming agents were isolated in baboon leukocytes inoculated with oral excretions from immunosuppressed chimpanzees. The transformed lymphoblasts had B cell surface markers and harbored herpes-type virus particles; 5-10% of the cells contained cytoplasmic antigens reactive with Epstein-Barr virus (EBV)-antibody-positive chimpanzee, human and baboon sera. These sera also neutralized the transforming activity of the chimpanzee virus. Long-term lymphoid cell lines were established from circulating lymphocytes of normal baboons: two from Papio cynocephalus and three from P. hamadryas. The cells had B cell surface markers, contained herpes-type virus particles and produced virus with leukocyte-transforming activity. No virus-associated nuclear antigen was detectable with reference baboon and chimpanzee sera; however, the cells reacted with selected human sera containing antibodies to EBV nuclear antigen (EBNA). Absorption experiments confirmed the specificity of this reaction. Baboon lymphoblasts produced baboon virus-associated soluble complement-fixing (CF/S) antigen. Baboon sera had CF antibodies to viral (CF/V) antigen derived from EBV but failed to react with EBV-associated CF/S antigen. Chimpanzee and baboon herpesviruses had similar in vitro host cell ranges but were different from those of EBV. Inoculation of baboons, rhesus monkeys and cottontop marmosets failed to produce detectable illness or palpable tumors.

Immunoprecipitation of herpes simplex virus type 1 antigens with different antisera and human cerebrospinal fluids

Rabbit convalescent and hyperimmune sera, human patient and blood donor sera, as well as cerebrospinal fluids of humans with herpes simplex virus encephalitis all recognize similar major antigenic components in herpes simplex virus infected rabbit or human cells as shown by electrophoretic analysis of immunoprecipitates. Besides the main glycoproteins with an apparent molecular weight of 100,000 (peak I) the antisera precipitate glycoproteins in a region of an apparent mol. wt. of 60,000--80,000 (peak II), which were resolved into distinct glycoprotein species only by antibody-containing cerebrospinal fluids. The peak II glycoproteins appear on the surface of the infected cell early, and absorb neutralizing antibodies, whereas the peak I glycoproteins are less accessible. Both antigens can be demonstrated in the cell as early as about 2 hours post infection. All major antigenic components studied were found to be glycosylated except one protein with an apparent mol. wt. of 110,000. The herpesvirus specificity of these antigens is demonstrated by a variety of control experiments. The antigens detected are virion components.

Contributions of electron microscopy to the study of corneal pathology

Most of the electron microscopic studies of pathological corneas have been done only recently. Keratoplasty has been the most important source of specimens for ultramicroscopic investigation. With the introduction of electron microscopic techniques, we have been able to confirm many light microscopic studies in pathological corneas. This contribution has been most valuable in the identification of the sites and types of pathological changes in corneal dystrophies and degenerations. This review of electron microscopic studies describes the present concepts on the nature of the histological changes in dystrophies and degenerations of the anterior and posterior corneal layers and corneal stroma. It also includes a review of some corneal inflammatory conditions as well as metabolic disorders affecting its transparency.

Proteins specified by herpes simplex virus. XIII. Glycosylation of viral polypeptides

In the course of herpes simplex virus 1 (HSV-1) replication in human epidermoid carcinoma no. 2 cells, the synthesis and glycosylation of host cell proteins ceases and is replaced by the synthesis and glycosylation of virus-specified polypeptides. Analyses of the synthesis of viral glycoproteins show that the glycosylation of viral polypeptides occurs late in the virus growth cycle and that certain of the precursors to major vital glycoproteins are members of the gamma group of polypeptides, i.e., polypeptides synthesized at increasing rates until 12 to 15 h postinfection. Viral glycoproteins are formed by stepwise additions of heterosaccharide chains to completed precursor polypeptides. The precursor and the highly glycosylated product are separable by gel electrophoresis and are localized in different fractions of infected cells. Within 15 min of their synthesis, precursor polypeptides acquire heterosaccharide chains of about 2,000 molecular weight, which contain glucosamine but little or nor fucose or sialic acid. Both precursor and product of this first stage of glycosylation are absent or present in low concentrations in the surface membranes of the infected cell and in the virion. The partially glycosylated product is then conjugated further in a slow, discontinuous process to form the mature glycoprotein of the virion and plasma membrane. These mature products bear large heterosaccharide units with molecular weights greater than 4,000 to 5,000; these contain fucose and sialic acid as well as glucosamine. Heterosaccharide chains from infected and uninfected cells are distributed among discrete size classes and the smallest chains consist of multiple saccharide residues.

Cell-mediated immunity to Herpes simplex in humans: lymphocyte cytotoxicity measured by 51-Cr release from infected cells

We assessed cell-mediated immunity to herpes simplex virus type 1 antigen in patients suffering from recurrent cold sores and in a series of healthy controls. Paradoxically, all those subject to recurrent herpetic infections had, without exception, evidence of cell-mediated immunity to herpes antigens. This was demonstrated by lymphocyte transformation and specific 51Cr release from infected human amnion cells after incubation with peripheal blood mononuclear cells. Where performed, skin tests with herpes antigen were also positive. In addition, serum from these patients specifically sensitized herpesvirus-infected cells to killing by nonimmune, control mononuclear cells. These tests were negative in the control patients except in a few cases, and it is suggested that these latter may be the asymptomatic herpesvirus carriers previously recognized or that they may have experienced a genital infection.

Inhibition of herpes virus-induced cell fusion by concanavalin A, antisera, and 2-deoxy-D-glucose

Pseudorabies virus-induced cell fusion in rabbit kidney cells can be prevented by Concanavalin A added early after infection. The infected cells are not agglutinated and the infectivity of cell-free virus is not reduced. Sera from productively infected animals also inhibit polykaryocytosis, whereas a hyperimmune serum directed against virus structural components has no effect. 2-Deoxy-d-glucose reversibly disturbs virus-induced fusion and reduces significantly the virus infectivity.

Hepatitis B antigen: antigenic sites related to human serum proteins revealed by affinity chromatography

Hepatitis B antigen-associated particles, isolated from sera of antigen carriers, were submitted to affinity chromatography on columns of insolubilized antibodies to normal human plasma. The particles adsorbed to the immunosorbent at pH 7.2 and were subsequently eluted at pH 2.2. Exposure of the particles to 8 M urea, 5 M KI, pH 2.2, detergents, organic solvents, or proteolytic enzymes failed to prevent their subsequent adsorption to the immunosorbent. This suggests that antigenic determinants related to human plasma proteins are constituent components of hepatitis B antigen-associated particles. These determinants are distinct from the group-specific (a) and subtype-specific (d or y) sites of the hepatitis B antigen and appear to be related to antigenic specificities on prealbumin, albumin, apolipoproteins C and D, and the gamma-chain of immunoglobulin G.

Biogenesis of Marek's disease (type II leukosis) virus in vitro: electron microscopy and immunological study

The kinetic events involved in Marek's disease herpesvirus infection of avian cell culture were investigated by assaying viral infectivity and antigenicity as well as by electron microscopy during the infectious cycle. The levels of viral infectivity and complement-fixing (CF) antigens revealed that the rates of appearance of infectious particles and CF antigens were not synchronous. Viral specific CF antigen could be detected 5 h after infection, whereas viral infectivity or the appearance of viral particles could be demonstrated only after 10 h of infection. High proportions of the recovered CF antigens during the various stages of the infectious cycle were found to be soluble and did not sediment with the virus particles. Cytological analysis of the developmental stages of the JM virus-infected cells by thin sectioning and electron microscopy revealed that at 8 h small particles approximately 35 nm in diameter appeared in the cell nuclei. The appearance of nucleocapsids occurred at 10 h, and these were of varying shapes; however, all were approximately 100 nm in diameter. At approximately 18 h postinfection, mature virus particles were observed. Viral maturation of the immature particles occurred by the acquisition of envelope from the inner leaflet of the nuclear membrane or from the cytoplasmic membrane of the cell.

Surface antigens produced by Herpesviruses Varicella-Zoster virus

Surface antigen(s) was demonstrated by the mixed agglutination technique on cell cultures infected with varicella-zoster virus (V-Z). The reactions appeared to be specific for V-Z, and no cross-reaction was obtained with herpes simplex virus (HSV). V-Z surface antigen had similar physicochemical properties to that of HSV. It was stable to heating at 56 C and treatment with 1% Formalin, 2,4-dinitrophenol, and periodate, whereas it was undetectable after exposure to acetone or ethanol. Antibodies detecting surface antigen were present in high titer in sera from varicella or herpes zoster patients and paralleled titers obtained by the complement fixation test.

Pathogenesis of herpetic neuritis and ganglionitis in mice: evidence for intra-axonal transport of infection

The pathogenesis of acute herpetic infection in the nervous system has been studied following rear footpad inoculation of mice. Viral assays performed on appropriate tissues at various time intervals indicated that the infection progressed sequentially from peripheral to the central nervous system, with infectious virus reaching the sacrosciatic spinal ganglia in 20 to 24 hr. The infection also progressed to ganglia in mice given high levels of anti-viral antibody. Immunofluorescent techniques demonstrated that both neurons and supporting cells produced virus-specific antigens. By electron microscopy, neurons were found to produce morphologically complete virions, but supporting cells replicated principally nucleocapsids. These results are discussed in the context of possible mechanisms by which herpes simplex virus might travel in nerve trunks. They are considered to offer strong support for centripetal transport in axons.

Proteins specified by herpes simplex virus. 8. Characterization and composition of multiple capsid forms of subtypes 1 and 2

Two classes of herpesvirus capsids, designated A and B, were isolated from the nuclei of human cells infected with herpes simplex virus (HSV). A and B capsids share in common four structural proteins, i.e., no. 5, 19, 23, and 24. B capsids contain 7.7 to 9.7 times more deoxyribonucleic acid than A capsids; moreover, they contain proteins no. 21 and 22a in addition. All of the proteins contained in the capsid except no. 22a are present in the enveloped nucleocapsids (virions) in approximately the same molar ratios. The capsid proteins of HSV-1 cannot be differentiated from their HSV-2 counterparts with respect to electrophoretic mobility. A third class of capsids, designated C capsids, was isolated from virions contained in the cytoplasm of infected cells by the same procedure used to obtain A and B capsids. The C capsids contain all of the proteins present in A capsids plus proteins 1 to 3 and 21.

Mouse cytomegalovirus. Necrosis of infected and morphologically normal submaxillary gland acinar cells during termination of chronic infection

The ultrastructural lesions in the submaxillary glands of C(3)H mice chronically infected with the murine cytomegalovirus are reported. Virus was synthesized in the nucleus of acinar glandular cells. After passage into the cytoplasm, virus was located in large vesicles which were derived from the Golgi apparatus. These vesicles, which were periodic acid-Schiff positive, migrated to the apex of the cell and released virus into the acinar lumen or canaliculi. Eventually, lymphocytes infiltrated the interstitium and surrounded the basal lamina of acini which contained infected cells. In acini encompassed by lymphocytes, both infected cells and morphologically normal acinar cells simultaneously degenerated, producing a small focus of necrosis. Physical contact between lymphocytes and necrotic cells did not occur for an intact basal lamina was always found interposed between them. Degeneration of infected cells coincided with a decrease in virus titer in the salivary glands. Degeneration of infected and normal acinar cells also occurred in DBA 2 mice which lack the fifth component of complement. In mice conditioned with cortisone to suppress inflammation, neither infected nor normal acinar cells degenerated. We concluded from the electron microscope observations that lymphocytes terminate chronic MCMV infection, that MCMV infection of acinar epithelium is not cytolytic and that normal cells also undergo necrosis during termination of chronic MCMV infection. It is postulated that lymphocytes in responding to infection release a cytotoxic substance which diffuses into the acini and causes indiscriminate necrosis of acinar cells.

Immunoperoxidase localization of herpes zoster virus and simian virus 40 in cell culture

The immunoperoxidase technique was used in an electron microscopy study to localize the virions of herpes zoster virus and simian virus 40 in cell cultures. Intranuclear and intracytoplasmic virions of herpes zoster virus were easily and specifically identified due to intense staining by the finely granular, black reaction product. With simian virus 40, intranuclear virions were not stained, whereas intracytoplasmic particles appeared densely black. There was essentially no background staining. Advantages of this technique over the ferritin-labeled antibody method include simpler preparative procedures for reagents, greater penetrability of the antibody conjugate, and internal amplification which substantially improves the ability to localize sites of antigen-antibody reaction. We believe that the immunoperoxidase method can be successfully applied to a wide variety of problems involving viral antigens.

Complement-fixing antigens of herpes simplex virus types 1 and 2: reactivity of capsid, envelope, and soluble antigens

Capsid, envelope, and nonvirion-associated soluble components of type 1 and type 2 herpes simplex virus (HSV) were obtained from infected monolayer cell cultures and used as complement fixation (CF) antigens. Capsids were prepared by treatment of cells with the nonionic detergent Nonidet-P40, envelope material by treatment of virions with ether and high pH, and soluble components were obtained from culture fluids of untreated cells. Serological studies with experimental anti-herpesvirus sera indicate that these serotypes share cross-reacting envelope, capsid, and soluble antigens with each other and with herpesvirus B but not with varicella virus. In addition, animals immunized with crude HSV preparations contain high levels of CF antibody (1:32 to 1:64) to soluble antigens, whereas sera from humans who have experienced natural infection contain low levels of antibody (</=1:8) to this antigen. Further testing with reference, capsid, and envelope antigens indicates that antibody levels to reference and capsid antigens are about the same in sera from healthy humans, whereas antibody to the envelope is decidedly lower in these sera. Herpes convalescent-phase sera contain higher levels of antibody to reference and envelope antigens than to capsid antigen.

Structure and development of viruses as observed in the electron microscope. XI. Entry and uncoating of herpes simplex virus

Two morphologically distinct types of capsids are described. The dense capsid appeared to be disrupted near the cellular membrane with release of core material. The light capsid was more stable and was frequently encountered close to the nucleus, where empty capsids were also found. Pretreatment of cells before infection with either puromycin or actinomycin D markedly decreased the percentage of empty capsids. It is suggested that the two types of capsids play different roles in the process of initiating infection. One (the dense capsid) releases deoxyribonucleic acid (DNA) shortly after entry. This DNA is transcribed into a virus-specific ribonucleic acid, which codes for an enzyme capable of altering the permeability of the second type of capsid (the light capsid). In proximity to the nucleus, the infectious DNA then escapes without gross disruption of the capsid.

Mechanism of intranuclear crystal formation of herpes simplex virus as revealed by the negative staining of thin sections

Structural alterations induced in HeLa cells by herpes simplex virus and the mechanism whereby the virus is formed in the nucleus in crystal arrays were studied by electron microscopy with both the usual and negatively stained sections. Aggregates of granular and filamentous material were observed in the cytoplasm of infected cells with both sections. On the other hand, no remarkable alterations in appearance of the cytoplasmic ground substance were observed with the usual sections of infected cells. However, the cytoplasmic ground substance of infected cells when negatively stained consisted of granular material which was different in appearance from the spongy material constituting the cytoplasmic matrix of uninfected cells. In the nucleus of infected cells, complexes consisting of round bodies, amorphous material, aggregates of uniform granules in rows, and viral crystals were often observed near the nuclear membrane in both types of sections. Examinations of the granular aggregates with negatively stained sections suggested that each granule represents a subunit and that the several adjoining subunits (approximately eight) constitute the requirement for formation of a single viral capsid with a core. Thus, rapid and simultaneous formation of the core and capsid within the aggregate would replace the rows of the granules with the viral crystal. The advantages of negative staining of thin sections for visualization of fine structural alterations are discussed.

Electron microscopic studies of tumor viruses. I. Entry of murine leukemia virus into mouse embryo fibroblasts

Entry of Rauscher leukemia virus into mouse embryo fibroblasts was studied by electron microscopy. The polycation diethylaminoethyl-dextran enhanced viral attachment and subsequent entry. At the site of viral attachment to the cell membrane, three distinct interactions occurred between the viral envelope and cell membrane, namely, (i) dissolution of viral envelopes on the cell membrane, which itself remained unaltered; (ii) simultaneous dissolution of both the envelope and cell membrane, resulting in passage of viral nucleoids directly into the cytoplasm; and (iii) dissolution of the cell membrane with direct penetration of intact enveloped particles into the cytoplasm, followed by intracytoplasmic disruption of the envelope, resulting in release of nucleoids into the cytoplasm. These interactions occurred with both mature and immature C-type particles. At no time was fusion of viral envelopes with the cell membrane observed. The mechanism of these interactions is discussed.

Synthesis of proteins in cells infected with herpesvirus, VI. Characterization of the proteins of the viral membrane

The envelope of pseudorabies virions can be removed by treatment with Triton X-100, leaving the nucleocapsid intact. The viral envelope removed in this fashion contains all the glycoproteins and about 40 per cent of the proteins of the virions. Analysis by polyacrylamide gel electrophoresis revealed that the envelope proteins migrate as four distinct peaks, all of which contain glycoproteins. The proteins of the nucleocapsids migrate in the gels as six distinct peaks.

Electron microscopic observations of Visna virus-infected cell cultures

Electron microscopic observations of three cell lines infected with visna virus revealed two types of extracellular particles. The smaller of these was 65–110 mμ in diameter and contained a 20–30 mμ electron-dense core. Ordered arrays of the latter type of particle occurred rarely in the cytoplasm. After cesium chloride density gradient centrifugation of the virus, the band that contained maximal infectivity was composed of numerous particles with osmiophilic cores similar to those found in infected cell cultures. This finding suggests that such particles represent the infective agent. The second type of extracellular particle was larger (100–140 mμ in diameter), lacked an electron-dense core, and contained material similar in appearance to cellular cytoplasm. This form appeared to develop by budding from the cell surface.

Replication of canine herpesvirus. II. Virus development and release in infected dog kidney cells

The studies reported in this paper demonstrate that, although canine herpesvirus differs from other herpesviruses in that it is characterized by a restricted host range, the pattern of virus development in the permissive host closely resembles that previously described for herpes simplex virus. These experiments also reveal the formation in the infected dog kidney cells of a system of tubules and channels in which virions accumulate. It is suggested that these membrane-bound structures serve to protect enveloped virus from being uncoated in the cytoplasm and function in virus release from the infected cells.