The cytopathic effect of animal viruses

SARS-CoV-2 Nucleocapsid Protein TR-FRET Assay Amenable to High Throughput Screening

Drug development for specific antiviral agents against coronavirus disease 2019 (COVID-19) is still an unmet medical need as the pandemic continues to spread globally. Although huge efforts for drug repurposing and compound screens have been put forth, only a few compounds are in late-stage clinical trials. New approaches and assays are needed to accelerate COVID-19 drug discovery and development. Here, we report a time-resolved fluorescence resonance energy transfer-based assay that detects the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (NP) produced in infected cells. It uses two specific anti-NP monoclonal antibodies conjugated to donor and acceptor fluorophores that produce a robust ratiometric signal for high throughput screening of large compound collections. Using this assay, we measured a half maximal inhibitory concentration (IC₅₀) for remdesivir of 9.3 μM against infection with SARS-CoV-2 USA/WA1/2020 (WA-1). The assay also detected SARS-CoV-2 South African (Beta, β), Brazilian/Japanese P.1 (Gamma, γ), and Californian (Epsilon, ε) variants of concern (VoC). Therefore, this homogeneous SARS-CoV-2 NP detection assay can be used for accelerating lead compound discovery for drug development and for evaluating drug efficacy against emerging SARS-CoV-2 VoC.

A SARS-CoV-2 nucleocapsid protein TR-FRET assay amenable to high-throughput screening

Drug development for specific antiviral agents against coronavirus disease 2019 (COVID-19) is still an unmet medical need as the pandemic continues to spread globally. Although huge efforts for drug repurposing and compound screens have put forth, only few compounds remain in late stage clinical trials. New approaches and assays are needed to accelerate COVID-19 drug discovery and development. Here we report a time-resolved fluorescence resonance energy transfer-based assay that detects the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein (NP) produced in infected cells. It uses two specific anti-NP monoclonal antibodies (MAbs) conjugated to donor and acceptor fluorophores that produces a robust ratiometric signal for high throughput screening of large compound collections. Using this assay, we measured a half maximal inhibitory concentration (IC₅₀) for Remdesivir of 9.3 μM against infection with SARS-CoV-2 USA/WA1/2020 (WA-1). The assay also detected SARS-CoV-2 South African (Beta, β), Brazilian/Japanese variant P.1 (Gamma, γ), and Californian (Epsilon, ε), variants of concern or interest (VoC). Therefore, this homogeneous SARS-CoV-2 NP detection assay can be used for accelerating lead compound discovery for drug development and for evaluating drug efficacy against emerging SARS-CoV-2 VoC.

Bombyx mori nucleopolyhedrovirus F-like protein Bm14 is a factor for viral-induced cytopathic effects via regulating oxidative phosphorylation and cellular ROS levels

Bombyx mori nucleopolyhedrovirus (BmNPV) is highly pathogenic to Bombyx mori, silkworm, which causes serious cytopathic effects (CPEs) during infection. However, the role of viral protein in the virus-induced CPEs remains unclear. Here, we discovered that BmNPV infection induced severe CPEs including titer-dependent cell floating and changes in cellular surface morphology. Further explorations revealed the involvement of F-like protein (Bm14), a viral envelope protein, in inducing cytotoxicity and detachment of adherent BmN cells, and its disruption significantly impaired the virus infection-mediated CPEs. Intriguingly, transcriptomic analysis identified the tight association of Bm14 deletion with the activation of cellular oxidative phosphorylation pathway, consistent with the elevated mitochondrial membrane potential (MMP) levels and ATP concentrations as well as reduced ROS levels. Collectively, our results characterized for the first time the novel role of Bm14 in accelerating viral-induced cytopathogenicity via suppressing the cellular oxidative phosphorylation levels and upregulating the ROS levels.

Label-Free Digital Holo-tomographic Microscopy Reveals Virus-Induced Cytopathic Effects in Live Cells

This study introduces label-free digital holo-tomographic microscopy (DHTM) and refractive index gradient (RIG) measurements of live, virus-infected cells. We use DHTM to describe virus type-specific cytopathic effects, including cyclic volume changes of vaccinia virus infections, and cytoplasmic condensations in herpesvirus and rhinovirus infections, distinct from apoptotic cells. This work shows for the first time that DHTM is suitable to observe virus-infected cells and distinguishes virus type-specific signatures under noninvasive conditions. It provides a basis for future studies, where correlative fluorescence microscopy of cell and virus structures annotate distinct RIG values derived from DHTM.

Cytopathic effects (CPEs) are a hallmark of infections. CPEs are difficult to observe due to phototoxicity from classical light microscopy. We report distinct patterns of virus infections in live cells using digital holo-tomographic microscopy (DHTM). DHTM is label-free and records the phase shift of low-energy light passing through the specimen on a transparent surface with minimal perturbation. DHTM measures the refractive index (RI) and computes the refractive index gradient (RIG), unveiling optical heterogeneity in cells. We find that vaccinia virus (VACV), herpes simplex virus (HSV), and rhinovirus (RV) infections progressively and distinctly increased RIG. VACV infection, but not HSV and RV infections, induced oscillations of cell volume, while all three viruses altered cytoplasmic membrane dynamics and induced apoptotic features akin to those caused by the chemical compound staurosporine. In sum, we introduce DHTM for quantitative label-free microscopy in infection research and uncover virus type-specific changes and CPE in living cells with minimal interference.

IMPORTANCE This study introduces label-free digital holo-tomographic microscopy (DHTM) and refractive index gradient (RIG) measurements of live, virus-infected cells. We use DHTM to describe virus type-specific cytopathic effects, including cyclic volume changes of vaccinia virus infections, and cytoplasmic condensations in herpesvirus and rhinovirus infections, distinct from apoptotic cells. This work shows for the first time that DHTM is suitable to observe virus-infected cells and distinguishes virus type-specific signatures under noninvasive conditions. It provides a basis for future studies, where correlative fluorescence microscopy of cell and virus structures annotate distinct RIG values derived from DHTM.

Feststellung der Felinen Infektiösen Peritonitis (FIP) bei Hauskatzen und Leoparden in Deutschland

Zusammenfassung

Bei 3 aus einem Wurf stammenden Siamkatzen und 2 ebenfalls spontan erkrankten, verschwisterten, schwarzen Leoparden (Panthera pardus) sowie bei 3 experimentell mit unfiltrierter und filtrierter Organsuspension von einer der Siamkatzen infizierten Hauskatzen wurden epizootiologische, klinische, pathologische und mikrobiologische Befunde erhoben, die dem Bild der Felinen Infektiösen Peritonitis (FIP) entsprechen. Damit ist diese Infektionskrankheit erstmals auch in Deutschland nachgewiesen worden.

Summary

Demonstration of Feline Infectious Peritonitis (FIP) in Domestic Cats and Leopards in Germany

Spontaneous cases of a disease resembling feline infectious peritonitis (FIP) with regard to epizootiological, clinical, pathological, and microbiological findings were demonstrated in 3 Siamese cats belonging to the same litter and in 2 black leopards (Panthera pardus) born in different litters of identical parents. Using unfiltered and filtered organ suspensions of one of the Siamese cats the disease was transmitted to 3 domestic cats. This is the first report on the occurence of FIP in Germany.

Résumé

Diagnostic de la péritonite infectieuse féline (FIP) chez des chats domestiques et des panthères en Allemagne

Des résultats épizootologiques, cliniques, pathologiques et microbiologiques correspondant à l'image de la péritonite infectieuse féline (FIP) ont été trouvés chez 3 chats siamois malades de la même portée, chez 2 soeurs panthères noires (Panthera pardus) malades et chez 3 chats domestiques infectés expérimentalement avec une suspension d'organes filtrée et non filtrée d'un des chats siamois. Cette maladie infectieuse est trouvée pour la première fois en Allemagne.

Resumen

Verificación de la peritonitis infecciosa felina (FIP) en los gatos domésticos y leopardos en Alemania

En 3 gatos siameses procedentes de una camada y en 2 leopardos (Panthera pardus) negros hermanos, enfermos también espontáneamente, así como en 3 gatos domésticos, infectados experimentalmente con una suspensión no filtrada y filtrada de órganos de uno de los gatos siameses, se evidenciaron los hallazgos epizootológicos, clínicos, patológicos y microbiológicos, correspondientes al cuadro de la peritonitis infecciosa felina (FIP). Con ello, esta enfermedad infecciosa también ha sido diagnosticada por vez primera en la República Federal de Alemania.

Activation of lysosomal enzymes in virus-infected cells and its possible relationship to cytopathic effects

Activities of the enzymes β-glucuronidase, acid phosphatase, acid DNAase, acid RNAase, and acid protease have been measured in the lysosomal and supernatant fractions of mouse liver cells and monkey kidney cells before and after infection with mouse hepatitis virus and vaccinia virus, respectively. In the infected cells there was easily measurable release of lysosomal enzymes into the supernatant fraction. Evidence was presented that this is not an artefact of homogenization and precedes cell degeneration demonstrable histologically. It is suggested that release of lysosomal enzymes may explain some of the biochemical changes found in infected cells and may contribute to the cytopathic effects of some viruses.

Progressive reorganization of the host cell cytoskeleton during adenovirus infection

Infection of cells with adenovirus lead to a characteristic reorganization of all cytoskeleton systems, starting with alterations at the microtubuli of the cells. During this progress, the flat, extended, and polar morphology of the cytoskeleton became nonpolar and rounder. These rearrangements were initiated before the appearance of adenovirus structural proteins hexon and fiber, as well as before the shutoff of host protein synthesis. We conclude that these alterations reflect a specific reorganization rather than an unorganized breakdown of the cell during adenovirus infection.

Studies on Herpesvirus scophthalmi infection of turbot Scophthalmus maximus (L.) ultrastructural observations

Abstract. Recent heavy mortalities amongst O+ group turbot at a fish farm were found to be associated with a herpes‐type viral infection of the epithelia of the skin and gills. The morphology of the virus is described with ultrastructural observations on its morphogenesis and release from infected cells.

Genetic and pathologic findings in a kindred with hereditary sarcoma, breast cancer, brain tumors, leukemia, lung, laryngeal, and adrenal cortical carcinoma

A familial cancer aggregation comprising sarcomas, brain tumors, leukemias, and carcinomas of breast, larynx, lung, adrenal, cortex, and other sites has been studied from a pathologic--genetic standpoint. Based upon sibships segregating for cancer, the genetic segregation parameter is estimated to be 45.6 +/- 11% which is compatible with that expected for a rare deleterious autosomal gene showing complete dominance. Pathologic review of 16 tumors by bright field microscopy revealed variable occurrences of intranuclear cytoplasmic invaginations, intranucleolar bodies, and acidophilic intracytoplasmic inclusions in eight lesions. Two tumors showed both intranuclear cytoplasmic invaginations and intranucleolar inclusions. Morphological findings coupled with the observed pattern and distribution of cancer in the subject kindred suggest that the cancer-prone genotype interacts with one or more exogenous factors in causing this familial tumor association.

Accelerated Cytopathology in HeLa Cells Induced by Reovirus and Cycloheximide

The addition of the protein inhibitor cycloheximide, at concentrations which suppress virus replication, to HeLa cell monolayers infected with reovirus type 2 results in the appearance of accelerated cytopathic effects (CPE). At high multiplicity of infection, CPE appeared after a lag period of 2 to 3 hr and increased progressively, until by 12 hr the entire monolayer had rounded and sloughed off. During this same period, both the uninfected cycloheximide-treated and untreated virus-infected controls exhibited no CPE. The phenomenon is affected by the kind of cell species employed and can be reversed if the antibiotic is removed within 1 hr after exposure. The evidence obtained through studies in which specific metabolic inhibitors and direct biochemical analyses were used suggests that the accelerated CPE observed in cycloheximide-treated reovirus-infected cells is the consequence of the combined inhibition of the synthesis of both cellular protein and ribonucleic acid. The accelerated CPE is also induced in the antibiotic-treated cells by reovirus serotypes 1 and 3.

Immunosuppression and experimental virus infection of the nervous system

This chapter describes the current views of the pathogenesis of virus infections of the nervous system, with particular attention to certain aspects of virus-host interactions. Following invasion of the central nervous system, infection can follow a variety of patterns, as to number and distribution of neuronal and non-neuronal cells involved. There is a corresponding diversity in the pathological lesions of the central nervous system (CNS) produced by acute virus infection. Infection can be pictured as a race between virus and host defenses, where many factors, acting through different mechanisms, can influence the outcome. Outcome is always determined by multiple virus and host variables, although single variables can be independently studied under experimentally controlled conditions in the laboratory. The chapter demonstrates that in many virus-host combinations, the immune response plays an important role in recovery from primary infections. It mentions that an immunopathological process mediates the disease which follows certain CNS virus infections.

The Production of Cytopathic Changes in Canine Cell Lines by Infectious Agents: Cell Lines Derived from Melanoma and Thyroidal Carcinoma

The cytopathic effect of more than 30 viruses and Toxoplasma gondii and Histoplasma capsulatum was determined in established canine thyroid adenocarcinoma and canine melanoma cell lines. Marked effect was observed with the viruses of canine hepatitis, pseudorabies, and canine distemper, and reo type 1 and vaccinia viruses in both cell lines. Moderate effect was found with human adenovirus type 1, swine adenovirus and the viruses of swine influenza and Newcastle disease. Cytopathic changes were produced with the virus of herpes simplex in the thyroid adenocarcinoma cells. A transient giant cell formation was produced by the virus of measles in the thyroid cell line. Hemadsorption was demonstrated in both cell lines with vaccinia virus. Toxoplasma gondii multiplied in both cell lines and produced cellular degeneration and necrosis. Histoplasma capsulatum grew in the thyroid adenocarcinoma cell line with little cellular degeneration.

Effect of visible light on canine distemper virus

Nemo, George J. (The Catholic University of America, Washington, D.C.), and Ernest C. Cutchins. Effect of visible light on canine distemper virus. J. Bacteriol. 91:798-802. 1966.-Canine distemper virus (CDV) was inactivated by visible light. The virus was light-sensitive in fluid suspension (in vitro) as well as during intracellular replication (in vivo). The addition of calf serum or glutathione reduced the extent of inactivation. CDV was less sensitive when suspended in distilled water or in the amino acid or Earle's salts components of the minimal essential medium of Eagle than when suspended in the vitamin component of the minimal essential medium of Eagle or in riboflavine (0.1 mg per liter). These findings indicate that, whereas some ingredient of the medium may enhance light sensitivity, its presence is not necessary for light inactivation of CDV. It is proposed that some substance derived from the host cell and intimately associated with the virus particle serves to render CDV light-sensitive.