Host effect on arbovirus replication: appearance of defective interfering particles in murine cells

Shared sequence characteristics identified in non-canonical rearrangements of HSV-1 genomes

IMPORTANCE

Mutations and genetic rearrangements are the primary driving forces of evolution. Viruses provide valuable model systems for investigating these mechanisms due to their rapid evolutionary rates and vast genetic variability. To investigate genetic rearrangements in the double-stranded DNA genome of herpes simplex virus type 1, the viral population was serially passaged in various cell types. The serial passaging led to formation of defective genomes, resulted from cell-specific non-canonical rearrangements (NCRs). Interestingly, we discovered shared sequence characteristics underlying the formation of these NCRs across all cell types. Moreover, most NCRs identified in clinical samples shared these characteristics. Based on our findings, we propose a model elucidating the formation of NCRs during viral replication within the nucleus of eukaryotic cells.

Laboratory Validation of a Real-Time RT-PCR Assay for the Detection of Jamestown Canyon Virus

The neuroinvasive disease caused by Jamestown Canyon virus (JCV) infection is rare. However, increasing incidence and widespread occurrence of the infection make JCV a growing public health concern. Presently, clinical diagnosis is achieved through serological testing, and mosquito pool surveillance requires virus isolation and identification. A rapid molecular detection test, such as real-time RT-PCR, for diagnosis and surveillance of JCV has not been widely utilized. To enhance testing and surveillance, here, we describe the development and validation of a real-time RT-PCR test for the detection of JCV RNA. Three primer and probe sets were evaluated for analytical sensitivity and specificity. One probe set, JCV132FAM, was found to be the most sensitive test detecting 7.2 genomic equivalents/µL. While less sensitive, a second probe set JCV231cFAM was the most specific test with limited detection of Keystone virus at high RNA loads. Taken together, these data indicate both probe sets can be utilized for a primary sensitive screening assay and a secondary specific confirmatory assay. While both primer and probe sets detected high viral loads of Keystone virus, these assays did not detect any virus in the California encephalitis virus clade, including negative detection of the medically important La Crosse virus (LACV) and snowshoe hare virus (SSHV). The real-time RT-PCR assay described herein could be utilized in diagnosis and surveillance in regions with co-circulation of JCV and LACV or SSHV to inform public health action.

Replication of standard and defective Ross River virus in BHK cells: patterns of viral RNA and polypeptide synthesis

Virus-specific macromolecule synthesis has been examined in BHK cells infected with Ross River virus. Unpassaged virus (R-0) and tenth-passage virus (R-10) have been compared. In infected cells R-0 generates i) 45S, 28S, 33S and 26S viral RNAs, ii) virus-specific precursor polypeptides of mol. wt. 127,000, 95,000 and 61,000 and iii) viral envelope proteins (mol. wts. 52,000 and 49,000) and nucleocapsid protein (mol. wt. 32,000). Thus in terms of virus-specific RNA and polypeptide synthesis, the replication of standard RRV is analogous to that of Semliki Forest virus and Sindbis virus. R-10 interferes with the replication of standard Ross River virus and generates large amounts of 19S and 24S defective RNA species; 45S and 26S RNA synthesis was not markedly affected. Defective RNAs are associated with RNAse-sensitive, 50S cytoplasmic particles which contain a variety of (mainly host) proteins but no nucleocapsid protein. No evidence for translation of defective RNAs was obtained. R-10 infection is also characterized by a relatively early shut down of host protein syntehsis and by a reduction in virus-specific polypeptide synthesis and nucleocapsid formation. The data suggest that defective Ross River virus interferes primarily at the translational level.

Failure of defective interfering particles of Sindbis virus produced in BHK or chicken cells to affect viral replication in Aedes albopictus cells

Whereas defective interfering particles of Sindbis virus are readily produced in BHK-21 cells or chicken embryo fibroblasts by the techniques of serial undiluted passage, similar methods failed to generate such particles in Aedes albopictus cell cultures. In addition, Sindbis virus stocks produced in BHK-21 cells or chicken embryo fibroblasts and which contained defective interfering particles, when tested in A. albopictus cells, failed (i) to interfere with the replication of standard Sindbis virus and (ii) to change the pattern of intracellular viral RNA synthesis from that produced by infection with standard Sindbis virus alone. We conclude that defective interfering particles of Sindbis virus generated in chicken or hamster cells are silent or inert in mosquito cells.

Cellular resistance to arbovirus infection

When an arbovirus enters an arthropod in an infected blood meal, several mechanisms may interact to affect its life cycle and ultimate transmissibility. Intrinsic absolute failure in the establishment of infection must be contrasted with infection that is successfully established but is variably modulated in its viral yield throughout the vector's life-span. Degrees of vertebrate host resistance make this modulation a central factor in determining whether an arthropod is an important vector in nature; moreover, human intervention that affects modulating mechanisms may become a basis for disease control. In the absence of evidence of real immune resistance to arbovirus infections in arthropods, other more primitive modulating mechanisms must be considered: interferonlike substances may be formed in arthropod cells; arthropod cells may "cure" themselves by a unique endophagocytic digestion of their virus burden; homologous interference with viral replicative processes may be mediated via wild or mutant viral RNA species acting to shut down further RNA synthesis; and homologous interference may be mediated by RNA of defective-interfering virus formed earlier in infection.

Production of defective interfering virus in the brains of mice by an avirulent, in contrast with a virulent, strain of Semliki forest virus

An avirulent strain (A7) of Semliki Forest virus formed nearly as much haemagglutinating and complement fixing antigen in the brains of adult mice as a virulent (V13) strain, yet the infectivities of the brain tissues were different by about 100-fold. It appeared therefore that defective virus particles were fomed by A7 but these were not demonstrated by fluorescent antibody studies. In short-term organ cultures of adult mouse brain, A7 derived from mouse brain showed a typical interference pattern in inoculum infectivity response curves. Furthermore, when mixed suspensions of brain-grown V13 and A7 with equal infectivities were inoculated the inoculum infectivity response patterns showed significant depressions of the V13 response at higher inocula. Such interference was not detected if chick cell grown A7 and V13 were substituted for the mouse grown virus. The avirulence of A7 in adult mice and its rapid protective effect against lethal V13 infection could be due to the production of defective interfering virus particles in the brain.

Limited infection of mouse brain cell cultures with Semliki forest virus

A simple technique for preparing tissue cultures containing morphologically different types of brain cells from young and adult mice is described. After infection with Semliki forest virus cytopathic effects are slight. The cultures usually support virus multiplication for only a limited period and ultimately no infectious virus can be detected. However, one batch of cultures developed a persistent carrier state of infection.

Homologous interference induced by Sindbis virus

Homologous interference during Sindbis virus infection has been investigated. Prior infection of either chicken embryo fibroblast or BHK(21) cell cultures results in reduced yields of progeny virions of the superinfecting genotype. This reduction in yield results from a reduction in the number of cells in the cultures capable of producing the superinfecting genotype. The development of interference parallels the attachment kinetics of Sindbis virus. Interference requires an active viral genome since the activity is sensitive to inactivation by ultraviolet light, and an RNA(-) mutant, ts-24, fails to induce interference under nonpermissive conditions. However, ts-6, an RNA(-) mutant belonging to a different complementation group, and the RNA(+) mutants, ts-2 and ts-20, interfere at both permissive and nonpermissive temperatures.

Deficiency of 60 to 70S RNA in murine leukemia virus particles assembled in cells treated with actinomycin D

Production of particles with the ultrastructural appearance of C-type virions persisted for at least 6 h in actinomycin D-treated cells infected with murine leukemia virus. This phenomenon occurred despite severe inhibition of viral RNA synthesis. Virus particles present in a 6-h harvest sedimented in sucrose gradients with the buoyant density characteristic of RNA tumor viruses (1.16 g/cm(3)) and exhibited high levels of reverse transcriptase activity in response to the exogenous template polyriboadenylic acid.oligo deoxythymidylic acid in the range of untreated controls. However, RNase-sensitive endogenous activity was only (1/5) the level found in controls. This observation correlated with a marked reduction in infectivity. Kinetic studies on the appearance of labeled RNA in banded virions revealed that within the first hour after addition of actinomycin D, particles contained 60 to 70S RNA and two low-molecular-weight RNA species corresponding to 8 and 4S RNA. After approximately 1 h of incubation with actinomycin D, 60 to 70S RNA could not be detected and 4S RNA was the predominant species. These findings suggest that murine leukemia virus particles assembled in the presence of actinomycin D are deficient in 60 to 70S viral RNA.