Lytic infection

Consequences of virus infection in animal cells Viruses can have varied effects on cells. Lytic infection results in the destruction of the host cell. However, there are several other possible effects following viral infection of animal cells. In the case of enveloped viruses, release of the viral particles, which occurs by a kind of budding process, may be slow and the host cell may not be lysed. The cell may remain alive and continue to produce vims over a long period of time. Such infections are referred to as persistent infections. 

The bioreactor operation mode is normally defined at the outset of process configuration. Insect cells have been cultured in almost all known cultivation modes batch [10], repeated-batch [70], perfusion [71-74], fed-batch [75, 76], semi-continuous [77,78] and continuous [79]. In spite of this multitude of different strategies, the batch or, eventually, fed-batch mode is normally preferred due to the lytic infection cycle of the baculovirus. 

Eukaryotic Animal (recombinant) virus vectors Transient or lytic infection Infection in susceptible cells All essential viral genes strong promoter/enhancers polyadenylation signal intron sequences... 

Lytic infection. A virus infection that leads to the lysis of the host cell, yielding progeny virus particles. 

F. D. Goodrum, and D. A. Qmelles, p53 status does not determine outcome of E1B 55-kilodalton mutant adenovirus lytic infection, J. Virol. 72 9479 (1998). 

Bacteriophages Bacteriophages (or phages) adsorb to the bacterial host cell and then inject the DNA genome into the cell, leaving the protein capsid outside. Two alternative modes of infection may follow lytic infection or lysogeny (Fig. 1). 

Bacteriophage lambda (X) is a good example for considering phage infection. In lytic infection, the injected linear double-stranded X DNA first circularizes. It is then transcribed to produce viral proteins needed for viral DNA replication and packaging as well as many molecules of viral capsid proteins. The viral DNA is replicated and the DNA copies are packaged into new phage... 

Infection of a cell by a virus has two outcomes, depending on the nature of the virus and the particular cell type. Some viruses go into a lytic cycle, which results in the replication of the virus and the lysis of the cell. This is the case with viruses such as poliovirus and vaccinia virus, both of which are used in vaccination. The use of live viruses expressing protein antigens in vaccination has been discussed in Chapter 3. In vaccination, the goal is the transient replication of viruses for a period sufficient to raise antibody response. Thus, the use of lytic viruses leading to transient, self-limiting lytic infection is acceptable or even desirable. 

In neurons, HSV-1 infection can result in a latent infection. Upon entry, the virion is transported to the nucleus by retrograde transport along the axon. It is currently unknown which viral genes arc involved in the establishment of a latent infection, but de novo viral protein synthesis is not required. However, latency is related to the expression of latency associated transcripts (LAT), which are expressed from a promotor that is highly active in neurons. LATs prevent the lytic replication cycle by down-regulation of genes associated with lytic infection. Reactivation of the latent virus can be induced by different stimuli like stress and UV irradiation. [For more details see (117).]... 

BZLPl (ZEBRA) is the gene encoding an immediate early transcription activator responsible for the lytic infection phase. 

Acute Lytic Infections of the Brain with Focal or Regional Necrosis, Edema and Brain Herniation... 

ORF74 expression is expressed during the early phase of lytic infection in vitro [104],... 

Buckler-White AJ, Humphrey GW, Pigiet V (1980) Association of polyoma T antigen and DNA with the nuclear matrix from lytically infected 3T6 cells. Cell 22 37-46... 

McGowan, J. J., Allen, G. P., Barnett, J. M., and Gentry, G. A., 1980, Biochemical characterization of equine herpes virus type 3-induced deoxythymiidine kinase purified from lytically infected horse embryo dermal fibroblasts, J. Virol. 34 474. 

Infection of animal cells with herpesviruses is commonly, though not invariably, followed by inhibition of the synthesis of cellular DNA, RNA, and protein, phenomena collectively and colloquially known as host shut-off. Host shut-off precedes most of the more obvious cytopathic effects which are characteristic of the late stages of a lytic infection and often precedes the replication of viral DNA. In the 20 years or so that have passed since the phenomena were first observed, little positive information has accumulated concerning the means by which the virus suppresses the synthesis of cellular macromolecules while directing the synthesis of its own. 

Modrow, S., and Wolf, H., 1983, Herpesvirus Saimiri-induced proteins in lytically infected cells. I. Time-ordered synthesis, J. Gen. Virol. 64 37. 

If this altered ganglioside metabolism is related to some viral function, is it a function involved in transformation, productive infection, or both Mouse cells are permissive for polyoma virus and are rarely transformed by it (cf. Eckhart, 1969). Upon viral infection, the cells undergo a series of discrete events which result in cell lysis and release of new virions (cf. Weil and Kara, 1970). These include the appearance of viral-specific T-antigen, induction of cellular and viral DNA synthesis which is maximum at 25-30 hr postinfection, synthesis of viral coat proteins and new virions (present at 50 hr.), and, finally, cell lysis and virus release (5-7 days after infection). Swiss 3T3 and TAL/N cells were treated with sufficient polyoma virus to ensure infection of all cells. Hematoside UDP-GalN AcA-acetylgalactosaminyl-transferase was then determined at two key times after infection (Table V). The activity of this enzyme was similar to that seen in mock-infected cells. The results indicate that the reduced aminosugar transferase activity in virally transformed cells is specifically related to some transforming function of the viruses and is not a consequence of lytic infection of the cell. 

TABLE V. A-Acetylgalactosaminyltransferase Activity in Mouse Cells Lytically Infected and Transformed by Polyoma Virus"... 

There are two very distinct components in the AAV lifecycle, a latent infection that is established in cells when there is no helper vims present and alytic infection that is initiated by adenoviral coinfection in addition, herpesvims can also function as a helper vims. It has been estabUshed that it is the expression of the adenoviral early region genes (El and E4) that is essential to triggering the lytic infection (22). 

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