The response of a host cell to infection by a virus ranges from: 1) little or no detectable effect; to 2) alteration of the antigenic specificity of the cell surface due to presence of virus glycoproteins; to 3) latent infections that, in some cases, cause cell transformation; or, ultimately, to 4) cell death due to expression of viral genes that shut off essential host cell functions (Figure 1).

Fig1. Effects of viral infection on a host cell.

1. Viral infections in which no progeny virus are produced: In this case, the infection is referred to as abortive. An abortive response to infection is commonly caused by: 1) a normal virus infecting cells that are lacking in enzymes, promoters, transcription factors, or other compounds required for complete viral replication, in which case the cells are referred to as nonpermissive; 2) infection by a defective virus of a cell that normally supports viral replication (that is, by a virus that itself has genetically lost the ability to replicate in that cell type); or 3) death of the cell as a consequence of the infection, before viral replication has been completed.

2. Viral infections in which the host cell may be altered antigenically but is not killed, although progeny virus are released: In this case, the host cell is permissive, and the infection is productive (progeny virus are released from the cell), but viral replication and release neither kills the host cell nor interferes with its ability to multiply and carry out differentiated functions. The infection is, therefore, said to be persistent. The antigenic specificity of the cell surface may be altered as a result of the insertion of viral glycoproteins.

3. Viral infections that result in a latent viral state in the host cell: Some viral infections result in the persistence of the viral genome inside a host cell with no production of progeny virus. Such latent viruses can be reactivated months or years in the future, leading to a productive infection. Some latently infected cells contain viral genomes that are stably integrated into a host cell chromosome. This can cause alterations in the host cell surface; cellular metabolic functions; and, significantly, cell growth and replication patterns. Such viruses may induce tumors in animals, in which case they are said to be tumor viruses, and the cells they infect are transformed.

4. Viral infections resulting in host cell death and production of progeny virus: Eliminating host cell competition for synthetic enzymes and precursor molecules increases the efficiency with which virus constituents can be synthesized. Therefore, the typical result of a productive (progeny-yielding) infection by a cytocidal virus is the shutoff of much of the cell’s macromolecular syntheses by one or more of the virus gene products, causing the death of the cell. Such an infection is said to be lytic. The mechanism of the shutoff varies among the viral families.

In summary, all viruses:

• are small;

• contain only one species of nucleic acid, either DNA or RNA;

• attach to their host cell with a specific receptor-binding protein; and

• express the information contained in the viral genome (DNA or RNA) using the cellular machinery of the host cell

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مواضيع ذات صلة

Papovaviridae: Subfamily Polyomavirinae

Assembly and release of progeny viruses

Clinical Syndromes of Adenovirus

JCPyV and progressive multifocal leukoencephalopathy (PML)

Polyomavirus-associated nephropathy (PVAN)

Mechanisms of RNA virus genome replication

Epidemiology Human Papillomavirus

Pathogenesis of Human Papillomavirus

Clinical Syndromes of EBV

EBV Life Cycle

Epstein–Barr virus

Treatment of Cytomegalovirus