Consequences of viral replication in cells

2021-08-25 06:47 PM

After the virus enters and multiplies in the cell, most of the cells are destroyed. Because the normal activities of the cell are inhibited, the substances necessary for the cell

When viruses enter and multiply in cells to produce new generations of viruses, the consequences can vary depending on the cell's and virus's biology.

Cells are destroyed

After the virus enters and multiplies in the cell, most of the cells are destroyed. Because the normal activities of the cell are inhibited, the substances necessary for the cell are not synthesized, but only new viral particles are synthesized, so the cell dies. This is the most common case.

In in vitro cell culture, infected cells can be seen to deform, stick together, and lysis.

Cells with chromosomal damage

Viruses can cause the host cell's chromosomes to be broken, fragmented, or reversed in order of arrangement, causing consequences such as:

Birth defects, stillbirth

In pregnant women, especially during the first trimester of pregnancy, who are infected with the virus, chromosomal aberrations can lead to some congenital defects in fetal formation and cause fetal death. viral infection status of the fetus.

Infinitely proliferating tumor cells

Cells infected with certain viruses (mainly tumor-causing viruses) lose contact inhibition as the cell reproduces, resulting in superimposed cell clumps.

Generating specific subtypes for different viruses

In infected cells, inclusions may appear in the nucleus (Adenovirus), or in the cytoplasm (Negri corpuscles of rabies virus), or in both places (measles virus). The nature of the globules may be due to the accumulation of virions or virion components or maybe cellular response particles to viral infection.

These globules can be seen under light microscopy and can indirectly diagnose viral infection in cells.

Defective interfering particles (DIP)

Incomplete virus particles are viruses with only capsid, no or incomplete nucleic acids. Therefore, the DIP particles are not capable of multiplying independently upon entering the cells, which means that the DIP particles are not capable of infecting the cells. DIP particles can specifically interfere with viruses of the same strain.

Consequences of viral genomic integration into host cell DNA

The integration of viral nucleic acids into the host cell's DNA can lead to different consequences:

Transformation and cause tumors or cancer.

Changes in cell surface antigens.

Changes some properties of cells.

Cells become cytolytic cells.

Stimulates cells to synthesize Interferon

Interferons are glycoproteins with a molecular weight of about 17,000 - 25,000 Daltons that are synthesized by cells after stimulation by inducers of interferon production such as viruses or other inducers.

There are 3 types of Interferons: Interferon-alpha, interferon-beta, and interferon-gamma. These types are distinguished by specific antibodies. Interferon-alpha is usually produced by white blood cells. Interferon-beta is produced by fibroblasts. Interferon-gamma is a lymphokine that is produced by T lymphocytes.

Some properties of interferon

Weak antigenicity.

Occurs early (several hours) after inducer stimulation.

The antiviral properties of interferons are species-specific but not virus-specific: Interferons produced by cells of any species only inhibit viral replication in cells of that species (e.g. only interferons). produced from cells of human origin have a protective effect on humans). In contrast, interferon has a broad spectrum of activity that inhibits the replication of many different viruses, not just viruses that induce interferon production.

Interferons do not act directly on viruses like antibodies do, but the reaction that inhibits viral replication occurs inside cells.

Mechanism of cell interferon production

In human cells, there are 15 different genes coding for interferon-alpha, only 1 gene encoding for interferon-beta, and 1 gene encoding for interferon-gamma. Normally these genes are in a repressed and inactive state. Inducers of interferon production have a depressive effect on these genes causing them to return to their active form and thus the cell to synthesize interferons. The most important inducers for the alpha and beta genes are viruses, but for the gamma, the gene is T-lymphocyte activators. Interferon-alpha and interferon-beta have stronger antiviral effects than interferon. -gamma. Interferon-gamma has a stronger immunomodulatory and inhibitory effect on cancer cells than interferon-alpha and interferon-beta.

Mechanism of antiviral action of interferon

Interferon binds to specific interferon receptors on the cell membrane surface, causing de-repression of several genes encoding viral suppressor proteins. Under the stimulation effect of interferon, at least 2 genes of the cell are activated to synthesize 2 enzymes: elF2 kinase and 2', 5'-oligoadenylate synthetase. elF2 is a necessary promoter for binding of messenger RNA to ribosomes; The elF2 kinase phosphorylates the elF2 factor and inactivates elF2 thereby preventing viral protein synthesis. Oligoadenylate activates cellular ribonuclease to degrade viral messenger RNA, thereby inhibiting viral protein synthesis.

Thus, interferon only exhibits antiviral effects in living cells and stimulates cells to use enzymatic mechanisms to degrade viral messenger RNA and inhibit viral protein synthesis.