Tissue tropism

Tissue tropism is the cells and tissues of a host which support growth of a particular virus or bacteria. Some bacteria and viruses have a broad tissue tropism and can infect many types of cells and tissues. Other viruses may infect primarily a single tissue. For example rabies virus affects primarily neuronal tissue.

Influencing factors

Factors influencing viral tissue tropism include:

• The presence of cellular receptors permitting viral entry.
• Availability of transcription factors involved in viral replication.
• The molecular nature of the viral tropogen.

The cellular receptors are the proteins found on a cell or viral surface. These receptors are like keys allowing the viral cell to fuse with a cell, or attach itself to a cell. The way that these proteins are acquired is through similar process to that of an infection cycle.

How 'tropic' tissue is acquired

HIV

Tissue tropism develops in the following stages:

• Virus with GPX enters body (where GP - glycoprotein and X is the numeric value given to the GP)
• Viral Cell 'targets' cell with a GPX receptors
• Viral Cell fuses with the cell and inserts its contents into it
• Reverse Transcription occurs
• Viral DNA is incorporated with host DNA via Viral Enzyme
• Production of RNA and Viral Protein
• Viral particle is assembled
• Viral particle buds out of the cell taking a chunk of the cell membrane with it acquiring a new tissue with all the receptors it needs to continue Tissue Tropism

Example: HIV has a gp120 which is precisely what the CD4 marker is on the surface of the macrophages and T cells, thus HIV can enter T cells and macrophages

See also

• Host tropism

References

• Raven, Peter H.(2008). "Biology 8th Edition". New York, McGraw-Hill.