Tissue tropism

In virology, Tissue tropism is the cells and tissues of a host which support growth of a particular virus or bacteria. Some 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

Steps of Infections Cycle (how Tissue Tropism works)

• 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 dumps 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

References

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