Tissue tropism

Tissue tropism is a term most often used in virology to define the cells and tissues of a host which support growth of a particular virus. Bacteria and other parasites may also be referred to as having a tissue tropism.

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, and Hepatitis primarily affects liver 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.



To help you understand

 * Note # 1: The cycle discussed below is similar to the HIV cycle
 * Note # 2: All cells in the human body have an array of Glycoprotein that are used to identify Cell A from Cell B, and that serve to identify Cell A to Cell A in case of White blood cells, they would state that a certain cell is native to the system.
 * Note # 3: It is these Protein "keys" that the viruses use to 'target' and Identify their proper hosts.

=How 'Tropic' Tissue is acquired= 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