Tissue tropism
{{Short description|Range of tissues that support pathogen growth}}
{{More citations needed|date=May 2022}}
Tissue tropism is the range of cells and tissues of a host that support growth of a particular pathogen, such as a virus, bacterium or parasite.{{cite journal |last1=McCall |first1=LI |last2=Siqueira-Neto |first2=JL |last3=McKerrow |first3=JH |title=Location, Location, Location: Five Facts about Tissue Tropism and Pathogenesis. |journal=PLOS Pathogens |date=May 2016 |volume=12 |issue=5 |pages=e1005519 |doi=10.1371/journal.ppat.1005519 |pmid=27227827|pmc=4881934 |doi-access=free }}{{cite journal |last1=Silva Pereira |first1=Sara |last2=Trindade |first2=Sandra |last3=De Niz |first3=Mariana |last4=Figueiredo |first4=Luisa M. |title=Tissue tropism in parasitic diseases |journal=Open Biology |date=31 May 2019 |volume=9 |issue=5 |pages=190036 |doi=10.1098/rsob.190036 |pmid=31088251 |pmc=6544988 |issn=2046-2441}}
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. Similarly, JC virus (JCV) primarily affects and resides in kidneys.{{cite journal | vauthors = Cayres-Vallinoto IM, Vallinoto AC, Azevedo VN, Machado LF, Ishak Mde O, Ishak R |title= Human JCV infections as a bio-anthropological marker of the formation of Brazilian Amazonian populations |journal= PLoS One |date=2012 | volume = 7| issue = 10|pages=e46523-e46523|doi=10.1371/journal.pone.0046523
|PMID=23071582 |PMC= 3470572|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0046523|doi-access=free}}
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 or virus surface, such as the glycoprotein, which interacts with the corresponding cell receptor.
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 or attach itself to a cell. The way that these proteins are acquired is through a similar process to that of an infection cycle.
How 'tropic' tissue is acquired
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 host cell and inserts its contents into the host cell
- 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 and 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