Tissue tropism is the range of cells and tissues of a

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

that support growth of a particular

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

, such as a

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

bacterium Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

. 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 Rabies is a viral disease that causes encephalitis in humans and other mammals. It was historically referred to as hydrophobia ("fear of water") because its victims panic when offered liquids to drink. Early symptoms can include fever and abn ...

virus affects primarily

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

al tissue. Similarly, JC virus (JCV) primarily affects and resides in kidneys.

Influencing factors

Factors influencing viral tissue tropism include: * The presence of cellular

receptors Receptor may refer to: *Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds ...

permitting viral entry. * Availability of

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription (genetics), transcription of genetics, genetic information from DNA to messenger RNA, by binding t ...

s 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

are the proteins found on a cell or viral surface. These

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 Glycoproteins are proteins which contain oligosaccharide (sugar) chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known a ...

and X is the numeric value given to the GP) * Viral cell "targets" cell with a GPX

* Viral cell fuses with the host cell and inserts its contents into the host cell * Reverse transcription occurs * Viral

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

is incorporated with host

via viral

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

* Production of

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

and viral

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

* 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

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 Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...

and

T cells T cells (also known as T lymphocytes) are an important part of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their ce ...

. Thus HIV can enter

and

References

{{Wiktionary, tropism Virology

Influencing factors

How 'tropic' tissue is acquired

See also

References