Host tropism
Tropism (Greek τροπός, turn ', in the sense of a change in an organism after infection ) referred to in virology the ability of a virus, a certain type of cells or certain tissues to infect and multiply there.
Properties
Most viruses can multiply productive only in certain tissues or a few cells. These then form within a host a " virus reservoir " in an infection. The cell-type tropism determines the host tropism (synonym host range ) and therefore the reservoir in a population of hosts, sometimes even in several species (eg influenza viruses). An infectable with a particular cell or cell line virus is also referred to as permissive for the virus. One for a particular pathogen non - permissive cell or cell line is also known to be resistant or restrictive for this pathogen. This is done by an incompatibility to proteins of the host cell or by restriction or resistance factors by the host.
The tropism is determined by several factors:
- The presence of a virus receptor on the surface of the cell in question. In return, the virus proteins must have at its surface ( Peplomere ) with which it can bind to the receptor. For example, HIV infects CD4-positive lymphocytes and thus is lymphotropic. The virus receptors are the CD4 surface antigen and the CXCR4 or CCR5 of the lymphocytes. HIV attaches itself via its gp120 protein ( " 120 - kDa glycoprotein " ) to the receptor.
- The biochemical " features " of the cell interior must facilitate viral replication and release of newly formed virions, otherwise it comes in spite of any successful penetration into the cell not to continue the chain of infection.
Examples of viral tropism
- Herpesviruses are lymphotropic and neurotropic, that is, infect lymphocytes but also nerve cells ( neurons )
- HIV is lymphotropic and neurotropic
- Papillomaviruses are epitheliotrop, that is, infect basal cells of the skin and mucous membranes
- Hepatitis viruses are hepatotropic, that is, they infect liver cells ( hepatocytes)
- Polio viruses are neurotropic. They infest preferred the anterior horn cells of the spinal cord (alpha- motoneurons )
- Influenza viruses are pulmotrop and bronchotrop and enterotrop in H5N1 influenza viruses.