Tropism (virology)

In virology, tropism ( Greek  τροπός , phrase) describes the ability of a virus to infect a certain type of cell or certain tissue and to multiply there.

properties

Most viruses can only reproduce productively in a very specific few cells or tissues. These then form a “virus reservoir” within a host in the event of an infection. The cell type tropism determines the host tropism (synonym host spectrum ) and thus the reservoir in a population of hosts, occasionally even in several species (e.g. influenza viruses ). A cell or cell line that can be infected with a particular virus is also referred to as being permissive for this virus. A cell or cell line that is non-permissive for a particular pathogen is also referred to as being resistant or restrictive to that pathogen. This occurs due to incompatibility with proteins of the host cell or due to restriction or resistance factors on the part of 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 must have proteins on its surface ( peplomeres ) with which it can bind to the receptor . For example, HIV infects CD4- positive lymphocytes and is therefore lymphotropic . The virus receptors are the CD4 surface antigen and the CXCR4 or CCR5 of the lymphocytes. HIV attaches itself to the receptor via its gp120 protein (“120 kDa - glycoprotein ”).
• the biochemical "equipment" of the cell interior must enable virus replication and the release of newly formed virions , otherwise the chain of infection will not continue despite possible successful penetration into the cell .

Examples of viral tropism

• Alphaherpesviruses are neurotrophic ; i.e., they infect nerve cells (neurons)
• Beta herpes viruses and viruses of the genus Lymphocryptovirus are lymphotropic , they infect lymphocytes
• HIV is lymphotropic and neurotrophic
• Papillomaviruses are epitheliotropic ; i.e., infect basal cells of the skin and mucous membranes
• Hepadnaviruses are hepatotropic , i. i.e. they infect liver cells (hepatocytes)
• Polioviruses are neurotrophic . They preferentially affect the anterior horn cells of the spinal cord (alpha motor neurons)
• Influenza viruses are pulmotropic and bronchotropic and, in the case of H5N1 influenza viruses, also enterotropic .

literature

• Susanne Modrow, Dietrich Falke , Uwe Truyen: Molecular Virology. 2nd edition, Spektrum, Heidelberg 2003, ISBN 3-8274-1086-X .
• JH Strauss, EG Strauss: Viruses and human disease. Academic Press, San Diego 2002, ISBN 0-12-673050-4 .
• David M. Knipe, Peter M. Howley , DE Griffin, (Eds.): Fields Virology. 5th edition, Lippincott Williams & Wilkins, Philadelphia 2007, ISBN 978-0-7817-6060-7 .