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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. [1] [2]Some bacteria and viruses have a broad tissue tropism and can infect many types of cells and tissues. [1]
It then enters the cell by endocytosis or by making a hole in the membrane of the host cell and inserting its viral genome. [2] Schematic of different pathways of viral entry: (A) membrane fusion, (B) endocytosis, and (C) macropinocytosis Membrane fusion mediated by paramyxovirus fusion proteins. Cell entry by enveloped viruses is more complicated.
Entry, or penetration, is the second step in viral replication. This step is characterized by the virus passing through the plasma membrane of the host cell. The most common way a virus gains entry to the host cell is by receptor-mediated endocytosis, which comes at no energy cost to the virus, only the host cell. Receptor-mediated endocytosis ...
To enter the cells, proteins on the surface of the virus interact with proteins of the cell. Attachment, or adsorption, occurs between the viral particle and the host cell membrane. A hole forms in the cell membrane, then the virus particle or its genetic contents are released into the host cell, where replication of the viral genome may commence.
If a host cell expresses the complementary surface receptor for the virus, then the virus can attach and enter the cell. If a cell does not express these receptors, then the virus cannot normally infect it. Therefore, if the virus cannot bind to the cell, it does not display tropism for that host. Bacteria infect hosts differently than viruses ...
Viruses have an extensive range of structural and biochemical effects on the host cell. [39] These are called cytopathic effects. [40] Most virus infections eventually result in the death of the host cell. The causes of death include cell lysis (bursting), alterations to the cell's surface membrane and apoptosis (cell "suicide"). [41]
It also functions to attach the virion to its host, and enable the virion to penetrate the host cell membrane. Many copies of a single viral protein or a number of different viral proteins make up the capsid, and each of these viral proteins are coded for by one gene from the viral genome. The structure of the capsid allows the virus to use a ...
These cell-cell interactions are mediated mainly by a group of Cell Adhesion Molecules (CAMs) called selectins. [1] T helper cells, central to the immune system, interact with other leukocytes by releasing signals known as cytokines which activate and stimulate the proliferation of B cells and killer T cells. T helper cells also directly ...