CELL-MEDIATED IMMUNITY
The immunity given by the T-cell lymphocytes is also known as 'cell-mediated' immunity, because the cells themselves do the actual killing of invading micro-organisms.
There are 4 subtypes of T-cell lymphocytes, and now ask yourself where the T-cells differentiate into these 4 subtypes?
These 4 types of T-cell lymphocyte are known as:
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T-cytotoxic (TC) - the killer cells |
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T-helper (TH) - mobilises the immune system following infection |
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T-Suppressor (TS) - suppresses the immune system following activation |
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T-memory (TM) - the brains of the cell-mediated immune system (remembers how to defeat previously encountered micro-organisms |
The pattern of development is illustrated below.
VIRAL REPRODUCTION
Now, before we continue learning about cell-mediated immunity, let us just take a detour to look at viral reproduction.
It is very important that you know about this because the T-cells play a crucial role in protecting us from viral infections, and this is linked to where the viruses reproduce once they have infected us.
Viruses, unlike bacteria, can only reproduce inside a cell.
They do this by entering it and then breaking up to release viral DNA (or RNA in the case of retroviruses) into the cell cytoplasm, so that the viral DNA can join on to the cell DNA.
Once the viral DNA has joined the cell DNA, it hijacks it and forces it to make hundreds (or even thousands) of copies of viral DNA and viral protein (for its outer coat).
Once the virus has exhausted the reserves of the cell, and has, in effect killed it, the viral protein and DNA join up to make hundred or thousands of new viruses, which in turn burst out of the dead or dying cell and proceed to infect new cells.
And so the cycle of infection, hijacking of DNA, new viral production, death of the cell, and infection of other cells continues.
For a simple diagram of this viral reproduction cycle, click on the icon below.
Because viruses spend almost all of their time hidden inside cells, they are difficult to eliminate, so the T-cells have devised a way of discovering them by finding which cells are actually infected, and then only destroying those cells (and the viruses inside) whilst leaving alone the healthy cells.
This they do by recognising certain receptor molecules on the surface membrane of the infected cell.
Because these particular receptor molecules are actually a combination of host cell receptors and virus protein particles, the T-cells recognise the cell as being 'foreign' or 'non-self', and therefore ready to be destroyed.
T-cell Lymphocyte Subtypes
Now to look at the different subtypes of T-cells in more detail.
Just click on the hyperlink for each subtype to access the information.
It is the balance between the T-helper and T-suppressor cells that forms the basis of our normal specific/acquired immune response.
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Of Interest The reason that the Human Immunodeficiency Virus (HIV which causes AIDS) is so deadly, even though it is not a very virulent virus, is that the main cells in the human body that it attacks are the T-helper lymphocytes. By attacking and destroying these T-helper lymphocytes, the ability of the body to mount a decent specific immune response to other infectious micro-organisms is very much reduced. People do not die of HIV, rather they die as a result of the infections (and cancers) which are allowed to occur and to spread unchecked. |
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DO/REFLECTION
Make a list of the viral infections that you know of. Recall when you or a member of your family had one of these infections and describe how you or they felt. What were your/their symptoms? Describe the care that you/they received? How long did the infection last for? |