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Immunity
Any disease is an interaction between the pathogen and the body's various defence mechanisms.

Sometimes the pathogen overwhelms the defences and the individual dies. Sometimes the body's
defence mechanisms overwhelm the pathogen and the individual recovers from the disease.

Having overwhelmed the pathogen, however, the body's defences seem to…

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The human body has a range of defences to protect itself from pathogens.
They are of two main types:


Non-Specific Mechanisms that do not distinguish between one type of pathogen and another,
but respond to all of them in the same way.
These mechanisms act immediately and take two forms:…

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Phagocytosis
If a pathogen is to infect the body it must first gain entry.
Clearly then, the body's first line of defence is to form a physical or chemical barrier to entry.
Should this fail, the next line of defence is the white blood cells.


There are two types of…

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1. Phagocyte is attracted to the pathogen by chemoattractants

2. It moves towards the pathogen along a concentration gradient



3. The phagocyte binds to the pathogen

4. Lysosomes within the phagocyte migrate towards the phagosome
formed by engulfing the bacterium



5. The lysosomes release their lytic enzymes into the phagosome…

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Antigens
An antigen is any part of an organism or substance that is recognised as non-self or foreign by
the immune system and stimulates an immune response.

Antigens are usually proteins that are part of the cell-surface membranes or cell walls of invading
cells, such as microorganisms, or diseased cells,…

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Cell Meditated Immunity
T lymphocytes respond to an organism's own cells that have been invaded by non-self
material, e.g. a virus or a cancer cell. They also respond to transplanted material, which is
generally different.

T lymphocytes can distinguish these invader cells from normal cells because:

- Phagocytes that have…

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B Cells and Humoral Immunity
Humoral immunity is so called because it involves antibodies and antibodies are soluble in the
blood and tissue fluid o the body.

Another word for body fluids is humour.

There are many different types of B cells and each type produces a different antibody that…

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1. The surface antigens of the invading pathogen are taken up by B cells
2. The B cells process the antigens and present them on their surfaces
3. T helper cells attach to the processed antigens on the B cells thereby activating them
4. The B cells are now activated…

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Antibodies
Antibodies are proteins synthesised by B cells. When the body is invaded by non self material, a B
cells produces antibodies. These antibodies react with antigens on the surface of non-self
material by binding to them precisely.

Antibodies are therefore very specific, each antigen having its own individual antibody.…

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Monoclonal Antibodies
Bacterium or other microorganisms that enter the body are likely to have hundreds of different
antigens on its surface. Each antigen will induce a different B cell to multiply and clone itself.
Each of these clones will produce a different antibody, known as polyclonal antibodies.

In the 1970s…

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