Defence Mechanisms

Question 1

What is an infection?

Answer 1

In effect, the interaction between the pathogen and the body’s various defence mechanisms.

Question 2

What are the general and immediate defences of the human body?

Answer 2

The skin forming a barrier to entry of pathogens and phagocytosis.

Question 3

What are the specific , less rapid, but longer lasting defences of the body and what do they involve?

Answer 3

These responses involve a type of white blood cell known as a lymphocyte and are either:

• Cell-mediated responses involving T Lymphocytes
• Humoral responses involving B Lymphocytes

Question 4

How do Lymphocytes distinguish the body’s own cells and molecules (self) from foreign (non-self)?

Answer 4

Each molecule has specific molecules on its surface that identify it. The proteins on the surface are most important due to their highly specific tertiary structure, which is what enables lymphocytes to distinguish between cells.

Question 5

What do the surface protein molecules allow the immune system to identify?

Answer 5

• Pathogens, e.g HIV
• Non-self material, such as cells from other organisms of the same species
• Toxins, including those produced by pathogens
• Abnormal body cells, such as cancer cells.

Question 6

What are the implications of the immune system to humans who have had tissue or organ transplants?

Answer 6

The immune system recognises these as non-self, even though they have come from individuals of the same species. It therefore attempts to destroy this transplant.

Question 7

What can be done to minimise the effect of the immune system rejecting transplants?

Answer 7

Match the tissues of the transplant as closely to the original tissue as possible.
Immunosuppressant drugs are often administered to reduce level of immune response that still occurs.

Question 8

Why is it beneficial to have so many different types of lymphocytes within the body?

Answer 8

There is a higher probability that when a pathogen invades the body, one of the lymphocytes will have a complimentary protein on its surface to one of the pathogens proteins.

Question 9

How do lymphocytes recognise cells belonging to the body?

Answer 9

• Lymphocytes collide with other cells in the fetus.
• Lymphocytes almost exclusively collide with self material.
• Some lymphocytes have receptors exactly fitting those of the body’s own cells.
• These lymphocytes die or are supressed.
• The remaining lymphocytes are those that might fit foreign (non-self) material.
• In adults, lymphocytes produced in bone marrow initially only encounter self-antigens.
• Any lymphocytes showing immune response to self-antigens undergo apoptosis (cell death) before differentiating into mature lymphocytes.
• No clones of these anti-self lymphocytes will appear in the blood, leaving only those that might respond to non-self antigens