3.6 Specific Cellular Defences Against Pathogens

Question 1

Name the type of white blood cells involved in the specific immune response

Answer 1

The specific immune response is carried out by lymphocytes

Question 2

State the definition of an antigen

Answer 2

An antigen is a molecule, normally a protein found on the outer surface of cells that triggers a specific immune response.

Question 3

Describe the role of lymphocytes in recognising non-self-antigens.

Answer 3

Within the circulation system there are a wide variety of lymphocytes. Each of these different lymphocytes have a single type of membrane receptor which is specific for one antigen. These lymphocytes are responsible for the body’s ability to distinguish and react to any non-self-antigen that they detect.

Question 4

Explain the phrase ‘clonal population’ of lymphocytes.

Answer 4

When a lymphocyte membrane receptor binds to a specific antigen, this stimulates repeated lymphocyte division. As the lymphocyte divides by mitosis all of the cells produced are identical and have the same specific membrane receptor. The resulting cells are described as a clonal population.

Question 5

Identify the two main types of lymphocyte

Answer 5

The two main types of lymphocytes are B-lymphocytes and T-lymphocytes

Question 6

Describe the role of B-lymphocytes.

Answer 6

B-lymphocytes produce specific antibodies against antigens and this leads to the destruction of the pathogen

Question 7

Describe antibodies

Answer 7

The antibodies are Y-shaped proteins that have receptor binding sites specific to a particular antigen on a pathogen. The antibodies become bound to the antigens, inactivating and immobilising the pathogen. The resulting antigen-antibody complex can then be destroyed by phagocytosis.

Question 8

Explain the role of B-lymphocytes in an allergic reaction

Answer 8

An allergic reaction is a hypersensitive response where B-lymphocytes have been triggered to respond to antigens on substances that are harmless to the body e.g. pollen causing hay fever.

Question 9

Describe the role of T-lymphocytes.

Answer 9

T-lymphocytes are also known as T-killer cells. T-lymphocytes destroy infected body cells by recognising antigens of the pathogen on the cell membrane of the infected cell, attaching to the infected cell and releasing proteins which diffuse into the infected cell and induce apoptosis

Question 10

What is apoptosis

Answer 10

Apoptosis is programmed cell death which is triggered when the proteins that diffuse into the infected cell switch on the production of self-destructive enzymes which cause the infected cell to digest itself. The remains of the cell are then removed by phagocytosis.

Question 11

Explain the role of T-lymphocytes in an auto-immune disease

Answer 11

T-lymphocytes can normally distinguish between self-antigens on the body’s own cells and non-self-antigens on infected body cells.

Question 12

What happens when there is a failure to regulate the immune system

Answer 12

However, failure of the regulation of the immune system can lead to T lymphocytes responding to self-antigens. This is what causes autoimmune diseases where the T-lymphocytes start to attack the body’s own cells.

Question 13

Give two examples of auto-immune diseases.

Answer 13

Type one diabetes
Rheumatoid arthritis

Question 14

Type one diabetes

Answer 14

Type 1 diabetes – T-lymphocytes attack the insulin-producing beta cells in the pancreas causing the blood sugar regulation system to breakdown.

Question 15

Rheumatoid arthritis

Answer 15

Rheumatoid arthritis – T-lymphocytes attack the tissues in the joints, resulting in inflammation and pin in the joints.

Question 16

State what memory cells are.

Answer 16

Memory cells are a selection of cloned B and T lymphocytes that are retained and survive long-term within the bloodstream.

Question 17

Explain the role of memory cells in a secondary exposure to a pathogen.

Answer 17

When a secondary exposure to the same antigen occurs, these memory cells rapidly give rise to a new clone of specific lymphocytes. These destroy the invading pathogens before the individual shows any symptoms of infection. Memory cells are critical to the process of vaccination.

Question 18

Compare antibody production during the primary and secondary response to a pathogen. (primary)

Answer 18

Primary response happens following the first exposure to a pathogen. During the primary response, the production of antibody is slower and the concentration of antibody is less

Question 19

Why does the primary response to antibody production occur

Answer 19

This is because it takes time for the lymphocytes to recognise and respond to a new pathogen / antigen by producing the specific antibody required and during this time the pathogen is causing the infected individual to suffer from disease symptoms.

Question 20

Compare antibody production during the primary and secondary response to a pathogen. (secondary)

Answer 20

Secondary response happens following exposure to a pathogen which has already been encountered. During the secondary response, antibody production is greater and more rapid than during the primary response and this is why the individual will not suffer from the same symptoms as experienced during the first exposure.

Question 21

Explain the impact of HIV on the immune system.

Answer 21

The human immunodeficiency virus (HIV) targets, attacks and destroys the T-lymphocytes of the immune system. As the T-lymphocyte numbers decline this leads to the development of the condition AIDS (acquired immune deficiency syndrome), where individuals with a weakened immune system are more vulnerable to opportunistic infections which can lead to their death.