The Immune System

Question 1

What are antigens?

Answer 1

Antigens are molecules (usually proteins) that can generate an immune response when detected by the body

Question 2

Where are antibodies usually found?

Answer 2

They are usually found on the surface of cells and are used by the immune system to identify: pathogens, abnormal body cells, toxins and cells from other individuals of the same species

Question 3

What are the four main stages of the immune response?

Answer 3

1. Phagocytes engulf pathogens
2. Phagocytes activate T-cells
3. T-cells activate B-cells, which divide into plasma cells
4. Plasma cells make more antibodies to a specific antigen

Question 4

What is a phagocyte?

Answer 4

A phagocyte is a type of white blood cell that carries out phagocytosis. They’re found in blood and in tissues and are the first cells to trigger an immune response

Question 5

Explain the process of phagocytosis

Answer 5

1. A phagocyte recognises the foreign antigens on a pathogen
2. The cytoplasm of the phagocyte moves round the pathogen, engulfing it
3. The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
4. A lysosome fuses with the phagocytic capsule. The lysozyme break down the pathogen
5. The phagocyte then presents the pathogens antigens - it sticks the antigens on its surface to activate other immune system cells

Question 6

What is a T-cell?

Answer 6

A T-cell is a type of white blood cell

Question 7

How do phagocytes activate T-cells?

Answer 7

T-cells have receptor proteins on their surface that bind to complimentary antigens presented to it by phagocytes. This activate the T-cell

Question 8

Do different types of T-cells respond the same way?

Answer 8

Different types of T-cell respond in different ways. Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells which kill abnormal and foreign cells. Helper T-cells also activate B-cells which secrete antibodies

Question 9

What are B-cells?

Answer 9

B-cells (B-lymphocytes) are a type of white blood cell. They’re covered with antibodies - proteins that bind antigens to form and antigen-antibody complex. Each B-cell has a different shaped antibody on it’s membrane, so different ones bind to different shaped antigens

Question 10

What happens when B-cells are activated?

Answer 10

When the antibody on the surface of a B-cell meets a complimentary shaped antigen, it binds to it. This, together with substances released from T-helper cells, activates the B-cell. This process is called clonal selection. The activated B-cell divides into plasma cells

Question 11

What are plasma cells?

Answer 11

Plasma cells are identical to B-cells (they’re clones)

Question 12

What do plasma cells secrete?

Answer 12

Plasmas cells secrete lots of antibodies specific to the antigen. These are called monoclonal antibodies. They bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes

Question 13

What happens when plasma cells make antibodies?

Answer 13

Antibodies have two binding sites, so they can bind to two pathogens at the same time. This means that pathogens become clumped together - this is called agglutination. Phagocytes then bind to the antibodies and phagocytose many pathogens at once. This process leads to the destruction of pathogens carrying this antigen in the body

Question 14

What are antibodies?

Answer 14

Antibodies are proteins - they’re made up of chains of amino acids

Question 15

What does the specificity of an antibody depend on?

Answer 15

The specificity of an antibody depends on its variable regions, which form the antigen binding sites. each antibody has a variable region with a unique tertiary structure that’s complimentary to one specific antigen

Question 16

Antibodies all have the same what?

Answer 16

All antibodies have the same constant regions

Question 17

The immune response can be split into what?

Answer 17

1. The cellular response

2. The humoral response

Question 18

What parts of the immune response make up the cellular response?

Answer 18

The T-cells and other immune system cells that they interact with, e.g. phagocytes, form the cellular response

Question 19

What parts of the immune response make up the humoral response?

Answer 19

B-cells, clonal selection and the production of monoclonal antibodies form the humoral response

Question 20

What is the primary immune response

Answer 20

When an antigen enters the body for the first time it activates the immune response. This is the primary response

Question 21

Is the primary response fast or slow?

Answer 21

The primary response is slow - there aren’t many B-cells that can make the right antibody to bind to the antigen. Eventually, the body will produce enough of the right antibody to overcome the infection - meanwhile the infected person will show symptoms of the disease

Question 22

In the primary response when is a person immune?

Answer 22

After being exposed to the antigen, both T-cells and B-cells produce memory cells which remain in the body for a long time. Memory T-cells remember the specific antigen and will recognise it. Memory B-cells record the specific antibodies needed to bind to the antigen. The person is now immune - their immune system has the ability to respond quickly to a second infection

Question 23

What happens in the secondary immune response?

Answer 23

If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells to produce the right antibody to the antigen. Memory T-cells are activated and divide into the right type of T-cell to kill the cell carrying the antigen. The secondary repose often gets rid of the pathogen before you begin to show any symptoms