Immune System Part 1

Question 1

Our first line of defence is the natural barriers we have, in order to prevent entry by pathogens. Give 3 examples

Answer 1

-Skin-a physical barrier of dead cells
-Lysozyme enzyme in tears, saliva and sweat-damages bacterial cell walls
-Stomach acid-high acidity can kill bacteria
-Mucus and cilia-mucus from epithelial cells traps bacteria in respiratory and digestive tracts and cilia sweep the mucus away

Question 2

What do the terms “self” and “non-self” mean?

Answer 2

“Self” refers to the surface chemicals or antigens on our own body cells (glycoproteins, glycolipids etc) and “non-self” refers to cells with different antigens on their cell surface membranes

Question 3

What is an antigen?

Answer 3

An antigen is a chemical capable of triggering the production of complementary antibodies and therefore, a specific immune response

Question 4

What is an antibody?

Answer 4

An antibody is a globular protein, made. By the B-lymphocytes which is complementary to, and reacts specifically with, particular antigens, helping destroy them.

Question 5

What is the non-specific line of defence?

Answer 5

This is a general response, often to tissue damage, which does not target individual pathogens. It includes phagocytosis and inflammation. It is a second line of defence.

Question 6

What is the specific line of defence?

Answer 6

This is a highly targeted response to specific pathogens, involving lymphocytes with specific complementary receptors, which results in long-term immunity

Question 7

Which cells are associated with ,1) cell-mediated immunity and 2) antibody-mediated or humoral immunity?

Answer 7

-Cell-mediated immunity: T-lymphocytes
-Antibody mediated/humoral immunity: B-lymphocytes

Question 8

What does cell-mediated immunity involve?

Answer 8

T-lymphocytes with specific surface receptors, responding to antigens on cells infected by viruses

Question 9

What does antibody-mediated immunity involve?

Answer 9

B-Lymphocytes which produce antibodies that are complementary to antigens of bacteria and viruses, found in body fluids

Question 10

Describe phagocytosis

Answer 10

-the polymorphs/macrophages are attracted to the pathogens by chemicals
-their membrane invaginates and they engulf it, forming a vesicle called a phagosome
-a lysosome fuses with the phagosome, releasing hydrolytic enzymes to digest the contents
-products are absorbed

Question 11

What happens during inflammation ?

Answer 11

-the damaged tissue becomes red and swollen as there is increased blood flow to the area and phagocytes and plasma leak out of the capillaries
-dead cells and pathogens form pus and the temperature rises (which helps to denature the pathogens enzymes)
-the rest of the immune system is alerted to what is going on

Question 12

What does the antibody-antigen reaction involve?

Answer 12

-the antibodies produced by the B-Lymphocytes attach to their complementary bacterial/viral antigens (each B-Lymphocyte has a specific binding site complementary in shape to one antigen)
-the pathogens are immobilised when they clump together, forming an antigen-antibody complex
-phagocytes/polymorphs engulf the complex (phagocytes) and digest it OR the antibodies destroy the antigens directly

Question 13

Outline the sequence that occur during the antibody mediated (or humoral) response

Answer 13

1. A B-Lymphocyte with a complementary receptor site binds to its bacterial (or viral) antigen. This SENSITISES it and it clones itself
2. Some cells become memory cells for long term immunity, most become short-lived plasma cells which secrete thousands of antibodies into blood plasma
3. It takes several days for antibody levels to rise to detectable levels. They attach onto their specific antigens, forming antigen-antibody complexes and the antibody-antigen reaction reactions occur (as described above), followed by destruction of antigens and phagocytosis

Question 14

Outline the sequence of events that occur during the cell-mediated response.

Answer 14

1. A T-LYMPHOCYTE with a complementary surface receptor binds onto its specific antigen, on an antigen presenting cell (APC), (i.e. it is sensitised) and clones itself
2. Some become T-HELPERS (which organise B-cells and phagocytes and other T-cells), some become T-KILLER cells (which use enzymes to destroy the APC directly), some become MEMORY CELLS (ready to divide rapidly if same infection occurs again) and some become SUPPRESSOR T-cells which switch off the T0cells when the antigens have been destroyed.

Question 15

Give 4 examples of antigen-presenting cells

Answer 15

-Your own cells which have been infected by a virus
-Cancerous tumour cells
-Cells of transplanted tissues and organs
-Macrophages/phagocytes which have digested and processed viruses already

Question 16

What is the secondary immune response?

Answer 16

This is the response that occurs when the memory B-lymphocytes detect the same complementary antigen, (i.e. the same infection), again. Already being sensitised their response is faster, they produce plasma cells quicker and since there are more of them, greater amounts of antibodies are produced. So many antibodies are produced sp quickly, that you may never have symptoms. You have achieved immunity.

Question 17

What is the primary immune response?

Answer 17

This is the response that occurs when B-lymphocytes come into contact with their complementary antigen (from a bacterium or free virus) for the first time (sensitisation). It results in cloned B-lymphocytes secreting thousands of antibodies but also produces memory cells which remain, ready to detect a secondary infection by the same antigen again

Question 18

What is a vaccine?

Answer 18

An injection of dead or weakened (attenuated) pathogens, modified toxins or isolated antigens that results in a specific immune response.

Question 19

What consideration must be taken when producing a vaccine?

Answer 19

-The pathogens used, must be killed or weakened (attenuated) by heat or irradiation so as not to cause the disease
-Antigens of the pathogens can be used to produce an immune response
-Modified toxins of the pathogens may be used to illicit an immune response, but they must be made harmless first

Question 20

What response does a “booster: injection bring about?

Answer 20

The secondary immune response

Question 21

What is herd immunity?

Answer 21

The idea that if enough people in the population are vaccinated, there is less likelihood of non-vaccinated, ill or the very young, coming into contact with the infection.

Question 22

What are the differences between active and passive immunity?

Answer 22

-In active immunity, the body’s own B and T cells produce antibodies, clones and memory cells in response to an antigen. Memory cells are produced so it lasts longer BUT it takes longer to achieve
-In passive immunity, B and T cells are not involved, as the person is given antibodies directly . There are no memory cells. This makes it rapid but temporary

Question 23

Both active and passive immunity can be achieved naturally or artificially. Explain how.

Answer 23

Active
1.naturally through catching the infection
2.artificially through vaccination

Passive
1. naturally via colostrum (breast milk) or placenta
2. artificially via injection of antibodies

Question 24

What are monoclonal antibodies?

Answer 24

Antibodies produced by cloned B-lymphocytes that have come from a mouse infected with a specific antigen.

Question 25

What are the advantages of using monoclonal antibodies for medical use rather than antibodies obtained from large mammals such as horses?

Answer 25

-They can be produced in large amounts in a laboratory
-They result in a single type of antibody being produced rather than lots of different ones

Question 26

How does society and the economy benefit from vaccination programmes?

Answer 26

-Fewer ill people, therefore less care needed to tend to them
-Lower child mortality
-Children do better at school when healthy
-Lower treatment costs if fewer people are ill
-Greater productivity at work of not off ill
-Carers do not need to take time off work