Module 4 : Section 1 - The Immune System

Question 1

What triggers an immune response

Answer 1

Foreign antigens

Question 2

What are antigens

Answer 2

Molecules (usually proteins or polysaccharide) found in the surface of cells

Question 3

What happens when a pathogen (e.g. bacterium) invades the body

Answer 3

The antigens in its cell surface are identified as foreign so this activated the cells in the immune system

Question 4

What two stages are involved in the immune response

Answer 4

• specific
• non-specific

Question 5

What is the specific and non specific responses

Answer 5

• non specific happens in the same way for all microorganisms no matter what antigens they have
• specific response is antigen-specific which involves white blood cells and T and B lymphocytes

Question 6

What are the four main stages in the immune response

Answer 6

• phagocytes engulf pathogens
• phagocytes activate T lymphocytes
• T lymphocytes activate B lymphocytes which divide to plasma cells
• plasma cells make more antibodies to a specific antigen

Question 7

What is a phagocyte

Answer 7

• A white blood cell that carries out phagocytosis
• they are found in blood and tissues, they carry out a non specific immune response

Question 8

How do phagocytes work

Answer 8

• it recognises the antigens on a pathogen
• phagocytes cytoplasm moves round the pathogen (engulfing it) presence of opsonins make it easier when engulfing
• the pathogen now contained in a phagosome in the cytoplasm of a phagocyte
• a lysosome fuses with the phagosome, the enzymes in the Lysosome break down the pathogen
• phagocyte then present the pathogens antigens on its surface to activate other immune system cells. It acts as an antigen presenting cell

Question 9

What are neutrophils

Answer 9

• first type of white blood cell to respond to a pathogen
• they move towards a wound in response to signals from cytokines which get released by cells at the site of the wound

Question 10

What are opsonins

Answer 10

Molecules in the blood that attach to foreign antigens to aid phagocytosis

Question 11

what does cell communication consist of (phagocytes activating t lymphocytes)

Answer 11

• presentation
• clonal selection
• clonal expansion
• differentiation

Question 12

what is the presentation stage of cell communication

Answer 12

the antigens are presented by an antigen presenting cell

Question 13

what is clonal selection

Answer 13

• when the receptor of a t lymphocytes meets a complementary antigen it binds to it
• each lymphocyte will bind to a different antigen
• this activates the t lymphocyte

Question 14

what is clonal expansion

Answer 14

when the chosen t lymphocyte divides to produce clones of itself

Question 15

what is differentiation

Answer 15

the process in which the t lymphocytes become either t helper, killer or regulatory cells or memory cells

Question 16

what do t helper cells do

Answer 16

these release substances to activate B lymphocytes and T killer cells

Question 17

what do t killer cells do

Answer 17

these attach to and kill cells that are infected with the virus

Question 18

what do t regulatory cells do

Answer 18

these suppress the immune response from other WBC’s. this helps stop immune system cells from mistakenly attacking the host’s body cell

Question 19

what are b lymphocytes

Answer 19

• type of white blood cell
• covered with proteins called antibodies
• each b lymphocyte has a different shaped antibody on its surface, meaning each of them will bind to a different antigen

Question 20

what do antibodies do

Answer 20

bind to antigens to form an antibody-antigen complex

Question 21

when a b lymphocyte is selected what happens

Answer 21

it divides by mitosis into plasma cells and memory cells

Question 22

What are plasma cells

Answer 22

• Clones of the b lymphocyte (identical to the selected b lymphocyte)
• they secrete loads of the antibody which is specific to the antigen into the blood

Question 23

What is the variable region of an antibody

Answer 23

• forms the antigen binding site and the shape of this is complementary to a particular antigen
• found in the tips of the antibody
• differs between antibodies

Question 24

What is the hinge region of an antibody

Answer 24

Allows flexibility when the antibody binds to the antigen

Question 25

What is the constant region of the antibody

Answer 25

- they allow binding to receptors on immune system cells - this is the same (same sequence of amino acids) in all antibodies

Question 26

What is the disulphide bridges in the antibody

Answer 26

A bond which hold the polypeptide chains of the protein (antibody) together

Question 27

What methods do anitbodies use to help clear infections

Answer 27

- agglutination - neutralising toxins - preventing the pathogen binding to human cells

Question 28

What is agglutination

Answer 28

- each antibody has two binding sites, so an antibody can bind to two pathogens at the same time - they then become clumped - phagocytes then bind to the antibodies and phagocytose all at once

Question 29

How does the method of neutralising toxins work when antibodies clear infections

Answer 29

- toxins have different shapes than antigens - antibodies called anti-toxins can bind to the toxins produced by pathogens - this prevents the toxins from affecting human cells - these are also phagocytosed

Question 30

What is the primary response

Answer 30

When a pathogen enters the body for the first time, the antigens on its surface activate the immune system

Question 31

Why is the primary response slow

Answer 31

- Because there aren’t many B lymphocytes that can make the antibody needed to bind to it - overtime the body will produce enough of the right antibody to overcome the infection while the infected person shows symptoms

Question 32

What happens after being exposed to an antigen

Answer 32

T and B lymphocytes produce memory cells

Question 33

Memory T lymphocytes remember….

Answer 33

The specific antigen and will recognise it the second time round

Question 34

Memory B lymphocytes remember

Answer 34

The specific antibodies needed to bind to the antigen

Question 35

What happens if the same pathogen enters the body again

Answer 35

The immune response will produce a quicker, stronger immune response. Known as the secondary response

Question 36

Why is the secondary response faster

Answer 36

- Clonal selection happens faster - The memory B lymphocytes are activated and divide into plasma cells that produce the right antibody to the antigen - the memory t lymphocytes are activated and divide into the correct type of t lymphocyte to kill the cell carrying the antigen - this happens before you show any symptoms