section 1: disease & the immune system - topic 3: the immune system

Question 1

what is an immune response?

Answer 1

the body’s reaction to a foreign antigen.

Question 2

what are antigens?

Answer 2

molecules (usually proteins or polysaccharides) found on the surface of cells.

Question 3

how do antigens activate the immune response?

Answer 3

when a pathogen (like a bacterium) invades the body, the antigens on its cell surface are identified as foreign, which activates cells in the immune system.

Question 4

what does the immune response involve?

Answer 4

specific and non-specific stages.

Question 5

what is the difference between the non-specific response and the specific response?

Answer 5

non-specific response - happens in the same way for all microorganisms, whatever foreign antigens they have.

specific response - antigen-specific.
^ it’s aimed at specific pathogens.

Question 6

what does the specific response involve?

Answer 6

white blood cells called T lymphocytes and B lymphocytes.

Question 7

what are the main stages of the immune response?

Answer 7

1. phagocytosis.
2. T lymphocyte activation.
3. B lymphocyte activation and plasma cell production.
4. antibody production.

Question 8

what is a phagocyte?

Answer 8

a type of white blood cell that carries out phagocytosis.

Question 9

what is phagocytosis?

Answer 9

engulfment of pathogens.

Question 10

where are phagocytes found?

Answer 10

in the blood and in tissues.

Question 11

what kind of immune response do phagocytes carry out?

Answer 11

a non-specific immune response.

Question 12

what are the key words to know in phagocytosis?

Answer 12

opsonins.
phagosome.
lysosome.
neutrophils.
cytokines.

Question 13

what are opsonins?

Answer 13

molecules in the blood that attach to foreign antigens to aid phagocytosis.

Question 14

what is a phagosome?

Answer 14

a type of vesicle.

Question 15

what is a lysosome?

Answer 15

an organelle that contains digestive enzymes.

Question 16

what are neutrophils?

Answer 16

a type of phagocyte.
- they’re the first white blood cells to respond to a pathogen inside the body.
- they move towards a wound in response to signals from cytokines.

Question 17

what are cytokines?

Answer 17

proteins that act as messenger molecules.
- they are released by cells at the site of the wound.

Question 18

how does phagocytosis work?

Answer 18

• a phagocyte recognises the antigens on a pathogen.
• the cytoplasm of the phagocyte moves round the pathogen, engulfing it.
  ^ this may be made easier by the presence of opsonins.
• the pathogen is now contained in a phagosome in the cytoplasm of the phagocyte.
• a lysosome fuses with the phagosome and the enzymes in the lysosome break down the pathogen.
• the phagocyte then presents the pathogens antigens.
  ^ it sticks the antigens on its surface to activate other immune system cells - acting as an antigen-presenting cell (APC).

Question 19

what is the second stage of the immune response?

Answer 19

T lymphocyte activation.

Question 20

what are T lymphocytes?

Answer 20

another type of white blood cell.

Question 21

what do T lymphocytes do?

Answer 21

their surface is covered with receptors - the receptors bind to antigens presented by APCs.

Question 22

how do T lymphocyte receptors bind to antigens?

Answer 22

when the receptor on the surface of a T lymphocyte meets a complementary antigen, it binds to it - so each T lymphocyte will bind to a different antigen.

Question 23

what happens when a T lymphocyte receptor binds to an antigen?

Answer 23

it activates the T lymphocyte.

Question 24

what is the process of a T lymphocyte binding to an antigen called?

Answer 24

clonal selection.

Question 25

what does the activated T lymphocyte then undergo?

Answer 25

clonal expansion.

Question 26

what is clonal expansion?

Answer 26

when the activated T lymphocyte divides to produce clones of itself.

Question 27

what are the different types of activated T lymphocytes?

Answer 27

T helper cells.
T killer cells.
T regulatory cells.

Question 28

what is the function of T helper cells?

Answer 28

they release substances to activate B lymphocytes and T killer cells.

Question 29

what is the function of T killer cells?

Answer 29

they attach to and kill cells that are infected with a virus.

Question 30

what is the function of T regulatory cells?

Answer 30

they suppress the immune response from other white blood cells.
- this helps to stop immune system cells from mistakenly attacking the host’s body cells.

Question 31

what do some activated T lymphocytes become?

Answer 31

memory cells.

Question 32

what is the third stage of the immune response?

Answer 32

B lymphocyte activation and plasma cell production.

Question 33

what are B lymphocytes?

Answer 33

another type of white blood cell.

Question 34

what are B lymphocytes covered with?

Answer 34

antibodies.

Question 35

what are antibodies?

Answer 35

proteins that bind to antigens to form an antigen-antibody complex.

Question 36

why is each B lymphocyte unique?

Answer 36

because each of them have a different shaped antibody on their membrane, so different ones bind to different shaped antigens.

Question 37

what activates the B lymphocyte?

Answer 37

when the B lymphocyte antibody binds to a complementary antigen + substances released from T helper cells.

Question 38

what is the process of B lymphocyte activation called?

Answer 38

clonal selection.

Question 39

what does the activated B lymphocyte then do?

Answer 39

it divides (by mitosis) into plasma cells and memory cells.

Question 40

what is the dividing of the activated B lymphocyte an example of?

Answer 40

clonal expansion.

Question 41

what is the fourth stage of the immune response?

Answer 41

antibody production.

Question 42

what are the plasma cells?

Answer 42

clones of the B lymphocyte.

Question 43

what do the plasma cells do?

Answer 43

secrete loads of the antibody, specific to the antigen, into the blood.

Question 44

what do the antibodies secreted by the plasma cells do?

Answer 44

they bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes.

this is the signal for the immune system to attack and destroy the pathogen.

Question 45

what is cell signalling?

Answer 45

how cells communicate.

a cell may release a substance that binds to the receptors on another cell.
^ this causes a response of some kind in the other cell.

Question 46

why is cell signalling important in the immune response?

Answer 46

because it helps to activate all the different types of white blood cells that are needed.

Question 47

what is an example of cell signalling in the immune response?

Answer 47

T helper cells release interleukins (a type of cytokine) that bind to receptors on B lymphocytes.
- this activates the B lymphocytes.
^ the T helper cells are signalling to the B lymphocytes that there’s a pathogen in the body.

Question 48

what is a blood smear?

Answer 48

a sample of blood smeared over a microscope slide.

Question 49

why are stains added to a blood smear?

Answer 49

to make the different cells easy to see.

Question 50

what are you likely to see when looking at a blood smear?

Answer 50

red blood cells.
white blood cells.
platelets (tiny fragments of cells involved in blood clotting).

some types of white blood cells have granules in their cytoplasm (look grainy) and others don’t.

Question 51

how to interpret a blood smear.

Answer 51

most of the cells are red blood cells - easy to spot because they don’t have a nucleus.

neutrophil - its nucleus looks like three interconnected blobs (multi-lobed) & the cytoplasm of a neutrophil is grainy.

lymphocyte - much smaller than a neutrophil, the nucleus takes up most of the cell & there’s very little cytoplasm to be seen (not grainy).

monocyte (biggest white blood cell and a type of phagocyte) - has a kidney-bean shaped nucleus & a non-grainy cytoplasm.