TOPIC 2C-CELLS AND THE IMMUNE SYSTEM

Question 1

A) Describe what an “antigen” is

B) Where are antigens found?

Answer 1

A)-molecules (usually proteins) able to generate immune response when detected by body
B)-on surface of cells

Question 2

C) What are antigens used by the immune system to identify?

Answer 2

C)1-pathogens–>disease causing organisms
2-abnormal body cells–>e.g cancerous/pathogen-infected cells that have abnormal antigens on their surface
3-toxins + cells from other individuals of same species (e.g: organ transplants)

Question 3

A) What are the 4 main stages in the immune response?

Answer 3

A)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

STAGE 1:
A) Define the term “phagocyte”

B) Where are phagocytes found and what do they do?

Answer 4

A)-(e.g a macrophage) is type of white blood cell that carries out phagocytosis (engulfs pathogens)
B)-in blood + tissues
–>first cells to repsond to immune system trigger in body

Question 5

C) Explain step by step as to how phagocytes work?

Answer 5

C)1-phagocyte recognises foreign antigens on pathogen
2-the cytoplasm of phagocyte moves round pathogen to engulf it
3-pathogen now contained in phagocytic vacuole (bubble) in cytoplasm of phagocyte
4-lysosome (organelle that contains enzymes called lysozymes) fuses with phagocytic vacuole
–>lysozymes break pathogen down
5-phagocyte then presents pathogen’s antigens–> sticks antigens on it’s surface to activate other immune system cells.

Question 6

STAGE 2:

A) What is a “T-cell(T-lymphocyte)” and how is it activated?

Answer 6

A)-another white blood cell type

• ->has receptor protein’s on it’s surface that bind to complementary antigens presented to it by phagocytes
• ->this activates the T-cell

Question 7

B) Outline the different way that different T-cells respond

Answer 7

B)1-helper t-cells(T h cells) release chemical signal that activate + stimulate phagocytes
2-cytotoxic t-cells (T c cells) kill abnormal + foreign cells
-B-cells: t-cells also activate these B-cells which secrete antibodies.

Question 8

STAGE 3:
A) Briefly explain what “B-cells (B-lymphocytes) are
B) Why does each B-cell have different shaped antibody on it’s membrane?
C) Explain how B-cells are activated and divide in to plasma cells

Answer 8

A)-type of white blood cell
–>they are covered with antibodies (proteins that bind to antigens to form antigen-antibody complex)
B)-so that different B-cells bind to different shaped antigens
C)1-when antibody on surface of B-cell meets complementary shaped antigen–>binds to it
2-this + with substances released from helper T-cells activates the B-cell–>this process called clonal selection
3-activated B-cell divides into plasma cells.

Question 9

STAGE 4:

A) What are “plasma cells” and what is their function?

Answer 9

A)-are identical to B-cells (clones)–>they secrete lots of antibodies specific to antigen
–>these called monoclonal antibodies and they bind to antigens on surface of pathogen to form lots of antigen-antibody complexes

Question 10

B) Explain what “agglutination” is

C) Outline what happens after this process of agglutnation and what that then leads to

Answer 10

B)-an antibody has 2 binding sites so can bind to 2 pathogens at same time
–>means that pathogens become clumped together (agglutination)
C)-phagocytes then bind to antibodies and phagocyte many pathogens in one go
–>this process leads to destruction of pathogens carrying this antigen in body.

Question 11

A) What doe it mean give the fact that antibodies are “proteins”?

B) Explain what the specificity of an antibody depends on

C) What is the nature of “constant regions” on antigens?

Answer 11

A)-they made up of amino acid chains
B)-it depends on the antibodies variable region which form the the antigen binding sites
–>each antibody has variable region with unique tertiary structure (due to different amino acid sequences) that’s complementary to specific antigen
C)-all antibodies have same constant regions.

Question 12

A) Outline what the 2 types of immune response are

B) What is the significance of the 2 types of immune responses described above?

Answer 12

A)1-CELLULAR: the t-cells + other immune system cells they interact with (e.g: phagocytes) form cellular response
2-HUMORAL: B-cells, clonal selection + production of monoclonal antibodies form humoral response.
B)-both are needed to remove pathogen from body +they interact with each other
–>E.G: T-cells help activate B-cells
–> antibodies coat pathogens making it easier for phagocytes to engulf them.

Question 13

A) What is the “primary immune response”?

Answer 13

A)-when antigen first enters body for first time it activates immune system

Question 14

B) Explain how this primary immune response works

Answer 14

B)1-primary response slow as not many B-cells able to make antibody needed to bind to it
2–>eventually body will produce enough of right antibody to overcome infection MEANWHILE person infected and will show symptoms of disease
3–>after exposure to antigen both T-cells + B-cells produce memory cells which remain in body long time
–> memory T-cells remember specific antigen + will recognise 2nd time
–>memory B-cells record specific antibodies needed to bind to the antigen
4–>person now immune->immune system has ability to repsond quickly to 2nd infection.

Question 15

A) What is a “secondary immune response”?

Answer 15

A)-if same pathogen enters body again immune system will produce quicker + stronger immune response

Question 16

B) Explain how this secondary immune response works

Answer 16

B)1-clonal selection happens faster
-memory B-cells activated + divide in to plasma cells that produce right antibody to right antigen
-memory T-cells activated + divide into correct T-cell type to kill cell carrying the antigen
2-secondary response often gets rid of pathogen before begin to show any symptoms (are immune to pathogen)

Question 17

A) What can “vaccines” help to avoid?

B) Briefly explain what vaccines are and how they work

Answer 17

A)-while B-cells dividing to build their numbers to deal with pathogen (primary response) you suffer from
disease–>vaccines can help avoid this
B)-they contain antigens that cause body to produce memory cells against particular pathogen without pathogen causing the disease
–>means become immune without getting any symptoms

Question 18

C) Describe “herd immunity” in terms of vaccinations

D) What type of antigens do vaccines always contain?

Answer 18

C)-vaccines protect individuals that have them and as they reduce occurrence of disease
–>so those not vaccinated also less likely to catch disease (as fewer people to catch it from)
D)-free antigens or antigens attached to a dead (or attenuated-weakened) pathogen.

Question 19

E) What are the different methods of vaccine delivery in to the human body

F) What are the disadvantages of taking a vaccine orally?

Answer 19

E)-they may be injected or taken orally
F)-it could be broken down by enzyme in gut
–>or the molecules of the vaccine may be too large to be absorbed into blood.

Question 20

G) What are “booster vaccines” used for?

Answer 20

G)-these are sometimes given later on (e.g: after several years) to make sure memory cells are produced

Question 21

A) Outline and explain how “antigenic variation” arises

Answer 21

A)-antigens on surface of pathogens activate primary response

• ->when infected 2nd time with same pathogen (which has same antigens on it’s surface)–>they activate secondary response
• ->BUT some of the pathogens able to change their surface antigens
• ->this antigenic variability is called antigenic variation
• ->different antigens formed due to changes in genes of a pathogen.

Question 22

B) How does antigenic variation cause a person to become ill?

Answer 22

B)-due to antigenic variation when a person is infected a 2nd time memory cells produced from first infection won’t recognise different antigens

• ->so immune system has to start from scratch and carry out primary response against these new antigens
• ->this primary response takes time to get rid of infection which is why you get ill again.

Question 23

C) What is the effect of antigenic variation on the production of vaccines against some pathogens?

Answer 23

C)-it makes it difficult to develop vaccines against some pathogens for same reason a person gets ill again
–>EXAMPLES of pathogens that show antigenic variation are HIV and the INFLUENZA VIRUS.

Question 24

D) Explain how antigenic variation affects the production of vaccines to help prevent people catching influenza

Answer 24

D)1-influenza (flue) vaccine changes very year as antigens on influenza virus surface change regularly to form new strains of the virus
2-memory cells produced from vaccination with one strain of flu wont recognise other strains with different antigens–>strains are immunologically distinct
3-every year there are different strains of influenza virus circulating population–>so different vaccine needed
4-new vaccines developed and 1 chosen each year that most effective against recently circulating influenza viruses
5-governments + health authorities then implement vaccination programme using most suitable vaccine.

Question 25

A) Define the term “active immunity”

B) Outline what the 2 types of active immunity are

Answer 25

A)-this is type of immunity get when your immune system makes it’s own antibodies after stimulation by an antigen
B)-NATURAL: this is when you become immune after catching a disease
-ARTIFICIAL VACCINATION: this is when you become immune after been given vaccination containing harmless antigen dose.

Question 26

A) What does “passive immunity” mean?

Answer 26

A)-this is immunity type you get from being given antibodies made by a different organism
–>your immune system doesn’t produce any antibodies of it’s own

Question 27

B) Describe the 2 types of passive immunity

Answer 27

B)-NATURAL: this when baby becomes immune due to antibodies receives from it’s mother via placenta + in breast milk

• ARTIFICIAL: this is when you become immune after being injected with antibodies from someone else
• ->E.G: if you contact tetanus–>can be injected with antibodies against the tetanus toxin collected from blood donations.

Question 28

A) Define “monoclonal antibodies”

B) Why are antibodies v. specific and how is that useful for monoclonal antibodies?

Answer 28

A)-antibodies produced from single group of genetically identical B-cells
–>means they all are identical in structure
B)-v. specific as their binding sites have unique tertiary structure that only 1 particular antigen will fit into (one with complementary shaped antigen)
–>therefore useful as can make monoclonal antibodies able to bind to anything you want like a cell antigen OR other substance
–>and they will only bind to target this molecule.

Question 29

A) EXAMPLE 1: Explain step by step as to how monoclonal antibodies may be used to target a particular cell type-like a CANCER CELL

Answer 29

A)1-different body cells ave different surface antigens
2-cancer cells have antigens on surface called tumour markers that not found on normal body cells
3-possible to make monoclonal antibodies that can bind to the tumour markers
4-can also attach anti-cancer drugs to antibodies
5-when antibodies in contact with cancer cells–>will bind to the tumour markers
6-means drug will accumulate in body where there are cancer cells
7-so side effects of antibody-based drug lower than other drugs as accumulate near specific cells.

Question 30

B) EXAMPLE 2: Similarly, explain how monoclonal antibodies may be used in targeting a particular substance for medical diagnosis-PREGNANCY TESTING

i) -What hormone do pregnancy tests detect and where is it found?
ii) -Explain the steps to follow to detect this hormone using monoclonal antibodies and how that could then indicate pregnancy

Answer 30

B)i)-detect the hormone “human chorionic gonadotropin (hCG)” which is found in urine of pregnant women
ii)1-application area contains antibodies for hCG bound to coloured bead (blue)
2-when urine applied to application area any hCG will bind to antibody on beads–>forming antigen-antibody complex
3-urine moves up stick to test strip area–>carrying beads with it
4-test strip contains antibodies to hCG that stuck in place (immobilised)
5-if hCG present test strip turns blue as imobilised antibody binds to any hCG
–>concentrating hCG-antibody complex with the blue beads attached
–>if no hCG present beads will pass through test area without binding to anything so won’t go blue.

Question 31

A) What is the enzyme-linked immunosorbent assay (ELISA) and what may it be used for?

Answer 31

A)-allows you to see if patient has any antibodies to certain antigen OR any antigen to certain antibody
-can be used to test for pathogenic infections/ for allergies (e.g: to nuts or lactose) and for just about anything you can make antibody for

Question 32

B) Explain how the (ELISA) test works

Answer 32

B)-in an ELISA test an antibody is used which has enzyme attached to it

• ->this enzyme can react with substrate to produce coloured product
• ->causes colour change in reaction vessel
• this colour change demonstrates that the antigen or antibody of intrest present in test sample (e.g: blood plasma)
• ->in some ELISA types quantity of this antigen/antibody can be worked out from colour change intensity.

Question 33

C) Describe the 2 types of ELISA- DIRECT and INDIRECT

Answer 33

C)-DIRECT: uses single antibody that complementary ro antigen testing
-INDIRECT: different as uses 2 different antibodies

Question 34

A) EXAMPLE: Outline and explain how using an indirect ELISA test can be used to see if a patient possess antibodies to the HIV virus

Answer 34

1-HIV antigen bound to bottom of well in well plate (plastic tray with lots circular bits)
2-sample of patient’s blood plasma which may contain several different antibodies added to well
–>if any HIV-specific antibodies (antibodies against HIV) present then will bind to HIV antigen stuck to well bottom
–>well then washed out to remove any unbound antibodies
3-secondary antibody that has specific enzyme attached to it added to well
–>this antibody washed out again to remove any unbound secondary antibody
–>if no primary antibody in sample all secondary antibody will be washed away
4-solution added to well which contains substrate able to react with enzyme attached to secondary enzyme and produce coloured product
–>if solution changes colour then indicates patient has HIV-specific antibodies in blood so is HIV infected.

Question 35

B) Why are the “washing” steps important?

C) What results should be expected if the ELISA test resulted negative?

Answer 35

B)-to make sure unbound antibodies not left in well as could affect results
–>E.G: unbound secondary antibodies could cause test appear (+) when no HIV antibodies present
C)-there would no longer be colour change as there would be no HIV-specific antibodies for secondary antibodies to bind to.

Question 36

A) What is normally importantly done or should be done when a study presents evidence for a new theory?

Answer 36

A)-important that other scientists come up with more evidence to validate (confirm) theory

• OR sometimes other scientists may repeat study to reproduce results OR conduct other studies to try and prove same theory
• ->E.G of a study: a vaccine has dangerous side effects.

Question 37

EXAMPLE 1: THE MMR VACCINE:

A) Outline the conflicting background to the production of the MMR vaccine

B) Why was the study published not convincing for everyone?

Answer 37

A)-1998 study published on safety of measles, mumps + rubella (MMR) vaccine
–>based on 12 children with autism (life-long development disability) which concluded may be link between MMR vaccine + autism
B)-the sample size v.small (12 children)–>increased liklihood of results by chance
–>also study may of been biased as one of scientists was helping gain evidence for law-suit against MMR vaccine manufacturer
-also studies carried out by different scientists found no link between autism + MMR vaccine.

Question 38

C) Describe the further scientific studies that were carried out to try and sort out the conflicting evidence

Answer 38

C)-in 2005 Japanese study published on incidence of autism in Yokohama (area in Japan)

• ->they looked at 30,000 children’s medical records brn between 1988-1996 and counted n. of children that developed autism before age 7
• ->MMR jab first introduced in Japan 1989 and stopepd in 1993
• ->during this time MMR vaccine was administered to children at 12 months old

Question 39

With reference to the graph:

A) DESCRIBE what the data shows

Answer 39

A)-it shows n. of children diagnosed with autism continued to rise after MMR vaccine stopped

• ->E.G: from all children born 1992 that received MMR jab about 60/10 000 diagnosed with autism before age 7
• ->BUT from all children born 1994 to not receive MMR jab about 160/10 000 diagnosed with autism before age 7

Question 40

B) What conclusions may be drawn from from this data?

Answer 40

B)-no link between MMR vaccine and autism

Question 41

C) Evaluate the methodology from this study and the results

Answer 41

C)-you can be much more confident in this study compared to 1998 study as sample size v. large (30, 000 children studied)
–>larger sample size means results less likely to be due to chance.

Question 42

EXAMPLE 2: HERCEPTIN-MONOCLONAL ANTIBODIES

A) Outline the medical background to HERCEPTIN

Answer 42

A)-about 20% women with breast cancer have tumours that produce more than usual amount of receptor called HER2
–>Herceptin is drug used to treat breast cancer type–> it contains monoclonal antibodies that bind the HER2 receptor on to tumour cell + prevents cell growth and division.

Question 43

B) What wasthe 2005 study that tested HERCEPTIN on women who had already undergone chemotherpay for HER2-type breast cancer?

Answer 43

B)-1694 women who took drug for year after chemotherapy and another 1694 women observed foe same time (control group)

Question 44

With reference to the graph showing the results from the study:

C) Describe the data

D) What conclusions can be drawn from the results?

Answer 44

C)-almost twice as many women in control group developed breast cancer again OR died compared to women group that took Herceptin
D)-1 year treatment with Herceptin, after chemotherapy increases disease-free survival rate for women with HER2-type breast cancer.

Question 45

DESCRIBE THE FOLLOWING ETHICAL ISSUES SURROUNDING VACCINES:

A) Testing on animals before testing on humans
B) Volunteers may put themselves at unnecessary risk
C) Some may fear side effect risk/unfairness of vaccines
D) Prioritising who receives the vaccine in epidemics

Answer 45

A)-compulsory rule–>some disagree with animal testing
–>also animal based substances may be used to produce vaccine which some disagree with
B)-volunteers may think they are fully protected so may have unprotected sex as have had new HIV vaccine and think they protected–>vaccine may not work
–>risk of contracting disease
C)-so some may not want to take vaccine due to risk of side effects BUT are still protected due to herd immunity–>others think this unfair
D)-if there was epidemic with new disease (e.g: new influenza virus) there would be rush to receive vaccine + difficult decisions would need to be made as to who would be first to receive it.

Question 46

A) Briefly explain the ethical issues surrounding MONOCLONAL ANTIBODY THERAPY

Answer 46

A)-often involve animal right issues

• ->animals are used to produce the cells from which the monoclonal antibodies are produced
• ->some disagree with use of animals in this way.

Question 47

A) Define “HIV (Human Immunodeficiency Virus)”

B) What is “AIDS”?

Answer 47

A)-virus that affects immune system
B)-condition where immune system deteriorates to eventually fail
–>so someone with AIDS more vulnerable to other infections like pneumonia

Question 48

A) What is the effect of HIV killing helper T-cells?

Answer 48

A)-it first infects these t-cell which act as hosts for HIV

• helper t-cells send chemical signals that activate phagocyte/cytotoxic T-cells + B-cells so they v. important cells in immune response
• ->without enough helper T-cells immune system unable to mount effective infection reponse as other immune system cells not behave as should.

Question 49

B) When do people with HIV develop AIDS?

Answer 49

B)-when helper T-cell numbers in their body reach critically low level

Question 50

STRUCTURE OF HIV: 
Describe the following parts of HIV: 
A) Core
B) Outer coating
C) Envelope
D) Attachment proteins

Answer 50

A)-core contains genetic material (RNA) + some proteins (including reverse transcriptase enzyme needed for virus replication)
B)-this outer coating of protein is called a capsid
C)-this extra outer layer is made of membrane stolen from cell membrane of previous host cell
D)-these stick out from envelope and there are lots of copies of these that help HIV attach to host helper T-cell.

Question 51

A) Where does HIV replicate and why does it replicate the way it does?

Answer 51

A)- HIV (+ all other viruses) only able to reproduce inside cells of organisms it has infected

• ->HIV replicates in helper T-cells of host
• ->this as it doesn’t have equipment (like enzymes + ribosomes) to replicate on it’s own so uses those of host cell.

Question 52

B) Explain how HIV replicates

Answer 52

1-attachment protein attaches to receptor molecules on cell membrane of host helper T-cell
2-capsid released into cell where it uncoats + releases genetic material (RNA) in to cell’s cytoplasm
3-inside cell–>reverse transcriptase used to make a complementary DNA strand from viral RNA template
4-from this double-stranded DNA made + inserted into human DNA
5-host cell enzymes used to make viral proteins from viral DNA found within human DNA
6-viral proteins are assembled into new viruses which bud from cell and go on to infect other cells.

Question 53

C) Over the period of being infected with HIV what symptoms do sufferers experience?

Answer 53

C)1-initial infection period–> HIV replicates rapidly and infected person may experience severe flu-like symptoms
2-latency period–> HIV replication stops and drops to low level
–>during this period infected person doesn’t experience any symptoms.

Question 54

A) When are people with HIV classed as having AIDS?

B) Outline the type of diseases that people with AIDS generally develop

C) What is the general length of time between infection with HIV and AID development?

Answer 54

A)-when symptoms of their failing immune system start to appear
-OR their helper T-cell count drops below certain level
B)-they develop diseases that wouldn’t cause serious problems in people with healthy immune systems
D)-varies from individual to individual but without treatment time length is about 10 years.

Question 55

A) Describe the INITIAL SYMPTOMS someone who suffers from AIDS experiences

B) Briefly explain the symptoms one experiences as AIDS PROGRESS

Answer 55

A)-minor infections of mucous mebranes (e.g: inside nose/ears/genitals etc.) as well as recurring respiratory infections.
B)-n. of immune system cells decreases further
–>patients become susceptible to more infections including chronic diarrhoea + severe bacterial infections + tuberculosis.

Question 56

C) Describe the LATE STAGE SYMPTOMS experienced by patient with AIDS

Answer 56

C)-have v.low number of immune system cells + can develop range of serious infections like toxoplasmosis of brain (a parasite infection) AND candidiasis of respiratory system (fungal infection)
–>it’s these serious infections that kill AID patients NOT HIV itself.

Question 57

D) Why does the length of time that people survive with AIDS vary a lot?

Answer 57

D)-factors that affect progression of HIV to AIDS and survival time with AIDS include existing infections, the strain of HIV infected with/age + access to healthcare.

Question 58

A) Explain how antibiotics are designed to target and kill bacteria

Answer 58

A)-antibiotics kill bacteria by interfering with their metabolic reactions

• ->they target the bacterial enzymes + ribosomes used in these reactions
• bacterial enzymes + ribosomes different from human enzymes/ribosomes
• ->antibiotics designed to only target bacterial ones so they don’t damage human cells

Question 59

B) Why do antibiotics not work against viruses like HIV?

Answer 59

B)-viruses not have their own enzymes and ribosomes as they use ones in host’s cells
–>so as human viruses use human enzymes + ribosomes to replicate, antibiotics can’t inhibit them as they don’t target human processes.

Question 60

C) Explain how antiviral drugs are designed to work

Answer 60

C)-designed to target the few virus-specific enzymes (enzymes only virus uses) that exist

• ->E.G: HIV uses reverse transcriptase to replicate
• ->human cells don’t use this enzyme so drugs can be designed to inhibit it without affecting the host cell
• ->these drugs called reverse-transcriptase inhibitors.

Question 61

A) What is the current treatment/cure for HIV if any?

Answer 61

A)-no cure or vaccine for HIV

–>BUT antiviral drugs cant be used to slow down progression of HIV infection + AIDS in infected person

Question 62

B) Outline the best way to control HIV infection in a population and how that may be carried out

Answer 62

B)-by reducing it’s spread

• HIV can be spread via unprotected sex OR infected bodily fluids (e.g: blood sharing from contaminated needles) OR HIV (+) mother to her fetus
• ->not all babies like this born infected with HIV and taking antiviral drugs during pregnancy can reduce chance of baby being HIV (+).