Topic 5 - Immunity

Question 1

Antigens

Answer 1

Foreign atigens are proteins which trigger an immune response. Usually found on the surface of pathogensand toxins. Allow the immune system to detect the pathogens and toxins

Question 2

4 stages to immune response

Answer 2

1. Phagocytosis
2. Phagocytes activate T cells
3. T cells acitvate B cells which divide into plasma cells
4. Plasma cells produce antibodies specific to antigen

Question 3

Stage 1: Phagocytosis

Answer 3

1. Phagocyte recognises foreign antigen on surface of pathogen
2. Cytoplasm of phagocyte moves around the pathogen and causes phagocyte to engulf pathogen
3. Phagocyte contains pathogen in a phagocytic vacuole inside cytoplasm
4. Lysosomes (which contain lysozymes) fuse with phagocytic vacuole and lysozymes break down the pathogen
5. Phagocyte then presents the antigens on its surface, to activate other immune system cells

Question 4

Stage 2: Phagocytes activate T cells

Answer 4

1. T cells have protein receptors on their surface which bind to complementary antigens presented to it by phagocyte
2. This activates the T cells.
3. Two types of T cells: Helper T cells, which release chemicals which activate more phagocyes and cytotoxic cells which kill abnormal and foreign cells

Question 5

Stage 3: T cells activate B cells which divide into plasma cells

Answer 5

1. B cells covered with antibodies on surface
2. Antibodies on B cells bind with antigens with complementary shape
3. Activates B cell (activates B cells)
4. B cell now divides into plasma cells

Question 6

Stage 4: Plasma cells produce antibodies specific to the antigen

Answer 6

1. Plasma cells are clones of B cells
2. Plasma cells produce antibodies called monoclonal antibodies
3. These antibodies are specifc to the antigen
4. These antibodies bind to the antigen on surface of pathogen forming antigen-antibody complexes
5. Antibodies have 2 binding sites, allowing them to bind to two pathogens at once, causing pathogens to be clumbed together (“agglutination”)
6. Phagocytes then bind to the antibodies and phagocytosis occurs to the pathogens

Question 7

Structure of antibody

Answer 7

DIAGRAM

1. Antigen-antibody binding site (all antibodies have 2)
2. Variable region (all antibodies have different variable regions with different tertiary structures, complementary to a specific antigen)
3. Constant region (all antibodies have same constanr region)
4. Hinge protein]
5. Light chain
6. Heavy chain
7. Disulfide bridge

Question 8

Cellular immune response

Answer 8

Stage 1 and 2 of immune response

Question 9

Humoral immune response

Answer 9

Stage 3 and 4 of immune response

Question 10

Primary immune response

Answer 10

This is the first exposure to the foreign antigen. The immune system is activated. The response is slow due to low no. of B cells and therefore, less of the right antibodies produced to that specifc antigen.

However, after some time, enough of the right antibodies will be produced to the specific antigen to overcome infection. However, person will have developed symptoms of the disease

After first exposure, memory T cells and B cells are formed and remain in body for long period of time

Memory T cells remember the specific antigen and recognise it if it enters body again

Memory B cells remember the specific antibodies needed to bind to that antigen

The person is now immune. The immune system can produce a strong and quick response to that specific antigen, and it is unlikely that the person will developany symptoms

Question 11

Secondary immune response

Answer 11

This is where the person is exposed to the pathogen for the second time. The immune response is stronger and quicker.

This is because clonal selection happens quicker. This is where B cells are activated and divide into plasma cells which then produce the right antibody to the specific antigen

Memory T cells then produce the right T cells to kill the cell carrying antigen (e.g. pathogen)

Secondary response destroys and removes pathogen before symtoms even show up.

Question 12

Vaccines

Answer 12

1. Provide immunity against a specific disease
2. Contains antigens from a particular pathogen
3. These antigens trigger a primary immune response and therefore, lead to formation of memory cells
4. However, the pathogens do not cause disease and therefore, person does not show symptoms because the antigens are either free (not attached to pathogen) or attached to dead / attenuated (weakened) pathogen
5. Vaccinations can be taken injected or taken orally. -ve of taking orally: enzymes in gut may break down the vaccine or molecules of vaccine too large to enter blood
6. Herd immunity: This is where those who are not vaccinated are less likely to get the disease because, those who are vaccinated are fully protected and therefore, there are less people to catch the disease from
7. Booster vaccines sometimes required (after few years) to ensure that enough memory cells are produced

Question 13

Antigenic Variability

Answer 13

1. This is where antigens on surface of pathogen change. 2. This is due to genes in the pathogen changing.
2. This means that memory cells produced by the first infection will not recognise the antigens on surface of pathogen
3. Primary immune response occurs which is slow. Low no. of B cells, therefore, less of right antobody produced to bind to the antigens. Infected person will show symptoms of disease

Question 14

Why is there a new version of the influenza vaccine developed each year?

Answer 14

1. Due to antigenic variability: The antigens on surface of virus change regularly. This is due to change in genes in the virus - new strains of virus formed
2. Therefore, memory cells produced by the vaccine for the previous strain of the virus, will not recognise the antigens on surface of new strain
   ]3. The strains are immulogically distinct

Question 15

Ethical issues surrounding vaccines

Answer 15

1. Vaccines are tested on animals before humans. Some vaccines require animal based substances to be produced.
2. Vaccines being tested on humans is risky. Volunteers are at risk of contracting disease. They may believe that they are fully protected
3. Some people may not want to take the vaccine due to potential side effects. However, they are still protected due to herd immunity. This can be seen as unfair
4. If there is an epidemic of a new disease, rush to get vaccine. Difficult decisions will need to be made regarding who to give the vaccine to first

Question 16

Ethical issues surrounding monoclonal antibody therapy

Answer 16

1. Animal rights issues

2. Animals are used to produce the cells from which monoclonal antibodies are produced from

Question 17

HIV

Answer 17

Human immunodeficiency virus

Question 18

AIDS

Answer 18

Aquired Immune Deficiency Syndrome

1. When no. of helper T cells is very low, person develops AIDS
2. HIV infects and eventually kills helper T cells
3. By using them as host cells when replicarting
4. Helper T cells release chemical signals which activate B cells, phagocytes, cytotoxic T cells
5. So, when no. of helper T cells low, the immune system cannot produce an effective response
6. AIDS causes the immune system to detoriate and fail. Therefore, someone who has AIDS is more vulnerable to other infections. For example, pneumonia.

Question 19

HIV structure

Answer 19

Core of genetic material - RNA
Capsid - protein coat surronding core of genetic materrial
Envolope - extra outer layer made from membrane “stolen” from cell membrane of previous host cell
Attatchment Proteins: Help HIV attach to host helper T cell

Question 20

HIV replication

Answer 20

HIV can only replicate inside helper T cells of host organism (organism it has infected)
It uses ribosomes, enzymes + other resources of helper T cells as it does not have these resources itself

Question 21

HIV replication process

Answer 21

1. HIV attachment proteins bind to complementary receptor proteins on host helper T cell
2. HIV releases capsid into host helper T cell. Capsid uncoats and releases its genetic material (RNA) and reverse transcriptase into cytoplasm of host helper T cell
3. Reverse transcriptase makes a complementary DNA strand from viral RNA template
4. A new double stranded DNA molecule is formed and this is inserted into human DNA
5. The host helper T cell now uses its resources, ribosomes and enzymes to make viral proteins following infro from viral DNA inserted into human DNA
6. Viral proteins are assembled into a new virus and the new viruses bud from cell to cell infecting more helper T cells

Question 22

Initial Infection Period

Answer 22

1. HIV replicates rapidly

2. Person usually experiences severe flu like symptoms

Question 23

Latency Period

Answer 23

1. Rate of HIV replication drops to a much lower level
2. Latency period usually lasts few years
3. Person does not experience any symptoms

Question 24

Initial symptoms of AIDS

Answer 24

1. infections of mucus membranes including ears, nose, genitals + recurring respiratory infections

Question 25

Symptoms as AIDS develops

Answer 25

1. As aid develops, fewer helper T cells | 2. Patient more vulnerable to serious infections including chronic diahorea and tuberculosis

Question 26

Final Symptoms of AIDS

Answer 26

1. No. of helper T cells very low | 2. Patient more vulnerable to a range of serious infections including toxoplasmosis of brain

Question 27

Facors affecting the length of time people survive with AIDS:

Answer 27

1. Age 2. Access to good healthcare 3. Existing infections 4. Strain of HIV person is infected with

Question 28

Antibiotics and Viruses

Answer 28

1. Antibiotics do not work against viruses 2. Antibiotics are designed to kill bacteria by inteferring with their metabolic reactions by targeting their ribosomes + enzymes which are used in these reactions 3. Bacteria ribosomes + enzymes are different to human ribosomes + enzymes. Antibiotics target bacteria ribosomes + enzymes so that they do not damage human ones 4. Viruses do not have their own ribosomes + enzymes and human viruses use the ribosomes + enzymes of human host cell. 5. Antibiotics do not target human ribosomes + enzymes therefore, cannot interfere with metabolic reactions of virus therefore, cannot kill virus

Question 29

Anti-Viral drugs

Answer 29

1. Designed to target virus specific enzymes without affecting host cell. Enzymes which are only used by the viruses. E.g. reverse transciptase (needed fot viral replication).

Question 30

Cure for HIV

Answer 30

1. Currently no cure / no vaccine 2. Anti-viral drugs. Slow down progression of HIV / AIDS 3. Best way ro control HIV is by preventing spread

Question 31

How is HIV spread?

Answer 31

1. Unprotected sexual intercourse 2. Infected bodily fluids (blood from sharing contaminatd needles) 3. HIV from mother to foetus