Cells and the immune system

Question 1

What molecules generate an immune response when detected by the body?

Answer 1

Antigens

Question 2

Where do antigens found and how are they used?

Answer 2

-Found on the surface of the cells
-Used by the immune system to identify pathogens, abnormal body cells and toxins

Question 3

What are the 4 stages of the immune response?

Answer 3

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

Explain the first stage of the immune response and how it works-

Answer 4

-Phagocytes engulf pathogens
-A phagocyte is a type of white blood cell that carries out phagocytosis (engulfment of pathogens)
-they are found in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body.
How it works-
1)A phagocyte recognises the foreign antigens on a pathogen
2)Cytoplasm of the phagocyte moves around the pathogen, engulfing it
3)Pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte
4)A lysosome (contains lysozymes) fuses with the phagocytic vacuole, Lysozymes break down the pathogen.
5)The phagocyte then presents the pathogens antigens- sticks the antigens on its surface to activate other immune system cells

Question 5

Explain the second stage of the immune system

Answer 5

-Phagocytes activate T-cells
-T-cell is another type of white blood cell
-It has receptor proteins on its surface that bind to complementary antigens presented by phagocytes. This activates the T-cell
-Different types of Tcells respond in different ways.
-Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells, which kill abnormal and foreign cells.
-Helper T-cells also activate the B-cells, which secrete antibodies

Question 6

Which cells secrete antibodies?

Answer 6

B-cells

Question 7

Explain the third stage of the immune system and how it happens-

Answer 7

-T-cells activate B-cells, which divide into plasma cells
-B-cells ( B-lymphocytes) are type of white blood cell that are covered with antibodies
-Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens
1)When the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it
2)this, Together with substances released from helper T-cells, activates the B-cell. This process called clonal selection
3)The activated B-cell divides into plasma cells

Question 8

What are antibodies?

Answer 8

Proteins that bind antigens to form an antigen-antibody complex

Question 9

Explain the forth (last) stage of the immune system-

Answer 9

-Plasma cells make more antibodies to a specific antigen
-Plasma cells are identical to the B-cells. They secrete lots of antibodies specific to the antigen. These are called monoclonal antibodies. They bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes.
-An antibody has two binding sites, so can bind to two pathogens at the same time. Means that pathogens become clumped together- called agglutination.
-Phagocytes then bind to the antibodies and phagocytose many pathogens at once- destruction of pathogens carrying the antigen in the body

Question 10

The specificity of an antibody depends on its ……. which form the antigen binding sites

Answer 10

-Variable regions

Question 11

What includes the cellular immune response?

Answer 11

-The T-cells and other immune system cells that they interact with (phagocytes) form the cellular response

Question 12

What includes the humoral immune response?

Answer 12

-B-cells, clonal selection and the production of monoclonal antibodies form the humoral immune system

Question 13

How does primary immune response work?

Answer 13

-when an antigen enters the body for the first time it activates the immune system- primary response
-Primary response is slow because there arent many B-cells that can make the antibody needed to bind to it.
-Eventually body produces enough of the right antibody to overcome the infection, meanwhile the infected person will show symptoms of the disease
-After being exposed to an antigen, both T-and B-cells produce memory cells- remain in the body for a long time
-Memory T-cells remember the specific antigen and will recognise it a second time round. Memory B-cells record the specific antibodies needed to bind the antigen
-Person is now immune- immune system has the ability to respond quickly to a second infection

Question 14

How does secondary immune system response work?

Answer 14

-If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response- the secondary response
-Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells that produce the right antibody ti the antigen. Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen
-Gets rid of the pathogen before showing any symptom

Question 15

How do vaccines work?

Answer 15

-Contain antigens that cause your body to produce memory cells against a particular pathogen without the pathogen causing a disease
-Can become immune without getting any symptoms

Question 16

What is herd immunity?

Answer 16

-Vaccines protect individuals that have them and because they reduce the occurrence of the disease, those not vaccinated are also less likely to catch the disease

Question 17

Disadvantage of taking a vaccine orally.

Answer 17

-It could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood

Question 18

What is antigenic variation

Answer 18

-Different antigens are formed due to changes in the genes of a pathogen
-When you are infected the second time, memory cells produced from the first infection will not recognise the different antigens, so the immune system has to start from the scratch and carry out a primary response against the new antigens
-HIV and influenza virus show antigenic variation

Question 19

How antigenic variation affects the production of vaccines?

Answer 19

-Influenza vaccine changes every year- antigens on the surface of the influenza virus change regularly, forming new strains of the virus
-Memory cells produced from vaccination with one strain of influenza will not recognise other strains with different antigens. -strains are immunologically distinct

Question 20

What is active immunity?

Answer 20

-Immune system makes its own antibodies after being stimulated by an antigen
1)Natural- after catching a disease
2)Artificial- after vaccination containing a harmless dose of antigen

Question 21

What is passive immunity?

Answer 21

-Being given antibodies made by a different organism
1)Natural- baby becomes immune due to the antibodies it receives from its mother through placenta and in breast milk
2)Artificial- being injected antibodies from someone else

Question 22

Differences of active and passive immunity?

Answer 22

Active-
-requires exposure to antigen
-Takes a while to develop
-Memory cells are produced
-protection is long term because the antibody is produced in response to complementary antigen being present in the body
Passive-
Protection is short term because the antibodies given are broken down

Question 23

What are monoclonal antibodies?

Answer 23

-Antibodies produced from a single group of genetically identical B-cells (plasma cells)- identical in structure

Question 24

How does targeting drugs to a particular cell type work- cancer cells

Answer 24

1)Different cells in the body have different surface antigens
2)Cancer cells have antigens called tumour markers that are not found on the normal body cells
3)Monoclonal antibodies can be made that will bind to the tumour markers
4)Can attach anti-cancer drugs to the antibodies
5)When the antibodies come into contact with the cancer cells they will bind to the tumour markers
6)Drug will only accumulate where there are cancer cells
7)So the side effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells

Question 25

How does targeting a particular substance for medical diagnosis work- pregnancy testing-

Answer 25

1)Application area contains antibodies for hCG
bound to a coloured bead (blue)
2)When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex
3)Urine moves up the stick to the test strip, carrying any beads with it
4)Test strip contains antibodies to hCG that are stuck in place (immobilised)
5)if hCG present the test strip turns blue because immobilised antibody binds to any hCG

Question 26

What does pregnancy test detect

Answer 26

Detect the hormone human chorionic gonadotropin (hCG) thats found in the urine of pregnant women

Question 27

Describe how ELISA test works

Answer 27

1)ELISA allows you to see if a patient has any antigen to a certain antibody
2)Used to test for pathogenic infections, for allergies and for about anything you can make an antibody for
3)In ELISA test, an antibody is used which has an enzyme attached to it. This enzyme can react with a substrate to produce a coloured product. -solution changes colour
4)If there is a colour change, it demonstrates that antigen or antibody of interest is present in the sample being tested. In some types of ELISA the quantity of this antigen/antibody can be worked out from the intensity of the colour change
5)Several types of ELISA, Direct ELISA uses a single antibody that is complementary to the antigen you’re testing for. Indirect ELISA uses two different antibodies

Question 28

How does using ELISA as a HIV test work?

Answer 28

Indirect ELISA used to see if a patient possesses antibodies to the HIV virus
1)HIV antigen is bound to the bottom of a well in a well plate
2)A sample of the patient’s blood plasma is added to the well. If there are any HIV-specific antibodies these will bind to the HIV antigen stuck to the bottom of the well. The well is then washed out to remove any unbounded antibodies
3)A secondary antibody, that has a specific enzyme attached to it is added to the well. the secondary antibody can bind to the HIV-specific antibody. The well is washed out to remove any unbound secondary antibody
4)A solution containing a substrate is added to the well which is able to react with the enzyme attached to the secondary antibody and produce a coloured product
5)Colour change indicates there is HIV-specific antibodies in the patient’s blood and is infected with HIV

Question 29

Ethical issues surrounding vaccines-

Answer 29

-All vaccines are tested on animals before tested on humans- animals based substances may be used to produce the vaccine
-Testing vaccines on humans can be tricky -volunteers may put themselves at unnecessary risk of contacting the disease

Question 30

Ethical issues surrounding monoclonal antibody therapy-

Answer 30

-Often involve animal right issues -animals are used to produce the cells from which monoclonal antibodies are produced, some people disagree with the use of animals

Question 31

What causes AIDS

Answer 31

HIV
-HIV infects helper T-cells which act as the host cells for the virus. Helper T-cells send chemical signals that activate phagocytes, cytotoxic T-cells and B-cells. Without enough helper T-cells, immune system is unable to mount an effective response to infections

Question 32

What is AIDS

Answer 32

Condition where the immune system deteriorates and eventually fails

Question 33

Describe the structure of HIV

Answer 33

-Core contains genetic material RNA and some proteins (enzyme reverse transcriptase which is needed for virus replication
-Capsid
-Extra outer layer called an envelope made of membrane stolen from the cell membrane of a previous host cell
- Attachment proteins that help HIV attach to the host helper T-cell

Question 34

How does HIV replicates?

Answer 34

1)Attachment protein attaches to the receptor protein on the surface of the host T-cell
2)Capsid is released into the cell, uncoats and releases RNA into the cells cytoplasm
3)Reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
4)Double stranded DNA is made and inserted into the human DNA
5)Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
6)Viral proteins are assembled into new viruses which bud from the cell and go to infect other cells