Immunity

Question 1

Define antibody.

Answer 1

A protein produced by lymphocytes in response to the presence of a specific foreign antigen.

Question 2

What is an antigen?

Answer 2

A protein that triggers an immune response by lymphocytes.

Question 3

What is antigen presentation?

Answer 3

When an antigen-presenting cell e.g. phagocyte displays foreign antigens on their own cell surface membrane.

Question 4

What is antigenic variability?

Answer 4

When an antigen randomly mutates, pathogens can form different strains and often have different antigens. This means that after being infected a second time, the memory cells created won’t recognise the antigen so antibodies will have to be made in a primary response again, and there will still be symptoms. This is common in influenza and HIV so vaccines are hard to produce.

Question 5

What are attachment proteins?

Answer 5

Proteins on the capsid essential for the virus to identify and attach to a host cell.

Question 6

What is process of the cell-mediated response?

Answer 6

1. antigen-presenting cells (either phagocytes or invaded cells that present the antigens of the pathogen on their surface) are responded to by T-cells
2. T-helper cells use their receptors, which are specific to the presented antigens, to activate the T-cells to divide by mitosis to create many clones.
3. the cloned T-cells secrete cytokines that stimulate B-cells to divide. They become memory cells which allow rapid response to the same pathogen in the future or plasma cells.
4. T-killer cells (cytotoxic cells) divide by mitosis and release perforin, which makes holes in cell membranes of foreign cells.

Question 7

What does an ELISA test stand for?

Answer 7

Enzyme-linked immunosorbent assay

Question 8

What is herd immunity?

Answer 8

The concept that says that if enough people have been vaccinated, a population can be protected from a certain disease without everyone being vaccinated. This is because the disease won’t be able to spread far enough.

Question 9

What is HIV?

Answer 9

Human immunodeficiency virus which causes AIDS.

Question 10

What is immunity?

Answer 10

The means by which the body protects itself from infection.

Question 11

What are lymphocytes?

Answer 11

Types of white blood cell responsible for the immune response.

Question 12

Define lysosome.

Answer 12

Contain enzymes called lysozymes which they release into the phagosome to hydrolyze the bacterium.

Question 13

What are memory B cells?

Answer 13

B cells that can respond to future infections by the same pathogen.

Question 14

What is a pathogen?

Answer 14

Any microorganism that causes disease.

Question 15

What is a phagosome?

Answer 15

A vesicle formed around a pathogen as it is engulfed by the phagocyte.

Question 16

What is a phagocyte?

Answer 16

Type of white blood cell that patrols the body, searching for non-self antigens so it can ingest and break down pathogens by phagocytosis.

Question 17

What is the process of phagocytosis?

Answer 17

1. pathogens are recognised as having non-self antigens due to the attachment of pathogens to the phagocyte by surface receptors.
2. the pathogen is engulfed by the phagocyte by endocytosis, forming a phagosome (vesicle around the pathogen)
3. lysosomes fuse with the phagosome to form a phagolysosome and release lysozymes to digest the pathogen by damaging their cell walls.
4. harmless products are excreted by exocytosis or used by the phagocyte

Question 18

What are plasma B cells?

Answer 18

B cells activated to divide and produce the specific antibody that fits the antigen.

Question 19

What is a retrovirus?

Answer 19

A group of viruses that can make DNA from RNA.

Question 20

What is reverse transcriptase?

Answer 20

An enzyme in HIV which enables the production of DNA from RNA.

Question 21

What is a T cell?

Answer 21

A type of white blood cell, made in the thymus that coordinates the immune response and kills infected cells.

Question 22

What are cytotoxic T cells?

Answer 22

Cells that kill abnormal cells and infected cells.

Question 23

What are T helper cells?

Answer 23

Cells that respond to a single antigen.

Question 24

What is vaccination?

Answer 24

The introduction of a dead, weakened or attenuated pathogen which stimulates the primary immune response so the body can produce memory cells, which produce complementary antibodies to a specific antigen.

Question 25

What is a virus?

Answer 25

Acellular, non-living particles that can only multiply inside living host cells.

Question 26

What are B cells?

Answer 26

Lymphocytes made in the bone marrow that secrete antibodies in response to antigens.

Question 27

What is clonal selection?

Answer 27

The method of cell proliferation of B-cells, where they divide and differentiate into plasma and memory cells.

Question 28

What is the process of the humoral response?

Answer 28

1. Antigen-presenting cells bind to a specific B-cell, which complementary surface receptors. 2. The B-cell takes in the antigen on the surface of the cell by endocytosis and presents it on it's own surface. 3. T-helper cells bind to the antigens on the surface of the B-cell, which releases cytokines in order to mature the B-cell. 4. Therefore, the B-cell differentiates and divides (by mitosis) into plasma cells, which make complementary antibodies to antigens, or memory cells, which produce plasma cells and antibodies much faster after already coming into contact with the same antigen.

Question 29

What is the difference between the primary and secondary response?

Answer 29

- primary response - there aren't many B-cells to make antibodies so it is slower - secondary response - antibodies are produced much more quickly because the memory cells in the bloodstream divide to form plasma cells in larger quantities and faster after coming into contact with the antigen again

Question 30

Describe the structure of antibodies.

Answer 30

Proteins made up of 4 polypeptide chains: 2 heavy and 2 light. Each chain has a variable region, which have a unique tertiary structure complementary to an antigen and a constant region, which allow them to bind to receptors. The chains are connected by disulphide bridges.

Question 31

What are the three ways antibodies work?

Answer 31

- Agglutination - where antibodies bind to antigens on pathogens and cause them to clump together, making them easier to be destroyed by phagocytosis - Neutralising toxins - Preventing viruses from entering host cells - antibodies bind onto the receptors on host cells so the viruses can't, meaning they can't enter.

Question 32

How is HIV spread?

Answer 32

Through infected bodily fluids via sex, sharing needles, direct blood transfer, and maternal transmission.

Question 33

How does the HIV virus replicate?

Answer 33

1. glycoprotein molecules on the virus bind to CD4 receptors on T-helper cells so the virus can fuse with the cell via endocytosis 2. the virus' capsid is released, which releases RNA and reverse transcriptase 3. reverse transcriptase makes DNA from HIV's RNA 4. HIV's DNA is inserted into the DNA of the host cell so it gets replicated when the host cell's DNA does 5. the replicated DNA is used to make proteins and HIV RNA at ribosomes 6. new viruses are assembled and leave the host cell membrane via exocytosis, hydrolysing and destroying the host cell as the new HIVs go on to infect other cells

Question 34

What are opportunistic infections?

Answer 34

Infections that occur when the body's defenses are weakened.

Question 35

What is formed when antigens and antibodies bind together?

Answer 35

An antigen-antibody complex

Question 36

What is the function of antiretroviral drugs in HIV treatment?

Answer 36

Prevent/slow the replication of the virus in the body.

Question 37

What are the initial symptoms of AIDS?

Answer 37

Minor infections of mucosal membranes and recurring respiratory infections caused by a lower than normal number of T helper cells.

Question 38

When are people with HIV classed as having AIDS?

Answer 38

When symptoms of failing immune system start to appear or their T helper cell count drops below a certain level.

Question 39

What is AIDS?

Answer 39

When the immune system deteriorates and eventually falls.

Question 40

Why should HIV testing not occur on a newborn baby?

Answer 40

Would give inaccurate results; need to wait 18 months before testing as HIV can pass from mother to baby's bloodstream.

Question 41

Give a short summary of how HIV weakens the immune system.

Answer 41

HIV invades T helper cells, preventing the activation of macrophages, B cells, and T killer cells, which weakens the immune response.

Question 42

List the main medical uses of monoclonal antibodies.

Answer 42

- To target medication to specific cell types by attaching a therapeutic drug to an antibody - Pregnancy testing - Medical diagnosis by identifying proteins or antigen presence using the ELISA test.

Question 43

What is radioimmunotherapy?

Answer 43

A method that allows doctors to target radiation to specific sites by linking radioactive atoms to monoclonal antibodies that seek out cancer cells. This means radiation is concentrated at tumour cells.

Question 44

How do pregnancy tests work?

Answer 44

1. Antibodies complementary to hCG protein are bound to a coloured bead 2. hCG in urine binds to antibodies 3. urine moves up the strip carrying coloured beads 4. immobilised antibodies bind to the hCG and create the first blue line (control line) 5. immoblised antibodies bind to coloured beads and create the second blue line if hCG is present

Question 45

What is the difference between a direct and an indirect ELISA test?

Answer 45

Direct involves one type of antibody applied to the sample while indirect involves many antibodies present, which makes it more sensitive

Question 46

How are monoclonal antibodies produced?

Answer 46

Antibodies are produced by plasma cells, which are all clones of one B-cell.

Question 47

Describe the steps of an ELISA test.

Answer 47

1. an antigen is attached to the bottom of a well in a test dish. 2. a sample of blood plasma is added to the well and if the specific antibodies are present, they bind to this antigen. 3. the well is washed, which removed unattached antibodies 4. a second antibody with an enzyme attached to it is added to the well, which will bind specifically to the present antibody. 5. the well is washed again 6. a solution is added which changes colour in the presence of the enzyme, and if the colour changes, the antibody is present.

Question 48

What are self and non-self cells?

Answer 48

Self cells are ones that the body recognises its antigens as its own. Non-self cells are cells that stimulate an immune response as they have antigens that are foreign to the body.

Question 49

What are all the different types of immunity?

Answer 49

- active natural immunity - antibodies that are made after being exposed to an antigen from catching a disease. It provides long term protection due to the production of memory cells. - active artificial immunity - antibodies that are made after being exposed to an antigen via vaccination. It provides long term protection due to the production of memory cells. - passive natural immunity - antibodies are given to a baby from their mother through the placenta or breast milk. It provides short term protection as there are no memory cells. - passive artificial immunity - antibodies are injected in the form of an antiserum/antivenom. It provides short term protection as there are no memory cells.

Question 50

What are the two types of phagocytes?

Answer 50

- neutrophils - engulf and digest pathogens - macrophages - punch holes into pathogens or stick proteins to them to signal for them to be engulfed by the neutrophils

Question 51

How are pathogens prepared for vaccinations?

Answer 51

- they can be killed but the antigens are left unaffected. - they are attenuated (weakened) but the antigens are left unaffected. - their antigens can be purified (removed from the pathogen) - inactivated toxins can be used (toxoids)

Question 52

What are ethical issues with vaccinations?

Answer 52

- they are all tested on animals first - humans in clinical trials may put themselves at risk - there are side effects which some people are scared of, so they refuse to have them and are protected by herd immunity - there are difficult decisions to make about who receives the first vaccines

Question 53

Why don't vaccines full eliminate diseases?

Answer 53

- some people suffer from immunodeficiency so don't become immune - people get infected before enough antibodies are generated by the vaccine - variation of pathogens in antigenic variability - there are many different strains of diseases so not all of them can be vaccinated against - morals, religion and ethics stop everyone from being vaccinated

Question 54

What are monoclonal antibodies?

Answer 54

They are antibodies produced by plasma cells, which are clones of one B-cell. This means they are specific to only one type of antigen.