10 Disease and Immunity

Question 1

2 parts of the immune system

Answer 1

• non specific
• specific

Question 2

What is an antigen?

Answer 2

A foreign/non-self protein (or glycoprotein) which stimulates an immune response / production of antibodies.

Can be on the surface of a cell or freely circulating in the blood

Question 3

Antigens allow the immune system to identify:

Answer 3

· Pathogens (e.g. HIV)

· Cells from other organisms of the same species (e.g. from transplants)

· Abnormal body cells (e.g. cancer cells)

· Toxins

Question 4

Lysosomes contain hydrolytic enzymes. What is the function of these?

Answer 4

Powerful, digestive enzymes which hydrolyse cell components

Question 5

phagocytosis:

Answer 5

· Phagocyte recognises and binds to an antigen on the pathogen

· Phagocyte engulfs pathogen

· Pathogen is enclosed in a vesicle

· Lysosomes fuse with the vesicle

· Lysosomes contain hydrolytic enzymes (lysozymes) that damage bacterial cell walls

· These digest the pathogen, by hydrolysis of its molecules.

Question 6

Antigen presenting cells can be:

Answer 6

· Cells that are infected by virus

· A phagocyte which has just engulfed and hydrolysed a pathogen

· An abnormal cell such as a cell which has become cancerous.

Question 7

role of T cells in cellular immunity.

Answer 7

· A specific helper T cell binds to an antigen on an antigen presenting cell (the helper T cell has receptors which have a complementary shape to the antigens)

· This activates the TH cell to divide rapidly by mitosis

· To produce more TH cells and memory cells

· TH cells release cytokines which stimulate specific cytotoxic T cells to divide by mitosis.

· Cytotoxic T cells release perforin which destroys virus infected cells

Question 8

b cell in humoral response

Answer 8

· Receptors on a specific B cell bind to an antigen

· The B cell is activated by cytokines released by a specific TH cell

· The B cell divides by mitosis to produce cells which differentiate into plasma cells and memory B cells (clonal selection)

· Plasma cells produce and release antibodies

· Memory cells remain in the body and divide to produce plasma cells which release more antibodies more rapidly following second exposure to the same antigen.

Question 9

primary immune response

Answer 9

initial response following the body’s first exposure to an antigen. It takes a few days for the body to activate a specific B cell, which then divides by mitosis to produce plasma cells, which then release antibodies.

During this time, disease symptoms develop.

Question 10

secondary immune response

Answer 10

much faster and occurs when the body is exposed to the same antigen again. Memory cells divide rapidly to produce plasma cells.

These plasma cells release more antibodies, more rapidly.

The pathogen is usually destroyed before symptoms develop.

Question 11

Antibodies

Answer 11

· Are proteins synthesised by plasma B cells.

· They have a specific tertiary structure, complementary to a particular antigen.

· They bind to specific antigens forming an antigen-antibody complex.

· They neutralise pathogens by clumping them together – this is called agglutination

Question 12

Monoclonal Antibodies

Answer 12

They all have the same tertiary structure and will therefore bind to one specific antigen.

· The mouse produces specific plasma cells by the normal immune response.

· The specific plasma cells are extracted and purified.

· They are then fused with myeloma cells to produce hybridoma cells

· These cells produce and release monoclonal antibodies specific for the antigen.

Question 13

Uses of monoclonal antibodies

Answer 13

Medical diagnosis To screen patients for specific infections

Targeted drug treatments Cancer drugs can be attached to monoclonal antibodies specific for antigens on cancer cells

Drug testing Used to identify a specific drug in a urine or blood sample

Pregnancy testing Used to detect a specific pregnancy hormone

COVID testing Used to detect antigens on coronavirus

Question 14

The ELISA Test

Answer 14

This uses monoclonal antibodies to detect the presence and amount of a specific protein in a sample

• Container coated with monoclonal antibodies, specific for the antigen being screened for
• Sample to be tested (e.g. blood/ urine) is added to the container. If the specific antigen is present it will bind to the antibodies.
• A second monoclonal antibody is added. This binds to another site on the antigens. The second Ab has an enzyme attached. The sample is then washed.
• The substrate for the enzyme is then added. The substrate is hydrolysed by the enzyme on the second antibody. This produces a colour change, indicating a positive result (ie the antigen was present in the original sample)

Question 15

Passive Immunity

Answer 15

Antibodies acquired from an outside
source

Immunity is immediate

Effect is short lived as the antibodies
will be broken down and not replaced

Example – foetus receives antibodies
from the mother across the placenta

Question 16

Active Immunity

Answer 16

Immune system is stimulated to produce antibodies

Immunity is not immediate – memory cells need to be produced

Effect is long lasting because memory cells are produced

Can be acquired naturally by becoming infected with a pathogen Or Can be acquired artificially by vaccination

Question 17

Vaccination

Answer 17

creating passive immune

· Vaccine contains specific antigens

· The antigen is displayed on an antigen presenting cell

· Specific helper T cell binds to the antigen

· Cytokines released by TH cells activate a specific B cell

· B cell divides by mitosis to produce plasma cells and memory cells

· On second exposure to the same antigen, memory cells divide to produce plasma cells so more antibodies are released, more rapidly

· Pathogen is destroyed before symptoms develop.

Question 18

Why vaccination does not eliminate a disease

Answer 18

· Some individuals may have a defective immune system

· The pathogen may mutate quickly and change its antigens

· There may be many varieties of the same organism, each with a different antigen.

Question 19

against for vaccinations

Answer 19

animal testing
side affects

Question 20

hiv replication

Answer 20

· Attachment proteins on the virus bind to specific complementary receptors on the surface of helper T cells.

· The capsid, containing the genetic material (RNA) and an enzyme called reverse transcriptase, is released into the TH cell.

· Inside the cell the RNA and enzyme are released

· Reverse transcriptase is used to make a complementary strand of DNA using the viral RNA as a template.

· From this, double-stranded DNA is made

· Double stranded DNA is incorporated into the T cell’s own DNA.

· The viral DNA is then used to make new viral proteins which are assembled into new viruses inside the cell.

· The new HIV viruses are released from the T helper cell and infect other TH cells.

Question 21

Development of AIDS

Answer 21

· Replication and release of HIV from the T helper cells leads to the destruction of the T helper cells and the number of T helper cells decrease.

· Fewer T helper cells means that fewer B cells, cytotoxic T cells and phagocytes become activated.

· Therefore the body’s immune response is reduced: fewer plasma cells and antibodies will be made, and cytotoxic T cells will not be able to destroy infected cells.

· The individual becomes more susceptible to other infections and cancers. The symptoms are as a result of these other infections, rather than HIV directly.

Question 22

Testing for HIV

Answer 22

The testing container is coated with HIV antigens. The blood sample to be tested is added (the plasma is used)

If the blood sample contains HIV antibodies, these will bind to the antigen forming an antigen – antibody complex

A second antibody, with an enzyme attached, is added. This binds to the HIV antibody. The container is washed to remove unbound 2nd antibody

The substrate to this enzyme is then added. An E-S complex is formed, causing a colour change. This indicates a positive result.