Cell recognition and the immune system

Question 1

Non-specific response meaning + examples

Answer 1

The response is immediate and the same for all pathogens

eg physical barrier or phagocytosis

Question 2

Specific response meaning + examples

Answer 2

The response is slower and specific to each pathogen

eg cell-mediated response (T cell) or humoral response (B cell)

Question 3

Antigen WHAT IS IT ???????

Answer 3

Molecules of which that, when recognised as non-self/foreign by the immune system, can stimulate an immune response and lead to the production of antibodies.

Often proteins on the surface of cells. Proteins have a specific tertiary structure/shape, allowing different proteins to act as specific antigens.

Question 4

What do antigens allow the immune system to identify, since they are specific?

Answer 4

Pathogens eg viruses, fungi and bacteria

Cells from other organisms of the same species eg organ transplants or blood transfusions

Abnormal body cells eg cancerous cells/tumours

Toxins released from bacteria

Question 5

Lymphocytes what are they and stuff

Answer 5

White blood cells that fight infection

If they have antigens (on their cell surface membrane) that are complementary to the body’s own (self) cells, they are suppressed or die

Question 6

Where are lymphocytes produced in an adult?

Answer 6

In an adult, lymphocytes are produced in the bone marrow.

Any that show an an immune response to self antigens undergo a programmed death (apoptosis) before they can differentiate into mature lymphocytes.

Question 7

Where are lymphocytes produced in a foetus?

Answer 7

Due to the protection of the placenta, infection is rare. Therefore, lymphocytes will only come into contact with self-cells.

Some of the lymphocytes will have receptors that match exactly those of the self cells. These will die or be suppressed.

Question 8

Phagocyte what is it and examples

Answer 8

A white blood cell that can carry out phagocytosis

eg the macrophage and the neutrophil

Question 9

Process of phagocytosis (non-specific immune response)

Answer 9

Phagocyte is attracted to pathogen due to the chemical products it produces

Phagocyte eg macrophage recognises foreign antigens on the pathogen and binds to the antigen.

Phagocyte engulfs pathogen by surrounding it with its cell surface membrane/cytoplasm

Pathogen contained in a vesicle called a phagosome in the cytoplasm of the phagocyte.

Lysosome fuses with the phagosome and releases lysozymes (hydrolytic enzymes) into the phagosome

These hydrolyse/digest the pathogen. Digestible materials are absorbed into the cytoplasm of the phagocyte, indigestible materials are excreted.

Phagocyte becomes antigen-presenting (displays foreign antigens on their surface) and stimulates specific immune response.

Question 10

T-lymphocytes where do they mature and what are they associated with

Answer 10

T-lymphocytes mature in the thymus gland

They are associated with cell-mediated immunity; immunity involving body cells

Question 11

T-lymphocytes what do they respond to

Answer 11

T-lymphocytes only respond to antigens that are presented on a body cell (rather than to antigens within the body fluids)

This is called cell-mediated immunity

Receptors on each T-cell respond to a single antigen

Question 12

The cellular response (T-lymphocytes and foreign antigens eg infected cells, cells of the same species)

Answer 12

T-lymphocyte recognises antigen-presenting cells after phagocytosis (foreign antigens)

Specific T-helper cell with receptor complimentary to specific antigen binds to it, triggers activation and dividing rapidly by mitosis to form T-cell clones

Question 13

T-cell clones what do they do

Answer 13

Stimulates B-cells for the humoral response

Stimulates cytotoxic T-cells to kill infected cells by producing perforin

Stimulates phagocytes to engulf pathogens by phagocytosis

Develops into memory cells that enable a rapid response to future infections by the same pathogen.

The action of T-cells is most effective against viruses because they replicate inside cells

Question 14

Cytotoxin T-cells

Answer 14

Cytotoxin T-cells kill abnormal cells by producing a protein called perforin in the cell surface membrane

Cell membrane becomes freely permeable to all substances and the cell dies as a result

Question 15

The humoral response (the response of B lymphocytes to a foreign antigen e.g. in blood/tissues)

Answer 15

Clonal selection:

• Specific B cell binds to antigen presenting cell and is stimulated by helper T cells
• Divides rapidly by mitosis to form clones (clonal expansion)

Some become B plasma cells for the primary immune response – secrete large amounts of monoclonal antibody into blood

Some become B memory cells for the secondary immune response

Question 16

Antigen variability is often an explanation for why…

Answer 16

New vaccines against a disease need to be developed more frequently e.g. influenza

Vaccines against a disease may be hard to develop or can’t be developed in the first place e.g. HIV

May experience a disease more than once e.g. common cold

Question 17

Primary response – antigen enters body for the first time (role of plasma cells)

Answer 17

Produces antibodies slower and at a lower concentration because:

Not many B cells available that can make the required antibody

T helpers need to activate B plasma cells to make the antibodies (takes time)

So infected individual will express symptoms

Question 18

Secondary response – same antigen enters body again (role of memory cells)

Answer 18

Produces antibodies faster and at a higher concentration because:

B and T memory cells present

B memory cells undergo mitosis quicker and quicker clonal selection

Question 19

Explain the effect of antigen variability on disease prevention (vaccines)

Answer 19

Change in antigen shape (due to a genetic mutation)

Existing antibodies with a specific shape unable to bind to changed antigens and form antigen-antibody complex

Immune system i.e. memory cells won’t recognise different antigens (strain)

Question 20

Antibodies

Answer 20

Quaternary structured protein (immunoglobin)

Secreted by B-lymphocytes (eg plasma cells) and produced in response to a specific antigen

Binds specifically to antigens forming an antigen-antibody complex

Question 21

Antibodies structure related to function

Answer 21

Primary structure of protein: sequence of amino acids in a polypeptide chain.

Determines the folds in the secondary structure as R groups interact

Determines the specific shape of the tertiary structure and position of hydrogen, ionic and disulfide bonds

Quaternary structure is comprised of 4 polypeptide chains (tertiary structured) held together by hydrogen, ionic and disulfide bonds

Enables the specific shaped variable region (binding site) to form which is a complementary shape to a specific antigen

Enables antigen-antibody complex to form

Question 22

Explain the effect of antigen variability on disease

Answer 22

Change in antigen shape (due to a genetic mutation)

Not recognised by B memory cell: no plasma cells/antibodies

Not immune

Must re-undergo primary immune response: slowly releases lower concentration of antibodies

Disease symptoms are felt

Question 23

How do antibodies work to destroy pathogens e.g. bacterial cells?

Answer 23

Binds to two pathogens at a time (at variable region/binding site) forming an antigen-antibody complex

Enables antibodies to clump the pathogens together - agglutination

Phagocytes bind to the antibodies and phagocytose many pathogens at once

Question 24

Vaccination

Answer 24

Injection of antigens

From attenuated (dead or weakened) pathogens

Stimulates the formation of memory cells

Question 25

The use of vaccines to provide protection for individuals against disease

Answer 25

Normal immune response but the important part is that memory cells are produced

On reinfection / secondary exposure to the same antigen, the secondary response therefore produces antibodies faster and at a higher concentration

Leading to the destruction of a pathogen/antigen (e.g. agglutination and phagocytosis) before it can cause harm/symptoms = immunity

Question 26

The use of vaccines to provide protection for populations against disease (herd immunity)

Answer 26

Large proportion but not 100% of population vaccinated against a disease – herd immunity

Makes it more difficult for the pathogen to spread through the population

More people are immune so fewer people in the population carry the pathogen

Fewer susceptible so less likely that a non-vaccinated individual will come into contact with an infected person and pass on the disease

Question 27

Active immunity

Answer 27

Initial exposure to antigen eg vaccine or primary infection

Memory cells involved

Antibody is produced and secreted by (B) plasma cells

Slow, takes time to develop

Long term immunity: antibody can be produced in response to a specific antigen again

Question 28

Passive immunity

Answer 28

No exposure to antigen

No memory cells involved

Antibody introduced into body from another organism e.g. breast milk/across placenta from mother

Fast acting

Short term immunity (antibody broken down)

Question 29

Ethical issues associated with the use of vaccines

Answer 29

Tested on animals before use on humans: animals have a central nervous system so feel pain (some animal based substances are also used to produce vaccines)

Tested on humans: volunteers may put themselves at unnecessary risk of contracting the disease because they think they’re fully protected e.g. HIV vaccine so have unprotected sex, vaccine might not work

Can have side effects

Expensive – less money spent on research and treatments of other diseases

Question 30

What are monoclonal antibodies

Answer 30

An antibody produced from a single group of genetically identical (clones) B cells / plasma cells

Identical structure

Bind to specific complimentary antigen

Have a binding site / variable region with a specific tertiary structure / shape

Only one complementary antigen will fit

Question 31

Why are monoclonal antibodies useful in medicine

Answer 31

Only bind to specific target molecules / antigens:

Antibodies have a specific tertiary structure (binding site / variable region) that’s complementary to a specific antigen which can bind/fit to the antibody

Question 32

Monoclonal antibodies: targeting medication to specific cell types by attaching a therapeutic drug to an antibody eg cancer cell

Answer 32

Monoclonal antibodies made to be complementary to antigens specific to cancer cells: cancer cells are abnormal body cells with different antigens (tumour markers)

Anti-cancer drug attached to antibody

Antibody binds / attaches to cancer cells (forming antigen-antibody complex)

Delivers attached anti-cancer drug directly to specific cancer cells so drug accumulates: fewer side effects e.g. fewer normal body cells killed

Question 33

Monoclonal antibodies: medical diagnosis eg pregnancy test

Answer 33

Pregnant women have the hormone hCG in their urine

The application area contains antibodies for hCG bound to a blue-coloured bead.

When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.

2 other test strips:
- Middle contains antibodies complementary to hCG-antibody complex
- End (control) contains antibodies complementary to antibody without hCG attached

If pregnant, binds to antibodies in the middle position

If not pregnant, binds to antibodies at the end position (control)

Question 34

Ethical issues associated with the use of monoclonal antibodies

Answer 34

Animals are involved in the production of monoclonal antibodies i.e. by producing cancer in mice who have a CNS so feel pain, and it is unfair to give them a disease

Although effective treatment for cancer and diabetes, it has caused deaths when used in treatment of Multiple Sclerosis

Patients need to be informed of risk and benefits before treatment so they can make informed decisions

Question 35

Structure of HIV

Answer 35

Envelope, capsid, RNA, reverse transcriptase, attachment proteins

Question 36

The replication of HIV in helper T cells

Answer 36

The attachment protein attaches to a receptor molecule on the cell membrane of a host helper T-cell

The capsid is released into the cell where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm

Inside the cell, reverse transcriptase is used to make a complementary strand of viral DNA from the viral RNA template.

From this, double stranded viral DNA is made and inserted into the human DNA.

Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA

The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells

Question 37

How HIV causes the symptoms of AIDS – acquired immune deficiency syndrome

Answer 37

Infects and kills helper T cells (host cell) as it multiplies rapidly

T helper cells then can’t stimulate cytotoxic T cells, B cells and phagocytes, leads to an impaired immune response

eg B plasma cells can’t secrete antibodies for agglutination and destruction of pathogens by phagocytosis

Immune system deteriorates
- More susceptible to infections
- Diseases that wouldn’t cause serious problems in a healthy immune system are deadly (opportunistic infections) e.g. pneumonia

Question 38

Why antibiotics are ineffective against viruses

Answer 38

Antibiotics can’t enter human calls – but viruses exists in its host cell (they are acellular)

Viruses don’t have own metabolic reactions e.g. ribosomes (use of the host cell’s) which antibiotics target

If we did use them… act as a selection pressure + gene mutation = resistant strain of bacteria via natural selection, therefore reducing effectiveness of antibiotics and waste money

Question 39

The use of antibodies in the ELISA test

Answer 39

Can determine if a patient has antibodies to a certain antigen or antigens to a certain antibody.

Used to diagnose diseases or allergies (eg HIV/lactose intolerance)

Question 40

Why do we use controls when performing the ELISA test

Answer 40

Control enables a comparison with the test to show that only the enzyme is causing the colour change.

Also to show that washing is effective and all unbound antibodies are washed away

Question 41

Explain why the secondary and detection antibody must be washed away (ELISA)

Answer 41

Enzyme attached to antibody reacts with substrate turning the solution a different colour; indicates a positive result.

If it is not washed out, enzymes will react with the substrate and give a positive result even if no antigens are present (false positive)

Question 42

Using an (indirect) ELISA as a HIV test

Answer 42

HIV antigen is bound to the bottom of a well in a well plate.

A sample of the patient’s blood plasma, which might contain several different antibodies, 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 unbound antibodies.

A secondary antibody, that has a specific enzyme attached to it, is added to the well. This secondary antibody can bind to the HIV-specific antibody. The well is washed out again to remove any unbound secondary antibody. If there is no primary antibody in the sample, all of the secondary antibody will be washed away.

A solution is then added to the well. This solution contains a substrate which is able to react with the enzyme attached to the secondary antibody and produce a coloured product. If the solution changes colour, it indicates that the patient has HIV-specific antibodies in their blood and is infected with HIV.