2-4 Cell recognition and the immune system

Question 1

What are the physical barriers to infection?

Answer 1

• Skin
• Stomach acid
• Gut and skin flora

Question 2

What are the non-specific immune responses?

Answer 2

• Inflammation
• Lysozyme action
• Interferon
• Phagocytosis

Question 3

What is phagocytosis?

Answer 3

• Process in which white blood cells engulf pathogens thus destroying them.
• They do this by fusing to a pathogen and enclose them in a phagocytic vacuole with a lysosome.
• After the pathogen is engulfed and destroyed, its chemical markers called antigens are then presented on the surface of the phagocyte.
• The phagocyte then becomes an antigen presenting cell which activates an immune response if the antigen is recognised as foreign.

Question 4

What is the specific immune response?

Answer 4

• Antigen specific and produces responses specific to one type of pathogen only.
• This type of immune response relies on lymphocytes produced in the bone marrow.

Question 5

What are B-cells?

Answer 5

• Mature in the bone marrow.
• Used in the humoral response.

Question 6

What are T-cells?

Answer 6

• Move from the bone marrow to the thymus gland where they mature and are involved in cell mediated response.

Question 7

What are memory cells?

Answer 7

• Cells which replicate themselves when exposed to an invading pathogen and remain in the lymph nodes for decades searching for the same antigen.
• This results in a much faster immune response should the individual be infected by the same pathogen again.

Question 8

What are plasma cells?

Answer 8

• Antibody producing cells

Question 9

What are T helper cells?

Answer 9

• Stimulate B cells and T killer cells to divide.

Question 10

What are T killer cells?

Answer 10

• Destroy pathogen infected cells.

Question 11

What are the stages of the cell mediated response?

Answer 11

1. Foreign microbe with antigens
2. Macrophage ingests antigens
3. Processes them
4. And presents them to T-cell
5. T-cell produces clones
6. Killer T cell destroys antigens.
7. Helper T cell stimulates T and B cells.
8. Suppressor T cell inhibits T and B cells.
9. Memory T cell remembers antigen for future encounters.

Question 12

What are the stages of the humoral response?

Answer 12

• A B-Cell is triggered when it encounters its matching antigen.
• The B-Cell engulfs the antigen and digests it.
• Then it displays antigen fragments bound to its unique MHC molecules.
• The combination of antigen and MHC attracts the help of a mature matching T cell.
• Cytokines secreted by the T cell help the B cell to multiply and mature into antibody producing plasma cells.
• Released into the blood, antibodies lock onto matching antigens.
• The antigen-antibody complexes are then cleared by the complement cascade or by the liver and spleen.

Question 13

Describe the structure of antibodies?

Answer 13

• Made of four polypeptide chains forming a Y shaped structure.
• These are complementary to only a single antigen.
• They work by forming an antigen-antibody complex which serve as markers for phagocytes to destroy attached cells.
• Due to antibodies having two binding sites they can also clump cells together making them easier for phagocytes to find.
• This process is called agglutination.

Question 14

What is active immunity?

Answer 14

• Results from the production of antibodies by the immune system in response to the presence of an antigen.

Question 15

What is passive immunity?

Answer 15

• Results from the introduction of antibodies from another person or animal.

Question 16

What is natural active immunity?

Answer 16

• Arises from being exposed to an antigen or getting the disease/

Question 17

What is natural passive immunity?

Answer 17

• Result of crossing mother’s antibodies through the placenta and their presence in breast milk.

Question 18

What is artificial active immunity?

Answer 18

• Acquired through vaccinations which stimulate the immune system and lead to production of antibodies.

Question 19

What is artificial passive immunity?

Answer 19

• Where antibodies are injected into the body.

Question 20

What are vaccines?

Answer 20

• Way of introducing a pathogen into the body in order to produce an immune response.
• The pathogen may be dead o inactivated, but the antigens on its surface will still produce the immune response.

Question 21

What are the factors that determine the success of a vaccination program?

Answer 21

• Cost of the vaccine
• Severity of the side effects
• Ease of production, transportation and administration
• Number of people who need to be vaccinated for herd immunity.

Question 22

What is herd immunity?

Answer 22

• If you vaccinate enough people in the population then eventually the pathogen won’t be able to be transmitted from different hosts.
• This therefore means that those who aren’t vaccinated are protected by those around them who are.

Question 23

What are vaccines not always effective?

Answer 23

• Antigen on the surface of the pathogen can change.

Question 24

What are the ethical considerations of vaccinations?

Answer 24

• Production and testing of vaccines may be done on animals
• The risks of the vaccine need to be balanced with the benefits
• The vaccine must be tested on humans first to determine toxicity
• Vaccinations are very expensive
• Should vaccinations be compulsory?

Question 25

What are the uses of monoclonal antibodies?

Answer 25

• Direct therapy, monoclonal antibodies that are specific to antigens found on the surface of cancerous cells can be used to target and then destroy the cells are part of an immune response.
• Indirect therapy, drugs can be attached to monoclonal antibodies such as a cytotoxic drug. The antibody then is used to direct the drug towards the cells displaying a particular antigen rather than towards other cells.
• Diagnosis, particular antigens are targeted by antibodies to measure levels of that antigen in the body.
• Pregnancy testing, monoclonal antibodies in home pregnancy kits are specific to the hormone.

Question 26

What is HIV?

Answer 26

• Pathogen that can lead to the disease AIDS.

Question 27

Describe the structure of HIV?

Answer 27

• A lipid envelope with embedded attachment proteins.
• Inside a protein capsid where the genetic material RNA and reverse transcriptase enzymes are present. This catalyses the production of DNA from the RNA.

Question 28

How does HIV replicate?

Answer 28

1. HIV virus binds to the protein CD4 which is found on helper t helper cells.
2. The capsid then fuses with the cell surface membrane and the RNA and reverse transcriptase enter the cell.
3. The reverse transcriptase converts the RNA to DNA, which then moves into the nucleus of the cell.
4. The cell now has the instructions to begin producing viral HIV components.

Question 29

How is HIV identified?

Answer 29

• ELISA test.

Question 30

What are the stages of an ELISA test?

Answer 30

1. Antigen coated well
2. Add specific antibody to be measured
3. Add enzyme conjugated second antibody
4. Add substrate and measure colour.

Question 31

Why are antibiotics ineffective against viruses?

Answer 31

• Many antibiotics work by preventing bacteria from making cell walls.
• Without this the bacteria cannot control the entry and exit of water and will therefore burst.
• However, since viruses don’t have a cell wall and are reproduced within a host cell they are unaffected by antibiotics.