7 - Immune System

Question 1

What is an immune response?

Answer 1

The detection and destruction of antigens

Question 2

What is an antigen?

Answer 2

A substance that causes an immune response

Question 3

How do foreign cells enter the body?

Answer 3

• Pathogens (an organism that causes disease) - have foreign antigens and come in through food, drink, air, bodily fluids or through the skin
• An organ transplant with antigens which can be detected as foreign and destroyed by rejection - has to come from twin or close relative and person given immunosuppressants
• DNA can become damaged and the cell divides too rapidly forming a tumour and changing its antigens, the immune system therefore destroys it before it becomes cancer
• Toxins (poisons)

Question 4

Phagocytosis

Answer 4

The destruction of foreign cells

• Phagocyte recognises foreign antigens
• Macrophage puts pseudopodia around the cell
• The Pseudopodia fuse and enclose the cell in a vacuole
• Lysosomes fuse with vacuoles, emptying hydrolytic enzymes into it
• Foreign cell digested
• Phagocyte presents the pathogens antigens

Question 5

What are lymphocytes?

Answer 5

White blood cells with a large nucleus that almost fills the cell
Two types:
- T lymphocytes (T cells) - involved in cellular response
- B lymphocytes (B cells) - involved in humeral response

Question 6

Cellular response

Answer 6

• Macrophage (antigen presenting cell) engulfs pathogen
• Presents foreign antigens on its cell surface
• T Cells stimulated by specific complementary antigens on the antigen presenting cells
• Goes through clonal selection (division through mitosis)
• Can divide to form Tc cells (cytotoxic T cell) which destroys cells with foreign antigens using secreting toxic substances such as hydrogen peroxide
• Can divide to form T helper cells which release cytokines which stimulate macrophages to carry out phagocytosis and also stimulate B cells and other T cells

Question 7

Humoral response

Answer 7

• B cell binds to antigen presenting cell and is stimulated
• B cells undergo clonal selection through mitosis
• Daughter cells are plasma cells and memory cells
• Plasma cells are filled with many ribosomes, endoplasmic reticulum and mitochondria so that they can produce many of the specific protein, antibodies - called monoclonal antibodies as they all come from the same cloned cell
• Antibodies stick bacteria together by agglutination which attract macrophages to destroy them by phagocytosis

Question 8

Structure of antibody?

Answer 8

Quaternary structure, 4 polypeptides
Disulphide bridge in between two longest polypeptides
2 ends on each side are the Antigen binding sites called the variable region
Constant region below
Small chains are the light chains
Long chains are the heavy chains

Question 9

Hows does immunity occur?

Answer 9

• Many memory cells produced by B cells
• When they come into contact with the same foreign antigen they produce plasma cells very quickly
• Plasma cells produce more antibodies faster

Question 10

Primary response to infection?

Answer 10

When antigen enters body for first time
Slow - art many B-cells that can make the antibody and bind to it
Infected person will show symptoms
Eventually the body will produce enough antibodies
T cells and B cells produce memory cells - remain in body - Memory T cells remember the specific antigens and Memory B cells record the specific antibodies
Person is now immune

Question 11

Secondary response to infection?

Answer 11

• Quicker, stonger
• Memory B-cells are activated and divide into plasma cells that produce the right antibody
  Memory-T cells are activated that divide into the correct type of T-cells
• The foreign cell does not have enough time to divide and make us ill, we are immune

Question 12

How does a vaccination work?

Answer 12

• Antigens in injection cause a primary response without the ability to divide and make us sick
• Creates immunity

Question 13

What is active immunity?

Answer 13

The person is exposed to the antigen and make their own antibodies against it, creating their own memory cells

Question 14

What is passive immunity?

Answer 14

Natural - Where someone else antibodies are put in someone to make them temporarily immune - breast milk in mothers (colostrum)
The baby does not produce its own antibodies and does not produce its own memory cells
Artificial - Injected with antibodies from someone else

Question 15

What is herd immunity?

Answer 15

When a large % of the population is vaccinated and made immune so that a disease can’t move from person to person very easily and cause an outbreak or epidemic

Question 16

What does HIV stand for?

Answer 16

Human Immunodeficiency Virus

Question 17

Structure of HIV

Answer 17

Retrovirus - genetic material is RNA
Contains reverse transcriptase enzyme
Phospholipid around itself called a viral envelope
Attachment proteins on outside to bind to host helper-T cell
Outside is protein called capsid
Protein capsomeres inside
Protein core inside
Protease inside

Question 18

Replication of HIV

Answer 18

• Infects a particular helper T cell by using attachment proteins attaching to receptor molecule
• Capsid released into cell where it unchaste and releases the RNA
• RNA template creates a complementary strand of DNA using reverse transcriptase
• DNA codes for production of new viruses
• DNA incorporated into host cell DNA
• When the cell divides the HIV is replicated
• People who have anti-HIV antibodies in the blood are HIV positive because the antibodies can’t reach the HIV in cells so they are just present in the blood
• After time, viral DNA is activates, it is transcribed and translated using the host cells own enzymes and ribosomes
• Large numbers of the virus are produced and burst out of the cells to infect new helper T cells

Question 19

How does HIV harm a person?

Answer 19

• Number of helper T cells decreases, ability to produce antibodies decreases
• People unable to fight off infections or cancerous cells
• Said to have AIDS, Acquired Immunodeficiency virus

Question 20

How to treat HIV?

Answer 20

• Antibiotics do not work - its a virus
• Uses antiretrovirals which bind to reverse transcriptase and stop it from copying RNA to DNA
• Keeps the quantity of the virus in the body at a low level so that the helper T cell count is maintained and the person has a working immune system

Question 21

What is a monoclonal antibody?

Answer 21

It is a clone from a single plasma cell

Question 22

How are monoclonal antibodies used in cancer treatment?

Answer 22

• Have complementary shapes to abnormal proteins
• Can be attached to a drug that kills cancer
• Will only deliver the drug to cancerous cells

Question 23

What are two autoimmune diseases? How are they treated?

Answer 23

• Rheumatoid arthritis
• Crohn’s disease
• TNF-a is disabled using monoclonal antibodies and the immune system attack is suppressed

Question 24

How are monoclonal antibodies used in pregnancy testing kits?

Answer 24

• Binds to HCG which is secreted in the early months of pregnancy
• Produces colour changes on a dipstick if HCG is present

Question 25

ELISA test

Answer 25

1. Monoclonal antibody that is complementary to substance is attached to enzyme
2. Antibody binds to substance
3. Dish washed to rid any unbound enzyme and antibody
4. The substrate to the enzyme is added and an enzyme-substrate complex forms to produce a colour change if the antibody did bind and the substance is present

Question 26

Disadvantage of vaccination?

Answer 26

Can be broken down by enzymes in the gut

Question 27

Why can you catch the flu multiple times?

Answer 27

Antigenic variability - antigens vary so the memory cells do not remember them

Question 28

Active vs Passive immunity?

Answer 28

Active - Requires exposure to antigen, takes time for protection to develop, Memory cells produces, Protection is long term
Passive - Docent require exposure to antigen, protection is immediate, memory cells aren’t produced, protection is short-term because the antibodies given are broken down