Immune response

Question 1

What is a pathogen and how do they cause disease?

Answer 1

An organism that causes disease AND an immune response by destroying cells and releasing toxins

Question 2

What is an antigen?

Answer 2

A protein with a specific tertiary structure found on the the surface of cells (antigens not found in body are “non-self” or “foreign”) - cause an immune response

Question 3

What are the defence systems in the body?

Answer 3

• Non-specific (immediate) - physical barrier, phagocytosis
• Specific (slower) - cellular/humoral response

Question 4

What are the 3 first lines of defence?

Answer 4

HCl, mucus and skin

Question 5

What is the anagram for phagocytosis?

Answer 5

PREP F E H A M

Phagocyte - white blood cell contains lysosomes
Recognises foreign antigens
Engulfs pathogen
Phagosome (pathogen inside a membrane)
Fuses with a lysosome
Enzymes - lysozymes released into phagosome
Hydrolyse molecules in pathogen
Antigen presenting cell - foreign antigens presented on the..
Membrane (cell surface)

Question 6

What are the two types of T cell?

Answer 6

1. Helper T cells stimulate phagocytes, B cells and cytotoxic T cells
2. Cytotoxic T cells kill infected cells by making the membrane fully permeable so cell dies (can’t synthesise viruses)

Question 7

What is clonal selection?

Answer 7

A specific T cell binds to presented antigen via its complementary receptor –> T cell activated and produces clones by mitosis to produce many T cells with complementary receptors to the antigen –> become either TH or TC cells

Question 8

What is the anagram for the cellular response?

Answer 8

An Armadillo Starts To Crawl Can He Stop Before Passing (out)

Antigen presenting cell will
Activate a
Specific
T cell which will
Clone by mitosis, forming
Cytotoxic T cells which kill infected cells
Helper T cell
Stimulates
B cells
Phagocytes

Question 9

What is a B cell?

Answer 9

A white blood cell responsible for producing antibodies - each produce a specific antibody

Question 10

How are specific B cells activated?

Answer 10

Has protein receptors that are complementary to an antigen presented by a phagocyte or a receptor on an activated helper T cell - when these bind B cell is activated

Question 11

What is the anagram for the humoral response?

Answer 11

Trevor Always Back Chats PAM

T helper cell
Activates
B cell (specific)
Clones by mitosis to form
Plasma cells which secrete
Antibodies
Memory cells formed

Question 12

What is the secondary immune response?

Answer 12

More antibodies produced more quickly

Question 13

What is the structure of an antibody?

Answer 13

• Variable region (complementary to 1 antigen)
• Constant region (same in every antibody)
• Antigen-antibody complex

Question 14

What are monoclonal antibodies?

Answer 14

Have the same tertiary structure and produced from the same plasma/B cell

Question 15

How are monoclonal antibodies used in treating/diagnosing cancer?

Answer 15

1. Monoclonal antibody complementary to cancer cell antigen binds to tumour markers on cancer cell
2. Treatment - maintains high drug concentration at tumour site
3. Diagnosis - tissue examined under microscope, fluorescent tag shows up for complementary antibody

Question 16

What are ethical issues involved with the use of monoclonal antibodies?

Answer 16

• Involves inducing tumours in mice
• Mice are genetically engineered to produce human antibodies
• Major side effects

Question 17

How does direct ELISA test for HIV?

Answer 17

1. HIV antigen bound to bottom of well
2. Add antibody + enzyme
3. Wash to remove false positives
4. Add substrate (when enzyme reacts with substrate = colour change)

Colour change = antigen/antibody testing for

Question 18

How does indirect ELISA test for HIV?

Answer 18

1. HIV antigen bound to bottom of well
2. Plasma sample added (might contain several different antibodies)
3. Wash out well to remove unwanted antibodies which are unbound
4. Secondary antibody added - antibody + enzyme that is complementary to HIV antigen
5. Wash out to prevent false positives
6. Substrate added - colour change = HIV is present

Question 19

What is immunity?

Answer 19

The ability of an organism to resist infection

Question 20

What are the 2 types of immunity?

Answer 20

Passive and active

Question 21

Compare the 2 types of immunity

Answer 21

Passive: Doesn’t require exposure to antigen, immediate protection, no memory cells produced, short term protection (antibodies hydrolysed) so needs to be redone

Active: Requires exposure to antigen, slower protection, memory cells produced, long term protection

Question 22

How does a vaccine stimulate an immune response?

Answer 22

Vaccines contain antigens –> phagocytosis –> T cell cellular response –> B cell humoral response –> memory cells = more antibodies more quickly when re-infected

Question 23

Why are vaccination programmes useful?

Answer 23

Herd immunity developed when vaccinations are carried out on large scales

Question 24

What are the ethical concerns with vaccination programmes?

Answer 24

• Often involves animals
• Side effects
• Who should they be tested on?

Question 25

What is antigenic variability?

Answer 25

Some pathogens have antigens that can constantly change (strains)

Question 26

What is agglutination?

Answer 26

All pathogens become clumped together (attracts phagocytes)