2.4-Immunology Flashcards

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1
Q

Define these Keywords:
Pathogen
Antigen
Antibody

A

Pathogen - A disease causing agent.
Antigen - A foreign protein or glycoprotein which stimulates an immune response
Antibody - A protein produced by B plasma cells which binds to a specific, complementary antigen

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2
Q
  1. Some white blood cells are phagocytic. Describe how these phagocytic white blood cells destroy bacteria
A
  • Pathogen produces chemo-attractants which attract the phagocyte towards it
  • The phagocyte engulfs the pathogen and holds it in a vesicle called a phagosome
  • The phagosome membrane fuses with the membrane of lysosomes
  • Lysosomes contain enzymes which are released into the phagosome
  • The enzymes hydrolyse the pathogen
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3
Q
  1. How do T-cells stimulate an immune response?
A

• Phagocyte engulfs pathogen and presents the antigens on its cell surface membrane. It is now an Antigen Presenting Cell (APC)
• Helper T-cells (TH cells) with specific shape receptors complementary to the specific antigen bind to the APC. The T-helper cells become activated.
• T-helper cells secrete chemicals which activate other T-cells which have the same receptors.
• T helper cells divide by mitosis.
• T-helper cells:
i. Activate Cytotoxic T-cells (TC) - Produce chemicals which make the APC membrane permeable which kills the infected cell.
The holes also allow toxins to get in, which will definitely kill the cell and everything in it (e.g. viruses which have invaded)
ii. Become T-memory cells - Enable rapid response to future infections by the same pathogen
b. Stimulate phagocytosis by phagocytes
c. Stimulate B-cells

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4
Q
  1. Describe how B-lymphocytes respond when they are stimulated by antigens
A

• A specific B-cell has receptors on its surface that are complementary to a specific antigen
• This specific B cell encounters the antigen on the surface of a pathogen or on the surface of an APC
• This specific B-cell engulfs and presents the antigens on its own cell surface membrane
• The receptor of the activated T-helper cell binds to the complementary antigen presented on the cell surface membrane of the SPECIFIC B-cell
• This activates B cell to divide by mitosis forming…
a. B plasma cells - Produce antibodies which circulate the blood and bind to the complementary antigen’s on the pathogen. Ultimately resulting in the pathogens being killed (e.g. phagocytosis by a macrophage)
b. B memory cells - remain in the blood so if the pathogen re-invades, these cells divide by mitosis to make B plasma cells à secondary response is much faster

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5
Q

What is Clonal selection =

A
  • There are many B cells that all have different antibodies on their surface.
  • Only the B cell with an antibody complementary to a specific antigen is SELECTED and activated
  • So only this B cell divides by mitosis (is CLONED) to produce loads of B cells with the same antibodies
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6
Q

Why might one type of pathogen cause the activation of more than one type of B cell and more than one type of T cell?

A
  • All cells (including pathogens) have more than 1 type of antigen on their surface.
  • B cells can also be activated by toxins (act as antigens) produced by pathogens.
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7
Q

Define Antibody

A

A protein produced by B-plasma cells which have a variable region with a shape that is complementary to a specific antigen.

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8
Q

What is a primary immune response?

A

primary immune response occurs the first time an organism comes in contact with a specific pathogen (or antigen).
It is a relatively slow response because it takes time for;
o Clonal selection to occur to identify the T-cells with the receptors complementary to the specific antigens present
o Clonal selection to occur to identify the B-cells with the antibodies complementary to the specific antigens present
o B-cells to be activated (by TH cells) and divide by mitosis to produce plasma cells
o Plasma cells to produce antibodies

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9
Q

What is a secondary immune response?

A

• A secondary immune response occurs when an organism comes into contact with a specific pathogen which it has come into contact with previously

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10
Q

It is faster than the primary immune response because

A
  • There are already lots of B-memory cells in the blood
  • The B-memory cells divide by mitosis to make plasma cells (without needing to be activated by TH cells)
  • So MORE antibodies are produced MORE QUICKLY
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11
Q

What is antigenic variability? And what are the consequences for an organism who encounters a pathogen with antigenic variability?

A

If a pathogen has antigenic variability it means that the genes which code for the antigen proteins mutate from one generation to the next  thus the antigens change from one generation to the next

The organism will not have B-memory cells with antibodies complementary to the antigens
Therefore the organism will have a new primary immune response and will experience symptoms of the disease

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12
Q

Why do we only get chicken pox once but we can get the flu many times?
Chicken pox

A

Chicken pox
1. The antigens are conserved from one generation to the next
2. Second infection is recognised by complimentary antibodies on memory B-cells
3. The secondary immune response is fast/destroys the pathogen before symptoms are felt
Flu
1. Has antigenic variability/antigens mutate from one generation to the next
2. Second infection is NOT recognised by complimentary antibodies on memory B-cells
3. The primary immune response is slow/symptoms are felt/the person contracts the disease

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13
Q

What is a vaccination?

A
  • A vaccination contains dead or weakened pathogens, or antigens from them.
  • The vaccination stimulates the production of plasma cells, antibodies and memory cells
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14
Q

Describe and explain how vaccination can lead to protection or people against bacterially caused diseases.

A
  1. A vaccine is made from dead or weakened bacteria or antigens from them.
  2. B cells with complementary receptors bind to the antigen
  3. Specific activated T helper cells, active these B cells.
  4. B cells divide by mitosis to produce B-plasma cells.
  5. The B plasma cells release antibodies, which are complementary to the bacterial antigens
  6. Some B plasma cells become B memory cells
  7. If the person is exposed again to the antigen or pathogen, the B memory cells become active and divide by mitosis to produce B plasma cells , which produce more antibodies more quickly.
  8. These antibodies lead to the destruction of the pathogen before symptoms appear
  9. Vaccinating a large proportion of the population results in the herd effect (which means that there are fewer people to pass on the disease, so unvaccinated people are protected)
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15
Q

What is Herd Immunity?

A

• Herd Immunity is when a large enough proportion of the population is vaccinated so that those who are not vaccinated are protected from the disease

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16
Q

Why is Herd Immunity useful/important?

A

• Herd immunity protects people in the population who cannot be vaccinated e.g. if they are very old, very young, have a weakened immune system, are taking immunosuppressants etc

17
Q

What are the dangers of vaccines containing inactive form of virus

A
  • Inactive virus may become active
  • Attenuated virus might become harmful;
  • Non-pathogenic virus may mutate and harm cells;
  • Genetic information / protein may harm cells;
  • People may test positive after vaccine used; Vaccinated people may develop disease from a different strain to that in the vaccine
  • This may affect their work / life;
18
Q

What is active immunity?

A

Active immunity is when the antigens enter the body and the body produces its own T-cells, B-cells and antibodies e.g. person infected with pathogen or a vaccine containing pathogen is introduced to the body

19
Q

What is passive immunity?

A

Passive immunity is when antibodies are given to a person e.g. from mother to child through breast milk, antibodies given via an injection, or anti-venom for snake bites

20
Q

Describe the differences between active and passive immunity

Active Immunity Passive Immunity

A

Memory Cells produced No memory cells produced
Antibodies produced by plasma cells Antibodies introduced into body from outside
Long term immunity as antibody is produced in response to antigen Short term as antibody that is introduced is broken down
Active immunity takes time to develop Passive immunity is fast acting

21
Q

What are monoclonal antibodies?

A
  • They are antibodies which are identical and come from one type of plasma cell
  • They are all specific to only one antigen
22
Q

What is an ELISA

A

Enzyme Linked ImmunoSorbent Assay
This is when enzymes are attached to monoclonal antibodies to help with the detection of the presence of a specific substance, e.g. in the PSA test described below

23
Q

Describe how they could be used to detect for the presence of antigens?
(you do not need to memorise this but must have an understanding of the procedure)

A

Monoclonal antibodies can be used in diagnostic tests for prostate cancer
The monoclonal antibodies are complementary to PSA (an antigen specific to prostate cancer)
1. Antibodies complementary to PSA are bound to the test plate
2. A sample of blood is added
3. If PSA is present, it will bind to the antibodies
4. The plate is washed
5. Secondary antibodies (also complementary to the PSA) which have an enzyme attached to them are added
6. The antibody will bind to the PSA
7. The plate is washed again and any unbound antibody is removed (this is important because if there is no PSA present then you need to wash away the secondary antibody with the enzyme attached, otherwise the substrate will change colour even if PSA is not there)
8. A colourless substrate is added
9. If the PSA is present, then the secondary antibody with the enzyme attached will be present, so the
enzyme will turn change the colour of the substrate

24
Q

1) Explain why this test detects prostate cancer, but not any other disease.

A

o antibodies are specific to PSA

o PSA is only associated with prostate cancer

25
Q

2) Explain why it is important to wash the well before the colourless substrate is added.

A
  • Removes unbound secondary antibodies;

* Otherwise enzyme may be present and you may get colour change anyway. This will be a false positive result

26
Q

3) Explain why there will not be a colour change if the blood sample does not contain PSA.

A
  • The antibody with the enzyme is washed away if no PSA is present
  • There will be no colour change without the enzyme
27
Q

How does HIV replicate (10)

A
  1. The HIV’s attachment proteins binds to the CD4 receptor proteins on the surface of the Th cell.
  2. The virus’s lipid envelope fuses with the cell membrane of the Th cell.
  3. The protein capsid breaks down
  4. RNA and enzymes (e.g. reverse transcriptase) of the virus are now released into the cytoplasm of the host cell.
  5. Reverse transcriptase converts the viral RNA to DNA.
  6. The viral DNA is incorporated into the cell’s DNA.
  7. The viral DNA can now be transcribed into mRNA
  8. Viral mRNA passes through the nuclear pore and attaches to a ribosome
  9. Viral mRNA is translated into viral proteins that can be assembled into new HIV particles.
  10. HIV particles bud off the Th cell (so that the Th cell’s membrane forms the lipid envelope of the virus).
28
Q

How are monoclonal antibodies used to treat cancer?

A
  • The monoclonal antibody is complementary to a receptor protein on cancer cells
  • In order for the cell to divide a growth factor needs to bind to that receptor protein
  • When the monoclonal antibody is present it binds to the receptor so the growth factor doesn’t find and the cell doesn’t divide

E.g. 2
• Use a monoclonal antibody that is complementary to an antigen on the cancer cell
• Bind a radioactive molecule to the monoclonal antibody
• The monoclonal antibody will bind to the cancer cell and thus take the radioactive molecule to the cell which causes the cell to be killed