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Biology - Mrs Dudley > 5.1 - 5.7 Immune system > Flashcards

5.1 - 5.7 Immune system Flashcards

1
Q

Define antigen

A

Molecules, usually made of protein, that are found on the surface of cells and can generate an immune response

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2
Q

List the 4 main stages of an immune response

A
  1. Phagocytes engulf pathogens
  2. Phagocytes activate T-cells
  3. T-cell activate B-cells, which divide into plasma cells
  4. Plasma cells make more antibodies to a specific antigen
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3
Q

Describe how phagocytes engulf pathogens

A
  1. Phagocyte detects chemicals release by pathogen and moves towards it, down a concentration gradient
  2. Receptors on phagocyte cell-surface membrane attach to the chemicals on the surface of the pathogen
  3. Phagocyte engulfs pathogen and forms phagosome
  4. Lysosomes fuse with the phagosome and release enzymes called lysozymes
  5. Lysozymes hydrolyse the pathogen
  6. Hydrolysis products of the pathogen are absorbed by the phagocyte
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4
Q

Describe how T-cells are activated by phagocytes and the role they then play

A

Activated:
- T-cells have receptor proteins on their surface that bind to the complementary antigens presented to it by phagocytes

Helper T-cells:
- This activates helper T-cells
- Clone by mitosis
- These release chemical signals which activate and stimulate phagocytes, cytotoxic T-cells and B-cells
- May then become memory cells

Cytotoxic T-cells:
- Activated by helper T-cells
- Can kill abnormal and foreign cells by making holes in their cell surface membrane

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5
Q

Describe how B-cells are activated and the role they then play

A

Activated:
- The antibody on the surface of a B-cell meets a complementary shaped antigen and binds to it
- Also meets with substances released from helper T-cells
- Activates B-cell
- This process is called clonal selection

B-cells:
- Activated by antigens and helper T-cells
- Cloning by mitosis forms plasma cells
- Plasma cells secrete specific antibodies
- May then become memory cells

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6
Q

Name the 2 sections of immune response

A
  • Cellular
  • Humoral
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7
Q

What part of the immune response is classed as cellular?

A
  • Phagocytes
  • T-cells
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8
Q

What part of the immune response is classed as humoral?

A
  • B-cells
  • Clonal selection
  • The production of monoclonal antibodies
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9
Q

Define antibody

A

A protein produced by lymphocytes in response to the presence of the appropriate antigen

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10
Q

How do antibodies contribute to the immune response?

A
  • An antibody has two binding sites so can bind to two complimentary antigens at once forming an antigen-antibody complex
  • This clumping together of pathogens is called agglutination
  • Antibodies then act as markers for phagocytes
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11
Q

Describe a primary immune response

A
  • When an antigen enters the body for the first time
  • Primary response is slow and produces fewer antibodies as there aren’t many B-cells that can make the complimentary antibody
  • Patient shows symptoms
  • Eventually, enough antibodies will be made and the disease will be overcome
  • Both T-cells and B-cells form memory cells
  • The person is now immune
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12
Q

Describe the function of memory T-cells and memory B-cells

A

Memory T-cells:
- Remember and recognise specific antigen

Memory B-cells:
- Remember specific antibodies needed for antigen

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13
Q

Describe a secondary immune response

A
  • When an antigen enters the body for the second time
  • Secondary response is faster and produces more antibodies as clonal selection happens faster and memory B-cells are activated and divide into plasma cells and memory T-cells are activated and divide into the correct type of T-cell
  • Usually patient shows no symptoms
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14
Q

Define a vaccine

A

Vaccines contain antigens (sometimes attached to dead or attenuated pathogens) and are inserted into the body to trigger an immune response and leave memory cells behind. This is to protect individuals and populations from future occurrences of the disease.

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15
Q

Define herd immunity

A

The principle that if most individuals in a population are vaccinated against a disease, even the non-vaccinated are less likely to contract it as there are fewer people to catch it from

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16
Q

Describe antigenic variation

A

This is when pathogens change their surface antigens. This means that if the body is infected with the same pathogen twice, the memory cells produced the first time will not recognise the antigens the second time. This means the body will instead undergo two primary responses.

17
Q

Define active immunity

A

The type of immunity created when the immune system makes its own antibodies after being stimulated by an antigen. There are 2 types:
1. Natural - Immunity after catching a disease
2. Artificial - Immunity following vaccination

18
Q

Define passive immunity

A

The type of immunity creates when the body is given antibodies made by a different organism. There are 2 types:
1. Natural - Immunity when a baby receives antibodies from its mother (either through the placenta or in breast milk)
2. Artificial - Immunity after the body has been injected with antibodies from someone else

19
Q

Describe the differences between active and passive immunity

A

Active immunity:
- Requires exposure to antigen
- Takes a while for protection to develop
- Memory cells produced (protection is long term)

Passive immunity:
- Doesn’t require exposure to antigen
- Protection is immediate
- No memory cells produced (protection is short term)

20
Q

Define monoclonal antibodies

A

Antibodies produced from a single group of genetically identical B-cells. They are all identical in structure.

21
Q

List the 3 uses of monoclonal antibodies in medicine

A
  • Targeting medication to specific cells (direct and indirect monoclonal antibody therapy)
  • Medical diagnosis
  • Pregnancy testing
22
Q

Describe how monoclonal antibodies are used for direct monoclonal antibody therapy

A

Direct monoclonal antibody therapy:
- MA’s produced which are specific to antigens on cancer cells
- Attach therapeutic drug to MA’s
- MA’s attach to the surface of the cancer cells and block chemical signals that stimulate their uncontrolled growth
(MA’s are non-toxic and highly specific so fewer side effects than other forms of therapy)

23
Q

Describe how monoclonal antibodies are used for indirect monoclonal antibody therapy

A

Indirect monoclonal antibody therapy:
- MA’s produced which are specific to antigens on cancer cells
- Attach radioactive or cytotoxic drug to MA’s
- MA’s attach to the surface of the cancer cells and they are destroyed
(Can be used in smaller doses so therefore cheaper and have fewer side effects

24
Q

Describe how monoclonal antibodies are used for medical diagnosis

A
  • Used to diagnose lots of diseases including flu, hepatitis, chlamydia and prostate cancer
  • ELISA test
25
Q

Describe how monoclonal antibodies are used for pregnancy testing

A
  • Placenta produces a hormone called hCG and this is found in the mothers urine
  • MA present on test strip are linked to coloured particles
  • If hCG present in urine it binds to these MA’s
  • hCG-antibody-colour complex moves along the strip until it is trapped by a different type of antibody, creating a coloured line
26
Q

Explain the ethical issues involved in the use of monoclonal antibodies

A

Productions of MA’s involves the use of mice:
- Used to produce both antibodies and tumour cells
- Must deliberately induce cancer in the mice
- Mice are eventually killed

MA’s have saved many lives but there have been some deaths associated with their use in the treatment of multiple sclerosis:
- Must get patients informed consent

Safety issues of testing new drugs:
- March 2006, 6 healthy volunteers in trial for a new MA. Within minutes, all suffered multi-organ failure. Fortunately, all survived.

27
Q

What is the ELISA test?

A

Enzyme Linked Immunosorbent Assay. This test uses antibodies to test for the presence and quantity of certain proteins.

28
Q

Summarise the stages of the ELISA test

A
  • Add sample to plate, if antigens present they will attach to the surface
  • Add antibody specific to antigen & wait for them to bind
  • Wash off any unbound antigens and antibodies
  • If there was no antigens present, all antibodies will be washed off at this stage
  • Add a second antibody with an enzyme attached
  • If there are any of the first antibody left, the second antibody will bind to them
  • Add a coloured substrate, this will bind to the enzyme and show colour change in the sample

If a colour change occurs, then the antigen is present. The intensity of the colour change indicates the quantity of the antigen present.

29
Q

Describe how HIV causes AIDS

A

HIV = Human immunodeficiency virus
AIDS = Acquired immune deficiency syndrome

  • HIV infects and kills helper T-cells as it uses them as host cells for viral replication
  • Without helper T-cells, the immune system cannot activate phagocytes, cytotoxic T-cells or B-cells
  • When the number of helper T-cells in the patients body reach a critically low level, this is described as having AIDS
30
Q

Describe the structure of HIV

A
  • A core that contains RNA and proteins such as reverse transcriptase enzyme
  • An outer coating of protein called a capsid
  • An extra outer layer called an evelope
  • Sticking out of the envelope are loads of copies of an attachment protein that helps HIV attach to host helper T-cell
31
Q

Describe the replication of HIV

A
  1. Attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell
  2. The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm
  3. Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
  4. From this, double-stranded DNA is made and inserted into the human DNA
  5. Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
  6. The viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells
32
Q

Explain why antibiotics don’t work against viruses

A
  • Antibiotics target bacterial enzymes and ribosomes to interfere with their metabolic reactions
  • Viruses contain human enzymes and ribosomes taken from host cells

Anti-viral drugs must be used instead which target virus-specific enzymes (such as reverse transcriptase)

33
Q

Define monoclonal antibodies

A
  • Antibodies with the same tertiary structure
  • Produced by identical plasma cells

Biology - Mrs Dudley (12 decks)

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