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AS Biology > Topic 2C - Cells and the immune system > Flashcards

Topic 2C - Cells and the immune system Flashcards

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1
Q

What are antigens and what are they used for?

A

Foreign molecules, found on surface of cells, (usually proteins) that can generate an immune response when detected by the body

  • They are used by the immune system to identify:
    1. Pathogens
    2. Abnormal body cells (e.g. cancerous or pathogen-infected cells, which have abnormal antigens on their surface)
    3. Toxins
    4. Cells from other individuals of the same species (e.g. organ transplants)
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2
Q

What are pathogens?

A

Organisms that cause disease

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3
Q

What are phagocytes?

A
  • Phagocytes are types of white blood cells that carry out phagocytosis (engulfment of pathogens).
  • They’re found in the blood and in tissues and are the first cells to respond to an immune system trigger in the body
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4
Q

What is the 1st main stage of the immune response?

A

(Phagocytes engulf pathogens)

  1. A phagocyte recognises the foreign antigens on a pathogen
  2. The cytoplasm of the phagocyte moves around the pathogen, engulfing it
  3. The pathogen is now contained in a phagocytic vacuole (a bubble) in the cytoplasm of the phagocyte
  4. A lysosome (an organelle that contain enzymes called lysozymes) fuses with the phagocytic vacuole. The lysozymes break down the pathogen
  5. The phagocyte then presents the pathogen’s antigens - it sticks the antigens on its surface to activate other immune system cells
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5
Q

What is the 2nd main stage of the immune response?

A

(Phagocytes activate T-cells)

  • T-cells is another type of white blood cell. They have receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes. This activates the T-cell
  • Different types of T-cells respond in different ways e.g. Helper T-cells release chemical signals that activate and stimulate phagocytes and cytotoxic T-cells (which kill abnormal and foreign cells). T-helper cells also activate B-cells, which secrete antibodies
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6
Q

What is the 3rd main stage of the immune response?

A

(T-cells activate B-cells, which divide into plasma cells)

  1. B-cells are also a type of white blood cell. They’re covered with antibodies
  2. Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens
  3. When the antibody on the surface of a B-cell meets a complementary shaped antigen, it binds to it
  4. This, together with substances released from T-helper cells, activates the B-cell. This process is called Clonal selection
  5. The activated B-cell divides into plasma cells
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7
Q

What is the 4th main stage of the immune response?

A

(Plasma cells make more antibodies to a specific antigen)

  1. Plasma cells are identical to the B-cell. They secrete loads of antibodies specific to the antigen (monoclonal antibodies).
  2. Antibodies have 2 binding sites, so they can bind to two pathogens at once. This means that pathogens become clumped together (agluttination)
  3. Phagocytes then bind to the antibodies and phagocytose many pathogens carrying antigen all at once.
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8
Q

Draw and label an antibody

A

DIAGRAM

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9
Q

What are antibodies and describe their structure?

A

Antibodies are proteins that bind to antigens to form an antibody-antigen complex and they are made up of chains of amino acids

  • Their specificity depends on their variable regions, which form the antigen binding sites
  • Each antibody has a variable region with a unique tertiary structure that’s complementary to 1 specific antigen
  • All antibodies have the same constant regions
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10
Q

What are the two divisions of the immune response and describe what they consist of?

A
  1. Cellular - The T-cells (T-lymphocytes) and other immune system cells that they interact with e.g. phagocytes, form the cellular response
  2. Humoral - B-cells (B-lymphocytes), clonal selection, and the production of monoclonal antibodies form the humoral response.
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11
Q

What are both divisions of the immune response needed for?

A

They are needed to remove a pathogen from the body

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12
Q

Give an example of how both divisions of the immune response interact with each other

A
  1. T-cells help activate B-cells

2. Antibodies coat pathogens, making it easier for phagocytes to engulf them

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13
Q

Describe the primary immune response process. (DIAGRAM)

A
  1. When an antigen first enters the body, it activates the immune system. This is called the primary response
  2. The primary response is slow as there aren’t many B-cells that can make the antibody needed to bind to the antigen
  3. Eventually, body produces enough of the right antibody to overcome infection, But the infected person will still show symptoms of the disease
  4. After being exposed to an antigen, both T- and B-cells produce memory cells. Memory cells stay in body for a long time and remember specific antigens so that they can recognise it a 2nd time round. They also record specific antibodies needed to bind the antigen
  5. The person is now immune-their immune system has the ability to respond quickly to a 2nd infection
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14
Q

Describe the secondary immune response process. (DIAGRAM)

A
  1. If the same pathogen enters the body again, the immune system will produce a quicker, stronger response - the secondary response.
  2. Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells are activated and divide into the correct type of T-cells to kill the cell carrying the antigen
  3. The secondary response often gets rid of the pathogen before you begin to show any symptoms (you are immune to the pathogen)
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15
Q

what is a better way to becoming immune to a disease without having to undergo the primary response?

A

Vaccinations

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16
Q

How do vaccines make you immune to a disease, without you having to catch the symptoms?

A

They contain antigens that cause your body to produce memory cells against a particular pathogen, without containing pathogen causing disease itself.

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17
Q

How do vaccines lead to herd immunity?

A

Vaccines protect individuals that have them and, because they reduce the occurence of the disease, those not vaccinated are also less likely to catch the disease (as there are fewer people to pass the pathogen on)

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18
Q

What do vaccines always contain?

A

They always contain antigens - these may be free or attached to a dead or attenuated (weakened) pathogens

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19
Q

How can vaccines enter the body?

A

Vaccines can be injected or taken orally

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20
Q

What are the disadvantages of taking a vaccine orally?

A
  1. It could be broken down by enzymes in the gut

2. the molecules of the vaccine may be too large to be absorbed into the blood

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21
Q

What are booster vaccines?

A

Vaccines given later on after e.g. several years, to ensure the production of memory cells

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22
Q

Define antigenic variation.

A

When some pathogens change their surface antigens (due to changes in the genes of a pathogen)

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23
Q

Why is antigenic variation a problem?

A
  • it means that when you get a 2nd infection, the memory cells produced from the 1st infection will not recognise the different antigens. So the immune system has to start from scratch and carry out a primary response against these new antigens. The primary response takes time to get rid of the infection, which is why you get ill again
    2. It also makes it difficult to develop vaccines against some pathogens for the same reasons
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24
Q

Give 2 examples of viruses that show antigenic variation

A
  • HIV

- Influenza virus

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25
Q

Describe how antigenic variability affects the production of vaccines (that help prevent people catching Influenza)

A
  1. The influenza vaccine changes each year because the antigens on the surface of the influenza virus change regularly, forming new strains of the virus
  2. Memory cells produced from vaccination from 1 strain of the flu will not recognise other strains with different antigens. The strains are immunologically distinct
  3. New vaccines are developed and 1 is chosen every year that is most effective against the current virus
  4. Governments and health authorities then implement a programme of vaccination using the most suitable vaccine
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26
Q

Define the terms active and passive immunity

A
  1. Active immunity - The type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen
  2. Passive immunity - The type of immunity you get from being given antibodies made by a different organism - your immune system doesnt produce any antibodies of its own
27
Q

Define and describe the 2 types of active immunity?

A
  1. Natural - when you become immune after catching a disease.
  2. Artificial - when you become immune after you’ve been given a vaccination containing a harmless dose of antigen.
28
Q

Define the two types of passive immunity

A
  1. Natural - When the baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk
  2. Artificial - When you become immune after being injected with antibodies from someone else. e.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations
29
Q

Give 4 differences between active immunity and passive immunity.

A
  1. Active immunity requires exposure to antigen whilst passive doesnt
  2. It takes a while for protection to develop in active immunity but protection is immediate for passive immunity
  3. Memory cells are produced in active immunity but aren’t in passive immunity
  4. Protection is long-term in active immunity as the antibody is produced (after activation of memory cells) in response to complementary antigen being present in the body but in passive immunity, protection is short-term because the antibodies given are broken down.
30
Q

What are monoclonal antibodies produced from?

A

They are produced from a single group of genetically identical B-cells (plasma cells).

31
Q

Why are antibodies very specific?

A

They are very specific as their binding sites have a unique tertiary structure that only 1 particular antigen will fit into (one with a complementary shape)

32
Q

Why are monoclonal antibodies useful? (give a general statement)

A

They are useful as they can bind to anything you want e.g. a cell or other substance, and they will only target this molecule

33
Q

How are monoclonal antibodies useful in regards to targeting drugs to cancer cells (or any other particular cell type) (DIAGRAM)

A
  1. Different cells in the body have different surface antigens
  2. Cancer cells have antigens called tumour markers that are not found on normal body cells.
  3. Monoclonal antibodies, attached to anti-cancer drugs, can be made that will bind to the tumour markers
  4. When the antibodies come into contact with the cancer cells, they will bind to the tumour markers.
  5. This means the drug will only accumulate in the body where there are cancer cells
  6. So, the side effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells
34
Q

How are monoclonal antibodies useful in regard to testing a particular substance for medical diagnosis? e.g. pregnancy testing (DIAGRAM)

A

Pregnancy tests detect the hormone Human Chorionic gonadtropin (HCG) that’s found in the urine of pregnant women

  1. The application area contains antibodies for hCG bound to a coloured bead (blue)
  2. When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
  3. The urine moves up the stick to the test strip, carrying any beads with it
  4. The test strip contains antibodies to hCG that are stuck in place (immobilised)
  5. If there is hCG present, the test strip turns blue because the immobilised antibody binds to any hCG - concentrating the hCG-antibody complex with the blue beads attached. If no hCG is present, the beads will pass through the test areas without binding to anything, and so it won’t go blue
35
Q

What is the ELISA test?

A

The enzyme-linked immunosorbent assay is a medical diagnostic test using antibodies, that allows you to see if a patient has any antibodies to a certain antigen or any antigen to a certain antibody

36
Q

What can the ELISA test be used to test for?

A

It can be used to test for pathogenic infections, allergies (e.g. to nuts or lactose) or just about anything you can make an antibody for

37
Q

How can the quantity of antibody/antigens found in some ELISA tests be worked out ?

A

By looking at the intensity of the colour change

38
Q

Outline the different types of ELISA

A
  1. Direct ELISA - uses a single antibody that is complementary to the antigen you’re testing for
  2. Indirect ELISA - uses 2 different antibodies
39
Q

Describe how an indirect ELISA test can be used to see if a patient possesses antibodies to the HIV virus (ONLY STEPS 1 AND 2)

(DIAGRAM)

A
  1. HIV antigen is bound to the bottom of a well in a well plate (a plastic tray with loads of little circular pits in it)
  2. A sample of patients blood plasma, which could contain several different antibodies, is added to well. If there are any HIV-specific antibodies (i.e. antibodies against HIV), these will bind to the HIV antigen stuck to the bottom of the well. The well is then washed out to remove any unbound antibodies
40
Q

Describe how an indirect ELISA test can be used to see if a patient possesses antibodies to the HIV virus (ONLY STEPS 3 AND 4)

(DIAGRAM)

A
  1. A secondary antibody, that has a specific enzyme attached to it, is added to well. This secondary antibody can bind to the HIV-specific antibody (whih is also called the primary antibody). The well is washed out again to remove any unbound secondary antibody If there’s no primary antibody in the sample, all of the secondary antibody will be washed away
  2. A solution is added to the well. This solution contains a substrate, which is able to react with the enzyme attached to the secondary antibody and produce a coloured product. If the solution changes colour, it indicates that the patient has HIV-specific antibodies in their blood and is infected with HIV.
41
Q

Why is the washing out step important in the ELISA test

A

It is important in making sure there are no unbound antibodies left in the well as these could affect the results e.g. unbound secondary antibodies could cause the test to appear positive when there are no HIV antibodies present.

42
Q

What would happen if the indirect ELISA test was negative?

A

There would be no colour change as there would be no HIV-specific antibodies for the secondary antibodies to bind to

43
Q

Look at data regarding the use of vaccines and monoclonal antibodies in investigations

A

(questions in books)

44
Q

What are 4 ethical issues surrounding the use of vaccines?

A
  1. Animal testing
  2. Volunteers may put themselves at unnecessary risk of contracting a disease because they think they’re protected (e.g. may have unprotected sex, without knowing a new ‘HIV vaccine’ did not work)
  3. Unfair that some dont want to take vaccine due to risk of side effects but will still be protected due to herd immunity
  4. If there was an epidemic of a new disease, there would be a rush to receive a vaccine and difficult decisions would have to be made about who would be the first to receive it.
45
Q

What is an ethical issue surrounding monoclonal antibody therapy?

A

They often involve animal rights issues as animals are used to produce the cells from which the monoclonal antibodies are produced (some disagree with the use of animals in this way)

46
Q

What is HIV?

A

HIV (Human immunodeficiency Virus) is a virus that affects the immune system and eventually leads to AIDS (acquired immune deficiency syndrome)

47
Q

What is AIDS?

A

AIDS is a condition where the immune system deteriorates and eventually fails. This makes someone with AIDS more vulnerable to other infections, like pneumonia

48
Q

How does HIV affect the immune system?

A

HIV infects (and eventually kills) helper T-cells which act as the host cells for the virus.

  • Helper T-cells are hugely important cells in the immune system as they send chemical signals that activate phagocytes, cytotoxic T-cells and B-cells
  • Without enough helper T-cells, the immune system is unable to mount an effective response to infections because other immune system cells don’t behave in the way that they should
49
Q

When do HIV-infected people develop AIDS?

A

When the helper T-cell numbers in their body reach a critically low level

50
Q

Describe the structure of HIV (DIAGRAM)

A

It has:

  1. A core that contains the genetic material (RNA) and some proteins (including the enzyme reverse transcriptase, which is needed for virus replication)
  2. An outer coating of protein called a capsid
  3. An extra outer layer called an envelope. This is made of membrane stolen from the cell membrane of a previous host cell
  4. Sticking out from the envelope are loads of copies of an attachment protein (envelope proteins) that help HIV attach to the host helper T-cell
51
Q

Where does a HIV replicate and why?

A

A HIV virus replicates inside the helper T-cells of the host (organism) as it doesn’t have the equipment (such as enzymes and ribosomes) to replicate on its own.

52
Q

Describe how HIV replicates. (DIAGRAM)

A
  1. The 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
53
Q

What is the Latency period and what causes it?

A
  • During the initial infection period (HIV infecting T-helper cells), HIV replicates rapidly and the infected person may experience severe flu-like symptoms.
    2. After this period, HIV replication drops to a lower level (start of latency period)
  • During the latency period, which can last for years, a person won’t experience any symptoms
54
Q

What is the typical length of time between infection with HIV and the development of AIDS?

A

Usuay around 10 years but can vary

55
Q

What are the stages of AIDS? (initial stages, progression and later stages)

A
  1. The initial symptoms of AIDS include minor infections of mucous membranes e.g. the inside of the nose, ears and genitals) and recurring respiratory infections
  2. As AIDS progresses the number of immune system cells decreases further. Patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and TB
  3. During the later stages of AIDS patients have a very low number of immune system cells and can develop a range of serious infections such as toxoplasmosis of the brain (a parasite infection) and candidiasis of the respiratory system (fungal infection). It’s these serious infections that kill AIDS patients not HIV itself
56
Q

What factors affect progression of HIV to AIDS ad survival time with AIDS?

A
  1. Existing infections
  2. The strain of HIV they’re infected with
  3. Age
  4. Access to health care
57
Q

How do antibiotics kill bacteria?

A
  1. Antibodies kill bacteria by interfering with their metabolic reactions.
  2. They target the bacterial enzymes and ribosomes used in these reactions
58
Q

Why cant antibodies be used on viruses?

A

They cant be used on viruses as viruses dont have their own enzymes and ribosomes - they use the ones in the host cells
- They use human enzymes and ribosomes and antibodies can’t inhibit them since they dont target human processes

59
Q

What is the function of anti-viral drugs?

A

Anti-viral drugs are designed to target the few virus-specific enzymes that exist
- e.g. HIV uses reverse transcriptase to replicate. Human cells dont use this enzyme so drugs can be designed to inhibit it without affecting the host cell. These drugs are called reverse transcriptase inhibitors

60
Q

Is there any cure/treatment for HIV?

A

There’s currently no cure or vaccine for HIV but antiviral drugs could be used to slow down the progression of HIV infection and AIDS in an infected person

61
Q

What is the best way to control HIV infection in a population?

A

By reducing its spread:

  • HIV can be spread via unprotected sexual intercourse, through infected bodily fluids e.g. blood from sharing contaminated needles) and from a HIV-positive mother to her fetus.
  • Not all babies from HIV-positive mother are born infected with HIV and taking antiviral drugs during pregnancy can reduce the chance of the baby being HIV-positive
62
Q

Why is HIV-testing based on HIV antibody detection, before a baby is 18 months old, inaccurate?

A

The baby of an HIV-positive mother may have some HIV antibodies in their blood regardless of whether or not they’re infected

63
Q

Why do scientists suggest treating patients with both a combination of antibiotics?

A
  1. Resistant bacteria would be resistant to the old antibiotic.
  2. The use of both bacteria kill bacteria resistant to old antibiotic
    - Unlikely that bacteria is resistant to both combinations of drugs.

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