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Biology A Level > Immunity > Flashcards

Immunity Flashcards

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1
Q

What are the two types of immune defences in the body?

A

Cell-mediated response using T lymphocytes

Humoral response using B lymphocytes

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2
Q

What allows for self recognition?

A

The major histocompatibility complex, a cluster of genes on chromosome 6.

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3
Q

What does the major histocompatibility complex do?

A

These genes code for MHC antigens that are attached to the surface of body cells, which are recognised as self

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4
Q

What are the two types of MHC antigens and what’s the difference?

A

Class 1 MHC antigens are found on the surfaces of almost all human cells, whilst class 2 MHC antigens are found only on macrophages and B-lymphocytes

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5
Q

What are antigens?

A

Molecules (usually proteins) that can generate an immune response when detected by the body.

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6
Q

Where are antigens found?

A

On the surface of all cells.

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7
Q

What are pathogens?

A

Microorganisms that cause disease

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8
Q

What are the four types of pathogens?

A

Bacteria, viruses, fungi, and protists.

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9
Q

What physical defences are there to pathogens?

A

The skin provides a physical barrier, with a tough outer layer of cells with little water.
Tears - lachrymal glands secrete tears which wash away microorganisms from eyes
Sebum - secreted by the sebaceous glands containing fatty acids that have an anti microbial action
Mucus - produced by goblet cells that trap airborne cells

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10
Q

What mechanical defences are there against pathogens?

A

Nasal hairs filter the air that is drawn into the nasal passages
Bacteria and other particles trapped in the mucus are swept out of the lungs+ trachea using cilia, tiny hairs that beat with a wave-like motion

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11
Q

What chemical defences are there against pathogens?

A

Hydrochloric acid in gastric juice kills most pathogens that reach the stomach.
Tears, mucus, saliva and sweat all contain lysozyme which breaks down pathogens by catalysing the hydrolysis of their cell walls.

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12
Q

What biological defences are there against pathogens (excluding immune system)?

A

There are natural populations of harmless bacteria living on the skin and mucus membranes that inhibit the growth of many pathogens by competing with them for nutrients.

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13
Q

What are antibodies?

A

Antibodies are glycoproteins which belong to a special group of blood proteins known as immunoglobulins.

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14
Q

Describe the structure of an antibody.

A

It consists of two pairs of polypeptide chains. Two of the chains are long and are referred to as heavy chains, and two shorter chains are referred to as light chains. These chains are held together by disulfide bridges. It has two identical antigen binding sites (for specific antigens) known as the variable region.

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15
Q

What is formed when an antibody binds to an antigen?

A

An antibody-antigen binding site

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16
Q

What do antibodies do to
A) pathogens
B) toxins

A

A)some antibodies act by immobilising the antigens so that the pathogen can be destroyed by phagocytosis
B) some antibodies can neutralise the toxins released by pathogens

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17
Q

Describe phagocytosis

A

)The phagocyte is attracted to the pathogen by toxins produced by it. It moves towards the pathogen along/up the concentration gradient of toxins.

2) The phagocyte engulfs the pathogen
3) lysosomes in the phagocyte migrate to the newly formed phagosome containing the pathogen
4) Lysosomes release lysozyme into the phagosome, which hydrolyses the bacterium
5) The products of this are absorbed by the phagocyte
(6) the phagocyte may wear the antibodies of the pathogen on the cell membrane.

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18
Q

What are lymphocytes?

A

White blood cells that recognise and react with antigens

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19
Q

What are the two types of lymphocytes?

A

T-lymphocytes and B-lymphocytes

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20
Q

Explain how lymphocytes are produced in the body

A

They are developed from stem cells in bone marrow. They migrate to the spleen and lymph nodes and mature. T-lymphocytes initially pass to the thymus where they are activated.

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21
Q

Explain the first steps of cell-mediated immunity

A

1) Binding sites on the surface of particular T-lymphocytes form an antigen-antibody complex with the antigens on antigen presenting cells.
2) The T-lymphocytes become activated and start to multiply rapidly, producing many clones which each recognise the same antigen from before as being foreign.
3) These clone differentiates into either
i) cytotoxic T-cells
ii) helper t-cells
iii) memory t-cells
iv) regulator t-cells

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22
Q

What do cytotoxic t-cells do?

A

They destroy the pathogen by binding to the antigen and releasing the chemical perforin, which creates holes in the cell membranes/walls of pathogens.

23
Q

What do helper T-cells do?

A

They attract and stimulate macrophages and promote the activity of other T- and B-cells to increase antibody production

24
Q

What do memory T-cells do?

A

They have no action but can multiply very fast if a second invasion of the pathogen with this antigen occurs, producing an ever bigger clone of t-lymphocytes and resulting in rapid destruction of this pathogen.

25
Q

What do regulator T-cells do?

A

They slow down the vigorous response of the t-cytotoxic cells and the t-helper cells, slowing down the immune response and controlling it.

26
Q

Where are B-lymphocytes made?

A

In the bone marrow

27
Q

Describe clone activation

A

1) A b-cell is triggered when it encounters its matching antigen
2) The B-cell engulfs the antigen
3) It displays antigen fragments bound to its unique MHC molecules
4) The combination of antigen and MHC attract the help of a mature matching T cell
5) Cytokines secreted by the T-cell help the B-cell to multiple and mature into plasma cells

28
Q

What is the primary response to a pathogen in the humoural response?

A

Clone activation

29
Q

Describe the secondary response to a pathogen in the humoural response

A
  • memory B-cells can live in the body for decades
  • Memory B-cells do not make antibodies but can divide rapidly and differentiate into plasma cells if they collide with a certain antigen
  • this results in large numbers of antibodies being created so rapidly that the pathogen is destroyed before any symptoms occur
30
Q

What is the secondary response to a pathogen in the humoural response known as?

A

Active immunity

31
Q

What is the process that allows for antibodies to destroy pathogens?

A

Agglutination

32
Q

Describe agglutination

A

Lots of antibodies attach to multiple pathogens causing clumping, meaning it is easier for phagocytes to attach and destroy them.

33
Q

What is passive immunity?

A

Antibodies are introduced into the body. As the pathogen doesn’t enter the body, plasma and memory B cells are not created so there is no long-term immunity.

34
Q

What is active immunity?

A

Immunity created by your own immune system following exposure to the pathogen or its antigen.

35
Q

Give an example of natural active immunity.

A

Following infection and the creation of antibodies from newly formed plasma cells (+ memory Bcells are created)

36
Q

Give an example of artificial active immunity.

A

Following the introduction of a weakened version of the pathogen or antigens using a vaccine, memory Bcells and plasma B cells are created.

37
Q

What are the two types of vaccines?

A
  • Whole-agent vaccines (contain whole, nonvirulent microorganisms)
  • subunit vaccine (contains some part or product of microorganisms that can produce an immune response)
38
Q

What are the types of whole agent vaccine?

A
  • Inactivated (killed) using formalin or other chemicals, meaning they present no risk of infection but have the antigen
  • Attenuated (weakened) viruses, which are usually strains in which mutations have accumulated
39
Q

Give examples of types of subunit vaccines

A
  • recombinant vaccines, which are non-pathogenic microbes that are genetically engineered to make an antigen
  • Toxoids (toxins) that are inactivated by heat or chemicals that stimulate the production of antibodies
  • Conjugated vaccines, which are polysaccharides from the pathogen combined with proteins from other pathogens
  • Acellular vaccines which are fragments of a whole-agent vaccine containing the desired antigens.
40
Q

What are monoclonal antibodies?

A

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

41
Q

What does HIV stand for?

A

Human immunodeficiency virus

42
Q

What does AIDS stand for?

A

Acquired immune deficiency syndrome

43
Q

What does HIV contain?

A

-A surface lipid envelope with attachment proteins (eg gp120), two single strands of RNA and enzymes inside a protein layer (the capsid), and reverse transcriptase, which forms DNA from the RNA.

44
Q

How does HIV enter a cell?

A

A protein on HIV readily binds to a receptor called CD4, which occurs most frequently on helper T cells as they have a coreceptor. The protein capsid fuses with the cell-surface membrane. The DNA and enzymes of HIV enter the helper Tcells

45
Q

What occurs after the HIV particle enters the cell?

A

The HIV reverse transriptase enzyme converts the virus’ RNA into DNA, which then is moved into the helper T cells nucleus where it is inserted into the DNA. The HIVDNA in the nucleus creates mRNA, using the cells enzymes, which creates new viral proteins through translation and new RNA to go into the new HIV particles. The mRNA passes out of the nucleus through a nuclear pore and uses the cell’s protein synthesis mechanisms to make HIV particles. The HIV particles break away from the helper T cell with a piece of its cell surface membrane surrounding them which forms their lipid envelope.

46
Q

What is an ELISA test?

A

Enzyme-linked immunosorbent assay

47
Q

Describe the direct ELISA test.

A

1) known antibody is absorbed (stuck to the well)
2) Add a sample of patient’s plasma
3) Wash and filter out any unbound antigens so only antibodies + bound antigens remain
4) add the enzyme linked antibodies which bind to the bound antigens
5) wash the plate, removing any unbound enzyme linked antibodies
6) add a substrate which reacts with the enzyme, meaning a colour change (orange to blue) is a positive result.

48
Q

Describe the indirect ELISA test.

A

1) A pathogen is attached to the well so the antigen is bound.
2) Solutions that contain antibodies specific to the pathogen (eg blood) will bind to the antigens. It is then washed.
3) Enzyme-linked antibodies are added which bind to the patient’s antibodies
4) Sample is washed to remove any unbound ELA.
5) Substrate is added that reacts with the enzyme causing a colour change.

49
Q

What are toxins?

A

Proteins

50
Q

Why are antibiotics ineffective against HIV

A 
HIV has
-No metabolic mechanisms
-No cell structures
-A protein coat not a cell wall (antibiotics target the peptidoglycan murein in
bacterial cell walls)
-No sites for antibiotics to target
-A place to hide inside host cells
51
Q

What ethical considerations are there with vaccines?

A
  • Production and testing of vaccines may be done on animals
  • “Risks” of certain vaccines
  • The vaccine must be tested on humans first to determine toxicity
  • Vaccines are expensive
  • Issues with autonomy
52
Q

What are the monoclonal antibodies in home pregnancy tests specific to?

A

Human chorionic gonadotrophin (hcg)

53
Q

Describe indirect therapies involving monoclonal antibodies?

A

Drugs can be attached to monoclonal antibodies such as a cytotoxic drug. The antibody is then used to direct the drug towards the cells displaying a particular antigen.

54
Q

What is herd immunity.

A
  • When a critical portion of a given population have active immunity against a particular pathogen.
  • This can also protect groups who do not have active immunity because the pathogen is being killed off before they are infected

Biology A Level (23 decks)

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