The Immune System (Chapter 5) Flashcards
What are antigens?
Molecules (usually proteins) that generate an immune response.
What is a pathogen?
An organism that causes disease
Where are antigens usually found?
On the surface of cells
What are the four main stages of the immune response?
Phagocytes engulf pathogens
Phagocytes activate t-cells
T-cells activate b cells, which divide into plasma cells
Plasma cells make more antibodies to a specific antigen
Describe phagocytosis
Phagocyte travels along the chemical trail released by a pathogen. (Down a conc gradient)
Phagocyte reaches the pathogen and engulfs it, a vesicle called a phagosome is formed.
Lysosome fuses with the phagosome and it releases lysozymes which hydrolyse the pathogen. (Breaks it down)
Pathogen debris remains, and then absorbed by phagocyte
What is a t-cell? (And structure)
Another type of white blood cell. It has receptor proteins on its surface that bind to complementary antigens presented by phagocytes. (This activates the T cell)
What do T helper cells do?
Release chemical signals which activate and stimulate phagocytes and cytotoxic T cells
What do cytotoxic T cells do?
They kill abnormal and foreign cells
They also activate b-cells which secrete antibodies
What are b cells (and structure)?
Another type of white blood cell. They are covered in antibodies.
Each b cell has different shaped antibody on its membrane, so different ones bind to different shaped antigens.
What is an antibody?
Proteins that bind to antigens to form an antigen-antibody complex
What causes B cells to divide into plasma cells? (3 steps)
When an antibody on the surface of a B cell meets complementary shaped antigen it binds
This together with substances released from helper T cells, activated the B cell (clonal selection)
The activated b cell divides into plasma cells
What are plasma cells?
Identical to B cells (clones) they secrete loads of antibodies specific to the antigen.
What are monoclonal antibodies?
Antibodies that are specific to one antigen
How many binding sites do antibodies have?
2
What is agglutination?
When pathogens clump together. (2 binding sites so they can clump)
What is phagocytose?
When phagocytes bind to antibodies and do phagocytosis on many pathogens at once. Leading to destruction of pathogens (carrying this antigen).
What does the specificity of an antibody depends on?
It’s variable regions, which form the antigen binding sites
What differers about the variable regions on an antibody?
A unique tertiary structure, that is complementary to one specific antigen
(All antibodies have the same constant regions)
What is the cellular response?
The T cells and other immune system cells that they interact with, eg. Phagocytes
What is the humoral response?
B cells, clonal selection and the production of monoclonal antibodies form the humoural response
How is the primary immune response activated?
When an antigen enters the body for the first time it activates the primary response
Describe the speed primary immune response and how the infected person will feel
Slow- as not many B-cells that can make the antibody needed to bind to the antigens
The infected person will show symptoms
How does the primary immune response lead to immunity?
After being exposed t-cells and b-cells produce memory cells (which remain in the body for a long time)
They are now immune
What do memory t-cells do?
Remember specific antigen (and remember it a second time round)
What do memory b-cells do?
Record specific antibodies needed to bind the antigen
Describe what happens during the secondary immune response (5 points)
Quicker and stronger response
Clonal selection happens faster
Memory b-cells divide into plasma cells that produce correct antibody
Memory t-cells kill antigen
Often no symptoms
What do vaccines often contain, and what does it do?
Contain antigens which cause the body to produce memory cells against a specific pathogen, without the pathogen causing the disease
(Immune without symptoms)
What is herd immunity?
Arises when a sufficiently large proportion of the population has been vaccinated, this makes it difficult for a pathogen to spread within that population.
(Who isnt vaccinated unlikely to catch the disease)
Disadvantage of taking a vaccine orally?
It could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into blood
Are booster vaccines needed?
Only sometimes (to make sure that memory cells are produced)
What happens to the antigens in antigenic variation?
Pathogens can change their surface antigens
Why do you become ill again when antigenic variation occurs?
Surface antigens have changed so memory cells from first infection will not recognise them.
(Primary response begins again so becomes ill)
How does antigenic variation affect vaccines?
Difficult to develop vaccines against some pathogens (as antigens keep changing) eg. Flu
What is active immunity?
When your immune system makes its own antibodies after being stimulated by an antigen.
What are the two types of active immunity?
Natural— become immune after catching a disease
Artificial— become immune after been given a vaccine
What is passive immunity?
Immunity you get from being given antibodies made by a different organism (your immune system doesn’t produce any antibodies of its own)
What are the two types of passive immunity?
Natural— baby becomes immune due to antibodies it receives from mother, through placenta and breast milk
Artificial— become immune after being injected with antibodies from someone else.
What are the four differences between active and passive immunity?
Active requires exposure to antigen passive doesn’t
Active takes a while to develop passive doesn’t
Active produces memory cells passive doesn’t
Active gives long term protection whereas passive protection is short term
How are monoclonal antibodies produced?
From a single group of genetically identical b-cells (plasma cells)
What antigens do cancer cells have?
Tumour markers (not found on normal body cells~)
How do you target specific drugs to a cancer cell?
Monoclonal antibodies can be made that will bind to the tumour markers.
Then you can bind an anti-cancer drug to the antibody
This means that the drug will only accumulate on cancer cells
What is the hormone produced by pregnant women?
Human chorionic gonadotropin (hCG)
Explain how pregnancy tests work?
Application area contains antibodies for hCG bound to a coloured bead
When urine is applied any hCG will bind to the antibody
Urine moves up stick carrying any beads
Test strip contains antibodies to hCG (immobilised)
If hCG present test strip turns blue- immobilised antibody binds to any hCG
Name the medical diagnostic test that uses antibodies
ELISA test
Describe the 4 steps of an ELISA test (for HIV)
- HIV antigen bound to the bottom of a well in a well plate.
- A sample of patients blood plasma is added to the well. If there are any HIV specific antibodies, they will bind to the HIV antigen stuck to the bottom of the well. The well is then washed out to remove any unbound antibodies.
- A secondary antibody, with specific enzyme attached, is added to the well. This antibody can bind to the HIV-specific antibody. Well is washed out again to remove any unbounded secondary antibody.
- A solution is added to the well, which 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.
What are the ethical issues surrounding monoclonal antibody therapy?
Animals are often used to produce the cells from which monoclonal antibodies are produced.
(Often mice)
List 3 ethical issues surrounding vaccines
Vaccines are tested on animals before humans
If there was an epidemic of a new disease there would be a rush to receive a vaccine, who should receive it first?
Not everyone wants to be vaccinated ie. Religion, side effects etc
What does HIV cause?
AIDS
What does HIV stand for?
Human immunodeficiency virus
What is AIDS?
Where the immune system deteriorates and eventually fails
What does HIV infect/ target?
Infects and eventually kills T-helper cells
How does HIV turn into AIDS?
When the T-helper cell numbers in the body reach a critically low level
What is the structure of HIV?
Spherical shape
Genetic material (RNA) and reverse transcriptase enzyme enclosed in a capsid
Matrix below the lipid envelope
Attachment proteins attached to the envelope
How does HIV replicate?
Attachment protein attaches to receptor molecule on membrane of helper T-cell
Capsid released into the the cell- uncoats and releases RNA into cytoplasm
Reverse transcriptase makes complementary strand of DNA form viral RNA template
Double stranded DNA inserted into human DNA
Host cell enzymes used to make viral proteins from viral DNA
Viral proteins assembled into new viruses, which bud from the cell and go on to infect other cells
What are people with AIDS susceptible to?
A range of illnesses due to their immune system failing.
How long does it take HIV to turn into AIDS (without treatment)
Around 10 years
What are the initial symptoms of AIDS?
Minor infections of mucous membranes (eg. Inside of nose, ears, genitals), and recurring respiratory infections.
What happens as AIDS progresses?
Immune system cells decrease.
More serious infections ie. Chronic diarrhoeas etc
What happens in the late stages of AIDS?
Very low number of immune system cells.
Develop serious infections which usually kill the individual (not the HIV)
Eg. Toxoplasmosis of the brain
Can antibiotics work against viruses?
No, antibiotics work against bacteria
How do antibiotics work against bacteria?
By interfering with their metabolic reactions. They target bacterial enzymes and ribosomes used in these reactions. (Bacterial is different to human so only targets bacterial)
Why cant we use antibiotics for a virus?
Viruses don’t have their own ribosomes and enzymes, they use the host cells ones. (Cannot target human processes)
What do antiviral drugs do?
Target virus-specific enzymes. Ie. Reverse transcriptase enzyme in HIV
Is there a cure for HIV?
NO
What can slow down the progression of HIV?
Antiviral drugs can help.
Best way to stop the spread is to have protected sex, and uncontaminated needles etc (not sharing body fluids)
Can HIV testing on children under 18 months be inaccurate?
Yes
