2. Micro-organisms
What 3 things must be met in order to be recognised as a pathogen?
1) Gain entry
2) Colonise and damage tissue
3) Resist the defence barriers
Name 3 types of pathogens
1) Bacteria
2) Fungi
3) Viruses
What two ways can micro-organisms enter the body?
A: through the gas exchange system. Also food and water that carry
pathogens into the stomach to the digestive system
3. Physical barriers
List 3 of the body barriers against infection
A: skin, lysozyme in tears and stomach acid
How do pathogens cause disease?
A: they produce toxins (cholera bacterium) and damage cells (viruses)
Name the 3 main responses of the non-specific response
A: fever, inflammation and phagocytosis
What makes the specific response different to the non-specific response?
A: it only responds to specific types of pathogens using the immune system
4. Phagocytosis
Which type of white blood cells is involved in phagocytosis?
A: phagocytes
What attracts the phagocytes to the pathogen?
A: the chemical attractants it gives off; chemotaxis
What does the phagocyte attach onto on the pathogen?
A: antigens on its surface
How does the phagocyte from a vesicle/phagosome?
A: by engulfing and ingesting it
What role do the lysosomes in phagocytosis?
A: enzymes within the lysosome break the phagosome via hydrolysis
What happens do the breakdown product of the pathogen?
A: the phagocyte absorbs it
5. Lymphocytes
Which type of white blood cell is involved in immunity?
A: lymphocytes
Name the 2 types of lymphocytes
A: b-cells an t-cells
What kind of immunity are b-cells involved in?
A: humoral immunity
What kind of immunity are t-cells involved in?
A: cell mediated immunity
6. T-Cells and Immune Response
What is an antigen?
A: proteins found on the surface of the pathogen that trigger an immune response
What is an antigen presenting cell?
A: cells that present the antigens from a digested pathogen on their cell surface membrane
What do proteins on the t-cell surface act as?
A: receptors for a specific antigen
Where do these receptors on the specific T helper-cell bind to?
A: the antigen on the antigen presenting cells
what does this binding activate?
A: other t-cells to divide rapidly by mitosis to from a clone
What 3 things do these cones differentiate into to do?
A: become cytoxic t-cells that kill infected body cells, stimulate phagocytosis and b-cells, or
produce memory t-cells
7. B-Cells and Immune Response
In terms of receptors how are b-cells similar to t-cells?
A: they have receptors on their surface with a specific shape that is complementary
to the antigen
Where can the antigen be found on the surface of?
A: an antigen presenting cell or the pathogen itself
When the b-cell binds to the antigen and activates, what happens to other b-cells?
A: other b-cells divide by mitosis to form clones of plasma and memory cells
What do plasma cells do?
A: produce antibodies to destroy pathogens
What do memory cells do?
A: they stay in the blood until the second infection where they’ll produce much
more plasma and memory cells rapidly
8. Antibodies
What is an antibody?
A: produced by the b-cell and it has a binding site specific to an antigen
What is the structure of an antibody and why?
A: tertiary structure because it a protein folded into 4 polypeptide chains
What is the shape of the antigen binding site the same as?
A: same as the receptors on the b-cell
Why are antibodies effective against a specific pathogen?
A: the antigens are complementary to the shape of the antibodies and
specific to that antibody
How does the specificity of an antibody depend on its variable regions?
A: the variable regions are made out of a specific sequence of amino acids
that makes its specific 3D shape which bids directly to the antigen
9. Monoclonal Antibodies
What does the specific binding site shape on the antibody allow us to do?
A: recognise specific antigens to help in medicine and science
What are monoclonal antibodies?
A: many copies of an antibody
Describe the 6 steps take to produce a monoclonal antibody
1) Antigen of interest injected into organism
2) Plasma cells from a b-cell specific to the antigen are extracted
3) The nucleus from a cancer cell is removed
4) The enucleated cancer cell and plasma cells diffuse to make a hybridoma cell
5) The hybridoma cell is screened to produce the desired antibody
6) The hybridoma b-cell is cloned to make many more copies
What are 3 uses of monoclonal antibodies?
A: to treat disease, detect specific antigens and identify molecules
10. Antigen Coated Well test
What is the antigen coated well?
A: a test to detect antibodies against a pathogen in the body fluids
Explain how this works
A: the antigen is bound to a plate and if complementary antibodies are
present they will form an antigen-antibody complex
How does the antigen target the antibody?
A: the antigen is a complementary specific shape to target the antibody
A sample of blood is added, what happens after this?
A: if the sample contains the antibody it will bind to the antigen binding
site
11. Antigen Coated Well test continued
What happens at the first wash stage?
A: any unbound antibody is removed by washing
A second antibody with an enzyme attached is added, what happens after this?
A: if the 1st antibody was present, the 2nd will bind to produce a complex
What is the second wash stage?
A: to remove any unbound antibodies
What is the last stage?
A: the substrate is added and a colour change means a positive result
What does the colour change mean?
A: that antibodies were present
Why will there be no colour change if there are no antibodies present?
A: the antigens won’t have any antibodies to bind to and therefore the 2nd antibody enzyme will not
be present
12. Monoclonal antibody coated well
What is the monoclonal antibody coated well?
A: when monoclonal antibodies are used to test for the presence of antigens
in body fluids
Explain how this works
A: the antibodies are bound to a plate and if complementary antigens are
present they will bind to them
How does the antibody target the antigen?
A: it will have a complementary binding site and specific shape
A sample of blood is added to the well, what happens after this?
A: if the antigen is present, it will bind to the antigen binding site on the 1st
antibody
13. Monoclonal antibody coated well continued
What is the purpose of the first wash stage?
A: to remove the sample and any unbound antigens
A 2nd monoclonal antibody with an enzyme attached is added, what happens after
this?
A: the antibody will bind to the immobilised antigen to form a complex
What is the purpose of the 2nd wash stage?
A: to remove any 2nd unbound antibodies
The substrate is then added, what happens to this?
A: if the 2nd antibody is present it will convert the substrate into a coloured product
What does the colour change mean?
A: that the antigen was present in the sample
14. Vaccines
What is passive immunity?
A: the production of antibodies into someone’s body from an external source but the effects are short lived
What is active immunity?
A: the production of antibodies from the individual’s own immune system. The effects are long lasting
What is vaccination?
A: the injection of a dead/weakened version of the pathogen in an attempt to stimulate active immunity
How does vaccination work?
A: it readies the body for what it thinks is the 2nd infection by preparing the plasma and memory cells to
produce antibodies more rapidly to fight the pathogen, and it allows the b and t cells to stay in the blood
What is herd immunity?
A: when the vast majority is vaccinated and the transmission of the pathogen is interrupted
Why can’t vaccination eradicate disease?
A: because some people may catch the disease before vaccination kicks in and had already spread it on and
they could have a defective immune system
15. Vaccines
State 3 reasons why it has proved difficult to control cholera by vaccination?
1) It is an intestinal disease which makes it harder for the immune system to
reach it
2) The antigens on the cholera pathogens change too rapidly to produce an
effective vaccine
3) Mobile populations spread cholera and make it harder to ensure people are
vaccinated
State 3 reasons why it has proved difficult to control TB by vaccination?
1) The increase in the HIV virus means a weakened immune system in people
2) The proportion of elderly people has increased and elderly people have less
effective immune systems
3) Mobile populations have spread TB making it harder to ensure people are
vaccinated
16. Antigenic Variation
Why can you get influenza virus several times but measles once?
A: the antigens on the surface change regularly because the DNA
mutates forming new strains of the virus.
As a result why is the primary repose repeated every time you’re
infected with a new strain of the flu?
A: the memory cells do not recognise the other strains with different
antigens
Why are elderly people and those with heart and respiratory disease
given the flu vaccine every winter?
A: they have a weaker immune system so are more likely to get infected
