Cell recognition and the immune system Flashcards
Define pathogen
Micro-organisms that cause diseases
Define antigen
A foreign protein that stimulates an immune response causing production of antibodies
Give examples where antigens can be found
Pathogens, toxins, cells from other organisms of the same species, mutated cells ( abnormal cells ), bacteria
Define antibody
A protein, produced by lymphocytes; in response to the presence of an appropriate antigen
Define immune system
A system of biological structures and processes that identifies and kills pathogens ( and tumour cells )
What are the stages of defence
1) Prevent invasion
2) Non-specific - phagocytes
3) Specific - lymphocytes
Describe phagocytosis
- Phagocyte attracted to pathogen by chemicals/ recognise antigens on pathogen as non-self
- Phagocyte engulfs the pathogen
- The pathogen in membrane bound pocket called a phagosome
- Lysosomes fuse with the phagosome and release digestive ( hydrolytic) enzymes into phagosome
- The enzyme digest ( hydrolyse) the pathogen, destroying it
- ## Antigens from the pathogen are displayed on the surface membrane
What two types of cell mediated immunity response
1) Cell- mediated - response by T-lymphocytes
2) Humoral - response by B-lymphocytes
Why are cell mediated responses more specific than phagocytosis
Each pathogen has a specific shaped antigen on its surface. These are different for different types or species of pathogens
Why are cell mediated responses slower than phagocytosis
Specific lymphocytes exist in the body already, there are millions of different types which each recognise a different antigen. They have proteins ( receptors) on the surface that binds to the proteins ( antigens) recognised as foreign on a pathogen
What cells can display the antigens of non-self antigens on their surface and what are they called collectively
1) Phagocytes
2) Body cells invaded by viruses
3) Cancer cells
4) Transplanted cells
Know as - antigen presenting cells ( APC)
Describe cell-mediated response
1) The receptor on a T cell binds to antigens present on body cells
2) It activates other cells to divide rapidly by mitosis ( clonal selection)
3) These cloned T cells take one of 3 roles
- Helper cell : Secret cytokinesis which stimulates phagocytosis/ B-lymphocytes to mitosis
- T-cytotoxic cells : Secret hydrogen peroxide to destroy body infected cells
- T-memory cells : Remain in the body for many years
What type of pathogen are T-cells most effective against and why
Viruses because they invade/ inside body cells
Define differentiation
Permanent change that occur in a cell when it specialised
Describe humoral immunity
1) Plasma B cells produce antibodies
2) Different shaped antibodies are produced by different B cells
3) B cells have surface receptors that are the same shape as the antibody that they make
4) Surface receptors are complementary to specific antigens
Describe the structure of an antibody
1) Antibodies are proteins
-2)They are made up of 4 polypeptide chains:
- 2 long, heavy chains
- 2 short, light chains
3) The variable region is specific to an antigen
Define monoclonal antibodies
Antibodies made from hybridoma which all the antibodies are the same
What is agglutination
Antibodies causes microbes to stick together. This makes it easier for phagocytes to engulf them
Why are antibodies made from proteins
Structure allows infinite number of forms
How does monoclonal antibodies help treat cancer
Monoclonal antibodies specific to antigens on a cancer cell are produced. Antibody binds to cancer cell and block the chemical signal that stimulates growth. Or, a radioactive or cytotoxic drug is attached to the antibody. When the antibody binds to the receptor on the cancer cell, the cell is killed.
How does monoclonal antibodies used in chemical diagnosis
Using antibodies that are complementary to specific pathogens or toxins in the blood to detect their presence. E.G Influenza
How are monoclonal antibodies used in pregnancy tests
1) Potential mother urinates on chromatography paper
2) Chromatography paper contains free HCG antibodies with attached coloured particles
3) If HCG is present, it will bind to the complementary antibodies and move up the chromatography paper
4) HCG- antibody complexes with the dye bind to a fixed HCG antibodies
5) Build up in the test area causes a coloured band to appear ( positive test)
6) No HCG present then the free antibodies flow past the fixed HCG antibodies
7) There is no build up of dye, so no colour appears ( negative test)
What is a vaccination
Contains an antigen that stimulates the production of antibodies
What is an attenuated microorganism
A microorganism that is alive but does not cause any symptoms
What is herd immunity
Stops infection spreading
Describe how a vaccination can lead to the production of antibodies against a specific pathogen
1) Vaccine contains antigen ( from specific pathogen)
2) Displayed on antigen-presenting cells
3) Specific helper T cell detects antigen and stimulates specific B cells
4) B cell divides and forms clones to give plasma cells
5) Plasma cells produce antibodies
What is active immunity
Your immune system makes its own antibodies after being stimulated by antigens
What is passive immunity
Antibodies are made by another organism and then given to you
What are some examples of natural immunity
- Through the placenta and breast milk
- Catching the disease
What are some examples of artificial immunity
- Injected with antibodies from someone else
- Being vaccinated
What are the differences between active and passive immunity
1) Active- You make your own antibodies by plasma cells.
Passive- An organisms antibodies are giver to you
2) Active- Slower
Passive- Faster
3) Active- Involves memory cells
Passive- Doesn’t involve memory cells
4) Active- Long term
Passive- Short term
What are the ethical issues of vaccines
- Testing on animals
- Testing on humans is risky
- Some people do not want to take the risk of side effects of using vaccines
- Who would get vaccine first?( the rich or the poor)
What are the ethical issues of monoclonal antibodies
- Animal testing, animals will die
- Animals used to produce the tumour cells- involves giving cancer in mice
- Testing on humans
Describe and explain the structure of HIV
1) Attachment proteins- Allows the virus to attach to host cells
2) Matrix- Main body of the virus
3) Reverse transcriptase- An enzyme that catalyse the production of cDNA from RNA
4) Lipid envelope- Surrounds the virus that contains attachment proteins
5) Capsid- Encloses the genetic material
6) RNA- The genetic material
Describe HIV
- Smaller then bacteria
- Contains nucleic acids ( RNA)
- Can only multiply inside living hosts
- Attachment proteins on the lipid envelope allows the virus to identify and attach to a host cell
How does HIV replicate?
- HIV enters the bloodstream
- A protein on HIV readily binds to a protein called CD4 on helper T cell
- The capsid fuses with the T cell membrane. RNA and enzymes of HIV enter helper T cell
- Reverse transcriptase converts RNA into cDNA
- The cDNA is inserted into the helper T cell
- DNA transcribed into HIV mRNA
- HIV mRNA translated into new HIV proteins for assembly into viral particles
- HIV particles break away from the T cell with a piece of its cell membrane, forming its own lipid envelope
Describe dormancy
- This process of HIV replication continuous for a few weeks, before the HIV virus goes into dormancy in the T helper cell
- Antibodies against HIV virus still circulates, and this is how someone can be said to be HIV positive
Describe ELISA ( enzyme-linked immunosorbent assay)
1) The HIV antigens applied to a surface, the HIV antigens would stick
2) Surface is washed to remove any unattached antigen
3) The sample is added and give time to bind if antibodies are present
4) Surface is washed to remove any unattached antibodies
5) A second antibody ( with an enzyme attached) is added, which is complementary to the first antibody. These bind together
6) Surface is washed to remove any unattached second antibody
7) A colourless substrate to the enzyme is added. The enzyme breaks down the substrate into coloured products
8) The amount of antigens present is related to the colour intensity
