The immune system Flashcards
What are antigens?
Molecules - usually proteins - found on the cell surface membrane which stimulate an immune response
What do antigens allow the immune system to identify?
Pathogens
Cells from other individuals
Abnormal body cells
Toxins
What is antigenic variability?
Where the antigens on viruses change
So you could be infected with the same virus again but this would produce a primary response rather than a secondary response because the antigens have changed
What type of immunity are B lymphocytes associated with?
Humoral immunity
e.g. immunity involving antibodies that are present in body fluids (‘humour’)
What type of immunity are T lymphocytes associated with?
Cell-mediated immunity
e.g. immunity involving body cells
What is a secondary response?
When the right antibodies to fight a particular pathogen are produced rapidly and in high numbers because you’ve been infected with the same pathogen before
Where are both B and T lymphocytes formed?
Stem cells found in the bone marrow
Where do T lymphocytes mature?
In the thymus gland
Where do B lymphocytes mature?
In the bone marrow
What is the process of phagocytosis?
1) The phagocyte is attracted to the pathogen by chemoattractants (released by the pathogen)
2) The phagocyte binds to the pathogen
3) They engulf the pathogen to form a vesicle known as a phagosome
4) The lysosomes release their lyctics enzymes into the phagosome where they break down (hydrolyse) the pathogen
5) The breakdown products of the pathogen are absorbed by the phagocyte
Why does phagocytosis happen?
Large particles, such as bacteria, are too big to cross surface membranes by diffusion or active transport. Instead they have to be engulfed by cells in the form of vesicles formed from the cell surface membrane
What are some non specific responses?
Physical barriers e.g. skin and scabs
Phagocytosis
Non specific responses are immediate and the same for all pathogens
What are some examples of specific defence systems?
Cell mediated response - T lymphocytes
Humoral response - B lymphocytes
Specific responses are slower and specific to each pathogen
What do helper T cells stimulate?
- Production of memory cells
- B cells to divide
- Phagocytosis
- Production of cytotoxic T lymphocytes
What do cytotoxic (TC cells) do?
Kill abnormal and foreign cells by making holes in the cell surface membrane
Why do we need antigen presenting cells (e.g. phagocytes) for T lymphocytes to respond?
Because T lymphocytes will only respond to antigens that are attached to a body cell
What is the process of B lymphocytes dealing with a pathogen?
1) The surface antigens are taken up by B cells
2) B cells then present antigens on their surface
3) T helper cells attach to processed antigens and activate the B cells
4) They are activated to divide by mitosis to give clones of plasma cells
5) These clones plasma cells produce antibodies that are complementary to the pathogen
6) These antibodies attach to antigens and destroy the pathogen
7) Some B cells develop into memory cells instead of plasma cells to respond to future infection
What is an antibody?
Proteins synthesised by B cells when the body is invaded by non self material
What are the two pairs of polypeptide chains in an antibody called?
Long pair - heavy chains
Short pair - lighter chains
What is the variable region on an antibody?
The binding site on the antibody
What is the constant region of an antibody?
The area that’s the same in all antibodies
What is clonal selection?
When the antibody on the surface of a B cell meets a complementary shaped antigen, it binds to it. This, together with substances released from helper T cells activated the B cell
What is agglutination?
When two pathogens bind to the two binding sites on an antibody and become clumped together
What is the difference between monoclonal antibodies and polyclonal antibodies?
Monoclonal antibodies are made by one type of B cell and are all clones of a unique parent cell, while polyclonal antibodies are made from several different types of B cells
What are three uses of monoclonal antibodies?
Separation of a chemical from a mixture
Immunoassay
Cancer treatment
What is immunoassay?
A method of calculating the amount of a substance in a mixture (used in pregnancy tests and drug tests)
How are monoclonal antibodies used for cancer treatments?
Monoclonal antibodies which attach themselves only to cancer cells can be created. They can then activate a cytotoxic drug so only cancer cells will be destroyed, not healthy ones
How do pregnancy tests work?
- The application area contains antibodies that are complementary to the hCG protein, bound to a blue coloured bead
- Any hCG in the urine will bind to the antibodies and form antigen-antibody complexes
- If there is any hCG present, the test strip turns blue because the immobilised antibody binds to any hCG with the blue beads attached to the antibody
- If there is no hCG present, the beads will pass through the test area without binding to anything so it won’t turn blue
What are ethical issues associated with monoclonal antibodies?
Animal rights issues because animals are used to produce cells from which the monoclonal antibodies are produced
What is herd immunity?
When the majority of individuals in a population are immunised, thus reducing the chance of spreading the disease to others. The contagious people who didn’t receive a vaccine are less likely to meet other people who aren’t vaccinated
What are three features of a successful vaccination programme?
- Side effects can’t be unmanageable
- It can’t be too expensive because it has to be administered on a large scale
- It must be possible to vaccinate the vast majority of the population
What is active immunity?
When our own immune system is responsible for protecting us from a pathogen
What is an example of naturally acquired active immunity?
Resistance to a common cold
What is an example of artificially acquired active immunity?
A vaccine
What is passive immunity?
When a person is given antibodies rather than making them through their own immune system
What is an example of naturally acquired passive immunity?
When a baby receives a mother’s antibodies through the placenta or breast milk
What is an example of artificially acquired passive immunity?
An injection of an antibody containing serum / immune globulin from another person or animal
What is a retrovirus?
A virus composes of RNA instead of DNA
How does HIV replicate?
- HIV enters the blood stream
- Attachment proteins on the virus bind to a helper T cell and the reverse transcriptase enzyme enters the helper T cell from the virus
- Reverse transcripts uses RNA to make DNA copies and the DNA joins to the host cell’s DNA
- The HIV DNA in the nucleus creates mRNA which codes for protein production
- mRNA passes out of the nucleus through the cytoplasm and the cell’s protein making machinery is activated so more HIV particles are made
- The HIV particle breaks away from the TH cell, taking with it a piece of the CSM, forming the lipid envelope
What is the process of the ELISA test?
1) HIV antigen is bound to the bottom of a well
2) A plasma sample is added abs the antibodies specific to the HIV antigens bind
3) The non specific antibodies are washed out
4) The secondary antibody is added which has an enzyme attached
5) The secondary antibodies bind to the primary antibodies and the unbound antibodies are washed out
6) The substrate is added which binds to the enzyme and activates a colour change
What is a monoclonal antibody?
An antibody produced from a single group of genetically identical B cells
How does a T cell work?
It has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes
