Cell recognition and the immune system Flashcards
Non-specific response meaning + examples
The response is immediate and the same for all pathogens
eg physical barrier or phagocytosis
Specific response meaning + examples
The response is slower and specific to each pathogen
eg cell-mediated response (T cell) or humoral response (B cell)
Antigen WHAT IS IT ???????
Molecules of which that, when recognised as non-self/foreign by the immune system, can stimulate an immune response and lead to the production of antibodies.
Often proteins on the surface of cells. Proteins have a specific tertiary structure/shape, allowing different proteins to act as specific antigens.
What do antigens allow the immune system to identify, since they are specific?
Pathogens eg viruses, fungi and bacteria
Cells from other organisms of the same species eg organ transplants or blood transfusions
Abnormal body cells eg cancerous cells/tumours
Toxins released from bacteria
Lymphocytes what are they and stuff
White blood cells that fight infection
If they have antigens (on their cell surface membrane) that are complementary to the body’s own (self) cells, they are suppressed or die
Where are lymphocytes produced in an adult?
In an adult, lymphocytes are produced in the bone marrow.
Any lymphocytes that show an immune response to self antigens undergo a programmed death (apoptosis) before they can differentiate into mature lymphocytes.
Where are lymphocytes produced in a foetus?
Due to the protection of the placenta, infection is rare. Therefore, lymphocytes will only come into contact with self-cells.
Some of the lymphocytes will have receptors that match exactly those of the self cells. These will die or be suppressed.
Phagocyte what is it and examples
A white blood cell that can carry out phagocytosis
eg the macrophage and the neutrophil
Process of phagocytosis (non-specific immune response)
Phagocyte is attracted to pathogen due to the chemical products it produces
Phagocyte eg macrophage recognises foreign antigens on the pathogen and binds to the antigen.
Phagocyte engulfs pathogen by surrounding it with its cell surface membrane/cytoplasm
Pathogen contained in a vesicle called a phagosome in the cytoplasm of the phagocyte.
Lysosome fuses with the phagosome and releases lysozymes (hydrolytic enzymes) into the phagosome
These hydrolyse/digest the pathogen. Digestible materials are absorbed into the cytoplasm of the phagocyte, indigestible materials are excreted.
Phagocyte becomes antigen-presenting (displays foreign antigens on their surface) and stimulates specific immune response.
T-lymphocytes where do they mature and what are they associated with
T-lymphocytes mature in the thymus gland
They are associated with cell-mediated immunity; immunity involving body cells
T-lymphocytes what do they respond to
T-lymphocytes only respond to antigens that are presented on a body cell (rather than to antigens within the body fluids)
This is called cell-mediated immunity
Receptors on each T-cell respond to a single antigen
The cellular response (T-lymphocytes and foreign antigens eg infected cells, cells of the same species)
T-lymphocyte recognises antigen-presenting cells after phagocytosis (foreign antigens)
Specific T-helper cell with receptor complimentary to specific antigen binds to it, triggers activation and dividing rapidly by mitosis to form T-cell clones
T-cell clones what do they do
Stimulates B-cells for the humoral response
Stimulates cytotoxic T-cells to kill infected cells by producing perforin
Stimulates phagocytes to engulf pathogens by phagocytosis
Develops into memory cells that enable a rapid response to future infections by the same pathogen.
The action of T-cells is most effective against viruses because they replicate inside cells
Cytotoxin T-cells
Cytotoxin T-cells kill abnormal cells by producing a protein called perforin in the cell surface membrane
Cell membrane becomes freely permeable to all substances and the cell dies as a result
The humoral response (the response of B lymphocytes to a foreign antigen e.g. in blood/tissues)
Clonal selection:
- Specific B cell binds to antigen presenting cell and is stimulated by helper T cells
- Divides rapidly by mitosis to form clones (clonal expansion)
Some become B plasma cells for the primary immune response – secrete large amounts of monoclonal antibody into blood
Some become B memory cells for the secondary immune response
Antigen variability is often an explanation for why…
New vaccines against a disease need to be developed more frequently e.g. influenza
Vaccines against a disease may be hard to develop or can’t be developed in the first place e.g. HIV
May experience a disease more than once e.g. common cold
Primary response – antigen enters body for the first time (role of plasma cells)
Produces antibodies slower and at a lower concentration because:
Not many B cells available that can make the required antibody
T helpers need to activate B plasma cells to make the antibodies (takes time)
So infected individual will express symptoms
Secondary response – same antigen enters body again (role of memory cells)
Produces antibodies faster and at a higher concentration because:
B and T memory cells present
B memory cells undergo mitosis quicker and quicker clonal selection
Explain the effect of antigen variability on disease prevention (vaccines)
Change in antigen shape (due to a genetic mutation)
Existing antibodies with a specific shape unable to bind to changed antigens and form antigen-antibody complex
Immune system i.e. memory cells won’t recognise different antigens (strain)
Antibodies
Quaternary structured protein (immunoglobin)
Secreted by B-lymphocytes (eg plasma cells) and produced in response to a specific antigen
Binds specifically to antigens forming an antigen-antibody complex
Antibodies structure related to function
Primary structure of protein: sequence of amino acids in a polypeptide chain.
Determines the folds in the secondary structure as R groups interact
Determines the specific shape of the tertiary structure and position of hydrogen, ionic and disulfide bonds
Quaternary structure is comprised of 4 polypeptide chains (tertiary structured) held together by hydrogen, ionic and disulfide bonds
Enables the specific shaped variable region (binding site) to form which is a complementary shape to a specific antigen
Enables antigen-antibody complex to form
Explain the effect of antigen variability on disease
Change in antigen shape (due to a genetic mutation)
Not recognised by B memory cell: no plasma cells/antibodies
Not immune
Must re-undergo primary immune response: slowly releases lower concentration of antibodies
Disease symptoms are felt
How do antibodies work to destroy pathogens e.g. bacterial cells?
Binds to two pathogens at a time (at variable region/binding site) forming an antigen-antibody complex
Enables antibodies to clump the pathogens together - agglutination
Phagocytes bind to the antibodies and phagocytose many pathogens at once
Vaccination
Injection of antigens
From attenuated (dead or weakened) pathogens
Stimulates the formation of memory cells
The use of vaccines to provide protection for individuals against disease
Normal immune response but the important part is that memory cells are produced
On reinfection / secondary exposure to the same antigen, the secondary response therefore produces antibodies faster and at a higher concentration
Leading to the destruction of a pathogen/antigen (e.g. agglutination and phagocytosis) before it can cause harm/symptoms = immunity
The use of vaccines to provide protection for populations against disease (herd immunity)
Large proportion but not 100% of population vaccinated against a disease – herd immunity
Makes it more difficult for the pathogen to spread through the population
More people are immune so fewer people in the population carry the pathogen
Fewer susceptible so less likely that a non-vaccinated individual will come into contact with an infected person and pass on the disease
Active immunity
Initial exposure to antigen eg vaccine or primary infection
Memory cells involved
Antibody is produced and secreted by (B) plasma cells
Slow, takes time to develop
Long term immunity: antibody can be produced in response to a specific antigen again
Passive immunity
No exposure to antigen
No memory cells involved
Antibody introduced into body from another organism e.g. breast milk/across placenta from mother
Fast acting
Short term immunity (antibody broken down)
Ethical issues associated with the use of vaccines
Tested on animals before use on humans: animals have a central nervous system so feel pain (some animal based substances are also used to produce vaccines)
Tested on humans: volunteers may put themselves at unnecessary risk of contracting the disease because they think they’re fully protected e.g. HIV vaccine so have unprotected sex, vaccine might not work
Can have side effects
Expensive – less money spent on research and treatments of other diseases
What are monoclonal antibodies
An antibody produced from a single group of genetically identical (clones) B cells / plasma cells
Identical structure
Bind to specific complimentary antigen
Have a binding site / variable region with a specific tertiary structure / shape
Only one complementary antigen will fit
Why are monoclonal antibodies useful in medicine
Only bind to specific target molecules / antigens:
Antibodies have a specific tertiary structure (binding site / variable region) that’s complementary to a specific antigen which can bind/fit to the antibody
Monoclonal antibodies: targeting medication to specific cell types by attaching a therapeutic drug to an antibody eg cancer cell
Monoclonal antibodies made to be complementary to antigens specific to cancer cells: cancer cells are abnormal body cells with different antigens (tumour markers)
Anti-cancer drug attached to antibody
Antibody binds / attaches to cancer cells (forming antigen-antibody complex)
Delivers attached anti-cancer drug directly to specific cancer cells so drug accumulates: fewer side effects e.g. fewer normal body cells killed
Monoclonal antibodies: medical diagnosis eg pregnancy test
Pregnant women have the hormone hCG in their urine
The application area contains antibodies for hCG bound to a blue-coloured bead.
When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
2 other test strips:
- Middle contains antibodies complementary to hCG-antibody complex
- End (control) contains antibodies complementary to antibody without hCG attached
If pregnant, binds to antibodies in the middle position
If not pregnant, binds to antibodies at the end position (control)
Ethical issues associated with the use of monoclonal antibodies
Animals are involved in the production of monoclonal antibodies i.e. by producing cancer in mice who have a CNS so feel pain, and it is unfair to give them a disease
Although effective treatment for cancer and diabetes, it has caused deaths when used in treatment of Multiple Sclerosis
Patients need to be informed of risk and benefits before treatment so they can make informed decisions
Structure of HIV
Envelope, capsid, RNA, reverse transcriptase, attachment proteins
The replication of HIV in helper T cells
The attachment protein attaches to a receptor molecule on the cell membrane of a host helper T-cell
The capsid is released into the cell where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm
Inside the cell, reverse transcriptase is used to make a complementary strand of viral DNA from the viral RNA template.
From this, double stranded viral DNA is made and inserted into the human DNA.
Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells
How HIV causes the symptoms of AIDS – acquired immune deficiency syndrome
Infects and kills helper T cells (host cell) as it multiplies rapidly
T helper cells then can’t stimulate cytotoxic T cells, B cells and phagocytes, leads to an impaired immune response
eg B plasma cells can’t secrete antibodies for agglutination and destruction of pathogens by phagocytosis
Immune system deteriorates
- More susceptible to infections
- Diseases that wouldn’t cause serious problems in a healthy immune system are deadly (opportunistic infections) e.g. pneumonia
Why antibiotics are ineffective against viruses
Antibiotics can’t enter human calls – but viruses exists in its host cell (they are acellular)
Viruses don’t have own metabolic reactions e.g. ribosomes (use of the host cell’s) which antibiotics target
If we did use them… act as a selection pressure + gene mutation = resistant strain of bacteria via natural selection, therefore reducing effectiveness of antibiotics and waste money
The use of antibodies in the ELISA test
Can determine if a patient has antibodies to a certain antigen or antigens to a certain antibody.
Used to diagnose diseases or allergies (eg HIV/lactose intolerance)
Why do we use controls when performing the ELISA test
Control enables a comparison with the test to show that only the enzyme is causing the colour change.
Also to show that washing is effective and all unbound antibodies are washed away
Explain why the secondary and detection antibody must be washed away (ELISA)
Enzyme attached to antibody reacts with substrate turning the solution a different colour; indicates a positive result.
If it is not washed out, enzymes will react with the substrate and give a positive result even if no antigens are present (false positive)
Using an (indirect) ELISA as a HIV test
HIV antigen is bound to the bottom of a well in a well plate.
A sample of the patient’s blood plasma, which might contain several different antibodies, is added to the well. If there are any HIV-specific antibodies these 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, that has a specific enzyme attached to it, is added to the well. This secondary antibody can bind to the HIV-specific antibody. The well is washed out again to remove any unbound secondary antibody. If there is no primary antibody in the sample, all of the secondary antibody will be washed away.
A solution is then added to the well. This solution 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-specific antibodies in their blood and is infected with HIV.
