Cell Recognition Flashcards
What molecules of the cell surface membrane help to identify specific non-self/forgein cells
Glycoproteins, glycolipids can act similarly
What do these surface proteins help to recognise
-pathogenic cells
-abnormal/ cancerous cells
-toxins
-cells from other individuals from the same species
Define antigen
A protein/glycoprotein found on the cell surface membrane.
A molecule that identifies a cell as self or non-self
Give 2 examples of places where non-self antigens might occur inside an organism
Surface of pathogens
Toxins
Infected body cells
Cancerous/tumour cells
Cells form another individual
Explain why it is important to have T-lymphocytes with different specific receptors
Each is specific/complementary to a different antigen
The immune system is able to recognise/respond to many different pathogens/toxins
Explain why it is important to have T-lymphocytes with different specific receptors
Each is specific/complementary to a different antigen
The immune system is able to recognise/respond to many different pathogens/toxins
What type of antigens are produces by the organisms own body?
Self antigens
What are self antigens
Antigens that do not stimulate an immune response
What are non-self antigens
Antigens not produces by the organisms own body, and they stimulate an immune response
Why do some pathogens hsve antigen variability
The antigens present on their surface can change frequently due to genetic mutations
Why is having antigen variability a problem for the immune system fo many mammals?
Surface receptors are complementary to only one antigen, so when the antigen on a pathogen changes the lymphocytes and memory cells can no longer bind - no secondary immune response, so host suffers form disease again
What are phagocytes and where are they produced?
They are white blood cells that are produced continuously in the bone marrow
What is the role of phagocytes?
The recognise and engulf pathogens in phagocytosis
What is phagocytosis as example of?
A non-specific immune response
What do phagocytes have on their surface that recognise antigens as non-self
Receptor proteins
What is the full process of phagocytosis?
-Chemicals released by pathogens attract phagocytes
-Phagocytes move toward site of infection, where pathogens can be identified due to presence of pathogenic antigens
-the phagocyte attaches to the pathogen by binding to its antigens
-once attached, the phagocytes csm engulf the pathogen (endocytosis)
- forms a phagosome
-the phagocytes vacuole fuses with a lysosome = phagolysosome
-lysosome releases lysozymes to digest the pathogen
- product of pathogen digestion can sometimes be displayed on the cell surface of a phagocyte to trigger specific immune response.
What are lymphocytes and what are they a part of?
WBC, plays part in the specific immune response
When are T-lymphocytes activated?
When they encounter and bind to their specific antigen that’s being presented by one of the hosts cells.
What do activated T-lymphocytes do?
They divide by mitosis to increase in number
What are the 2 main types of T-cell that T-lymphocytes differentiate into?
-helper T cells
-cytotoxic T cells (killer T cells)
When do T-lymphocytes produce an immune response ?
When they are exposed to a specific antigen
When do T-cells bind?
To an antigen if it’s present on the surface of an antigen-presenting cell
What is an antigen presenting cell?
One of the hosts cells that has been invaded by a pathogen and is displaying them antigen on the cell surface membrane.
Describe the cell-mediated immune response
First, a naive helper T cells receptors bind to an antigen on an antigen presenting cell. This stimulates the helper T cell to clone itself.
The clones helper T cells stimulate B cells to clone, phagocytes to undergo phagocytosis and cytotoxic T cells to target virus-infected body cells.
When cytotoxic T cell receptors bind to antigens on virus-infected body cells, they release perforin. This protein creates holes in the cell surface membrane leading to cell death
Describe the different ways that the specific immune response leads to the destruction of antigens
B cell clones differentiate into plasma cells, which secrete antibodies, antibodies bind into antigens on pathogens, causing them to agglutinate-making it easier for phagocytes to engulf and destroy forgein antigens.
Helper T cell clones stimulate phagocytes to destroy foreign antigens by phagocytosis. They also stimulate cytotoxic T cells to secrete perforin, which kills infected cells and destroys antigens within them
HIV is a virus that invades and destroys helper T cells. Explain why people with HIV are more susceptible to infection with other pathogens.
They have fewer cytotoxic T cells
They produce fewer antibodies following infection
Fewer pathogen-infected cells are killed
Explain why it is important that there is lots of diversity between lymphocytes
The body needs lymphocytes with a diverse range of receptors, each of which can recognise a different antigen, this allows the body to respond to infection by a wide variety of pathogens
What is a vaccine?
A suspension of antigens put into the body to induce artificial active immunity. A specific immune response where antibodies are released by plasma cells
Problems with vaccines
People can have a poor response
Antigenic variation
What is antigenic variation
The variation due to major changes in the antigens of pathogens causes the vaccine to not trigger an immune response
Which component of a cell is most likely to act as an antigen during a blood transfusion , why
Glycoprotein
Found on the outside of a cell and is a different shape to body proteins
2 structures a bacterial cell wall may have what a WBC does not have
Bacterial cells have a cell wall whereas WBC dont
Bacterial cells have plasmids WBC don’t
What are the 2 parts of the specific immune response
Cell-mediated response
Humoral response
What is the cell mediated response
T helper cells recruiting killer / cytotoxic T cells
What feature of the T helper cell allows it to identify specific forgein antigens
Specific receptors which complementary bind to antigens on APCx
Describe how B lymphocytes respond when they are stimulated by antigens
Mitosis occurs
Differentiation into plasma cells and some memory B cells
Plasma cells make antibodies and memory cells
An antigen in a vaccine leads to the production of antibodies . Describe the part played by B lymphocytes in this process
B lymphocytes bind to the antigen on the T helper cell to activate the antigen
Antigen is complementary to receptor on a lymphocyte
Then clonal expansion occurs through mitosis, creating many plasma cells which create antibodies
Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen
Helper t cells bind to antigen on the antigen presenting phagocyte
Helper t cells stimulate a specific b cell to undergo clonal selection
These cells form plasma cells
These release antibodies specific to the viral antigen that was presented
Scientists have found a virus that produces a protein similar to human collagen
Suggest how the immune response to this viral protein can result in an auto immune disease
B lymphocyres will stimulate mitosis of b cells which will destruct human cells and collagen
Why is the primary response slow
Aren’t many b cells that make the antibody needed to bind to the antigen
Why is the secondary response quicker than the primary immune response
B memory cells are activated and divide into plasma cells producing antibodies
T memory cells are activated and produce cytotoxic T cells to kill the pathogen
There are fewer steps
What is the structure of an antibody
Antibodies are proteins made up of four polypeptide chains , 2 heavy , 2 light
Each chain has a variable and a constant region
Chains are connected by disulphide bridges
Why do all antibodies have the same constant regions
Allow them to bind to receptors on immune system cells
What is agglutination
Antibodies bind to antigens on pathogens and cause them to clump together ,
These clumps are then destroyed by phagocytosis
This makes it easier for phagocytes to engulf more pathogens at a time
Scientists use an antibody to detect an antigen on the bacterium that causes stomach ulcers
Explain why the antibody will only detect this antigen
Antibody has 2 variable regions where the antigen will bind to
These have a unique tertiary structure which will only be complementary to that antigen
Variable region has specific primary structure and c=forms complex between antigen and antibody
What is an antibody
Protein complementary in shape to an antigen
Ethical issues with vaccines
All are tested on animals first
Humans in clinical trials may put themselves at risk because they believe they may be ‘immune’
If there was a new disease difficult decisions would be made about who would get the vaccine first
What is herd immunity
A population can be protected from a certain virus if a threshold of vaccination is reached
Describe the differences between active + passive immunity
Active immunity is where your body makes its own antibodies after being exposed to an antigen whereas passive immunising is where the body is given the antibodies that have been made by a different organism
Active immunity is long term because memory cells are produced whereas passive immunity is short term because no immune response is involves and no memory cells are produced
Active takes time to develop , passive is faster acting
Active involves memory cells , passive does not
What is a vaccination
Presentation of antigens to the body via a dead form of the pathogen to stimulate antibodies
Injecting antivenom deos not give a person long lasting protection , why ?
It’s passive immunity no memory cells are produced
Why is it essential to use passive immunity rather than active immunity with antivenom
Active immunity would be too slow
Passive immunity is an immediate response
Antibodies bind to toxin and destruct
To produce antivenom a mixture of venoms from several snakes of the same species are used , suggest why .
All strains from different snakes will be covered
May be a different form of antigen / toxin
Different antibodies may be required
Describe how HIV is replicated after it has entered a human cell
Glycoprotein molecules on virus bind to CD4 receptors on the surface of the T helper cells ,
This allows the envelope surrounding the virus to fuse with the T helper cell membrane
The capsid is released into the cell where it releases the RNA and reverse transcriptase
MRNA goes to ribosomes to make viral RNA and proteins
Reverse transcriptase used RNA to make DNA
DNA joins to host cells DNA
DNA is used to make HIV RNA and proteins at host ribosomes
Virus buds off at the cell membrane to go and infect other cells
The destruction of T cells by HIV can lead to death of an infected person , how
Helper T cell count decreases
Not enough T cells to active b cells to activate the immune system
Weakening the persons immune system, so t cant fight off simple infections
So when the person eventually contracts pneumonia the person cant fight it
Explain why the number of HIV particles in the blood rises
1)during the first few months after infection
2) remains low between 1-7 years after infection
1)HIV is invading cells which makes new viruses
2) virus remains dormant
Why are antibodies referred to as monoclonal
Antibodies produced from a single clone of B cells
Why are monoclonal antibodies useful
They can be produced outside the body and are reactive with only one type of antigen
3 main medical uses of vaccines
To target medication to specific cells by attaching a therapeutic drug to an antibody
Pregnancy testing
Medical diagnosis by identifying proteins or antigens using ELISA test
How does radioimmunotherapy work
Links radioactive atoms to monoclonal antibodies that deliver the radioactivity by seeking out and latching onto proteins found on cancer cells
What does doctors concentrating radiation at tumour sites reduce?
Reduces the amount of radiation that reaches healthy tissue
Explain how a pregnancy test works
Antibodies complementary to the hCG protein are bound to a coloured bead
hCG in urine binds to antibodies
Urine moves up the strip by carrying beads
Immobilised antibodies which bind to hCG create first “blue line”
Immobilised antibodies which bind to coloured beads create second blue line is hCG is present
Describe the ELISA test
1 attach antigen to well
2 add sample, if it contains antibodies that match the antigen, they will bind to it
3 wash to remove any unbound secondary antibodies
4 secondary antibody added which binds to the first antibody , this antibody has an enzyme attached
5 wash again to remove any unbound secondary antibodies
6 a substrate is added that reacts with the enzyme to produce a coloured product
