Cells and the immune system Flashcards
What are antigens?
molecules that can generate an immune response when detected by the body
What do antigens allow the body to identify?
pathogens, abnormal body cells, toxins and cells from other individuals of the same species
Describe the steps of phagocytosis.
- A phagocyte recognises foreign antigens on a pathogen.
- Cytoplasm of the phagocyte moves round the pathogen, engulfing it.
- Pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte.
- A lysosome fuses with the vacuole and lysozymes are released and break down the pathogen.
- Phagocyte presents the pathogens antigens and acts as an antigen-presenting cell.
Describe the role of T-cells during immune response.
-white blood cell
-receptor cells that are complementary to antigens presented by the phagocytes
-helper T-cells release chemical signals that activate and stimulate phagocytes, they also activate B-cells
-cytotoxic T-cells kill abnormal and foreign cells
Describe the role of B-cells during immune response.
-white blood cell
-covered with antibodies, which bind to antigens to form an antigen-antibody complex
-the antibodies have a specific shape and only bind to antigens that they are complementary to
-when the B-cell is activated it divides into plasma cells which are identical to the B-cells
Describe what happens during antibody production during immune response.
-Plasma cells release loads of antibodies which are specific to the antigen, these are called monoclonal antibodies
-antibodies have two binding sites so can bind to two pathogens so they become clumped together, this is called agglutination
What are antibodies made up of?
chains of amino acids, variable regions
What is cellular response?
T-cells and other immune system cells that they interact with
Give an example of cellular response.
Phagocytes
What is humoral response?
B-cells, clonal selection and the production of monoclonal antibodies
What is primary response?
-When an antibody enters the body for the first time
-slow because there aren’t many B-cells that make the antibody
What are memory cells and how are they produced?
-produced by B-cells and T-cells
-they remember a specific antigen and recognise it at second infection
-cause immunity to diseases
What is secondary response?
-same pathogens infects body
-much quicker and stronger immune response
-Often gets rid of pathogen before you show symptoms
What is active immunity?
when your immune system makes its own antibodies after being stimulated by an antigen
What is natural active immunity?
when you become immune after catching a disease
What is artificial active immunity?
when you become immune after you’ve been given a vaccination containing a harmless dose of antigen
What is passive immunity?
when you become immune from being given antibodies make by a different organism, your immune system doesn’t produce antibodies of its own
What is natural passive immunity?
when a baby becomes immune due to the antibodies it receives from its mother, through placenta or breast milk
What is artificial passive immunity?
when you become immune after being injected with antibodies from someone else, eg. if you contract tetanus you can be injected with antibodies against the toxins collected from blood donations
Name 4 differences between active and passive immunity.
Active-requires exposure form the antigen, takes time for protection to develop, memory cells are produced, protection is long-term
Passive-doesn’t require exposure to antigen, protection is immediate, memory cells aren’t produced, protection is short-term
What are vaccines made of?
antigens and dead or weakened pathogens
What are some ethical issues with vaccines?
-they are tested on animals
-testing on humans is risky
-risk of side effects
-during an epidemic, a decision has to be made for who receives the vaccines first
What is antigenic variation?
different antigens are formed due to changes in the genes of a pathogen
Name two pathogens that show antigenic variation.
HIV and influenza
What are monoclonal antibodies used in?
pregnancy tests and anti-cancer drugs
What does the ELISA test for?
if you have any antibodies to a certain antigen and vice versa
What are the two types of ELISA test?
Direct ELISA and indirect ELISA
Explain how the direct ELISA works.
- antigens from a sample are bound to the inside of a well in a well plate
- A detection antibody that’s complementary to the antigen being tested for is added
- If antigen is present, it will be immobilised on the inside surface of the well and the detection antibody binds to it
- The well is washed out to remove any unbound antibody and a substrate solution is added
- the enzyme will react with the substrate to give a colour change
How is the indirect ELISA different to the direct ELISA?
the indirect ELISA uses two different antibodies and the direct ELISA uses one antibody
Explain how you would test for HIV using the indirect ELISA.
- HIV antigen is bound to the bottom of a well in a well plate
- A sample of the patients blood plasma is added to the well, if there are any HIV-specific antibodies they will bind to the HIV antigen in the well
- The well is washed out to remove any unbound antibodies
- A secondary antibody, with a specific enzyme attached to it, is added to the well, the secondary antibody can bind to the HIV-specific antibody
- The well is washed out again to remove any unbound secondary antibodies, if no primary antibodies were in the sample then all of the secondary antibodies will be washed away as they have nothing to bind to
- A substrate solution is added to the well which will react with the enzyme attached to the secondary antibody and produce a colour change
What are ethical issues surrounding the use of monoclonal antibodies?
-animal rights issues as animals are used to produce cells which make monoclonal antibodies
Once infected by HIV, what cells act as host cells for the virus?
helper T-cells
How does HIV affect the immune system?
without enough helper T-cells, the immune system is unable to mount an effective response to infections
What is the latency period during HIV infection?
After initial infection the virus replicates rapidly and the person displays flu-like symptoms, after this the replication rate decreases and this is the latency period
When is somebody classed as having AIDS?
when their immune system starts to fail and their helper T-cell count drops below a certain level
What are the initial symptoms of AIDS?
minor infections of mucous membranes and recurring respiratory infections
What are the symptoms of AIDS as it develops?
chronic diarrhoea, severe bacterial infections and tuberculosis
What are the last symptoms of AIDS?
toxoplasmosis of the brain and candidiasis of the respiratory system
What is the structure of HIV?
-spherical structure
-contains RNA and proteins (including reverse transcriptase)
-outer layer of protein called a capsid
-extra outer layer called an envelope
-attachment proteins
How does HIV replicate?
- Attachment protein attaches to a receptor molecule on cell membrane
- Capsid is released into the cell, where it uncoats and releases the RNA into the cytoplasm
- Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
- Double stranded DNA is made and inserted into the human DNA
- Host cell enzymes are used to make viral proteins from the viral DNA found in the human DNA
- Viral proteins are assembled into new viruses, which bud from the cell and infect other cells
How do antiviral drugs kill viruses?
they target the few virus-specific enzymes
How can the spread of HIV be controlled?
-reducing the spread
-use condoms
-don’t share needles
