cell recognition and the immune system Flashcards
Define an Antigen [4]
- When recognised as foreign by the immune system
- Can stimulate an immune response
- Leading to the production of antibodies
- Usually proteins on the surface of cells
What do Antigens allow the immune system to identify? [4]
- Pathogens
(e.g. bacteria, viruses, fungi) - Cells from other organisms of the same species
(e.g. organ transplant, blood transfusion) - Abnormal body cells
(e.g. cancerous cells / tumours) - Toxins released from bacteria
Describe the Phagocytosis of Pathogens [6]
- Phagocyte recognises foreign antigens on the pathogen surface and binds to the antigen
- Phagocyte engulfs pathogen by surrounding it with its cell surface membrane and cytoplasm
- Pathogen contained in phagosome in cytoplasm of phagocyte
- Lysosome fuses with phagosome and releases lysozymes (hydrolytic enzymes) into the phagosome
- These hydrolyse / digest the pathogen
- Phagocyte becomes antigen presenting and stimulates specific immune response
The Cellular Response [6]
- T lymphocytes recognise antigen presenting cells after phagocytosis of foreign antigen
- The Specific T lymphocyte (T helper cell) with receptor complementary to specific antigen binds to the antigen presenting cell
- Becoming activated and dividing rapidly by mitosis to form clones which then
- Stimulate B cells for the humoral response
- Stimulate phagocytes to engulf pathogens by phagocytosis
- Stimulate cytotoxic T cells to kill infected cells by producing perforin
The Humoral Response [5]
- Specific complementary B cell binds to antigen presenting cell
- And is stimulated by helper T cells to
- Divide 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
Primary Response [4]
- Produces antibodies slower and at a lower concentration
- Not many B cells available that can make the required antibody
- T helpers need to activate B cells to make the antibodies which takes time
- So infected individual will express symptoms
Secondary Response [3]
- Produces antibodies faster and at a higher concentration because
- B and T memory cells present
- B memory cells undergo mitosis quicker
- Infected individual doesn’t express symptoms
Define an Antibody [3]
- Quaternary structured protein
- Secreted by B lymphocytes
- Binds specifically to antigens forming an antigen-antibody complex
How do antibodies work to destroy pathogens? [3]
- Binds to two pathogens at a time forming an antigen-antibody complex
- Enables antibodies to clump the pathogens together via agglutination
- Phagocytes bind to the antibodies and engulf many pathogens at once
Vaccination [3]
- Injection of antigens
- From attenuated (dead or weakened) pathogens
- Stimulating the formation of memory cells
How does the use of vaccines provide protection for individuals against disease? [3]
- Stimmulates the formation of memory cells
- On reinfection/secondary exposure to the same antigen, the secondary response produces antibodies faster and at a higher concentration
- Leading to the destruction of a pathogen before it can cause harm / symptoms
How does the use of vaccines provide protection for populations against disease? [2]
Makes it more difficult for the pathogen to spread through the population because…
- More people are immune so fewer people in the population carry the pathogen / are infected
- Fewer susceptible so less likely that a susceptible (non-vaccinated) individual will come into contact with an infected person and pass on the disease
What is Herd Immunity?
Large proportion but not 100% of population vaccinated against a disease
What is Active Immunity? [3]
- Initial exposure to antigen
(e.g. vaccine or primary infection) - Memory cells involved
- Antibody is produced and secreted by B plasma cells
Give one advantage and disadvantage of Active Immunity
ADVANTAGE
Provides long term immunity
(antibody can be produced again in response to a specific antigen)
DISADVANTAGE
Slow, takes time to develop
What is Passive Immunity? [3]
- No exposure to antigen
- No memory cells involved
- Antibody introduced into body from another
organism
(e.g. breast milk / across placenta from mother)
Give one advantage and disadvantage of Passive Immunity
ADVANTAGE
Fast acting
DISADVANTAGE
Short term immunity
(antibody broken down / can’t be produced again)
Give 4 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
Expensive →
less money spent on research and treatments of other diseases
Can have side effects
What is Antigen Variability an explanation for? [3]
- 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)
Explain the effect of antigen variability on disease [6]
- Change in antigen shape (due to a genetic mutation)
- Antigen not recognised by B memory cell
- No plasma cells / antibodies produced
- Not immune
- Must re-undergo primary immune response
- Disease symptoms felt
Explain the effect of antigen variability on disease prevention (vaccines) [3]
- Change in antigen shape (due to a genetic mutation)
- Existing antibodies with a specific shape unable to bind to changed antigens / form antigen-antibody complex
- Immune system won’t recognise different antigens
Monoclonal Antibody [2]
- Antibody produced from a single group of genetically identical B plasma cells
- Which bind to specific complimentary antigen
Monoclonal Antibodies and therapeutic drugs (e.g. cancer) [5]
- Monoclonal antibodies made to be complementary to antigens specific to cancer cells
- Anti-cancer drug attached to antibody
- Antibody binds to cancer cells, forming antigen-antibody complex
- Delivering attached anti-cancer drug directly to specific cancer cells
- Fewer side effects as fewer normal body cells killed
Monoclonal Antibodies and medical diagnosis (e.g. pregnancy test) [9]
- Pregnant women have the hormone hCG in their urine
- Urine test strip has 3 parts with 3 different antibodies
- Application area, position 1: antibodies complementary to hCG (bound to a blue coloured bead)
- Middle, position 2: antibodies complementary to hCG-antibody complex
- End, position 3: antibodies complementary to non-hCG hormone
If pregnant… - hCG binds to antibodies in application area forming hCG-antibody complex
- Travels up test strip, binds to antibodies at position 2 forming a blue line
If not pregnant… - No hCG in urine so hCG doesn’t bind to antibodies in application area so doesn’t bind to antibodies at position 2 meaning no blue line
Control > non-hCG hormones bind to complementary antibodies at third position, forming a blue line
The use of antibodies in the ELISA (enzyme linked immunosorbent assay) test [3]
Can determine if a patient has…
- Antibodies to a certain antigen
- Antigen to a certain antibody
- Used to diagnose diseases or allergies
How does the ELISA test work? [8]
- Antigen bound to the bottom of the well
- Patients blood sample added
- If specific complementary antibodies are present, they will bind to the antigen
- Wash out the well to remove unbound antibodies
- Add a secondary antibody, complimentary to the bound antigen-antibody complex, with a specific enzyme attached to it
- Wash well out to remove unbound secondary antibody
- Solution containing a substrate which can react with the enzyme attached to the secondary antibody is added
- If the solution changes colour the result is positive
Give 2 ethical issues associated with the use of monoclonal antibody
- Animals are involved in the production of monoclonal antibodies
(e.g. by producing cancer in mice who have a central nervous system so feel pain, and it is unfair to give them a disease) - Although it is effective treatment for cancer and diabetes monoclonal antibodies have caused deaths when used in treatment of Multiple Sclerosis
Give 5 components of a HIV virus
- Envelope
- Attachment Protein
- Capsid
- Reverse Transcriptase
- RNA
How is HIV replicated? [11]
- HIV infects T helper cells (host cell)
- HIV attachment protein attaches to complementary receptor on the helper T-cell membrane
- Virus lipid envelope fuses with cell surface membrane and capsid released into cell
- Capsid uncoats, releasing RNA and reverse transcriptase into cytoplasm
- Viral DNA is made from viral RNA by reverse transcriptase
- Viral DNA integrated into host cell’s DNA
- This remains latent for a long time in host cell until activated
- Host cell enzymes used to make viral proteins from viral DNA, which assemble to make a new virus
- New virus bud from cell, taking some of cell surface membrane as envelope
- Eventually kills helper T cells
- Most host cells are infected and process repeats
How does HIV cause the symptoms of AIDS? [4]
- 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
- Immune response impaired and deteriorates
- More susceptible to infections and diseases that wouldn’t cause serious problems in a healthy immune system are deadly
Why antibiotics are ineffective against viruses? [3]
- Antibiotics can’t enter human calls but viruses exist within its host cell as they are acellular
- Viruses don’t have own metabolic reactions which antibiotics target
- If we did use them it would act as a selection pressure = resistant strain of bacteria via natural selection = reducing effectiveness of antibiotics and waste money
