2.4 cell recognition and the immune system Flashcards
Antigen
Molecules which, when recognised as non-self, can trigger an immune response and lead to the production of antibodies
Often proteins on the surface of cells
Proteins have a specific tertiary structure allowing different proteins to act as specific antigens
What the immune system identifies
Pathogens e.g. viruses, fungi, bacteria
Cells from other organisms of the same species e.g. organ transplant
Abnormal body cells
Toxins released from pathogens
Phagocytosis of pathogens
Phagocyte recognises foreign antigens on the pathogen and binds to the antigen
Phagocyte engulfs pathogen by surrounding it with its cell surface membrane
Pathogen contained in vacuole 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
Cellular response (T lymphocytes)
T lymphocytes recognise antigen presenting cells after phagocytosis
Specific T helper cell with receptor complementary to specific antigen binds to it, becoming activated and dividing rapidly by mitosis to form clones which:
Stimulate B cells for the humoral response
Stimulate cytotoxic T cells to kill infected cells by producing perforin
Stimulate phagocytes to engulf pathogens by phagocytosis
Humoral response
Clonal selection: in which specific B cell binds to APC and is stimulated by helper T cells which releases cytokines
Divides rapidly via mitosis to from clones
Some become B plasma cells for the primary immune response - secrete large amounts of monoclonal antibodies into the blood
Some become B memory cells for the secondary immune response
Primary response
Produces antibodies slower and at a lower concentration
as not many B cells available that can make the required antibody &
T helpers need to activate B plasma cells to make the antibody
So infected individual will experience symptoms
Secondary response
Produces antibodies at faster and higher concentration as
B and T memory cells present
B memory cells undergo mitosis quicker
Describe and explain how the structure of an antibody relates to its 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 disulphide bonds
Quaternary structure contains 4 polypeptide chains held together by H, I, D bonds
- enables the specific shaped variable region to form which is a complementary shape to specific antigen
- enables antigen-antibody complex to form
How do antibodies work to destroy pathogens
Binds to 2 pathogens at same time, forming an antigen-antibody complex
Enables antibodies to clump pathogens together - agglutination
Phagocytes bind to the antibodies and phagocytise many pathogens at once
Vaccination
Injection of antigens
From attenuated pathogens
Stimulates formation of memory cells
A vaccine can lead to symptoms because some of the pathogens may be live and reproduce and release toxins
Use of vaccines to provide protection
Normal immune response but the memory cells are produced
On reinfection, the secondary response therefore produces antibodies faster and at higher concentration
Leading to the destruction of a pathogen/antigen before it can cause harm
Herd immunity
Large proportion but not 100% vaccinated against a disease
Makes it more difficult for pathogen to spread as more people are immune so fewer in population carry the pathogen
Fewer susceptible so less likely that non-vaccinated will come in contact with disease
Active immunity v Passive immunity
Initial exposure to antigen | no exposure to antigen
Memory cells involved | no memory cells involved
Antibody is produced & secreted by B plasma cells | antigen introduced into body from another organism
Slow, takes time to develop | fast acting
Long term immunity > antibody can be produced in response to a specific antigen again | short term immunity (antibody broken down)
Ethical issues associated with the use of vaccines
Tested on animals before use on humans > animals have a CNS so feel pain
Tested on humans > volunteers may put themselves at unnecessary risk of contracting the disease because they think they’re fully protected
Can have side effects
Expensive - less money spent on research and treatments of diseases
Antigen variability as 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
Explain the effect of antigen variability on disease
Change in antigen shape
Not recognised by B memory cells > no plasma cells
Not immune
Must re-undergo primary immune response > slower / releases lower concentration of antibodies
Disease symptoms felt
Explain the effect of antigen variability on disease prevention
Change in antigen shape
Existing antibodies with specific shape unable to bind to changed antigens / form antigen-antibody complex
Immune system e.g memory cells wont recognise different antigens
Evaluate methodology, evidence and data relating to the use of vaccinations
Successful vaccination programme:
- provides suitable vaccine: effective, no major side effects, low cost, easily produced
- provides herd immunity
Evaluating a conclusion from data: check correlation (could be due to another variable), repeatability (other studies?), validity (does it answer the question), potential bias
Use of monoclonal antibodies
Monoclonal antibody = antibody produced from a single group of genetically identical B cells/plasma cells. Identical tertiary structure
Bind to specific complementary antigen
- have a binding site with a specific tertiary structure
- only 1 complementary antigen will fit
Why are monoclonal antibodies useful in medicine
Only bind to specific target antigens
As
Antibodies have a specific tertiary structure that’s complementary to a specific antigen which can bind to the antibody
Monoclonal antibodies & cancer cells
Monoclonal antibodies made to be complementary to antigens specific to cancer cells > cancer cells are abnormal body cells with different antigens
Anti-cancer drug attached to antibody
Antibody binds to cancer cells, forming antigen-antibody complex
Delivers attached anti-cancer drug directly to specific cancer cells so drug accumulates > fewer side effects
Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour
Antibody has a specific tertiary structure
Complementary shape to receptor protein
Prevents __ binding to receptor
Monoclonal antibodies & pregnancy test
If pregnant , hCG binds to antibodies in application area = hCG-antibody complex
Travels up test strip, binds to antibodies at position 2 (blue line)
If not pregnant, no hCG in urine so hCG doesnt bind to antibodies in application area so doesnt bind to antibodies at position 2 = no blue line
Bind to antibodies at position 3 > blue line = control
Use of antibodies in ELISA
Can determine if a patient has: antibodies to a certain antigen, antigen to a certain antibody (used to diagnose diseases or allergies)
