cell recognition and the immune system Flashcards
what is an antigen
molecules which have been recognised as non-self by the immune system, can stimulate an immune response and lead to the production of antibodies
often protein on the surface of cells
why are antigens specific
tertiary structure protein
what do specific antigens allow the immune system to identify
pathogens
cells from other organisms of the same species
abnormal body cells
toxins released from bacteria
what is phagocytosis
non-specific immune response
1. phagocyte recognises foreign antigens on the pathogen and bind to the antigen
2. phagocyte engulfs pathogen by surrounding it with its cell surface membrane
3. pathogen contained in phagosome in cytoplasm of phagocyte
4. lysosomes fuse with phagosome and release lysozymes
5. these hydrolyse pathogen
6. phagocyte becomes antigen presenting and stimulates specific immune response
what is the cellular response (T lymphocytes to a foreign antigen)
- T lymphocytes recognises antigen presenting cells after phagocytosis
- specific T helper cell with receptor complementary to specific antigen binds to it, becoming activated and dividing rapidly to form clones that
- 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
what is the humoral response (B lymphocytes to a foreign antigen)
- clonal selection
- specific B cell binds to antigen presenting cell and is stimulated by helper T cells which release cytokines
- divides rapidly by mitosis to form clones - some become B plasma cells for the primary immune response - secrete large amounts of monoclonal antibodies into blood
- some become B memory cells for secondary immune response
what is the primary immune response
produces antibodies and slower and lower conc. because
- not many B cells available that can make required antibody
- T helpers need to activate B plasma cells to make the antibodies
so infected individuals will express symptoms
what is the secondary immune response
produces antibodies faster and at higher conc. because
- B and T memory cells present
- B memory cells undergo mitosis quicker
what is an antibody
quaternary structured protein
secreted by B lymphocytes in response to a specific antigen
binds specifically to antigens forming a antigen-antibody complex
what is the structure of a antibody
heavy chain and light chain
constant region and variable region
2 disulfide bridges
antigen binding site
describe and explain how the structure of an antibody relates to it function
primary structure protein = sequence of amino acids in a polypeptide chain
- determines the folds in the secondary structure as the 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 held together by hydrogen ionic and disulfide bonds
- enables the specific shaped variable region to form which is complementary to specific antigen
- enables antigen- antibody complex to form
how to antibodies work to destroy pathogens
binds to two pathogens at a time forming antigen-antibody complex
enables antibodies to clump the pathogen together - agglutination
phagocytes bind to the antibodies and phagocytoses many pathogens at once
what is a vaccination
injection of antigens
from dead or weakened pathogens
stimulates the formation of memory cells
how are vaccines used to provide protection against disease
normal immune response meaning memory cells are produced
secondary exposure to the same antigen stimulates the secondary response
producing antibodies faster and at a higher conc.
how to vaccinations protect populations against disease
herd immunity
makes it more difficult for pathogen to spread because
- more people immune so fewer carry pathogen
- less likely that non vaccinated will come into contact with infected person
what is the difference between active and passive immunity
active
- initial exposure to antigen eg. vacation or
pathogen
- memory cells involved
- antibody is produced and secreted by B plasma cells
- slow takes time to develop
- long term immunity, memory cells
passive
- no exposure to antigen
- no memory cells involved
- antibody introduced from another organism eg. breast milk, placenta
- fast acting
- short term immunity
what are the ethical issues associated with vaccinations
- tested on animals before humans
- tested on humans, volunteers may put themselves at unnecessary risk
- can have side effects
- expensive
antigen variability is often an explanation for why …
new vaccine need to be developed more frequently
vaccines against disease may be hard
to develop
many experience a disease more than once
what is 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
symptoms
what is the effect of antigen variability on vaccinations
change in antigen shape
existing antibodies with a specific shape unable to bind to changed antigen
immune system won’t recognise different antigens
evaluate methodology, evidence and data relating to the use of vaccinations
a successful vaccination programme
- effective to make memory cells
- no major side effects
- low cost
- easily produced transported stored and administered
- provides herd immunity
evaluating a conclusion
- scatter graph = positive negative or no correlation, correlation doesn’t mean causation
- repeatability - have there been other experiments showing the same
- validity - does data answer question
- bias ?
what are the uses of monoclonal antibodies
monoclonal antibody - antibody produced from a single group of genetically identical B cells
bind to specific complimentary antigen
- have a bind site with specific tertiary structure
- only one complementary antigen will fit
why are monoclonal antibodies useful in medicine
- only bind to specific target molecules
- antibodies have specific tertiary structure that’s completely to a specific antigen which can bind to the antibody
how are monoclonal antibodies used to target medication to specific cell types by attaching a therapeutic drug to an antibody
eg. cancer cell
1. monoclonal antibodies made to be complementary to antigens in specific cancer cells
2. anti cancer drug attached to antibody
3. antibody vibes to cancer cell
4. delivers attached anti cancer drug directly to specific cancer cells so drug accumulates - fewer side effects
how are monoclonal antibodies used in medical diagnosis
eg. pregnancy test
- pregnant women have hormone hCG in urine
- urine test strip as 3 parts with 3 specific antibodies
position 1: antibodies complementary to hCG
position 2: antibodies complementary to hCG antibody complex
position 3: antibodies complementary to antibody without hCG attached
- if pregnant hCG bind to antibodies in position 1, the antibody complex travels to position 2 = blue line
- if not pregnant no antibody complex formed, travels to position 3 control
how are antibodies used in the ELISA test
enzyme linked immunosorbent assay
can determine if patient had
- antibodies to a certain antigen
- antigen to a certain antibody
diagnose disease or allergies
controls enable comparison with the test to show that
- only the enzyme and nothing else caused colour change
- washing is effective and all unbound antibodies washed away
secondary and detection antibody must be washed away so that
- enzyme attached to antibody reacts with substance turning the solution a different colour
- not washed = enzymes will react with substance and give false positive
draw a diagram to explain ELISA test
step 1- mumps antigen is attached to a well in a test dish
step 2- a sample of blood plasma is added to the well, if mumps antibodies are present they bind to the mumps antigen
step 3- the well is washed, the second antibody with enzyme attached is added, this binds specifically to the mumps antibody
step 4- the well is washed again, a solution is added which will change colour if the enzyme is present, colour change shows that the person has mumps antibodies
what are the ethical issues associated with the use of monoclonal antibodies
animals involved in production
effective treatments for cancer and diabetes that have caused death when used as treatment for multiple sclerosis
patient needs to be informed on risks and benefits
how does HIV replicate
in helper T cells
1. HIV infects helper T cell (host)
- attachment protein attaches to receptor on helper T membrane
2. virus lipid envelope fuses with cell surface membrane and capsid released releasing RNA and reverse transcriptase into cytoplasm
3. viral DNA is made from viral RNA
- reverse transcriptase produces complementary DNA strand from viral RNA template
4. viral DNA is integrated with hosts DNA
5. this remains latent for a long time until host is activated
6. host enzymes make viral proteins from viral DNA which assemble with viral RNA to make new virus
7. new virus bud from cell
8. eventually kills helper T cell
9. most host cells infected and process repeats
how does HIV cause the symptoms of AIDS
acquired immune deficiency syndrome
infects helper T cells as it multiplies rapidly
- helper T cells can’t stimulate cytotoxic T cells B cells and phagocytes
impaired immune response
immune system deteriorates
more infections
why are antibiotic ineffective against viruses
antibiotics can’t enter human cells
viruses don’t have own metabolic reactions which antibiotics target
would increase risk of antibiotic resistant bacteria
