3.2.4 Cell recognition and the immune system Flashcards
What is an antigen?
A molecule/protein that triggers an immune response
Name the 4 main stages of immune response
- Phagocytosis
- phagocytosis activate T-cells
- T-cells activate B-cells which divide into plasma cells
- Plasma cells make more antibodies to a specific antigen
where are phagoyctes found
in blood and tissues
Describe phagocytosis (5)
Phagocyte is attracted to pathogen by chemicals it produces
Phagocyte attaches itself to the surface membrane of the pathogen
phagocyte engulfs the pathogen within a vesicle to form a phagosome
lysosomes in the phagocyte fuse with the phagosome to form a phagolysosome
lysozymes in the lysosome hydrolyse/digest the pathogen
Why does phagocytes moves towards pathogens
they’re attracted to pathogen’s chemical products
Phagocytes engulf pathogens by _____
endocytosis
Waste products removed by _____
exocytosis
How do lysozymes break down bacteria
Hydrolyse the cell walls of bacteria
What do phagocytes do at the end of phagocytosis?
Phagocyte presents pathogen’s antigens on its surface to activate other immune system cells
What do T-cells only respond to
Antigen-presenting cells
Where do T-cells (aka T-lymphocyte) mature?
In thymus gland
Describe what T-cells do and what response are they usually associated with mainly?
Respond to antigens on foreign and infected cells
Specific receptors on helper T cells bind to specific antigen presented by phagocytes (antigen-presenting cell)
This activates T-cell: Binding triggers rapid mitosis = T cells are cloned
Cellular response
Name 4 things that the cloned helper T-cells do
Activate cytotoxic T cells
Activate B-cells to divide and secrete their antibodies
Develop into memory cells
Release chemical signals that activate and stimulate phagocytes
Describe how cytotoxic T-cells kill infected cells
Produce protein called perforin that makes holes in cell-surface membrane
Holes means cell membrane becomes freely permeable
Control of substances no longer controls and cell dies
Why is the action of T-cells most effective against viruses?
they replicate inside cells, sacrificing these body cells prevents viruses from multiplying and infecting more cells
What is the role of macrophages in stimulating B lymphocytes?
Antigen in membrane presented to lymphocytes
Produce cytokinins
What are B-cells (B-lymphocytes)? Where do they mature?
White blood cell that’s covered with antibodies
thymus gland
What are antibodies?
A protein produced by lymphocytes in response to the presence of an appropriate antigen
Describe how T-cells activate B-cells, which divide into plasma cells
When antibody on surface of B-cells meets complementary shaped antigen = binds to it
This, together with chemicals released from helper T-cells, activates B-cell = divides by mitosis
Clonal selection: form clones/produce plasma cells
Make antibodies
Plasma cells produce memory cells
What do plasma cells do?
Secrete loads of antibodies specific to antigen
called monoclonal antibodies
Describe what antibodies do to destroy pathogens
Antibody has 2 binding sites = can bind 2 pathogens at same time
Means pathogens & antibodies become clumped together = called agglutination
Phagocytes bind to antibodies and phagocytose many pathogens at once
Process leads to destruction of pathogens carrying this antigen in
All antibodies have same _____ region
All antibodies have same constant region
What does the constant region allow antibodies to do?
To bind to receptors on B-cells
What does the hinge region allow antibodies to do?
Allows flexibility so molecules can group more than one antigens
Why are antibodies specific to one antigen? (3)
Variable region has specific primary structure
Tertiary structure of binding site is complementary to bind with these antigens
Forms complex between antigen and antibody
What is the primary response?
When antigen enters body for 1st time & activates immune system
Why is the primary response slow?
there aren’t many B-cells that can make antibody needed to bind to pathogen
Primary Immune Response
After being exposed to antigens, T- and B-cells produce ____ ___
memory cells
Memory cells remain in body for ____ time
long
What do memory B-cells do
Record specific antibodies needed to bind the antigen
What do memory T-cells do?
Remember specific antigen and will recognise it 2nd time round
Explain why antigenic variability causes some people to get infected more than once
Memory B/T cells don’t recognise new antigens
Antibodies previously produced are not effective ∵ shape not complementary to new antigen
What is the secondary response?
When same pathogen enters body = immune system will produce quicker, stronger immune response
Why is the secondary response quicker than the primary response? Explain in terms of memory T-cells/B-cells
Clonal selection happens faster
Memory T-cells are activated and divide into correct type of T-cells to kill cell carrying antigen
Memory B-cells are activated and divide into plasma cells that produce right antibody to antigen
Why do you suffer from symptoms?
B-cells busy dividing to increase their numbers to deal with pathogen
What are vaccinations?
Injection of (Antigen from) dead pathogen
Stimulates the formation of antibodies & memory cells
which are complementary to antigen
memory cells stay in blood
result in rapid production of correct antibodies if there is a future exposure
How do vaccinations protect people against disease? (5)
- Vaccines contain dead antigens from pathogen
- Memory cells are made
- On second exposure memory cells produce antibodies as they recognise pathogen
- They rapidly produce more antibodies
- Antibodies destroy pathogen before symptoms can occur
What is meant by herd immunity?
Many vaccinated = reduces occurrence of disease ∴ those unvaccinated, less likely to catch disease
Chance of disease spreading is reduced
FEW PPL TO INFECT
FEWER PPL TO DO INFECTING
Name 2 disadvantages of oral vaccines
Could be broken down by enzymes in gut
Molecules of vaccine = too large to be absorbed into blood
Describe how vaccination lead to immunity (7
Vaccine contains antigen from pathogen
Macrophage presents antigen on its surface
T cell with complementary receptor protein binds to antigen
T cell stimulates B cell, with complementary antibody on its surface
B-cells undergo mitosis/form clones
Plasma cells produce lots of antibodies
Memory cells produced = more antibodies produced faster in secondary response on reinfection
What is antigenic variation?
When pathogens change their surface antigens
Why do different antigens form?
of changes in genes
Why does antigenic variation makes it difficult to develop vaccines against some pathogens?
If infected, T/B memory cells produced from vaccination won’t recognise different antigens
Antibodies previously produced not effective as shape not complementary to new antigen
Strains of Influenza are _______ ___
immunologically distinct
What is active immunity?
When your immune system makes its own antibodies after being stimulated by antigen
What is passive immunity?
Immunity gotten from being given antibodies made by different organism
(immune system doesn’t produce any antibodies of its own)
Active Immunity
What is natural immunity?
Becoming immune after catching a disease
Active Immunity
What is artificial immunity?
Becoming immune after being given vaccination
Passive Immunity
What is natural immunity?
Baby become immune due to antibodies it receives from mother, through placenta and breast milk
Passive Immunity
What is artificial immunity?
Becoming immune after being injected with antibodies from something else
Name 4 differences between active and passive immunity
AI- requires exposure to antigen PI Doesn’t
AI- takes a while for protection to develop PI is immediate
AI- memory cells are produced PI aren’t
A person may develop influenza twice within a short time. Explain why. (2)
New strain of virus
New strain not recognised by memory cells
Explain why during the secondary response, the person doesn’t show any symptoms (4)
Memory cells produced
Infection with same pathogen causes secondary response
More antibodies produced
Pathogen killed before symptoms occur
What is an antigen presenting cell?
A cell of the body infected by a virus or a phagocyte that presents the foreign antigen on its surface
What is purpose of agglutination?
Acts as marker = makes phagocytosis easier
Stops entry into cells
Give 2 ways in which pathogens can cause disease.
- releases toxins
- destroys/kills cells
How does putting bee honey on a cut kill bacteria?
- Water potential in bacteria is HIGHER than water potential in honey
- Water leaves the bacteria cells by osmosis
- The loss of water stops metabolic reactions
Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable immune system to identify:
- pathogens
- abnormal body cells
- toxins
- cells from other organisms of the same species
What are the 2 nonspecific immune responses?
Phagocytosis and inflammation
What is inflammation?
- When cells become damaged local area becomes red, swollen, warm and painful.
- Histamines are released when tissues are damaged and they stimulate arteries leading to the infected tissues to dilate, increasing permeability
- As a result white blood cells can destroy the pathogen on the infected tissue
Cellular response
PHAGOCYTOSIS AND OPONISATION
1. Receptors on T cells will be complementary to antigens on phagocyte
2. attachment to antigen activates t cell to divide by mitosis
3. cloned t cells can now develop into memory cells
(fast 2y response)
4. can now stimulate b cells to divide by mitosis and phagocytes to destroy pathogens
5. also activate cytotoxic cells
Humoral Response
PHAGOCYTOSIS AND OPONISATION
- T helper cell can bind with antigens on APC
- this activates the b cells which make complementary antibodies to the antigen (specific b cells)
- Clonal selection- this activates b cells to divide by mitosis to produce many plasma cells
- plasma cells are now able to produce the correct antibody (monoclonal antibodies) for the pathogen’s antigen and destroy them
- some b cells develop into memory cells which are prepared to quickly secrete the correct antibodies in 2y immune response these can exist for decades
What occurs during primary response (flat before curve)
time for specific complementary b cell to collide randomly with antigen and form AGAB complexes
then divide to form a clone of plasma cells which then release antibodies
What occurs during primary response? (curve)
- antigen exposure 1st time, activates immune system
- slow as there arent many b cells which can make correct antibody ∴ person will show symptoms of disease
- after exposure t and b cells form memory cells which will recognise the antigen in the future IMMUNITY
- as antibodies destroy the pathogens fewer b cells made and conc of antibodies decrease
What occurs during secondary response?
- same pathogen enters body
- 2y response faster stronger and prolonged, higher conc of antibodies in the blood
- clonal selection b cell occurs faster
- memory b cells can nopw divide into plasma cells
- memory t cells can divide to kill cells carrying antigen
- pathogen is destroyed before symptoms shown
what is a pathogen?
disease causing microorganism
Can you describe the structure of an antibody?
protein produced by b cells
4 polypep chains , 2 heavy 2 light
each antibody has 2 binding sites where it can bind to an antigen forming agab complexes
why will an antibody only bind to 1 antigen? (4)
- variable region has a specific sequence of amino acids
- this determines the 3y structure and binding site
- this will then be complementary in shape to antigens
- forms specific antigen antibodyc omplexes
why do antibodies have quaternary structure?
they are made of more than 2 polypetide chains
why vaccinations may not eliminate disease?
- defective immune systems
- ppl may develop disease immediately after vaccination ∴ immunity levels not high enough to prevent it, correct antibodies not made yet
- pathogen may mutate frequently antigen variability
what are non self antigens?
antigens that arent recognises by the body which cause an immune response
what are monoclonal antibodies?
ANTIBODIES WITH THE SAME TERTIARY STRUCTURE
a single type of antibody that can be isolated and cloned
antibodies which are identical and produced from a group of genetically identical b cells
same structures
v specific only bind to specif antigens
why are monoclonal antibodies ultraspecific and ultraprecise?
- only will act on specific cells
- only a small amount is needed
how are monoclonal antibodies formed
- mouse infected with antigen
- b cells make lots of antibodies
- tumour cells (divide rapidly) and b cells make hybridoma cell which produces lots of antibodies whilst rapidly dividing
- to produce identical complementary antibodies to the antigen
Uses of monoclonal antibodies.
- pregnancy test, medical diagnosis
- separate chemicals from mixture
- immunotherapy, attaching a theraputic drug to antibodies
how are they used for killing cancer cells?
cancer cells have antigens called tumour markers that arent on normal body cells
monoclonal antibodies can be made that will bind to tumour markers
drugs can be attached to these antibodies due to specificity of monoclonal antibodies
Monoclonal antibodies- pregnancy tests.
- application are contains antibodies for HCG which are bound to a coloured dye
- when urine is applied if HCG is present it will bind to the antibody on the blue dye forming an AGAB complex
- urine then moves to the test strip which contains immobilised antibodies for HCG
- if HCG is present at test strip it will turn blue as immobilised antibodies bind to HCG AGAB complex if no HCG will not turn blue
Ethics of monoclonal antibodies
- human genes put into mice, immoral
production involves testing on mice - drugs tested on humans
- animals can also be tested on in drug trials
- saves lives by treating diesease but also some deaths occur
ELISA test
- monoclonal antibodies can be used in test kit form to diagnose diseases or conditions
- quick and reliable and sensitive as they can detect small amount of substance in a sample
How do ELISA tests work?
- antigens isolated and attached to base of a well in test dish WASH ( remove unattached antigens)
- sample (e.g blood) added to well if suspected antibody present it will bind to antigen on the well.
WASH - a second antibody with an enzyme attached is added to the well. This antibody is specific to the antibody that has binded the antigen. WASH to remove any unattached 2nd antibody as this could give a false positive.
- indicator is used and will change colour if enzyme is present and therefore if person has antibody, as enzyme would only be present if it has bound
Describe the role of antibodies in producing a positive result in an ELISA test.
- 1st antibody binds to antigen
- 2nd antibody with enzyme attached is added
- 2nd antibody binds to antgen
- substrate/indicator added and colour changes
Ethic of vaccines.
- On whom should new vaccines be tested on
- possible side effects could sometimes cause LT harm
- development uses animals, acceptable?
- should vaccines be compulsory to achieve herd immunity
- expensive vaccines continue even if disease nearly eradicated ?
What is a virus and how do they work?
accellular (not a cell) and nonliving, no cell division
viruses invade and reproduce in a host cell
cell burst as a result of virus replicates in cell
bursting of cell causes symptoms
Can you describe the structure of the human immunodeficiency virus (HIV)
- attachment protein/glycoprotein
- capsid
- rna
- reverse transcriptase
- lipid nvelope
Why dont antibiotics have an effect of viruses?
antibiotics are used against bacteria in which they interfere with metabolism, stop cell wall synthesis, stops protein production ect.
however viruses are not cells.
HIV is a virus and cannot replicate itself
How does HIV replicate?
- HIV enters bloodstream and circulates body
- protein on HIV binds to CD4 which is most commonly on T cells
- protein capsid fuses with cell membrane of t cell and rna enzymes enter the cell
- HIV reverse transcriptase converts RNA to DNA
- This DNA is inserted into T cell’s nucleus
- HIV DNA creates mrna which contains the instructions for making viral proteins
How can HIV cause symptoms of AIDS?
By killing or interfering with normal functioning of helper T cells
What happens if immune system does not have sufficient helper T cells?
It cannot stimulate B cells to produce antibodies or cytotoxic T cells that kill infected cells.
