Cell recognition and the immune system Flashcards
YType of defence mechanisms
Non specific = immediate (physical barrier and phagocytosis)
Specific = slow and specific to all pathogens (cell-mediated responses and humoral response)
What do cell-mediated and humoral responses involve
Cell-mediated = T lymphocytes
Humoral responses = B lymphocytes
What must lymphocytes be able to do to defend the body?
Distinguish self and non-self molecules
How do lymphocytes distinguish between self and non-self material
Proteins on surface
Have specific tertiary structure so can be distinguished between cells
What do the proteins on the surface help lymphocytes identify
Pathogens
Non-self material
Toxins
Abnormal bods cells
What is phagocytosis
When large particles are engulfed in the vesicles of the cell-surface membrane
Where do phagocytes travel
In the blood and tissues
Stages of phagocytosis
1) Pathogens toxins attract phagocyte
2) Lysosomes fuse with phagosome
3) Lysozymes hydrolyse ingested bacteria
What is an antigen
Substance that is recognised as non-self and stimulates your immune system to produce antibodies
How are lymphocytes produced
By stem cells in the bone marrow
What are the two types of lymphocytes
B lymphocytes and T lymphocytes
What are B lymphocytes
In bone marrow
Humoral immunity
Involve antibodies
Present in body fluids
What are T lymphocytes
In thymus gland
Cell-mediated immunity
Involve body cells
What do lymphocytes respond to
Non-self material from different species and from other individuals (because they are genetically different)
How can T lymphocytes distinguish invader cells from normal ones?
Once hydrolysed, they keep some of pathogens antigens on their cell-surface membrane
What do T lymphocytes response to
Antigens presented on body cell
Response of T lymphocytes to infection by pathogen stages
1) Pathogens taken in by Phagocytes
2) Receptors on T cell fix onto antigens
4) T cell undergoes mitosis
5) Cloned cells turn into memory cells which stimulates phagocytosis, so B cells divide, activating cytotoxic t cells
What are cytotoxic t cells
Kill abnormal cells and body cells infected by pathogens
What do cytotoxic t cells do
Produce perforin that makes holes in cell-surface membrane
Why do cytotoxic cells make holes in cell-surface membrane
Mean cell membrane becomes freely permeable to all substances, so cell dies
What’s it called when an antigen enters a C cell
Endocytosis
What does humoral immunity produce
Antigen specific antibodies
What plasma cells do and what defence they are
Secrete antibodies
Produce antibodies that destroy antigens
Immediate defence
What do memory cells do, how do they help defend the body from pathogens and what response are they
Secondary immune response
When encounter same antigen, divide rapidly and develop into plasma and memory cells
Plasma cells produce antibodies
Memory cells remember killing antigen process
Long-term immunity
How B cells work
1) B cells with complementary receptors divide by mitosis
2) Some B cells become plasma cells producing antibodies
3) Some B cells turn into memory cells
Antibodies
Proteins with specific binding sites synthesised by B cells
What are antibodies made up of
4 polypeptide chains
Heavy chains
Light chains
How is an antigen-antibody complex formed
Antibody has specific binding site that fits onto specific antigen
What is the binding site on antibodies called
Variable region
What do variable regions contain that make them different on different antibodies
They consist of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen
What is the bottom part of an antibody knows as
Constant region
What are the two ways antibodies assist in destroying antibodies
Cause agglutination in bacterial cells
Stimulate phagocytes to engulf bacterial cells
What is agglutination
Clumps of bacteria form so phagocytes can locate them easier as they are less spread out in the body
Monoclonal antibodies definition
artificially produced antibodies produced from a single B cell clone
What does direct monoclonal antibody therapy do
Stop growth of cancer cells
How does direct monoclonal antibody therapy work
MA are specific to antigens on cancer cells
Antibodies given to patient and attach to receptors on cancer cells on their surface
Block chemical signals that cause mitosis of cancer cells
Advantage of direct monoclonal
Not toxic
Highly specific
Few side effects than other forms of therapy
What does indirect monoclonal antibody therapy do
Kill cancer cells
How does indirect monoclonal antibody therapy work
Radioactive or cytotoxic drug attaches with monoclonal antibody
Antibody attaches to cancer cells and kills them
Advantages of indirect monoclonal antibody therapy
Can be used in smaller doses
Targeted on specific sites
Cheaper in small doses
Reduces side effects other drugs might have
Monoclonal antibodies also used in
Medical diagnosis -> ELISA tests
Pregnancy testing -> placenta produces hormone (human chorionic gonaclatrophin), monoclonal antibodies attach and bind to coloured particles. HCG-antibody-colour complex moves along strip, trapped by different antibody creating colour on pregnancy test
Ethical issues of monoclonal antibodies
Infuse mice with cancer and extract tumour cells and antibodies
Been some deaths in treatment
6 patients suffered organ failures in durg trial
Suggest two further investigations that should be done before this ADC is tested on human breast cancer patients [2 marks]
Test on healthy humans
Test on other mammals to check for side effects
Investigate difference concentrations of ADC to find safe dosage
Production of monoclonal antibodies
1) Mouse exposed to non-self material
2) B cells produce antibodies
3) B cells extracted from spleen
4) B cells mix with cancer cells
5) Detergent added to break down cell-surface membranes
6) Cells fuse together forming hybridoma cells
7) Hybridoma cells separated under microscope
8) Each cell is cultured to form clone
9) Clones tested so that they are producing correct antibody
10) Antibody grown and antibodies extracted from from growth medium
Passive Immunity
Introduction of antibodies into individuals from outside source
Antibodies aren’t being produced by individuals so cannot be replaced by them
Active immunity
Stimulating production of antibodies by individual’s own immune system
Direct contact with pathogen is necessary
Long-lasting
Natural active immunity
Individual infected with disease under normal conditions
Body produces its own antibodies
Artificial active immunity
Vaccination
Inducing immune response
(Without suffering symptoms)
What do vaccinations force the body to do
Stimulte immune response
What happens to the injected vaccine
Remains in blood
What do vaccinations allow
Greater, more immediate response to future infections
Resulting in rapid production of antibodies
What are some things vaccinations success depends on
Economically available
Few side effects
Producing storing transporting vaccine must be available
Appropriate time of training staff
Herd immunity must be possible
What is herd immunity
When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to pass from individual to individual
Why is herd immunity important
Never possible to vaccinate everyones (children, ill people)
Primary response
Multi-step pathway from antigen presenting cells to create antibodies
Secondary response
Stimulates B cells to cause secretion of more antibodies more rapidly
Cell-mediated response
Product Cytotoxic T cells
Only bind to antigens presenting host cell and destroy that cell
Why might a vaccination not eliminate a disease
Fails to induce immunity in certain individuals
Develop disease immediately after vaccination
Antigenic variability = may mutate its antigens to change suddenly, so vaccines are ineffective
Too many varieties of the pathogen its impossible to develop vaccine for them all
Some pathogens hide from body’s immune system
Objections to vaccination for religious, ethical or medical reasons
Ethical issues with vaccines
Uses animals
Side effects -> can be long term
Taking risks in interest of public
Who should vaccines be tested on
Is it acceptable to trial a new vaccine with unknown health risks
Expensive
How does HIV replicate
1) Enters bloodstream circulates body
2) Protein on HIV binds to helper T cells
3) Protein capsid fuses with cell-surface membrane
4) RNA and enzymes of HIV enter T cell
5) HIV reverse transcriptase converts virus’s RNA into DNA
6) DNA inserted into helper T cell’s nucleus
7) HIV DNA in nucleus created mRNA
8) mRNA passes out nucleus through nuclear pore and uses cell’s protein synthesis mechanisms to maKe HIV particles
9) HIV particles break away from helper T cell with piece of its cell-surface membrane forming lipid envelope
What is an ELISA test used for
Uses antibodies to detect presence of a protein
How do bacterias cell walls not burst
walls made out of murein
Cell wall resists expansion
Why are antibiotics ineffective in Viruses
Viruses rely on host cells to carry out metabolic activities
Ineffective because there are no metabolic mechanisms
AND they have protein coats so do not have sites where antibiotics can work
Outside layer of HIV
Lipid envelope
Pegs going into HIV
Attachment proteins
Rectangle envelope surrounding subsystems in HIV
Capsid
What does capsid contain HIV
RNA and enzymes
What’s an important enzyme contained in the capsid in HIV and what does it do
Reverse transcriptase
Catalyses production of RNA to DNA
Name of viruses that can transfer RNA to DNA
Retroviruses
Second inner layer of HIV
Matrix
What are red blod cells official name
Erythrocytes
What is white blod cells official name
Leucocytes
What are the two types of white blod cells
Phagocytes and lymphocytes
What do phagocytes do
Phagocytosis
Engulf pathogens, hydrolysing enzymes to digest pathogen
Present antigens on cell surface membrane
What do lymphocytes and phagocytes have to distinguish them
Lymphocytes have much larger nucleus
What are the two types of lymphocytes
T and B cells
What do t cells do
Identify non-self
What are the three types of T cells
T helper
T cytotoxic
T memory
What are B cells used for
Monoclonal antibody production
How does the ELISA test work
1) Apply sample to surface of slide for antigens to attach to
2) Wash surface to remove unattached antigens
3) Add antibody specific to antigen to detect and leave two to bind (apply patients blood with HIV)
4) Wash surface to remove excess antibody (wash blood off)
5) Add second antibody to bind with first antibody
6) Add colourless substrate of enzyme, enzyme attach to substrate and changes colour
7) Amount of antigen present shows different colour intensity
Why are antibiotics ineffective against viral diseases
1) Viruses rely on host cells to carry out metabolic activities (they dont have metabolic pathway), no cell structure or mechanism for antibiotics to disrupt
2) Protein coat does not have sites where antibiotics work so antibiotics can’t reach them
How do antibiotics work
In bacterial cells water constantly enters by osmsis
Murein wall surrounding bacterial cell is tough, as water enters cell expands and wall resists.
Antibitics inhibit enzymes required for synthesising peptide cross-linkages in cell walls of bacteria
Weakening the walls, making them unable to withstand pressure and burst
How does HIV cause AIDS symptoms
HIV attacks T helper cells
Immune system can’t stimulate B cells to produce antibodies and cytotoxic T cells
Also affecting memory cells
Body can’t produce effective response to other infections and cancers
How does your body not kill it’s self material
1) T cells mature in thymus
2) When the T cells are maturing, immature lymphocytes will only encounter self antigens
3) If they react to self antigens (which they are not meant to), they will undergo apoptosis (Self death of cell)
4) This measn that we dont get any self reactive lymphocytes in the bloodstream
What is apoptosis
Programmed cell death
Describe phagocytosis
1) Chemicals from the non-self material act as attractants for the phagocytes
2) Phagocytes move towards the attractants
3) Phagocytes will detect the pathogens using their cell surface receptors
4) They engulf the pathogen inside a phagosome
5) The lysosome releases enzymes/lysozymes into the phagosome
6) This breaks down the pathogen into debris which can be absorbed into the cytoplasm
7) The cycle repeats with another pathogen
Difference between phagocytes and lymphocytes
Phagocytes = non specific
Lymphocytes = specific
Two types of lymphocytes
T cells and B cells
Types of t cells and b cells
T cells = memory T cell, helper cells (th), cytotoxic t cells (Tc)
B cells = plasma cells, memory B cell
How are T helper cells activated
1) Phagocyte presents non self material (pathogen) on its cell surface membrane
2) T helper cells recognise the antigen and activate the specific response
What do cytotoxic t cells do
Stop the infected cells replicating through perforin (making holes in virus)
What do plasma cells from B cells do
Activated when virus complementary attaches to presented antigen receptor on B cell
In order to produce more B cells by mitosis with specific antigens present that are also complementary to the pathogens antigen, so there are more B cells to kill the pathogens
What are plasma cells
Name we give to B cells that produce antibodies
What type of molecules do antigens detect are non self
Pathogens
Cells from other organisms of the same species
Abnormal body cells
Toxins
What is an antigen
The effect of antigen variability on disease and disease prevention
What is phagocytosis definition
Destruction of ingested pathogens by lysozymes
What is an antigen presenting cell
ANtigen-presenting cell is one of the host’s cels that has been invaded by a pathogen and is displaying the antigen on its cell surface membrane
T cells only bind to antigen if it’s present on an antigen-presenting cell
What does an antigen presenting cell do
Present antigens from toxins, foreign cells and ingested pathogens
Help recruit other cells for specific immune response
Once surface receptor of T cell binds to specific complementary antigen on antigen presenting cell is becomes sensitised and starts dividing to produce a clone of cells
Example of antigen-presenting cells
Macrophages and dendritic cells
