B5 Cell Recognition And The Immune System Flashcards
(103 cards)
1
Q
What is a phagocyte
A
a macrophage (type of white blood cell) that carries out phagocytosis.
2
Q
Where are phagocytes found
A
in the blood and in tissues
3
Q
Is phagocytosis a specific response
A
No its a non-specific response
Any non-self cell (e.g. pathogen) that is detected will trigger the same response to destroy it.
4
Q
What are the 2nd line of defence
A
White blood cells
5
Q
Which white blood cells have a specific/non-specific response
A
Phagocytes - non-specific
Lymphocytes - specific
6
Q
What happens id a pathogen gets past the chemical and physical barriers (e.g. skin and stomach acid)
A
It enters the blood and the white blood cells are the 2nd line of defence
7
Q
Explain the steps of phagocytosis
A
1.Phagocytes are in the blood and tissues and any chemicals or debris released by pathogens or abnormal cells attract the phagocytes and they will move towards these cells.
- There are many receptor binding points on the surface of phagocytes. They will attach to chemicals or antigens on the pathogen via these receptors.
- The phagocyte changes shape to move around and engulf the pathogen.
- Once engulfed the pathogen is contained with a phagosome vesicle.
- A lysosome within the phagocyte will fuse with the phagosome and release its contents.
6.The lysozyme enzyme is released into the phagosome. This is a lytic enzyme which hydrolyses the pathogen.
- This destroys the pathogen.
- The soluble products are absorbed and used by the phagocyte
8
Q
What does a lysozyme enzyme do
A
It hydrolyses and destroys the pathogen
9
Q
What are lymphocytes
A
WBCs involved in the specific immune response
10
Q
Where are all lymphocytes made
A
In the bone marrow
11
Q
Where do T cells mature
A
In the thymus
12
Q
What does the cell mediated response involve
A
T cells and body cells
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Q
Why is the cell-mediated response specific
A
T cells respond to antigens on the surface of cells
14
Q
What are antigen presenting cells (APC)
A
Any cell that presents a non-self antigen on their surface
15
Q
Examples of antigen presenting cells
A
Infected body cells - present viral antigen on their surface
Macrophage - which has engulfed & destroyed a pathogen will present the antigens on their surface
Cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens
Cancer cells will have abnormal shaped self-cell antigens.
16
Q
Why is the T cell response described ad ‘cell-mediated response’
A
because T cells only respond to antigens which are presented on cells (APC), and not antigens detached from cells and within body fluids, such as the blood.
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Q
Explain the steps in the cell-mediated response
A
I. Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface.
This is now called an antigen presenting cell (APC)
- HelperT cells have receptors on their surface which can attach to the antigens on APC.
- Once attached this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones
- Cloned helper T cells differentiate into different cells
• Some remain as helper T cells and activate B lymphocytes
.Some stimulate macrophages to perform more phagocytosis
.Some become memory cells for that shaped antigen
.Some become cytotoxic T cells (killer T cells)
18
Q
What do cytotoxic T cells do
A
Destroy abnormal or infected cells
19
Q
How do cytotoxic T cells cause cell death
A
They release a protein, perforin, which embeds in the cell surface membrane and makes a pore (a hole) so that any substances can enter or leave the cell.
This causes the cell death.
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Q
Why is cell death most common in viral infections
A
because viruses infect body cells.
Body cells are sacrificed to prevent viral replication.
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Q
Why do you get a sore throat when you have a cold
A
the cytotoxic T cells are destroyed infected body cells in your throat.
22
Q
What are lymphocytes involved in?
A
Specific immune response
23
Q
Where do B cells mature
A
In the bone marrow
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Q
Why is it called ‘humoral response’
A
‘humour’ is an old term for body fluids, hence the name humoral response.
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What does the humoral response involve
B cells and antibodies
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What do antibodies do
Soluble and transport in bodily fluids
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How long can memory b cells live in your body compared to plasma cells
B cells = For decades
Plasma cells are short lived
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What is active immunity
Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they peviously encountered.
This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur.
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What type of protein structure is an antibody
A quaternary structure protein
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How do antibodies make it easier for phagocytes to locate and destroy pathogens
Antibodies are flexible and can bind to multiple antigens to clump them together
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How do b cells trigger a response
Different B cells that have antibodies on their surface complementary to diff antigens
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What do plasma cells make
Antibodies
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What do b memory cells do when re-infected with the same pathogen
B memory cells can divide rapidly into plasma cells to make large numbers of antibodies rapidly
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The role of b cells in humoral immunity
1 The surface antigens of an invading pathogen are taken up by a B cell.
2 The B cell processes the antigens and presents them on its surface.
3 Helper T cells attach to the processed antigens on the B cell thereby activating the B cell.
4 The B cell is now activated to divide by mitosis to give a clone of plasma cells.
5 The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogen's surface.
6 The antibody attaches to antigens on the pathogen and destroys them
7 Some B cells develop into memory cells. These can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies. This is the secondary immune response.
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What happens when antigens in blood collide with conplementary antibody on B cells
B cell takes in the antigen by endocytosis and then presents it on its cell surface membrane.
When this B cell collides with a helper T cell receptor, this activates the B cell to go through clonal expansion and differentiation (clonal selection)
B cells undergo mitosis to make large numbers of cells, these differentiate into plasma cells or memory B cells.
Plasma cells make antibodies
B memory cells can divide rapidly into plasma cells when re-infected with the same pathogen to make large numbers of antibodies rapidly.
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What are antigens
Antigens are molecules that generate an immune response by lymphocyte cells when detected in the body.
They are usually proteins and they are located on the surface of cells.
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Antigen variability
Pathogens DNA can mutate frequently. If a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change.
Any previous immunity to this pathogen (either naturally through prior infection or artificially through vaccination) is no longer effective, as all the memory cells in the blood will have a memory of the old antigen shape.
This known as antigen variability. influenza virus mutates and changes its antigens very quickly and this is why a new flu vaccine has to be created each year.
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What is active immunity
Immunity created by your own immune system following exposure to the pathogen or its antigen
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What is natural active immunity
Following infection and the creation of the bodies own antibodies and memory cells
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What is artificial active immunity
Following the introduction of a weakened version of the pathogen or antigens via a vaccine.
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What’s herd immunity
If enough of population are vaccinated pathogen cannot spread easily amongst population.
This provides protection for those who are not vaccinated e.g those with already too ill to have a vaccine, or have lowered immunity unable, or those who are too young.
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Where do viruses replicate
Inside cells - difficult to destroy them with out harming host cells
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Why can viruses not be destroyed by antibiotics
Viruses also have different mechanisms to replicate and no cell wall, like bacteria
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HIV structure
Core = genetic material (RNA) and the
enzyme reverse transcriptase, which are needed for viral replication.
Capsid = outer protein coat
Envelope = extra outer layer, made out of
membrane taken from the host's cell membrane.
Protein Attachments = On the exterior
of the envelope to enable the virus to attach to the host's helper T cell.
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Replication of HIV in helper T cells
HIV is transported around in the blood until it attaches to a CD4 protein on the helper T cells.
The HIV protein capsule then fuses with the helper T cell membrane, enabling the RNA and enzymes from HIV to enter.
The HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the helper T cell nucleus, this is why it is called a retrovirus.
Here mRNA is transcribed, and the helper T cell starts to create viral proteins to make new viral particles.
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What does ELISA stand for
Enzyme linked immunosorbent assay (ELISA)
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How do you carry out an ELISA test
1.Add the test sample from a patient to the base of the beaker.
2. Wash to remove any unbound test sample.
3. Add an antibody complementary in shape to the antigen you are testing the presence of in the test sample.
4.Wash to remove any unbound antibody.
5.Add a second antibody the is complementary in shape to the first antibody, and binds to the first. The second antibody has an enzyme attached to it.
6. The substrate for the enzyme, which is colourless, is added. This substrate produces coloured products in the presence of the enzyme.
7.The presence of the colour indicates the presence of the antigen in the test sample and the intensity of the colour indicates the quantity present.
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What are the use of 2 antibodies in ELISA test
First mobile antibody, complementary to the antigen being tested for, and has a coloured dye attached.
second antibody complementary in shape to the antigen is immobilised in the test.
third antibody is immobilised and is complimentary in shape to the first antibody.
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What can monoclonal antibodies be used to test for
Pregnancy
• Influenza
• Hepatitis
• Chlamydia
• Prostate cancer
. Covid 19
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What do b lymphocytes respond to to
B lymphocytes respond to foreign antigens through clonal selection and the release of monoclonal antibodies (the humoral response).
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What does clonal selection create
Clonal selection creates plasma cells and memory cells. Plasma cells release antibodies. Memory cells remain in the blood for decades and will quickly produce plasma cells if they encounter a known antigen.
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What do antibodies bind to
Antibodies bind to antigens to create an antigen-antibody complex, leading to the destruction of the antigen through agglutination and phagocytosis of bacterial cells.
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What are antibodies
Antibodies are quaternary proteins made of up 4 polypeptide chains. The variable region of an antibody is a unique shape complementary for each antigen.
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What are lymphocytes
Your body's immune system has cells to identify the presence of pathogens and potentially harmful foreign substances in the body and to then destroy of neutralise them to prevent harm.
These cells and lymphocytes.
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how can lymphocytes distinguish between pathogens and self-cells?
Each type of cell has specific molecules on its surface that identify it. These molecules are usually proteins, as their 3D tertiary structures enables lots of unique and identifiable shapes to be made.
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Identifying self and non-self cells
Ifa non-self cell is detected a response will be triggered to destroy the cell.
These different surface molecules enable them to identify:
1. Pathogens (e.g. bacteria, fungi or viruses such as HIV)
2. Cells from other organisms of the same species (harmful for those with organ transplants)
30 seconds
3. Abnormal body cells (e.g. cancer cells)
4. Toxins (some pathogens release toxins into the blood, such as Cholera)
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How lymphocytes recognise cells
You have 10 million different types of lymphocytes in your body - each one can recognise a different shaped antigen.
Lymphocytes are made when you are a foetus. When you are a foetus in the womb you are unlikely to be exposed to any cells other than self cells.
The lymphocytes complementary to the antigens on self-cells will die or production will be suppressed. This is to prevent your lymphocytes from attacking your own cells.
This only remaining lymphocytes are complementary to pathogenic and non-self cells.
The same process occurs after birth in the bone marrow. Any new lymphocytes made in the bone marrow which are complementary in shape to antigens on self-cells will be destroyed.
Sometimes this process doesn't work properly and lymphocytes which will attack self-cells are produced, this is what causes the symptoms of autoimmune diseases.
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What are antigens
Antigens are molecules that generate an immune response by lymphocyte cells when detected in the body.
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What happens to lymphocytes before they can harm self cells
You have 10 million lymphocytes and any that may harm self-cells are destroyed before they can mature and differentiate
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Antigen variability
• Pathogen's DNA mutates regularly and can result in new shapes of antigens being made. This is known as antigen variability. It results in individuals no longer being immune to that pathogen.
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Vaccines
Small amounts of weakened or dead pathogen, or antigens are introduced in the mouth or by injection.
Exposure to the antigens activates the B cell to go through clonal expansion and differentiation (clonal selection)
B cells undergo mitosis to make large numbers of cells, these differentiate into plasma cells or memory B cells.
Plasma cells make antibodies
B memory cells can divide rapidly into plasma cells when re-infected with the same pathogen to make large numbers of antibodies rapidly.
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Memory b cells
Memory B cells can live for decades in your body, where as plasma cells are short lived.
Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered.
This results in large numbers of antibodies being produced so rapidly that the pathogen is destroyed before any symptoms can occur.
This is active immunity
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What’s passive immunity
Passive immunity is when antibodies are introduced into the body, where as active is when you created them yourself and you will create memory cells.
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What’s herd immunity
Herd immunity is when if enough of the population are vaccinated the pathogen cannot spread easily amongst the population.
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What do vaccines do
Vaccines provide protection for individuals and populations against disease.
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AIDS and HIV
HIV positive is when a person is infected with HIV. AIDS is when the replicating viruses in the helper T cells interfere with their normal functioning of the immune system.
With the helperT cells being destroyed by the virus, the host is unable to produce an adequate immune response to other pathogens and is left vulnerable to infections and cancer.
It is this destruction of the immune system that leads to death, rather than the HIV directly.
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Where do viruses replicate
Viruses replicate inside of host cells and cannot be destroyed by antibiotics.
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How is AIDS developed
When the replicating viruses in the helper T cells interfere with their normal functioning of the immune system that symptoms develop, resulting in AIDS.
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What could happen when helper T cells are destroyed
With the helper T cells being destroyed the host is unable to produce an adequate immune response to other pathogens and is left vulnerable to infections and cancer.
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What does HIV attach to
HIV attaches to a CD4 protein on the helper T cells. The HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy.
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HIV structure
HIV structure consist of a core made of RNA and reverse transcriptase, a capsid outer protein coat, and envelope made of the host cell membrane and protein attachments.
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What are monoclonal antibodies
monoclonal antibody is a single type of antibody that can be isolated and cloned.
Antibodies are proteins which have binding sites complementary in shape to certain antigens.
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Antibodies have been manipulated to create monoclonal antibodies for what
This has been manipulated to create monoclonal antibodies for:
• Medical treatment
• Medical diagnosis
• Pregnancy tests
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Ethical issues of monoclonal antibodies
Creating monoclonal antibodies requires mice to produce the antibodies and tumour cells, which leads to ethical debates as to whether this use of animals is justified to enable the better treatment of cancers in humans and to detect disease.
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Targeted medication - direct monoclonal antibody therapy
Some cancer can be treated using monoclonal antibodies which are designed with a binding site complementary in shape to the antigens on the outside of cancer cells.
The antibodies are given to the cancer patient and attach to the cancer cells. While the antibodies are bound to the cancer antigens, this prevents chemicals binding to the cancer cells which enable uncontrolled cell division.
Therefore, the monoclonal antibodies prevent the cancer cells growing, and as they are designed to only attach to cancer cells they do not cause harm to other normal cells.
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Targeted medication - indirect monoclonal antibody therapy
Cancer can also be treated with monoclonal antibodies complementary.in shape to the antigens on the outside of cancer cells which have drugs attached to them.
This cancer drugs are therefore delivered directly to the cancer cells and kill them. This reduces the harmful side effects that traditional chemotherapy and radiotherapy can produce.
This is often referred to as 'bullet drugs'
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What’s an antigen
Cell-surface molecule which stimulates immune response
Usually (glyco)protein, sometimes (glyco)lipid or polysaccharide
Immune system recognises as ‘self’ or ‘non-self’ = enables identification of cells from other organisms of same species, pathogens, toxins and abnormal body cells
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How does phagocytosis destroy pathogens
1. Phagocyte moves towards pathogen via chemotaxis
2. Phagocyte engulfs pathogen via endocytosis to form a phagosome
3. Phagosome fuses with lysosome (phagolysosome)
4. Lysozymes digest pathogen
5. Phagocyte absorbs products from pathogen hydrolysis
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What does APCs stand for
Antigen-presenting cells
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Explain role of antigen-presenting cells (APCs)
Macrophage displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)
Enhances recognition by T H cells, which cannot directly interface with pathogens/antigens in body fluid
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Give 2 differences between specific and non-specific immune responses
Non-specific (inflammation, phagocytosis) = same for all pathogens
Specific (B & T lymphocytes) = complementary pathogen
Non-specific = immediate
Specific = time lag
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Name 2 types of specific immune response
Cell-mediated
Humoral
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Outline process of cell-mediated response
1. Complementary T H lymphocytes bind to foreign antigen on APC
2. Release cytokines that stimulate:
a) Clonal expansion of complementary T H cells (rapid mitosis): become memory cells or trigger humoral response
b) clonal expansion of cytotoxic T cells ( T c):
Secrete enzyme perforin to destroy infected cells
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Outline process of humoral response
1. Complementary T h cells lymphocytes bind to foreign antigen on antigen-presenting T cells
2. Release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes
3. B cells differentiate into plasma cells
4. Plasma cells secrete antibodies with complementary variable region to antigen
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What’s an antibody
Proteins secreted by plasma cells
Quaternary structure: 2 ‘light chains’ held together by disulfide bridges, 2 longer ‘heavy chains’.
Binding sites on variable region of light chains have specific tertiary structures complementary to an antigen
The rest of the molecule is known as the constant region
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How do antibodies lead to destruction of a pathogen
Formation of antigen-antibody complex results in agglutination, which enhances phagocytosis
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What are monoclonal antibodies
Antibody produced from a single clone of B cells
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What are memory cells
Specialised T h/ B cells produced from primary immune response
Remain in low levels in the blood
Can divide very rapidly by mitosis if organism encounters the same pathogen again
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Contrast primary and secondary immune response
Secondary response:
- faster rate of antibody production
- shorter time lag between exposure & antibody production
- higher conc of antibodies
- antibody level remains higher after secondary response
- pathogen usually destroyed before any symptoms
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What causes antigen variability
1. Random genetic mutation changes DNA base sequence
2. Results in diff sequence of codons on mRNA
3. Different primary structure of antigen = HBs, IB & disulfide bridges form in diff places in tertiary structure
4. Diff shape of antigen
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Compare passive and active immunity.
Give examples of both types
- Both involve antibodies
- Can both be natural or artificial
Passive natural: antibodies in breast milk/ across placenta
Passive artificial: anti-venom, needle stick injections
Active natural: humoral response to infection
Active artificial: vaccination
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Explain how antigen variability affects incidence of disease
Memory cells no longer complementary to antigen = individual not immune = can catch disease more thta once
Many varieties of a pathogen = difficult to develop vaccine containing all antigen types
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Contrast passive and active immunity
Passive:
- no memory cells & antibodies not replaces when broke down = short-term
- immediate
- antibodies from external source
- direct contact with antigen not necessary
Active:
- memory cells produced = long-term
- Time lag
- lymphocytes produce antibodies
- direct contact with antigen necessary
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Explain principles of vaccination
1. Vaccine contains dead/inactive form of pathogen/antigen
2. Triggers primary immune response
3. Memory cells are produced & remain in bloodstrea, so secondary response is rapid & produces higher conc of antibodies
4. Pathogen is destroyed before it causes symptoms
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What herd immunity
Vaccinating large proportion of population reduces available carriers of pathogen
Protects individuals who have not been vaccinated e.g. those with a weak immune system
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Suggest some ethical issues surrounding the use of vaccines
Production may involve use of animals
Potentially dangerous side-effects
Clinical tests may be fatal
Compulsory vs opt-out
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Describe HIV structure
Genetic material (2 X RNA) & viral enzymes (integrate & reverse transcriptase) surrounded by capsid
Surrounded by viral envelope derived from host cell membrane
GP120 attachment proteins on surface
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How does HIV result in symptoms of AIDS
1. Attachment proteins bind to complementary CD4 receptor on T H cells
2. HIV particles replicate inside T H cells, killing or damaging them
3. AIDS develops when there are too few T H cells for immune system to function
4. Individuals cannot destroy other pathogens & suffer from secondary diseases/infections
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Why are antibiotics ineffective against viruses
Antibiotics often work by damaging murein cell walls to cause osmotic lysis. Viruses have no cell wall
Viruses replicate inside host cells = difficult to destroy them without damaging normal body cells
100
Suggest the clinical applications of monoclonal antibodies
Pregnancy tests by detecting HCG hormones in urine
Diagnostic procedures e.g. ELISA test
Targeted treatment by attaching drug to antibody so that it only binds to cells with abnormal antigen e.g. cancer cells due to specificity of tertiary structure of binding site
101
Explain principle of a direct ELISA test
Detects presence of a specific antigen
1. Monoclonal antibodies bind to bottom of test plate
2. Antigen molecules in sample bind to antibody. Rinse excess
3. Mobile antibody with ‘reporter enzyme’ attached binds to antigens that are ‘fixed’ on monoclonal antibodies. Rinse excess
4. Add substrate for reporter enzyme. Pos result = colour change
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Explain principle of an indirect ELISA test
Detects presence of an antibody against a specific antigen
1. Antigens bind to bottom of test plate
2. Antibodies in sample bind to antigen. Wash away excess
3. Secondary antibody with reporter enzyme attached binds to primary antibodies from the sample
4. Add substrate for reporter enzyme. POS result = colour change
103
Suggest some ethical issues surrounding the use of monoclonal antibodies
Production involves animals
Drug trials against arthritis & leukaemia resulted in multiple organ failure
