Immunity Flashcards
Defence Mechanisms
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What does non-specific reaction mean?
An immediate response that’s the same for all pathogens
What is in a non-specific reaction?
Physical barriers
Phagocytosis
What does a specific reaction mean?
A response which is slower but is specific to each pathogen
What is in a specific reaction?
Cellular response (T-Cells)
Humoral response (B-cells)
Antigens and Phagocytosis
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What is an antigen?
It is a protein that triggers an immune response by lymphocytes and have their own unique shape
Where are antigens found?
On the surface of all cells as they are chemical markers
What is a self antigen ?
When your body recognises the antigens on your cells as your own
What is a non-self (foreign) antigen?
Anything with different antigens to your body that stimulates an immune response since it’s recognised as foreign
What happens in an immune response?
Your body recognised the cells antigens as foreign so attacks it
What can antigens enable the immune system to identify?
- pathogens (micro-organisms that cause disease)
- cells from other organisms of the same species (transplants)
- abnormal body cells (cancerous cells)
- toxins (poisonous molecules released from bacteria)
Where are phagocytes made?
In the bone marrow
How do phagocytes travel?
Through capillaries but they can also squeeze through walls into tissues
Name the two types of phagocytes
- Neutrophils
- Macrophages
What do phagocytes do?
They both (Neutrophilis & Macrophages) patrol the body, searching for invaders (non-self antigens)
What do neutrophils do?
Engulf and digest pathogens along with dead human cells and debris.
What do neutrophils do?
Engulf and digest pathogens, dead human cells and debris.
What do macrophages do?
They can punch holes in bacteria or stick proteins to the outside of the bacteria to make them more appealing for the neutrophils to destroy
What is a lysozyme?
Mucosal surfaces produce secretions that contain lysozyme
It kills bacteria by damaging their cell walls making them burst open
Define phagocytosis.
It is the cellular process of engulfing solid particles using the cell membrane which is carried out by phagocytes
What is the first step in the process of phagocytosis?
- Pathogen recognised as having foreign/non-self antigens. Pathogen attaches to the phagocyte by surface receptors
What is the second step in the process of phagocytosis?
The pathogen is engulfed by the phagocyte by endocytosis forming a phagosome
What is the third step in the process of phagocytosis?
Lysosome fuse to phagosome to form a phagolysosome and release H₂O₂, HCI and digestive enzymes into phagosomes to digest the pathogen
What is the fourth step in the process of phagocytosis?
Harmless products removed (egested/excreted) by exocytosis or used by phagocytes
Cell Mediated Immune Response
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How are Antigen Presenting Cells (APCs) formed?
They are formed when phagocytes engulf the virus present some of the pathogens antigens on their own cell membrane
What are APC’s?
Any cell that presents a non self antigen on their surface
What example are there of APCs?
Infected body cells
Macrophage
Cells of a transplanted organ
Cancer cells
What do antigen presenting cells activate?
T-helper cells
What do T-helper cells do?
They stimulate and recruit more phagocytes and T-cells to assist in the immune response
What do cytotoxin (killer) T cells do?
Destroy infected or foreign cells by releasing chemicals
e.g. perforin (makes pores in the membrane) into the invaded cell
What can activated T-cells activate?
Can activate B cells causing them to divide by mitosis, signifies the start of the humoral response
What are the two parts of a specific immune response?
Cell mediated response - Involves specialised white blood cells called T-lymphocytes which targets pathogens inside and outside cells
Humoral response - Involves specialised whit blood cells called B-lymphocytes which target pathogens by producing antibodies
What is the first step in the process of a cell mediated response?
APCs can either be either phagocytes or cells that have been invaded by
What is the second step in the process of a cell mediated response?
Once phagocytosis has taken place, phathogenic antigens are present on the the cell surface membrane
What is the third step in the process of a cell mediated response?
T cells respond to the cell which is presenting the antigens
What is the fourth step in the process of a cell mediated response?
T helper cells respond first - they have receptors which fit exactly to the presenting antigens
What is the fifth step in the process of a cell mediated response?
This activates the T cells and they begin two differentiate and recruit other T-cells and activate B-cells
B cells and Humoral Response
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What are B cells?
Lymphocytes that secrete antibodies in response to antigens, the antibodies bind to the antigens on the cell surface membrane to form an antigen antibody complex
Each b cell has a different shaped antibody which binds to a specific antigen
Allow phagocytes to recognise and destroy cell
How do B cells get the antigen?
From the pathogens of APCs
What does the B cell do with the antigen and what does this allow to happen?
Presents the antigen onto its cell surface membrane
T helper cells can then bind to this antigen to activate the B cells
What happens once the B cells are activated?
The begin to divide by mitosis to form plasma cells and memory cells - known as clonal selection
What are B plasma cells?
A type of B cell that secretes lots of monoclonal antibodies
What is the role of plasma cells?
They produce antibodies that are complimentary to the antigens (primary response)
What is a memory cell?
A cell that remains in the body for years, enabling an individual to respond more quickly to the same antigen in the future
What do memory cells do?
Memory cells stay in the blood stream circulating
If they come into contact with the antigen again they divide to form the plasma and the memory cells again (secondary immune response)
What is a primary immune response?
In this response there are not many B cells initially to make the antibody and the antibodies only survive in the bloodstream for a few days (slower response)
What is a secondary immune response?
In this response they produce antibodies much more quickly and more new memory cells enter the bloodstream to provide long-term immunity from reinfection of the pathogen
Antibodies and Natural/Passive Immunity
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What is an antibodies structure?
They are proteins made up of four polypeptide chains (quaternary structure) 2 heavy and 2 light chains.
Each chain has a variable region and a constant region.
The chains are connected by disulphide bridges
Why to antibodies have two variable regions?
They are antigen binding sites so have unique tertiary structures complementary to an antigen
One antibody can bind to two pathogens at once
Why do all antibodies have the same constant regions?
It allows them to bind to receptors on immune system sells
What are the ways that antibodies can work?
Agglutination
Neutralising toxins
Preventing viruses from entering host cells
What is the process of agglutination?
Antibodies bind to antigens on pathogens and cause them to clump together, these clumps are then destroyed by phagocytosis.
Makes it easier for phagocytes to engulf more pathogens at a time
What is the process of neutralising toxins?
Some antibodies work by neutralising toxins released by pathogens
What is the process of preventing viruses from entering host cells?
Viruses have spike proteins on their surface which recognise and bind to receptors on the surface of the host cell which allow entry into the cell
Antibodies can bind to these on viruses and stop them attaching to their host cells
Why do you typically only get chicken pox or measles once?
Because of the memory cell function
The pathogens causing these diseases are of a single type and thus the same antigen so are rapidly identified by the memory cells and a secondary immune response is triggered - quickly removes virus
How do some pathogens form different strains?
Caused by mutations in genetic material
So they often have different antigens - called antigenic variation
What does antigenic variation mean if you get reinfected for a second time?
The memory cells will not recognise the antigen and won’t be activated and the antibodies made last time will no longer be complimentary so the body has to start again with a primary response so you still get symptoms
What is antigenic variation common in?
Its common in influenza and HIV
What does antigenic variation make difficult?
They make it hard to produce vaccines against these pathogens (HIV & influenza)
e.g every year a new flu vaccine has to be made that is most effective against the most recent circulating strain of the virus
Natural/Passive Immunity and Vaccines
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How do vaccines work?
Vaccines work by introducing the antigens of a dead or weakened pathogen into the body to stimulate the production of antibodies and memory cells
What do the different amount of doses of vaccines do?
One dose induces a primary immune response, multiple doses can increase the number of antibodies and memory cells in the bloodstream through the secondary response
Why are vaccines long lasting?
They are long lasting because they produce memory cells which can produce complimentary antibodies to the antigen
Why do most vaccines contain multiple antigens?
To make sure there is protection against different strains of pathogens (flu) or different diseases (MMR)
How are the pathogens prepared for viruses made harmless?
Killing but leaving antigens unaffected e.g cholera vaccine
Weakening (attenuation - heating) but leaving antigens unaffected e.g oral vaccine against polio
Purified antigens removed from pathogen e.g vaccine against hepatitis B
Using inactivated toxins called toxins that are harmless but trigger same immune response e.g Tetanus injections
What type of immune response do vaccines make?
Because they contain foreign antigens there will still be a primary immune response which can have symptoms such as swelling, mild fever, runny nose etc
What ethical issues are there with vaccines?
All vaccines are tested on animals first (same as drugs)
Humans in clinical trials may put themselves at risk because they believe they may be immune
Some people refuse vaccines over fears of side effects, they are protected by herd immunity alike those who can’t get vaccines
If there is a new disease, difficult decisions would be made about who would be first to receive it
Why can’t vaccines fully eliminate disease?
- Fails to induce immunity in some people (immunodeficiency)
- People get infected before enough Abs are generated by vaccine to afford protection (slow primary response)
- Antigenic variability - pathogens can mutate
- Many different strains - can’t vaccinate against all
- Objection to vaccines based on moral, religious, and ethical grounds
What is herd immunity?
It is a concept used for vaccination, in which a population can be protected from a certain virus if a threshold of vaccination is reached
What percentage of a population has to be vaccinated to get herd immunity?
95%
How is herd immunity achieved?
By vaccinating a large amount of the population so that enough people are immune to the virus it cannot spread far through the population.
Who does herd immunity protect?
Protects those who can’t have the vaccine for medical reasons
What is active immunity?
The body makes antibodies after being exposed to an antigen
Gives long term immunity since memory cells are. involved
What is natural active immunity?
You become immune after catching the disease
What is artificial active immunity?
You become immune after being given a vaccination containing a harmless dose of the antigen
What is passive immunity?
The body is given antibodies that have been made by a different organism
Short term as no immune response involved and no memory cells produced
What is natural passive immunity?
A baby gets antibodies through the placenta and breast milk
What is artificial passive immunity?
You are injected with antibodies e.g if you get tetanus, you will be injected with antibodies against the tetanus toxin
What are the problems with passive immunity?
Maternal antibodies pass from placenta into foetal blood
Breast feeding passesantibomdies into the colostrum (first milk produced after birth)
Protection is only temporary and only lasts a few months after birth - antibodies will be broken down in the spleen & liver, no memory cells are formed
HIV
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What is the structure of HIV?
Membrane Envelope - outer layer
Capsid - protects genetic information
RNA (can be DNA in others)
Glycoprotein - antigens
Reverse transcriptase enzyme - turns RNA into DNA
What does HIV stand for?
Human Immunodeficiency Viruses
What is the HIV disease?
Its two species of Lentivirus (sub group of retrovirus) that infect humans
How does HIV work?
It works by infecting helper T cells (preventing humoral response)
Virus replicates in the T cells using their cellular machinery, eventually the cells swell and burst (destroying the cell)
What can HIV become?
Over time, the number of T cells decreases and eventually causes AIDS
How is HIV diagnosed?
Those with HIV are said to be ‘HIV positive’ they can be diagnosed through a low white blood cell count or through a test to check for the presence of viral DNA
What is the first step of HIV replication?
Glycoprotein molecules on the virus surface bind to CD4 receptors on the surface of T helper cells. This allows the envelope surrounding the virus to fuse with the T helper cell membrane
What is the second step of HIV replication?
The capsid is released into the cell where it releases the RNA and reverse transcriptase
What is the third step of HIV replication?
Reverse transcriptase is used to make DNA from HIV RNA template
What is the fourth step of HIV replication?
The DNA is inserted into the cell’s DNA which gets replicated when cells replicate
What is the fifth step of HIV replication?
DNA used to make HIV RNA and proteins host ribosomes
What is the sixth step of HIV replication?
Virus particles are assembled which bud off from the cell membrane and go on to infect other cells
How is HIV transmitted?
You can only be infected with HIV through another person with the virus. HIV is found in the blood and the sexual fluids of an infected person, or in the breast milk of an infected woman
What are the ways that cause HIV to be transmitted?
Having unprotected sex with an infected person
Close contact with an infected persons blood e.g sharing needles for drug use
Use of infected blood in a blood transfusion
Mother to child - a mother with HIV giving birth to a child (shared through placenta) or child drinking the mothers milk - known as vertical transmission
Babies must be tested at 18mths - takes time for virus to replicate to be detectable
What does AIDS stand for?
Acquired immunodeficiency syndrome
What is AIDS?
It’s a condition which is caused by failure of the immune system which allows opportunistic infections (infections that take advantage of the lowering of the body’s defences) and cancers to thrive
How do people contract AIDS?
People who are HIV positive contact it when their number of helper T cells reach a critical level
The immune system cannot fight off simple/opportunistic infections that the body would usually defend against such as pneumonia and so often kill the patient
What are the initial symptoms of AIDS?
Lots of minor infections of mucosal membranes
Recurring respiratory infections caused by lower than normal number of T helper cells
How long can it take for a HIV patient to develop AIDS?
Around 10 years (if undiagnosed or without any treatment) for a HIV positive patient to develop the symptoms of AIDS
This is because the virus can remain dormant as DNA in host cells
Is there a cure for HIV?
No - its incurable once acquired but there is treatments to slow replication
What treatment is there for HIV?
Antiretroviral drugs
Pre-exposure prophylaxis (PrEP)
Stem cell therapy
How do you help prevent the transmission of HIV?
Using the treatments
Practicing safe sex
Not sharing needles
How do antiretroviral drugs work for the treatment of HIV?
They reduce the viral load in the body to an ‘undetectable level’ - means HIV can’t be passed from them
Can’t remove the virus from the body instead the drugs slow/prevent the replication of the virus in the body by blocking the reverse transcriptase
How does pre-exposure prophylaxis (PrEP) work for the treatment of HIV?
Is a HIV prevention strategy where HIV negative individuals take anti-retrovirals before coming into contact with HIV - reduce their risk of infection
Why is pre-exposure prophylaxis (PrEP) not widely accepted as a treatment of HIV?
Isn’t currently accepted on the NHS or widely in the world
Critics argue that many who use the drug see it as an excuse to engage in unsafe sexual practices & that encouraging PeEP in tantamount to giving them permission to to have sex without condoms
How does stem cell therapy work for the treatment of HIV?
Two people have been ‘cured’ of HIV using it where chemotherapy killed their white blood cells and they received a bone marrow transplant from someone with naturally occurring CD4 mutation (so HIV can’t bind to cells)
Still considered a cancer treatment - too aggressive & expensive to be used as a regular HIV cure
Antibiotics In medicine
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What are monoclonal antibodies?
Antibodies that are produced by plasma cells which are clones of one B-cell
Why are monoclonal antibodies useful?
They can be produced outside the body and they are reactive with only one type of antigen
What are monoclonal antibodies main medical uses?
To target medication to specific cell types by attaching a therapeutic drug to an antibody (radioimmunitherapy)
Pregnancy testing
Medical diagnosis by identifying proteins or antigen presence using the ELISA test
What is radioimmunotherapy?
It links radioactive atoms to monoclonal antibodies that deliver the radioactivity by seeking out and latching onto proteins found on cancer cells
How does radioimmunotherapy help doctors?
Allows doctors to target radiation to specific sites
Doctors can concentrate radiation at tumour sites, reducing amount of radiation that reaches healthy tissue
Can be used to find tumours that may have spread in the body to target therapy where needed
How do pregnancy tests work?
Antibodies complimentary to hCG protein are bound to coloured beads
hCG in urine binds to antibodies
Urine moves up the strip carrying beads
Immobilised antibodies which bind to hCG create first “blue line”
Immobilised antibodies which bind to coloured beads create second “blue line” if hCG present
What does an ELISA test stand for?
Enzyme Linked ImmunoSorbent Assay
What can an ELISA test be used for?
To test for the presence of any antigen or antibody e.g HIV diagnosis or allergies
How does an ELISA test work?
An antigen is bound to an enzyme, this enzyme reacts with a substrate to produce a colour change
The antibody will be complementary and bind to the antigen or an antibody the test is designed to detect
There is a washing step which will remove any unbound antibodies (plus attached enzyme) so the more antigen there is in sample the more colour change there will be because the more enzymes present to react with substrate
What is a direct ELISA?
This involves one antibody binding to an antigen - used to look for antigen in sample
What is an indirect ELISA?
This uses multiple antibodies
Antigens are immobilised and the sample being checked for antibodies is added, a wash step is added which will bind to the antibodies attached to antigens if present, this antibody has the enzyme bound that will change colour
Example is the mumps diagram
What are the risks with indirect ELISAs?
Indirect ELISAs can be more sensitive that direct detection methods
Risk of cross-reactivity with the antigen, could cause higher background readings
Take longer due to extra step
An advantage is you can use the same secondary antibody (with the enzyme) for multiple different assays
