Immunity Flashcards
The human body has a range of defences to protect itself from pathogens- some are general and immediate defences such as
- The skin forming a barrier of entry of pathogens
- phagocytosis
Some defences are specific, less rapid however
Longer-lasting
Specific responses involve a type of white blood cell called a
Lymphocyte
What are the 2 types of lymphocyte?
T lymphocyte and B lymphocyte
T lymphocytes are involved in
Cell-mediated response
B lymphocytes are involved in
Humoral response
To defend the body from invasion by foreign materials, lymphocytes must be able to distinguish the body’s own cells and molecules (self) from
Those that are foreign (non self)
What would happen if lymphocytes could not distinguish cells and molecules that are self and non self?
The lymphocytes would destroy the organism’s own tissues
Each type of cell has specific molecules on its surface that identify it. These molecules include
Proteins
What do proteins on cell surfaces enable the immune system to identify?
- pathogens e.g. HIV
- non-self materials such as cells from other organisms of the same species
- toxins (including those produced by certain pathogens like the bacterium that causes cholera)
- abnormal body cells such as cancer cells
Why does the immune system attempt to destroy organ or tissue transplants?
The immune system recognises these as non-self, even though they come from individuals of the same species; it therefore attempts to destroy the transplant.
What is done to minimise the effect of tissue rejection?
- Donor tissues for transplant are normally matched as close as possible to those of the recipient. The best matches often come from relatives that are genetically close.
- immunosuppressant drugs are often administered to reduce the levels of immune response
What is clonal selection?
When an infection occurs, the one type of lymphocyte already present that has complementary proteins to those of the pathogen is stimulated to divide to build up its numbers to a level where it can be effective in destroying it
Why is clonal selection necessary?
With so many different types of lymphocytes, there are very few of each type
Colonial selection explains why there is a lag time between exposure to the pathogen and ___ _____ ______ in brining it under control
The body’s defence
Explain how lymphocytes recognise cells belonging to the body
- approximately around 10 million lymphocytes present at any time, each capable of recognising a different chemical shape
- in the foetus, these lymphocytes are constantly colliding with other cells and because infection in the foetus is rare (protected from outside world and by placenta) lymphocytes will collide almost exclusively with the body’s own material (self)
- some of the lymphocytes will have receptors that exactly fit those of the body’s own cells and these lymphocytes either die or are suppressed
- only remaining lymphocytes are those that might fight fit foreign material (non-self) and therefore only respond to foreign material
- in adults, any lymphocytes produced in the bone marrow initially only encounter self-antigens
- any lymphocyte that shows an immune response to these self-antigens undergo programmed cell death (apoptosis) before they can differentiate into mature lymphocytes
- no clones of these ‘anti-self’ lymphocytes will appear in the blood, leaving only those that might respond to non-self antigens
If first line of defence fails (physical or chemical barrier), the next line of defence is
The white blood cells
2 types of white blood cell
- lymphocytes (involved in immune response)
- phagocytes (involved in phagocytosis)
Explain the stages of phagocytosis
1- phagocytes is attracted to the pathogen by the chemical products of the pathogen. The phagocytes moves towards the pathogen along a concentration gradient
2- phagocytes has several receptors in its cell surface membrane that attach to chemicals on the surface of the pathogen
3- phagocyte engulfs pathogen to form a vesicle known as a phagosome
4- lysosomes within the phagocyte migrate towards the phagosome
5- lysozymes are present within the lysosome; these lysozymes destroy ingested bacterium by hydrolysis of their cell wall
6- the soluble products from the break down of the pathogen are absorbed into the cytoplasm of the phagocyte
The initial response of the body to infection is non-specific(phagocytosis) the next stage is
The primary immune response that confers immunity
What is immunity?
Ability of organisms to resist infection by protecting against disease- causing microorganisms or their toxins that invade the body. It involves the recognition of foreign material (antigens)
What is an antigen?
Molecules (usually proteins) that generate an immune response when detected by the body as they are recognised as non-self (foreign) by the immune system and stimulates an immune response
Antigens are usually ___ that are part of the cell-surface membranes or cell walls of invading cells, such as microorganisms or abnormal body cells such as cancer cells
Proteins
The presence of an antigen triggers the production of
An antibody as part of the body’s defence system
Immune responses such as phagocytosis are non-specific and occur whatever the infection. The body also has specific responses that react to
Specific antigens
Specific responses are slower in action at first but
Can provide long term immunity
Specific response depends upon depends on a type of white blood cell called a
Lymphocyte
Where are lymphocytes produced?
In the bone marrow by stem cells
What are the 2 types of lymphocyte and their role in the immune response?
- B lymphocytes (B cells) are so called because they mature in the bone marrow- they’re associate with humoral immunity, immunity involving antibodies that are present in body fluids or ‘humor’ such as blood plasma
- T lymphocytes (T cells) are so called because they mature in the thymus gland- they are associated with cell-mediated immunity, immunity involving body cells
Lymphocytes respond to:
- an organism’s own cells that have been infected by non-self material from a different species e.g. a virus
- cells from other individuals of the same species because they are genetically different and therefore have different antigens on their cell-surface membrane from the antigens of the organism’s own cells
how do T lymphocytes distinguish invader cells from normal cells?
- phagocytes that have engulfed and hydrolysed a pathogen, present some of a pathogen’s antigens on their own cell-surface membrane
- body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
- transplanted cells from individuals of the same species have different antigens on their cell-surface membranes
- cancer cells are different from normal body cells and present antigens on their cell-surface membranes
What are cells that display foreign antigens on their surface called?
Antigen-presenting cells
T lymphocytes will only respond to
Antigens that are presented on a body cell (rather than antigens within the body fluids) and this type of response = cell-mediated immunity
Why is the role of receptors on T cells important?
The receptors on each T cell respond to a single antigen
Explain the stages in response of T lymphocytes to infection by a pathogen
1- pathogen invades body cells or are taken in by phagocytes
2- the phagocyte places antigens from the pathogen on its cell-surface membrane
3- receptors on helper T cells fit exactly onto these antigens
4- this attachment activates the T cells to divide rapidly
5- the cloned T cell:
- develop further into memory cells that enable a rapid response to future infections by the same pathogen
- stimulate phagocytes to engulf the pathogen by phagocytosis
- stimulate B cells to divide and secrete their antibody
- activate cytoxic T cells
How do cytoxic T cells kill abnormal cells and body cells that are infected by pathogens?
By producing a protein called perforin that makes holes in the cell-surface membrane; these holes mean the cell membrane becomes freely permeable to all substances and the cell dies as a result
The action of T cells is most effective against
Viruses because viruses replicate inside cells- as viruses use living cells in which to replicate, this sacrifice of body cells prevents viruses multiplying and infecting more cells
State some similarities between T cells and B cells
- Both types of white blood cell
- both have a role in immunity
- produced from stem cells
State some differences between T cells and B cells
- T cells mature in the thymus gland, while B cells mature in the bone marrow
- T cells are involved in cell-mediated immunity while B cells are involved in humoral immunity
First phase of the specific response to infection is
The mitotic division of specific T cells to form a clone of the relevant T cells to build up their numbers- some of these T cells produce factors that stimulate B cells to divide; it is these B cells that are involved in the next phase of the immune response: humoral immunity
Humoral immunity is called so because it involves
Antibodies and antibodies are soluble in blood and tissue fluid of the body
There are many different types of B cell and each B cell starts to produce a
Specific antibody that responds to one specific antigen
When an antigen, for example, a protein on the surface of a pathogen, foreign cell, toxin, damaged or abnormal cell enters the blood or tissue fluid, there will be one B cell that has an
Antibody on its surface whose shape exactly fits the antigen (they’re complementary) and so the antibody therefore attaches to the antigen
Explain the role of B cells in humoral immunity
1- the surface antigens of invading pathogen are taken up by a B cell (endocytosis)
2- the B cell processes the antigens and presents it on its surface
3- helper T cells attach to the processed antigens on the B cell, activating the B cell
4- B cell is activated to divide by mitosis to give a clone of plasma cells (clonal selection)
5- the cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogen surface- as each clone produces one specific antibody, these antibodies are referred to as monocolonal antibodies.
6- the antibodies attaches to the antigen on the pathogen and destroys them
7- some B cells develop into memory cells; these can respond to future infection by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies = secondary immune response
In each cloned plasma cell, the cells produced develop into one of 2 types of cell
Plasma cells or memory cells
What are plasma cells?
Mature B lymphocytes that secrete antibodies- rough ER is where antibodies are synthesised
Plasma cells secrete antibodies usually into
Blood plasma- these cells can only survive for a few days but each can make around 2000 antibodies every second during its brief life span
The plasma cells are responsible for the immediate defence of the body against infection because
Plasma cells secrete antibodies and antibodies lead to the destruction of antigens
The production of antibodies and memory cells is known as
The primary immune response
Memory cells are responsible for the ____ immune response
Secondary
Memory cells live considerably longer than plasma cells, approximately
Decades
Memory cells do not produce antibodies directly but
Circulate in the tissue fluid
What happens when a memory cell encounters the same antigen at a later date?
Memory cell divides rapidly and develop into plasma cells and more memory cells
The plasma cells produce the antibodies needed to destroy the pathogen while the new memory cells circulate in readiness for
Further infection; in this way, memory cells provide long term immunity against the original infection
(In secondary immune response) an increase quantity of antibodies is secreted at a faster rate than in
Primary immune response, ensuring that a new infection is destroyed before it can cause any harm (individuals are often totally unaware they were ever infected)
Why is secondary immune response much quicker than the first one?
In the primary response, the antigens of the pathogen have to be ingested, processed and presented by the B cells. Helper T cells need to link with the B cells that then clone, some of the cells developing into plasma cells that produce antibodies. These processes occur consecutively and therefore take time. In the secondary response, memory cells are already present and the only processes are cloning and development into plasma cells that produce antibodies. Fewer processes mean a quicker response.
What are some differences between cell mediated immunity and humoral immunity?
1- cell mediated immunity involves T cells whereas humoral immunity involves mostly B cells
2- no antibodies are involved in cell mediated immunity whereas antibodies are produced in humoral immunity
3- cell mediated immunity is the first stage of immune response whereas humoral immunity is the second stage of immune response, after cell mediated immunity
4- cell mediated immunity is effective through cells, whereas humoral immunity is effective through body fluids
Plasma cells can produce around 2000 protein antibodies each second. Suggest 3 organelles that you might expect to find in large quantities in a plasma cell
- Rough ER= make and transport proteins of antibodies
- Golgi apparatus= sort, process and compile proteins
- mitochondria= release the energy needed for such massive antibody production
What is the primary immune response?
When an antigen enters the body for the first time, it activates the immune system
Why is the primary response slow?
There aren’t many B cells that can make the antibody needed to bind to the antigen
State the stages of the primary immune response
1- antigen enters the body for the first time, activates immune system
2- however there aren’t that many B cells that can make the antibody needed to bind to it
3- eventually the body will produce enough of the right antibody to overcome the infection- meanwhile the person will show symptoms of the disease
4- after being exposed to the antigen, both T and B cells produce memory cells that remain in the body for a long time. Memory T cells remember the specific antigen and will recognise it the second time around and memory B cells record the specific antibody needed to bind to the antigen
5- the person is now immune- their immune system has the ability to respond quickly to a second infection
What is the secondary immune response?
If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response
State the stages of the secondary immune response
- clonal selection happens much faster- memory B cells are activated and divide into plasma cells that produce the right antibody to the right antigen. Memory T cells are activated and divide into the correct type of T cells to kill the cell carrying the antigen
- secondary response often gets rid of the pathogen before you begin to show any symptoms (immune to pathogen)
What are antibodies?
Proteins with specific binding sites synthesised by B cells
When the body is infected with non-self material, a B cell produces a specific
Antibody
Specific antibodies react with an antigen on the surface of non-self material by
Binding to them
How many identical binding sites does each antibody have?
2
The antibody binding site are complementary to
A specific antigen
The massive variety of antibodies is possible because
They are made of proteins (molecules that occur in an almost infinite number of forms)
Describe the structure of an antibody
- antibodies are made up of 4 polypeptide chains
- the chains of one pair are long and called the heavy chain, while the chains of the other pair are shorter and are called the light chain
- each antibody has 2 specific binding sites that fit precisely onto a specific antigen to form an antigen-antibody complex- each binding site is different in different antibodies and is therefore called the variable region. Each binding site consists of a sequence of amino acids that form a specific 3D shape that binds directly to a specific antigen
- rest of the antibody is known as the constant region; this binds to receptor sites such as B cells
Antibodies do not destroy antigens directly but rather
Prepare the antigen for destruction
How do antibodies lead to the destruction of the antigen?
- antibody has 2 binding sites so can bind to two pathogens at the same time
- this means that pathogens become clumped together: agglutination, making it easier for the phagocytes to locate them as they are less spread out within the body
- phagocytes then bind to the antibodies and phagocytose many pathogens at once- this process leads to the destruction of pathogens carrying this antigen in the body
Antibodies are very specific because
Their binding sites have a unique tertiary structure that only one particular antigen will fit into (complementary shape) = one antibody forms one antigen-antibody complex
It is of considerable medical value to be able to produce antibodies
Outside the body- and even better that a single type of antibody can be isolated and cloned
Describe how monoclonal antibodies (antibodies produced from a single group of genetically identical B-cells) can be used to target a drug to cancer cells
- different cells in the body have different surface antigens
- cancer cells have antigens caller tumour markers that are not found on normal body cells
- monoclonal antibodies can be made that will bind to the tumour markers
- you can also attach anti-cancer drugs to the antibodies
- when the antibodies come into contact with the cancer cells they will bind to the tumour marker
- this means the drug will only accumulate in the body where there are cancer cells
- so the side effect of an antibody-based drug are lower than other drugs because they accumulate near specific cells
Monoclonal antibodies are an invaluable tool in diagnosing disease, with over a hundred different
Diagnostic products based on them
Monoclonal antibodies are used for the diagnosis of
Influenza, hepatitis and chlamydia infection where they produce a much more rapid result than conventional methods of diagnosis
Explain how monoclonal antibodies are important in diagnosing certain cancers (such as men with prostate cancer)
- men with prostate cancer often produce more of a protein called prostate specific antigen (PSA), leading to unusually high levels of it in the blood
- by using a monoclonal antibody that interacts with this antigen, it is possible to obtain a measure of PSA in a sample of blood.
- while a higher than normal level of PSA is not itself diagnostic of the disease, it gives an early warning of its possibility and need for further tests
Explain how monoclonal antibodies are used in pregnancy tests
- pregnancy tests detect the hormone hCG that’s found in the urine of pregnant women
- application area of pregnancy test contains antibodies for hCG bound to a (blue) coloured bead
- when urine is applied to the application area any hCG will bind to the antibody of the beads forming an antigen-antibody complex
- the urine moves up the stick to the test strip, carrying any beads with it
- the test strip contains immobilised antibodies to hCG
- if there is hCG present, the strip turns blue because the immobilised antibody binds to the hCG- If no hCG is present, the beads will pass through the test area without binding to anything, and so it won’t go blue
Discuss ethics around the use of monoclonal antiodies
❌production of monoclonal antibodies involves the use of mice- mice are used to produce both antibodies and tumour cells. The production of tumour cells involves deliberately inducing cancer into mice- despite the specific guidelines drawn up to minimise any suffering, some people still have reservations about using animals in this way
✅/❌monoclonal antibodies have been used successfully to treat a number of diseases including cancer and diabetes, saving many lives.
However, there has also been some deaths associated with their use in treatment of multiple sclerosis; so it is important that the patient has full knowledge of the risks and benefits of these drugs before their informed consent
❌testing for the safety of new drugs presents certain dangers- in March 2006, 6 healthy volunteers took part in the trial of new monoclonal antibodies (TGN1412) in London. Within minutes, they suffered multiple organ failure (probably as a result of T cells overproducing chemicals that stimulate an immune response or attacking the body tissues). All volunteers survived, but it raises issues about the conduct of drug trials
Vaccines can protect individuals and populations against
Disease
Vaccines contain antigens that cause your body to produce
Memory cells against a certain pathogen, without the pathogen causing disease = become immune without getting any symptoms
How is herd immunity linked to vaccines?
Vaccines protect individuals that have them, and because they reduce occurrence of the disease, those not vaccinated are less likely to catch the disease, as there are less people to catch it from = herd immunity
Vaccines always contain antigens- these may be:
Free or attached to a dead or attenuated pathogen
Vaccines may be be injected or
Taken orally
What are some disadvantages of taking vaccines orally?
- could be broken down by enzymes in the gut
- molecules of the vaccine may be too large to be absorbed into the blood
Why are booster vaccines sometimes given?
To ensure memory cells are produced
What are the 2 types of immunity?
Passive immunity and active immunity
What is passive immunity?
Type of immunity you get from being given antibodies made by a different organism
What is active immunity?
Type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen
What are the characteristics of passive immunity?
- doesn’t require exposure to antigen
- protection is immediate
- memory cells aren’t produced- no lasting immunity
- protection is short term as the antibodies given are broken down
What are the characteristics of active immunity?
- requires exposure to the antigen
- takes a while for protection to develop
- memory cells produced
- protection is long term as the antibody is produced in response to complementary antigen present in the body
What are the sub categories of passive immunity and some examples?
- natural: when baby becomes immune due to antibodies it receives from its mother through the placenta and breast milk
- artificial: when you become immune after being infected with antibodies from someone else e.g. if you contract tetanus, you can be injected with antibodies against the tetanus toxin collected from blood donation
What are the features of a successful vaccination programme?
- suitable vaccination must be economically viable in sufficient quantities to immune most of vulnerable population (to produce herd immunity)
- must be few side-effects, if any, from vaccination as unpleasant side effects may discourage individuals in the population from being vaccinated
- means of producing, storing and transporting vaccine must be available
- must be means of administering vaccine properly at appropriate times- involves training staff with appropriate skills
Antigenic variation helps some pathogens evade
The immune system
Explain how antigenic variation helps some pathogens evade the immune system
- antigens on surface of pathogens activate the primary response
- when you’re infected a second time with the same pathogen (which has same antigen on its surface) they activate the secondary response so you don’t get ill
- however, some pathogens can change their surface antigen: antigenic variation, where different antigens are formed due to changes in the genes of a pathogen
- this means that when you’re infected a second time, the memory cells produced from the first infection will not recognise the different antigens
- so the immune system has to start from scratch and carry out a primary response against these new antigens
- primary response takes time to get rid of the infection which is why you’re ill again
Antigenic variation also makes it difficult to develop Vaccines against some pathogens, why is this?
- high mutation rate leads to antigenic variability
- vaccine contains specific antigen
- antibodies no longer complementary = won’t bind to antigen
What are examples of pathogens which show antigenic variation?
HIV and influenza virus (flu)
How does antigenic variation affect the production of vaccines to help prevent people catching influenza?
- influenza vaccine changes every year because the antigens on the surface of the influenza virus change regularly, forming a new strain of the virus
- memory cells produced from the vaccination with one strain of the flu will not recognise other strains with different antigens
- every year there are different strains of the influenza circulating in the population, so a different vaccine has to be made
- new vaccines are developed and one is chosen every year that is the most effective against the recently circulating influenza viruses
- governments and health authorities then implement a programme of vaccination using the most suitable vaccine
Why may vaccinations not eliminate disease?
- vaccination fails to induce immunity in certain individuals e.g. people with defective immune systems
- individuals may develop the disease immediately after vaccination but before their immunity levels are are high enough to prevent it- these individuals may harbour the pathogen and reinfect others
- antigenic variation
- may be so many varieties of a pathogen that it is almost impossible to develop a vaccine that is effective against them all e.g. over 100 varieties of the common cold virus
- certain pathogens ‘hide’ from the body’s immune system either by concealing themselves inside cells or by living in places out of reach such as the small intestine
What are some ethical issues surrounding the use of vaccines?
- all vaccines are tested on animals before humans- raises concerns with many people despite guidelines
- testing vaccines on humans may be tricky e.g. volunteers may put themselves at unnecessary risk of contracting the disease because they may think they’re fully protected e.g. may have unprotected sex because they had a new HIV vaccine and think they’re protected- however the vaccine may not work
- some people don’t want the vaccine due to the risk of side effects, but they are still protected because of herd immunity- people think this is unfair
- if there was an epidemic of a new disease e.g. new influenza virus, there would be a rush to receive a vaccine and difficult decisions would have to be made about who would be the first to receive it
What does HIV stand for?
Human immunodeficiency virus
HIV eventually leads to
AIDS (acquired immune deficiency syndrome)
AIDS is a condition where
The immune system deteriorates and eventually fails- this makes someone with AIDS more vulnerable to other infections e.g. pneumonia
HIV infects
Helper T-cells, which act as the host cells
What is the consequence of HIV infecting helper T-cells
Helper T-cells send chemical signals that activate phagocytosis, cytotoxic T-cells and B-cells, so they’re hugely important in the immune response. Without enough helper T-cells the immune system is unable to mount an effective response to infections because other immune system cells don’t behave how they should
People infected with HIV develop AIDS when
The helper T-cell numbers in the body reach a critically low level
Describe the structure of HIV
- HIV has a spherical structure
- HIV has a core that contains the genetic material in the form of RNA and some proteins including the enzyme reverse transcriptase that catalyses the production of DNA from RNA
- an outer coating of protein called a capsid
- an extra outer layer called an envelope- this is made of membrane stolen from the cell membrane of a previous host cell
- sticking out from the envelope are loads of copies of an attachment protein that help HIV attach to the host helper T-cell
Why is HIV considered a retrovirus?
It possesses RNA and the enzyme reverse transcriptase which can make DNA from RNA- RNA so the strand would be opposite)
HIV replicates inside helper T-cells of the host because
It doesn’t have the equipment such as enzymes and ribosomes to replicate on its own
Explain the stages of how HIV replicates
1- the attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell
2- the capsid is released into the cell, where it uncoats and releases its genetic material RNA into the cell’s cytoplasm
3- inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template
4- from this, double-stranded DNA is made and inserted into the human DNA
5- host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
6- the viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells
During the initial infection period,HIV replicates rapidly and the infected person
May experience severe flu-like symptoms
What is the latency period?
After initial infection period (where individual may experience severe flu-like symptoms) HIV replication drops to a lower level
During the latency period (which may last many years) the infected person won’t
Experience any symptoms
What does the ELISA test stand for and do?
- Enzyme linked immunoabsorbant assay
- allows you to see if a patient has any antibodies to a certain antigen = can be used for pathogenic infections, for allergies e.g. to nuts or lactose
- an antibody is used which has an enzyme attached; this enzyme can react with a substrate to produced a coloured product = causes solution in the reaction vessel to change colour
- colour change= antigen or antibody of interest present in sample tested e.g. blood plasma (in some tests, quantity can be worked out from intensity of colour change)
There are several different types of ELISA:
- direct ELISA= uses a single antibody that is complementary to antigen being tested for
- indirect ELISA= uses two different antibodies
Explain the steps of using ELISA as a HIV test
- HIV antigen is bound to the bottom of a well in a well plate
- sample of patient’s blood plasma which may contain several different antibodies is added to the well
- if there are any HIV-specific antibodies, these will bind to HIV antigen stuck to the bottom of the well
- well then washed to remove any unbound antibodies
- a secondary antibody that has a specific enzyme attached is added to the well
- this secondary antibody can bind to HIV-specific antibody
- well is washed again to remove any unbound secondary antibodies NOTE: if there’s no primary antibody in the sample, all of the secondary antibody will be washed away
- a solution is added to the well that contains a substrate able to react with the enzyme attached to the secondary antibody and produce a coloured product
- if the solution changes colour, it indicates that the patient has HIV-specific antibodies = BLOOD INFECTED WITH HIV
How can antigenic variability occur?
- pathogens can mutate frequently
- when proteins are synthesised, mistakes occur. These could be a substitution, deletion or addition of a base within a triplet of bases
- this means the amino acid sequence of a polypeptide can be altered
- this can lead to alteration in the secondary and tertiary structure of this antigen
- this can lead to a new strain of the pathogen
- the immune system may not therefore recognise this new pathogen
Human Papilloma virus (HPV) is the main cause of cervical cancer. A vaccine has been developed to protect girls and women from HPV. Describe how this vaccine leads to the production of antibody against HPV (4)
- vaccine contains HPV antigen
- this antigen is then displayed on antigen presenting cells
- specific helper T cells detects antigen and stimulated particular B cell
- B cell divides/undergoes mitosis to become a plasma cell
- plasma cell produces antibodies
What molecules can act as antigens?
Proteins and polysaccharides (not phospholipids as part of the cell membrane)
Describe how an antigen binds with a specific antibody that occurs in the plasma membrane of a B cell?
- antigen specific shape
- antibody 2 binding sites that have complementary shape
- held/bind by hydrogen bonds
Outline how the binding of an antigen to B cell receptor leads to raised antibody levels in a mouse
B cells divide by mitosis so antibody secreting cells produced
What is the benefit of using a logarithmic scale on the y-axis rather than an arithmetic scale?
Exaggerates low numbers
In the production of mouse monoclonal antibodies, the level of antibodies in the blood of a mouse reaches much higher levels after several injections of the same antigen over several weeks than if there were just a single injection of the antigen. Explain why.
After each injection, increasing numbers of memory cells = increasing number of antibody secreting cells
Define monoclonal antibody
An antibody produced by a single clone of cells
Regarding HIV, its attachment proteins attach to a glycoprotein found on the surface of T-helper cells called
CD4
What is AZT?
An antiviral drug that prevents the synthesis of DNA from HIV’s RNA- some patients can live with low infection for 20+ years
Why is it impossible to create a vaccine against HIV?
HIV chooses what antigens it presents on its surface (antigenic variability)
Why are washing steps important in ELISA test?
Ensure unbound antibodies aren’t left in the well which could affect the results e.g. unbound secondary antibodies could cause the test to appear positive when there are no HIV antibodies present
If the ELISA test was negative, why would there be no colour change?
Be no HIV-specific antibodies for the secondary antibodies to bind to
Why don’t antibiotics work on viruses?
- antibiotics kill bacteria by interfering with their metabolic reactions- they target bacterial enzymes and ribosomes used in these reactions
- bacterial enzymes and ribosomes are different from human ones = antibiotics designed to only target bacterial ones so they don’t damage human cells
- viruses don’t have their own enzymes= use ones in host’s cell
- so because human viruses use human enzymes and ribosomes to replicate, antibiotics can’t inhibit them because they don’t target human processes
- most antiviral drugs are designed to target the few virus-specific enzymes (that only the viruses use) that exist e.g. HIV uses reverse transcriptase to replicate and human cells don’t use this enzyme so drugs can be designed to inhibit it without affecting the host cell = these drugs called reverse-transcriptase inhibitors
Currently no cure for HIV but antiviral drugs can be used to
Slow down the progression of HIV infections and AIDS in an infected person
The best way to control HIV infection in a population is by reducing its spread- HIV can be spread via
Unprotected sexual intercourse, through infected bodily fluids e.g. like blood from sharing contaminated needles and from a HIV-positive mother to her foetus (not all babies from HIV-positive mothers are born infected with HIV and taking antiviral drugs during pregnancy can reduce the chance of the baby being HIV-positive)
Why can HIV testing based on HIV antibody detection, before a baby is 18 months old ne inaccurate?
The baby of a HIV-positive mother may have some HIV antibodies in their blood regardless of whether they’re infected
