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B3 - Infection & Response (Monoclonal Antibodies (How they are…
B3 - Infection & Response
Vaccinations
If live pathogens of the same type appear, the WBC can remember and recognise it so can rapidly mass-produce the specific antibody (as it has already made this antibody before)
Advantages
Epidemics (outbreaks of disease) can be prevented if a large percentage of the population is vaccinated
This results in people who aren't vaccinated being less likely to catch it as fewer people are able to pass it on
If significant amounts of people aren't vaccinated, the disease can spread quickly and cause lots of people to be ill at the same time
Help control communicable diseases (eg. in the past - smallpox, polio etc.)
Vaccinations involve injecting dead/inactive pathogens
These carry antigens which cause your body to produce antibodies to attack them (even though the pathogen is harmless)
eg. the MMR vaccine contains weakened version of the viruses that cause measles, mumps and rubella all in one vaccine
Disadvantages
Don't always work (don't five you immunity)
You may have a bad reaction (eg. swelling, fever or seizures). These are very rare
When you are infected with a pathogen, it takes time for your WBC to recognise it and created antigens, by this time you can be pretty ill
Viral, Fungal & Protist Diseases
Fungi
Some are single-celled, others have a body (made up of hyphae - thread-like structures)
The hyphae can grow and penetrate human skin and the surface of plants, causing disease
Hyphae can produce spores, which can be spread to other animals/plants
Example
Rose Black Spot
Cause less photosynthesis to happen so hinders the plants' growth
Spreads through the environment in water or by the wind
Causes purple/black spots to develop on the leaves of rose plants, they then turn yellow and drop off
Gardeners treat it using fungicides and by striping it of its affected leaves, these leaves are destroyed so that the fungus can't spread to other rose plants
Protists
Single-celled eukaryotes
Lots of different types
Some are parasitic (they live on or inside other organisms and cause them damage)
They are often transferred by a vector which is immune to the disease (eg. mosquitoes are vectors for malaria)
Example
Malaria
Every time the mosquito feeds on another animal, it infects it by inserting the protist into the animal's blood vessels
It causes repeated episodes of fever and can be fatal
Part of its life cycle takes place inside the mosquito
The spread of malaria can be reduced by stopping the mosquitoes from breeding
Mosquitoes are vectors - they pick up the malarial protist when they feed on an an infected animal
People can be protected by using insecticides and mosquito nets
Viruses
Are not cells (1/100th size of bacterium)
Reproduce rapidly inside your body
Live inside your cells and replicate inside the host cell, damaging them when they do so
Once inside the cell, they take over it and make hundreds of thousands of copies of themselves
Eventually the copies fill the whole cell and cause it to burst open
The virus then passes through the blood stream, the airways or by other routes around your body to other cells
Examples
HIV
Initially causes flue-like symptoms for several weeks
Then the person usually doesn't experience any symptoms for several years (during this time it can be controlled with antiretroviral drugs which stop the virus replicating)
It attacks the immune cells
This results in the body's immune system becoming badly damaged and it not being able to cope with other infections or cancers. It is now known as late stage HIV infection or AIDS
Spread by sexual contact or by exchanging bodily fluids (eg. blood - when sharing needles when taking drugs)
It is very dangerous as if you get a common cold you can potentially die as your immune system can't fight it off
Tobacco Mosaic Virus (TMV)
Causes a mosaic pattern on the leaves - part of the leaves become discoloured
This results in the plants not being able to photosynthesise well and hence affects their growth
Affects many species of plant (ie. tomatoes)
Measles
Spread by droplets from an infected person's sneeze/cough
Causes a red skin rash, and show signs of a fever (high temperature)
Can be very serious, even fatal if there are complications, eg. it can sometimes lead to pneumonia (a lung infection) or encephalitis (a brain infection)
Most people are vaccinated when they are young
Pathogens
Is a microorganism that enters your body and causes disease (infections)
They are communicable (contagious) diseases
Both plants and animals can be infected
How they spread
Water
Some can be picked up by drinking/bathing in dirty water
eg. Cholera is spread by drinking water contaminated with the diarrhoea of other sufferers
Air
Can be carried in the are and breathed in
Airborne pathogens are carried in the air droplets produced when you sneeze/cough
eg. Influenza (virus) causes flu to spread this way
Direct Contact
Some can be picked up by toughing contaminated surfaces (inc. skin)
eg. Athlete's foot (fungus) makes skin itch and flake off - most commonly spread by touching the same things as an infected person
Bacteria
Very small cells (1/100th the size of body cells)
Reproduce rapidly inside your body
Can make you feel ill by producing toxins which damage your cells and tissues
Examples
Salmonella
You can get Salmonella food poisoning by eating food that's been contaminated with Salmonella bacteria eg. eating chicken that caught the disease whilst it was alive or by eating food that was contaminated by being prepared in unhygienic conditions
In the UK, most poultry (eg. chickens and turkeys) is given a vaccination against it in order to control the spread of the disease
Symptoms include fever, stomach cramps, vomiting and diarrhoea
These are caused by the toxins the bacteria produces
Causes food poisoning
Gonorrhoea
Symptoms include pain when urinating and thick yellow or green discharge from the penis/vagina
Originally treated with an antibiotic (penicillin) however some strains of the bacteria have become resistant to it
Passed on by sexual contact (eg. unprotected sex)
To prevent the spread, people can be treated with antibiotics and should use barrier methods of contraception (eg. condoms)
Is a sexually transmitted disease (STD)
Fighting Disease
Immune System
Produce Antibodies
Antibodies are then rapidly produced and carried around the body to find all similar bacteria/viruses
Phagocytosis can't be done on some certain antigens
Therefore, the WBC make an antibody (protein) specific for that antigen so that other WBC can come and do phagocytosis
Every pathogen has antigens unique to that pathogen
If a person is then infected with the same pathogen again, the WBC will recognise the antigen and so can rapidly produce the antibodies to kill it - the person is naturally immune to that pathogen and won't get ill
Produce Antitoxins
These counteract toxins produced by invading bacteria
Phagocytosis
WBC engulf foreign cells and digest them
If pathogens make it into your body, your immune system destoys them. Your white blood cells travel through your blood so when they come across invading microbe they can:
Defence System
Nose
Have hairs and mucus to trap particles that could contain pathogens
Trachea & Bronchi
Secrete mucus to trap pathogens
Lined with cilia (hair-like structures) which waft the mucus up to the back of the throat where it can be swallowed
Skin
Acts as a physical barrier to pathogens
Also secretes antimicrobial substances to kill pathogens
Stomach
Produces hydrochloric acid which kills pathogens that manage to enter the body
Disease
Spread of Disease
Isolating infected individuals
Isolate someone with a communicable disease so they can't pass it on to anyone else
Vaccinations
This means they can't develop the infection and then pass it on to someone else
Destroying vectors
Insects can be killed using insecticides or by destroying their habitat (so they can no longer breed)
Being hygienic
Washing your hands thoroughly before preparing food or after you've sneezed to stop you from infecting another person
Plant Diseases
Physical Defenses
They have cell walls made from cellulose to stop pathogens that make it past the waxy cuticle
Plants have layers of dead cells around their stems, (eg. the outer part of the bark on trees) to stop pathogens entering
Leaves has a waxy cuticle, which provides a barrier to stop pathogens entering
Chemical Defenses
Other plants produce poisons to deter herbivores (eg. tobacco plants, foxgloves and deadly nightshade)
Some can produce antibacterial chemicals to kill bacteria (eg. the mint plant and witch hazel)
Mechanical Defenses
Some have adapted to have thorns and hairs to stop animals touching/eating them
Others have leaves that droop/curl when something touches them which means they can prevent themselves from being eaten by knocking off insects and moving away from things
Some can mimic other organisms (eg. the passion flower has bright yellow spots on its leaves which look like butterfly eggs to stop other butterflies laying their eggs there)
Recognition
Signs of plant disease
Patches of decay
Abnormal growths (eg. lumps)
Spots on the leaves
Stunted growth
Malformed stems or leaves
Discolouration
Infestation of pests
Identification
Taking it to a lab so scientists can identify the pathogen
Using testing kits to identify the pathogen (using monoclonal antibodies)
Looking it up in a gardening manual/website
Plants need mineral ions (from the soil)
Nitrates
Needed to make proteins (and therefore for growth)
A lack of causes stunted growth
Magnesium ions
Needed for making chlorophyll
A lack of causes plants to suffer from chlorosis and have yellow leaves (due to a lack of photosynthesis)
If there aren't enough, plants may suffer deficiency symptoms
Disease
Plants can be infected by viral, bacterial and fungal pathogens
They can also be infected and damaged by insects
eg. Aphids are an insect that can cause huge damage to plants
Drugs
Antibiotics
Different antibiotics kill different bacteria, so you must be treated with the right one
Antibiotics don't destroy viruses (eg. flu) because they reproduce using your body cells
This makes it difficult to develop drugs that destroy just the virus without killing your body cells
Antibiotics (eg. penicillin) kill (or prevent the growth of) the bacteria causing the problem, without killing your own body cells
Their use has greatly reduced the number of deaths
Antibiotic Resistance
If you have an infection, some of the bacteria might be resistant
This means that when you treat the the infection, only non-resistant strains of bacteria will be killed
The individual resistant bacteria will survive and reproduce and the population of resistant bacteria will increase
This is an example of natural selection
This resistant strain could cause a serious infection that can't be treated with antibiotics
eg. MRSA (meticillin-resistant Staphylococcus aureus) causes serious wound infections and is resistant to meticillin
Bacteria can mutate and sometimes these mutations cause them to be resistant to antibiotics
How to slow down the rate of development of resistant strains
Ensure you finish the whole course of antibiotics (and not stop just when you feel better)
Doctors should avoid over-prescribing antibiotics
Developing Drugs
Clinical Testing
The drug is firstly tested on healthy human volunteers
This is to make sure it doesn't have any harmful side effects when the body is working normally (a very low dose is initially given and this is gradually increased)
The drug is then tested on people suffering with the illness
The optimum dose is found - the dose that is most effective and has the few side effects
To test how well it works, patients are randomly put in two groups - one is given the real drug and the other a placebo
This is so the doctor can see the actual difference the drug makes
These are blind (the patient doesn't know) and most are double-blind (where the doctor and patient both don't know who has the placebo/real thing) until results have been gathered so doctors monitoring patients /analysing data can't be subconsciously be influenced by their knowledge
The results aren't published until they've been peer reviewed
This helps to prevent false claims
Preclinical Testing
Human Cells/Tissue Testing
Limitation - you can't test drugs that affect the whole/multiple body systems (eg. a drug for blood pressure)
Live Animal Testing
Test the:
-
Efficacy
(whether the drug works and produces the effect you're looking for)
-
Toxicity
(how harmful it is)
-
Dosage
(the concentration and frequency it should be given)
In the UK, the law states that any new drug must be tested on 2 different live animals - this has ethical implications
Painkillers
Painkillers (eg. aspirin) only relieve the symptoms caused by the pathogen and don't actually do anything to kill pathogens
Many drugs originally came from plants
Examples
Digitalis
Used to treat heart conditions
Developed from a chemical found in foxgloves
Aspirin
Developed from a chemical found in willow
A painkiller to lower fever
Some drugs were extracted from microorganisms
Alexander Fleming was clearing out Petri dishes containing bacteria
He noticed that one of the dishes of bacteria also had mould on it and the area around the mould was free of the bacteria
He found that the mould (Penicillium notatum) on the dish produced a substance that killed the bacteria - penicillin
Plants produce chemicals to defend themselves (from pests and pathogens)
Some of these can be used as drugs to treat human diseases/relieve symptoms
These days, drugs are made on a large scale in the pharmaceutical industry - they;re synthesised by chemists in labs
The process might sill start with a chemical extracted from a plant though
Monoclonal Antibodies
Are produced by B-lymphocytes (type of WBC)
Pregnancy Tests
At the beginning of the test strip, there will be some antibodies to HCG, with blue beads attached
Further down the test strip (at the bit that turns blue if you're pregnant), there will be more antibodies to HCG stuck to the strip (so they can't move)
Positive
If you're pregnant, when you urinate on the stick the HCG in your urine will bind to the antibodies on the blue beads
The urine moves up the stick (carrying the antibodies and the beads)
The beads and HCG then bind to the antibodies that are stuck down on the strip
The blue beads are then also stuck down which turn it blue
A hormone - HCG - is found in the urine of women only when they are pregnant
Pregnancy tests detect this hormone
Negative
If your're not pregnant, the urine still moves up the stick carrying the blue beads but there's nothing to stick the blue beads onto the strip so it doesn't turn blue
They are produced from lots of clones of a single WBC - hence are identical and only target one specific antigen
How they are produced
You can't just clone lymphocytes though, they don't divide easily
Tumour cells divide a lot (so can be grown easily)
Hybridoma can be cloned and they produce the same antibodies - monoclonal antibodies
These can be collected and purified
So, scientists fuse a B-lymphocyte and a tumor cell to create a cell called hybridoma
You can make monoclonal antibodies that bind to anything you want (eg. an antigen that's only found n the surface of one type of cell)
They are really useful because they will only bind to (target) this molecule which means you can use them to target a specific cell or chemical in the body
Mouse
Injected with a dead/inactive pathogen
The B-lymphocyte cells in the mouse produce antibodies
The B-lymphocyte cells are taken from the mouse and fused with a tumour cell (in a lab) to make hybridoma
This then quickly divides to produce lots of clones that produce the monoclonal antibodies
Uses
Research
They bind to hormones and other chemicals in the blood to measure their levels
They test blood samples in labs for certain pathogens
Locate specific molecules on a cell or in a tissue
They're made to bind to the specific molecules
They are then bound to a fluorescent dye
If the molecules are present in the sample, the antibodies will attach to them, and they can be detected using the dye
Treat Diseases
Cancer cells have antigens on their cell membranes that aren't found on normal body cells
Called tumour markers
In a lab, you can make monoclonal antibodies which bind to these tumour markers
An anti-cancer drug can be attached to these monoclonal antibodies
These might be a radioactive substance, a toxic drug or a chemical which stops cancer cells growing and dividing
They are given to a patient through a drip
They target specific cells (the cancer cells) because the only bind to the tumour markers
The drug kills the cancer cells but not any normal body cells near the tumour
This is a huge advantage over other cancer treatments (eg. chemotherapy and radiotherapy) as they affect normal body cells also
Disadvantages
As a result, they aren't as widely used as treatments as scientists originally thought
Cause more side effects than originally expected
eg. fever, vomiting and low blood pressure
Scientists originally though that as they targeted a very specific cell/molecule, they wouldn't cause many side effects