Body Defence Mechanisms PDF

The mucus produced from your nose turns green when you have a cold. Why does this happen? It is all part of the way your body defends itself against disease. Preventing microorganisms getting into your body Each day, you meet millions of disease-causing microorganisms. Every body opening as we...

The mucus produced from your nose turns green when you have a cold. Why does this happen? It is all part of the way your body defends itself against disease. Preventing microorganisms getting into your body Each day, you meet millions of disease-causing microorganisms. Every body opening as well as any breaks in the skin give pathogens a way in. The more pathogens that get into your body, the more likely it is that you will get an infectious disease, Fortunately, your body has many defence mechanisms that work together to keep the pathogens out. Skin defences @ Your skin covers your body and acts as a barrier. It prevents bacteria and viruses reaching the tissues beneath, If you damage or cut your skin, the barrier is broken but your body restores it. You bleed, and the platelets in your blood set up a chain of events ta form a clot that dries into a scab (Figure 1). This forms a seal over the cut, stopping pathogens getting in. It also stops you bleeding to death. @ 'Your Skin produces antimicrobial secretions to destroy pathogenic bacteria. @ Healthy skin is covered with microorganisms that help keep you healthy and act as an extra barrier to the entry of pathogens, Defences of the respiratory and digestive systems Your respiratory system is a weak link in your body defences. Every time you breathe in, you draw air full of pathogens into the airways of the lungs. In the same way, you take food and drink, as well as air, into your digestive system through your mouth, Both systems have good defences to help prevent pathogens constantly causing infections. e@ 'Your nose is full of hairs and produces a sticky liquid, called mucus. The hairs and mucus trap particles in the air that may contain pathogens or irritate your lungs. If you spend time in an environment with lots of air pollution, the mucus you produce when you blow your nose is blackened, showing that the system works, @ The trachea and bronchi also secrete mucus that traps pathogens frorn the air. The lining of the tubes is covered in cilia --- tiny hair-like projections from the cells. The cilia beat to waft the mucus up to the back of the throat where it is swallowed. @ The stomach produces acid and this destroys the microorganisms in the mucus you swallow, as well as the majority of the pathogens you take in through your mouth in your food and drink. The immune system - internal defences In spite of your body\'s defence mechanisms, same pathogens still get inside your body. Once there, they will meet your second line of defence --- the white blood cells ef your immune system. The immune system will try to destroy any pathogens that enter the body in séveral ways. Table 1 Ways in which your white blood cells destroy pathogens and protect you against disease Role of white blood cell How it protects you against disease Ingesting microorganisms Some white blood cells ingest (take in) , ------ pathogens, digesting and destroying bacterium.\_» white. : 5 --- a blood cell then so they cannot make you ill, Producing antibodies Some white blood cells produce spacial antibody antigen chemicals called antibodies. These target 7 particular bacteria or viruses and destroy \_aa, bacterium them, You need a unique antibody for \| ae} at each type of pathogen. When your white \\ a blood cells have produced antibodies --- --- once against a particular pathogen, they white blood cell antibody attached can be made very quickly if that pathogen to antigen gets into the body again, This stops you getting the disease twice. Producing antitoxins Some white blood cells produce white blood cell antitoxins. These counteract (cancel out} aniitaath riclacume: aa ------i the toxins released by pathogens. toxin and x QD ! antitoxin Ws ay --- joined together bo toxin molecule bacterium The different body systems work together to help protect you from disease. For example, some white blood cells contain green-coloured enzymes. These white blood cells destroy the cold viruses and any bacteria trapped in the mucus of your nose when you have a cold, The dead white blood cells, along with the dead bacteria and viruses, are removed in the mucus, making it look green. The global loss of food crops to plant pathogens is 15-40% a year. Understanding the causes and preventing the spread of plant diseases can help provide a secure food supply for everyone, More plant pathogens As you have seen, plants are vulnerable to viruses, bacteria, and fungi but they are also attacked by pests that cause a lot of damage. Insect pests may both destroy plants directly and act as vectors of disease. One important group of insect plant pests is the aphids. Aphids have sharp mouthparts that penetrate into the phloem vessels of the plant so they can feed on the sugar-rich phloem sap. Aphids attack in huge numbers, depriving the plant cells of the products of photosynthesis. This can seriously damage and weaken the plant. Aphids also act as vectors, transferring viruses, bacteria, and fungi from diseased plants into the tissues of healthy plants on their mouthparts, Aphids can be destroyed using chemical pesticides ar, in enclosed spaces such as greenhouses, using biological pest control, Releasing aphid- eating insects such as ladybirds and their larvae can control the pathogen population as it does not have an impact on the success of the crop. Other plant pests, including tiny nematode worms and many insect larvae that live in the soil, feed in or on plant roots, damaging them so they cannot absorb water and mineral ions effectively. As a result the plant fails to grow and thrive. Mineral deficiency - non-communicable diseases in plants Some plant diseases are the result of mineral deficiencies in the sail where the plants are growing. They are nan-communicable - they are not passed from one plant to another. For example, plants need a good supply of nitrate ions from the soil to convert the sugars made in photosynthesis into proteins needed for growth in protein synthesis. lf there is a nitrate deficiency in the soil, protein growth will be limited, the growth of plants will be stunted, and they will nat produce a crop properly. Plants take magnesium ions from the soil to make the chlorophyll needed for photosynthesis. If the level of magnesium ions in the the sail is low, the plant cannot make enough chlorophyll. The leaves become yellow and growth slows dawn because the plant cannat photosynthesise fully, The yellowing of the leaves due to lack of Magnesium ions are known as chlorosis. Ifthe missing mineral ions are replaced using fertilisers fairly quickly, the damage can be repaired and the plant recovers. If not it will eventually die, 4 Detecting disease a Bo E8 In plants as in people, the sooner a disease can be detected, the more likely it is that it can be treated effectively. Fast detection also helps reduce the spread of disease between plants, because diseased plants can be treated or removed. Symptoms of disease in plants include: stunted growth (e.g, nitrate deficiency) spots on leaves (e.g, black spot fungus on roses) areas of decay or rotting (e.g, black spot on roses, blights on potatoes) growths (2.9, crown galls caused by bacterial infections) malformed stems and leaves (e.g, due to aphid or nematode infestation) discoloration (e.g, yellowing or chlorosis in magnesium deficiency, mosaic patterns resulting from tobacco mosaic virus) ® presence of visible pests (e.g, aphids, caterpillars). Identifying plant diseases is not easy. Many diseases give similar symptoms. However, it is very important to identify the cause of problems in plants, Some can be treated using pesticides or antifungal treatments. Mineral deficiencies can also be treated. But the sooner treatment starts, the more likely it is to be successful. Same diseases cannot be treated - in such cases, it is important to remove the diseased plants 45 quickly as possible to prevent the pathogens spreading through the garden, field, or woodland, Diseases in garden plants may be identified by comparing the symptoms in the living plant with disease descriptions in a gardening manual or online, When the symptoms of disease occur in crop plants or forest trees, experts may visit the fleld or woodland to observe the symptoms in their natural environment. They may then take sarnples of diseased materials to the laboratory to identify the pathogen using techniques that include DNA analysis, Plant scientists, foresters, farmers, and market gardeners can use testing kits that contain monoclonal antibodies ta identify the presence of certain plant pathogens, for example, the fungal pathogen Botrytis, You are familiar with some of the ways the human body defends itself against the entry of pathogens. Plants have also evalyed some very effective defences against the attacks of microorganisms, insects, and even larger herbivores, Plants have evolved both physical and chemical defences against pathogenic microorganisms: Physical barriers Plants have a number of physical barriers that reduce the invasion of pathagens: ® The cellulose cell walls that strengthen olant cells also help to resist invasion by microorganisms. This is one reason why the actions of aphids that pierce the cellulose cell walls are so damaging. It breaches the barrier and gives pathogens a way into the cells. @ The tough waxy cuticle on the surface of leaves acts as a barrier to the entry of pathogens. It is only at the stomata that pathogens actually have access to the cells within the leaf. ®@ = Bark on trees, and a layer of dead cells an the outside of stems, form a protective layer that is hard for pathogens to penetrate, When the dead cells are lost or shed, the pathogens fall off with them. ® = Leaf fall --- deciduous trees lose their leaves in autumn. Any pathogens that infect the leaves, such as rose black spot, fall off the tree when the leaves are lost. Chemical barriers Many plants produce antibacterial chemicals that protect then against invading pathogens, and these are very effective at preventing bacterial diseases in many plants. Until recently people have not extracted and used plant chemicals as antibiotics. As current antibiotics become less effective, scientists are increasingly investigating plant antibacterial chemicals to see if they can be adapted for use as antibiotics against human pathogens. Mint and witch hazel are often used as mild antiseptics in cosmetics and over-the-counter medicines. Compounds from plants including pines, cypress, and euphorbias also have promising antibiotic properties. Defence against herbivores Plants don\'t just defend themselves against microorganisms. They also defend themselves against the large and small anirnals that want to eat them, Obviously ifa plant is eaten by a lange herbivare it is destroyed and will not flower ang reproduce, If smaller herbivores such as aphics, caterpillars, or beetles attack a plant, they can damage the plants and act as vectors of pathogens themselves. Not only that, the damage they do may allow other disease-causing organisms to get in. Some of these defences are chemical and others are mechanical (Figure 2), Poisons to deter herbivores, for example, foxgloves, deadly nightshade and yew. Animals quickly learn to avoid eating plants that make them feel unwell. Thorns ta make it unpleasant or painful for large herbivores to eat them, for example, brambles, cacti and gorse, Thorns are unlikely to deter insects. Hairy stems and/or leaves deter insects and larger animals from feeding an them or laying their eggs on the leaves or sterns, for example, larnb's ears, and some pelargoniums. Some plants combine hairs with poisons, for example, nettles Drooping or curling when touched - a rare but effective adaptation is for the leaves to collapse suddenly, dislodging insects and frightening larger animals, for example, the sensitive plant Mimosa pudica, Mimicry --- some plants droop to mimic unhealthy plants and this tricks animals into not eating them. Some mimic butterfly egas on their surfaces, so real butterflies do not lay eqqgs on them to avoid competitian with other caterpillars. Every cell has unique proteins on its surface called antigens. The antigens on the microorganisms that get into your body are different to the ones on your own cells. Your immune system recognises that they are different. Your white blood cells then make specific antibodies, which join up with the antigens and inactivate or destroy that particular pathogen. Some of your white blood cells (the memory cells) remember' the right antibody needed to destroy a particular pathogen. If you meet that pathogen again, these memory cells can make the same antibody very quickly to kill the pathogen, so you become immune to the disease. The first time you meet a new pathogen you get ill because there is a delay while your body sorts out the right antibody needed, The next time, your immune system destroys the invaders before they can make you feel unwell. Vaccination Some pathogens, such as meningitis, can make you seriously ill very quickly. In fact, you can die before your body manages to make the right antibodies. Fortunately, you can be protected against many of these serious diseases by vaccination (also known as immunisation). Immunisation invalves giving you a vaccine made of a dead or inactivated form of a disease-causing microorganism. It stimulates your body\'s natural immune response to invading pathogens. A small amount of dead or inactive forms of a pathogen is introduced into your body. This stimulates the white blood cells to produce the antibodies needed to fight the pathogen and prevent you from getting ill. Then, if you meet the same, live pathogen, your white blood cells can respond rapidly. They can make the right antibodies just as if you had already had the disease, so that you aré protected against it. Doctors use vaccines to protect us both against bacterial diseases, such as tetanus and diphtheria, and viral diseases such as polio, measles and mumps. For example, the MMR vaccine protects against measles, mumps, and rubella. Vaccines have saved millions of lives around the world, One disease --- smallpox --- has been completely wiped out by vaccinations. Doctors hope polio will also disappear in the next few years. pathogen \> W a antibody t on ' z \> zs (as = : oa \>. = € 2 \- a white blood cell \"¥ eS x a vaccine white blood cell Small amounts of dead or inactive pathogen The antigens in the vaccine stimulate your You are immune to future infections by the are put into your body, often by injection white blood cells into making antibodies. pathogen. That\'s because your body can The antibodies destroy the antigens without respond rapidly and make the correct antibody any risk of you getting the disease as if you had already had the disease Figure 2 This is how vaccination protects you against dangerous infectious diseases i 2005 --- Herd immunity "yactinato eS If a large proportion of the population is immune toa i t E 34% disease, the spread of the pathogen in the population is very much reduced and the disease may even disappear. This is known as herd immunity. If, for any reason, the number of people taking up a vaccine falls, the herd immunity is lost and the disease can reappear. This is what happened in the UK in the 1970s when there was a scare about the safety of the whooping cough vaccine. Vaccination rates fell from over 80% to around 30% (Figure 3). In the following years, thousands of children 0 r T r T T got whooping cough again and a substantial number Io40 1950 1960 1970 1980 1980 died. Yet the vaccine was as safe as any medicine. --- Eventually people realised this and enough children were vaccinated las sch, eetarsecode for herd immunity to be effective again. There are global vaccination SHECUAGSInG Guid Thanuiiber bheabue Drie Programmes to control a number of diseases, including tetanus in asa mothers and new-born babies, polio, and measles. The World Health Organisation want 95% of children to have two doses of measles vaccine to give global herd immunity, Current global figures show that 85% of children get the first dose and 56% get the second. It will take money and e Ifa pathogen enters the body the 1504 1004 507 reported cases (thousands) Source: Open University determination to get global herd immunity against a range of different immune system tries to destroy the diseases, but the advantages both to individuals and to global economies pathogen. ; ; are huge. e Vaccination involves introducing Ses a eee J 2 Sw eee When you have an infectious disease, you generally take medicines that contain useful drugs. Often the medicine doesn\'t affect the pathogen that is causing the problems --- it just eases the symptoms and makes you feel better, Treating the symptoms Drugs such as aspirin and paracetamol are very useful painkillers. When you have a cold, they will help relieve your headache and sore thiraat. On the other hand, they will have no effect on the viruses that have entered your tissues and made you feel ill, Many of the medicines you can buy al a chemists or supermarket relieve your symptoms but do not kill the pathogens, 50 they do not cure you any faster. You have to wait for your immune system ta overcome the pathogens before you actually get well again. Antibiotics - drugs to cure bacterial diseases Drugs that make you feel better are useful, but in sorme cases what you really need are drugs that can cure you. You can use antiseptics and disinfectants to kill bacteria outside the body, but they are far too poisonous to use inside your bady. They would kill you and your pathogens at the same tirne, The drugs that have really changed the treatment of communicable diseases are antibiotics. These are medicines that can work inside your body to kill bacterial pathogens. The impact of antibiotics on deaths from cammunicable diseases has been enarmous, Antibiotics first became widely available in the 1940s, They were regarded as wonder drugs, For example, the number of women who died of infections in the first days after giving birth dropped dramatically (Figure 2). How antibiotics work Antibiotics, such as penicillin, work by killing the bacteria that cause disease whilst they are inside your body. They darnage the bacterial cells without harming your own cells. Bacterial diseases that killed millions of peaple in the past can now be cured using antibiotics. They have had an enormous effect an our society. If you need antibiotics, you usually take a pill or syrup, but if you are very ilantiblotics may be put straight into your bloodstream. This rakes sure that they reach the pathogens in your cells as quickly as possible, Some antibiotics kill a wide range of bacteria, Others are very specific and only work against particular bacteria. It is important that the right antibiotic is chosen and used. Specific bacteria should be treated with the specific antibiotic that is effective against them. B g 8 : 8 number of deaths per 100000 live births 1900 1910 1920 1930 1940 1950 1960 year Figure 2 The introduction of antibiotics in the 1940s had an enormous impact on deaths from maternal septicaemia 0 i --- 1970 1980 1990 Unfortunately, antibiotics are not the complete answer to the problem of infectious diseases: @ Antibiotics cannot kill viral pathogens so they have no effect on diseases caused by viruses. Viruses reproduce inside the cells of your body. It is extremely difficult to develop drugs that will kill the viruses without damaging the cells and tissues of your body at the same time. @ Strains of bacteria that are resistant to antibiotics are evolving. This means that antibiotics which used to kill a particular type of bacteria no longer have an effect, so they cannot cure the disease. There are some types of bacteria that are resistant to all known antibiotics. The emergence of antibiotic-resistant strains of bacteria is a matter of great concern. Unless scientists can discover new antibiotics soon, we may no longer be able to cure bacterial diseases. This means that many millions of people in the future will die of bacterial diseases that we can currently cure, You will learn more about the discovery of antibiotics in Topic B64. Traditionally drugs were extracted from plants or microorganisms such as moulds. In ancient Egypt mouldy bread was used on septic wounds, perhaps an early form of antibiotic treatment, Now scientists often adapt chemicals fram microorganisms, plants, and animals to make more effective drugs. Drugs from plants There are a number of drugs used today thet are based on traditional medicines extracted fram plants, Digitalis is one of several drugs extracted from foxgloves, and the drug digoxin is another. They have been used since the 18th century to help strengthen the heartbeat. There are many more modern drugs but doctors still use digoxin, especially for alder patients with heart problems. Large amounts of these chemicals can act as poisons, The painkiller aspirin originates from a compound found in the bark of willow trees. The anti-inflammatory and pain-réelieving properties were first recorded in 400BC. In 1897, Felix Hoffman synthesised acetyl salicylic acid (aspirin), which not only relieves pain and inflammation better than willow bark but has fewer side effects. Aspirin is still commonly used to real a wide range of health proolerns. Drugs from microorganisms - discovering penicillin In the early 20th century, scientists were locking for chemicals that might kill bacteria and cure infectious diseases. In 1928, Alexander Heming was growing bacteria for study purposes. He was rather careless, often leaving the lids off his culture plates --- health and safety procedures were not as good in those days, After one holiday, Fleming saw that lots of his culture plates had mould growing on them, He noticed a clear ring in the jelly around some of the spots of mould and realised something had killed the bacteria covering the gel. Fleming recognised the importance of his observations. He called the substance that killed bacteria 'penicillin' after the Penicilfum mould that produced it. He tried unsuccessfully for several years to extract an active juice fram the mould before giving up and moving on to other work, About 10 years after Fleming\'s discavery, Ernst Chain and Howard Florey set about trying to extract penicillin, and they succeeded. They gave same penicillin to aman dying of a blood infection and he recovered almast miraculously - until the penicillin ran out. Even though their patient died, Florey and Chain demonstrated that penicillin could cure bacterial infections in people. Eventually, working with the company Phizer in the USA, Florey and Chain made penicillin on an industrial scale, producing enough to supply the demands of World War Il It is still used today. There is a continuing drive to find new medicines but it is difficult For example, it is not easy to find chemicals that kill bacteria without damaging human cells. Most drugs are now synthesised by research chemists working in the pharmaceutical industry using chemical banks and computer models. However, the starting point may still be a chemical extracted from a plant or microorganism. Compounds showing promise as antibiotics can be modified to produce more powerful molecules that can be synthesised easily and cheaply. For example, the noni fruit is widely used in traditional medicine in Costa Rica and many other countries to treat both infections and non-cormmunicable diseases. People have also used it for food and drink for centuries with no apparent problems, Recent research shows that it has antibiotic properties. More research is taking place to see if this traditional healing plant might be the source of new antibiotics or other medicines. Figure 3 The noni fruit looks strange and smells stranger, but will it provide us with medicines far the future? Scientists are also collecting sail samples globally and searching for microorganisms to produce a new antibiotic against antibiotic-resistant bacteria. Only about 1% of soil microorganisms can be cultured in the lab. Scientists have developed a special unit that enables them to grow microorganisms in the soil in a controlled way. Using this technology, in 2015 they announced a completely new type of antibiotic froarn some soil bacteria. In tests so far, this antibiotic has destroyed all bacteria including MRSA and other antibiotic resistant pathogens. It worked in mice --- will it work in hurnans? New medicines are being developed all the time, as scientists and doctors try to find ways of curing more diseases, Scientists test new medicines in the laboratory. Every new medical treatment has to be extensively tested and trialled ina series of stages before it is used. This process makes sure that it works well and is as safe as possible. A good medicine is: ® Effective --- it must prevent or cure a disease or at least make you feel better. @ Safe - the drug must not be too toxic (polsanous) or have unacceptable side effects for the patient @ Stable - you must be able to use the medicine under normal conditions and store it for same time. ® Successfully taken into and removed fram your body = it must reach its target and be cleared fram your system once it has done its work. Developing and testing a new drug When scientists research a new medicine they have ta make sure all these conditions are met. It can take up to 12 years to bring a new medicine into your doctor\'s surgery and costs around £1700 million, including failures and capital costs. Researchers target a disease and make lots of possible new crugs. These are tested in the laboratory to find out if they are toxic (toxicity) and if they seem te do their job (efficacy). In the laboratory they are tested on calls, tissues, and even whole organs, Many chemicals fail at this stage, The small nurnbers of chemicals, which pass the earlier tests, are then laboratory tested on animals, to find out haw they work in a whole living arganism, It also gives informatian about possible doses and side effects. The tissues and animals are used as models to predict how the drugs may behave in humans. Up to this point the chemicals are undergoing preclinical testing, This always takes place in the laboratory using cells, tissues, and live animals. Drugs that pass animal testing move on to clinical trials, Clinical trials use healthy volunteers and patients. First, very low doses are given to healthy people to check for side effects. If the drug is found to be safe, it is tried on a small nurnber of patients to see if it treats the disease. If it seems to be safe and effective, bigger clinical trials take place to find the optimum dese for the drug. If the medicine passes all the legal tests, itis licenced so your doctor can prescribe it. Its safety will be manitered for as long as it Is used. Double blind trials In human trials, scientists use a double blind trial to see just how effective the new medicine is. A group of patients with the target disease agree to take part in the trials. Some are given a placebo that does not contain the drug and some are given the new medicine. Patients are randomly allocated to the different groups. Then neither the doctor nor the patients know who has received the real drug or the placebo until the trial is complete. The patients' health is monitored carefully. Often the placebo will contain a different drug that is already used to treat the disease, This means the patient is not deprived of treatment whilst taking part in the trial. Figure 2 An enormous number of chemicais start the selection process but few actually become a new, useful medicine Publishing results The results of drug tests and trials, like all scientific research, are published in journals after they have been scrutinised in a process of peer review. This means other scientists working in the same area can check the results aver, helping to prevent false claims. National bodies such the National Institute for Health and Care Excellence (NICE) look at the published results of drugs trials and decide which drugs give good value for money and e New medical drugs are extensively should be prescribed by the NHS. tested for efficacy, toxicity, and. Imagine combining cells from mice or people and cancer cells to form a new type of cell. Then using thase new cells in human and animal medicine and in the diagnosis of plant diseases. This might sound farfetched or even dangerous. However, scientists and doctors are finding more and more ways of using these unusual cells, known as hybridomas. Making monoclonal antibodies Moneclonal antibodies, like vaccinations, are a form of medical treatment that relies on the immune system. Monoclonal antibodies are proteins that are produced to target particular cells or chemicals in the bady. Some white blood cells known as lymphocytes make antibodies but cannot divide. Tumour cells do not usually make antibodies but they can divide rapidly to make a clone of cells. All mammals, including mice, produce lymphocytes. Scientists combine mice lymphocytes (that have been stimulated to make a particular antibody! with a type of turnaur cell to make a cell called a hybridoma, Single hybridoma cells divide to make a large number of identical cells that all praduce the same antibodies (Figure 1). These antibodies are collected and purified. They are monaclonal antibodies - antibodies produced fram a single clone of cells. More recently scientists have combined the mice cells with human cells as well to produce monoclonal antibodies that are less likely to be rejected by human cells, Gy --- B lymphocytes make specie coe antibodies but Za Oo --- es see% 2---\* rans Sig ao not divide a hybridoma cell the cells monacional (makes specific are cloned antibodies are @ Lo ------+\_ antibodies and divides) separated, purified, (.) and can be used turriour cells that do not make antibodies but divide Figure 1 The production of monoclonal antibodies Using monoclonal antibodies Antigens aré protein molecules that are often found on the surface of cells, although free protein molecules can alsa act as antigens. The monoclonal antibodies produced from a single clone of cells are specific to one binding site on one specific antigen. This antigen might be found only on specific types of cell in the body, or it might be a specific chemical. Because the monoclonal antibodies only target and bind to one specific antigen, they can then be used in a number of ways. Pregnancy tests --- these = rely on manoclonal & a antibodies that bind "SS een ta the hormone gs \> human chorionic ---\