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We all have the capacity unconsciously to blot out things we find too uncomfortable or upsetting to think about. This psychological defence mechanism is known as denial. However, the mind’s ability to belittle or even ignore symptoms is something of a mixed blessing. Being excessively stoical or negligent about your own health is risky.
When people react to illness by denying the reality of their symptoms they may save themselves the unpleasantness of confronting an unpalatable reality. But their denial can be positively dangerous if it prevents them from seeking timely medical attention. A woman who fails to notice a lump in her breast, for example, or chooses to disregard it until her breast cancer is at an advanced stage, may pay for her insouciance with her life.
It is an unfortunate fact that people are less likely to seek medical help if it is difficult, inconvenient or embarrassing for them to do so – perhaps because they are too busy, or cannot afford the fees, or because they are simply afraid of calling a doctor out on a false alarm. Heart attacks are notoriously more likely to prove fatal at weekends, when it is inconvenient or potentially embarrassing to seek expert medical help. The lives of countless heart attack victims might have been saved had they not incorrectly attributed their chest pains to indigestion.
The disastrous consequences of denial are sombrely portrayed in Arnold Bennett’s Riceyman Steps. The tightfisted Clerkenwell bookseller Henry Earlforward has cancer of the stomach but steadfastly denies that he is ill. Earlforward insists that it is merely a temporary indisposition and that he has a constitution of iron.
For a long time Earlforward’s wife interprets his lack of interest in food as a symptom of his miserliness rather than any medical problem. Even when it becomes obvious that the emaciated bookseller is gravely ill he obstinately refuses to be examined by a doctor, let alone admitted into hospital. His wife rails at him for concealing from her the seriousness of his illness until it is too late to do anything about it. She tries hard to persuade Henry to accept medical help, but is forced to concede for ‘nobody can keep on fighting a cushion for ever’. Faced with Henry’s bland obstinacy, his wife and doctor eventually abandon their attempts to help him and he dies from his cancer – a victim of his own misplaced psychological defences.
Whether or not an illness has psychological origins it will certainly have psychological consequences. Feeling ill for any length of time is a psychologically debilitating experience. One of the simple but important ideas I hope to convey in this book is that the relationships between mind, body and disease work both ways. The mind affects the body and hence physical health. Conversely, physical health affects the mind and hence our thoughts, emotions and behaviour.
All but the most trivial of illnesses produce some sort of emotional reaction, whether it be mild irritation, anxiety, anger, denial or depression. Other things being equal, a serious illness should provoke a more intense emotional reaction than a minor illness. But other things seldom are equal. Illness means different things to different people, and just because an illness is not life-threatening this does not mean the sufferer will be emotionally untouched by it. An individual who has never before experienced any significant illness, pain or discomfort may be upset by relatively minor symptoms which would seem insignificant to someone who has suffered a string of serious diseases.
Our emotional responses to illness can have a crucial bearing on our recovery and future health. If being ill makes us depressed we may become careless about adhering to our doctor’s advice or taking our medicine. This may, in turn, impede recovery. Whether or not a cancer patient adheres strictly to a programme of radiotherapy or chemotherapy can have a major impact on their chances of survival. There are patients who simply give up and sink into decline.
In extreme cases the emotional reaction to an illness can prove a bigger problem than the illness itself. Severe depression is far more debilitating and intrusive than many physical ailments. As we shall see in the next chapter, severe depression can also have detrimental effects on immune function and subsequent health, creating a spiral of decline. Doctors and patients ignore the psychological and emotional consequences of illness at their peril.
Finally, please do not go away with the impression that an individual’s perception of their own health is an entirely meaningless or deceptive index, indicating only their degree of hypochondria. On the contrary. Research has shown that in certain respects perception is a good guide to reality. Although our subjective judgement is not always an accurate index of our current state of health, it does provide a reasonably good predictor of our long-term risk of dying prematurely. Depressing though it may be if you are an arch hypochondriac, the research indicates that people who believe they are unhealthy do die younger on average. Moreover, perceptions are clearly important for practical and economic reasons: people’s perceptions of their health, rather than objective measures of health, are what largely determine their initial usage of medical facilities.
Bad behaviour (#ulink_faed3c0a-9141-59b9-8a61-eae3c52f688d)
Sex and drugs and rock and roll
Is all my brain and body need
Ian Dury, ‘Sex and Drugs and Rock and Roll’ (1977)
A cousin of mine who was a casualty surgeon in Manhattan tells me that he and his colleagues had a one-word nickname for bikers: Donors. Rather chilling.
Stephen Fry, Paperweight (1992)
Our minds can have a profound impact on the physical health of our bodies by altering the way we behave. Psychological and emotional factors can dispose us to do all manner of unhealthy and self-destructive things. The self-destruction may be absolute and abrupt, as in suicide or fatal accidents, or gradual and cumulative, as in smoking.
Stress and anxiety, for example, can prevent us from sleeping properly and make us more inclined to smoke, drink excessive amounts of alcohol, eat too much of the wrong sorts of food, omit to take our medicine, neglect physical exercise, consume harmful recreational drugs, indulge in risky sexual behaviour, drive too fast without wearing a seat belt, have a violent accident, or even commit suicide (though not usually all at once).
Anna Karenin offers an impressive catalogue of self-destructive behaviour engendered by psychological and emotional trauma. Anna abandons her husband, the colourless bureaucrat Karenin, for the dynamic Count Vronsky. But their love is doomed and the emotional pressures on Anna build up to a fatal climax.
As a preamble to her eventual self-destruction, Anna nearly dies giving birth to Vronsky’s illegitimate daughter. In what she thinks are her final hours Anna appears to reconcile herself with her husband. Mad with emotional torment at this turn of events, Vronsky goes off and shoots himself – but not fatally. Although Vronsky is an army officer, and therefore presumably capable of hitting his own heart at point blank range, the bullet misses. He is seriously wounded – enough to make it a meaningful parasuicidal gesture – but does not die. Anna and the baby go to live with Vronsky, but her husband refuses to divorce her and she becomes a social outcast. The strain of her position renders Anna increasingly unstable and she develops paranoid delusions about Vronsky’s supposed unfaithfulness. Consumed by the madness of her passion, Anna suddenly decides that she must end her torment and punish Vronsky for his imagined misdeeds by killing herself. Anna famously ends her own life under the wheels of a train:
‘There,’ she said to herself, looking in the shadow of the trucks at the mixture of sand and coal dust which covered the sleepers. ‘There, in the very middle, and I shall punish him and escape from them all and from myself.’
And she does. And there is more. Almost insane with grief at Anna’s death, the bereaved Vronsky volunteers to fight, and very probably die, in a war between the Serbians and the Turks. Vronsky no longer places any value on his life and relishes the prospect of death: ‘I am glad there is something for which I can lay down the life which is not simply useless but loathsome to me. Anyone’s welcome to it …’
The melodrama of Anna Karenin’s suicide and Vronsky’s death wish are positively restrained in comparison with the high-camp posturings of Werther, the suicidal hero of Goethe’s The Sorrows of Young Werther. This eighteenth-century piece of unfettered Teutonic sentimentality tells the tragic tale of an unbalanced youth who tops himself after a bad dose of unrequited love.
The story is a simple but eternal one. Werther loves Lotte. Oh, how he loves her! But, alas, he cannot have her. Lotte is already promised to the worthy Albert and soon marries him, leaving Werther to wallow in emotional excess. He sheds a thousand tears one moment and ‘overflows with rapture’ the next, and each step on the way is recounted in copious letters to his long-suffering chum Wilhelm. So it comes as no surprise that, denied his one true love, Werther decides to end it all. Characteristically, his suicidal decision is reached only after much beating of chest, gnashing of teeth, shedding of tears and general languishing in melancholy, during which time an unkind reader might be forgiven for urging the lad to get on with it. Even when Werther finally does get round to pulling the trigger he takes several hours to die.
Incidentally, the tragic tale of young Werther had a fairly profound effect on the health of a number of readers. So resonant was Goethe’s writing with the romantic spirit of the times that the book triggered an epidemic of copy-cat suicides and was consequently banned in many places.
(#litres_trial_promo)
All the leading causes of death in industrialized nations – including heart disease, cancer, accidental injury and AIDS – depend to some extent on how we behave. Smoking, eating habits, alcohol consumption, physical exercise, sleep patterns, sexual behaviour and choosing to wear a seatbelt, to name but a few, have ramifications for our health and wellbeing.
In industrialized societies, for example, accidental injuries and violence now account for at least half of all deaths among young men: a fact that is not wholly unrelated to the behavioural characteristics of young men. In extreme cases people who are very depressed or upset commit suicide or deliberately behave in a way which invites serious injury or death. Severe depression can lead to self-destructive behaviour. Besides making us act in positively unhealthy ways, psychological factors like anxiety, stress or depression can also inhibit us from engaging in activities that are beneficial to health, such as physical activity or social relationships with others.
In certain cases, such as crashing your car or committing suicide, the causal connection between behaviour and the subsequent damage to health is pretty obvious and requires no intimate knowledge of medical science to understand. Thanks to education and constant repetition in the media, less obvious connections between behaviour and health are also now widely recognized. The public accept that there are links between smoking and all manner of fatal diseases; between slothfulness and heart disease; between alcohol abuse and cirrhosis; and between unprotected sex and AIDS.
A stark illustration of how behaviour affects health is provided by AIDS. There are enormous geographical variations in the incidence of HIV infection and AIDS. For example, the incidence of AIDS in Honduras is fourteen times higher than in neighbouring Guatemala. Even within a single country or a single city there are massive variations in rates of infection between different social groups.
Since the HIV retrovirus was discovered to be the causal agent for AIDS in 1983 it has become clear that these large variations result primarily from differences in people’s behaviour – especially their sexual behaviour, which remains the route by which the virus is transmitted in the vast majority of HIV infections. It is generally accepted that a practical vaccine or cure for HIV/AIDS is at least a decade away.
(#litres_trial_promo) In the meantime, the only effective means available for limiting its spread is to change the way we behave.
There are plenty of commonplace behaviour patterns that kill people gradually but in huge numbers. Smoking is the prime example. As long ago as 1604 King James I, in his treatise A Counterblast to Tobacco, did not exactly pull his punches when he described the new-fangled habit of smoking as:
A custom loathsome to the eye, hateful to the nose, harmful to the brain, dangerous to the lungs, and in the black, stinking fume thereof, nearest resembling the horrible Stygian smoke of the pit that is bottomless.
Smoking is the riskiest thing that most people will ever do in their lives. At present, smoking-related diseases account for 15–20 per cent of all deaths and result in over 100,000 premature deaths every year in Britain alone. Smoking greatly increases the risk of lung cancer, now the commonest fatal cancer in Britain. Smokers are ten times more likely to die from lung cancer than non-smokers and around 90 per cent of lung cancers are attributable to smoking.
Smoking also increases the risks of various other fatal or debilitating diseases including coronary heart disease (the biggest cause of death in most industrialized countries), chronic bronchitis, emphysema, and cancers of the oesophagus, bladder and pancreas. A quarter of all deaths from coronary heart disease are smoking-related. As if that were not enough, smoking causes birth complications and doubles the risk of a pregnant woman miscarrying.
Think about these statistics from the British Medical Association. The average risk that you will die from leukaemia within the next year is about 1 in 12,500. The average risk that you will die in a vehicle accident is 1 in 8,000. If you are, say, forty years old, your risk of dying from natural causes of any sort during the next twelve months is 1 in 850. However, if you smoke ten cigarettes a day your odds of dying within the year are 1 in 200. Or look at it another way: take a random sample of a thousand young men who smoke; on the basis of actuarial data it can confidently be predicted that one of these young men will eventually be murdered, six will be killed on the roads and two hundred and fifty will die prematurely from the effects of smoking.
Smoking is clearly bound up with what goes on in people’s minds. The reasons why individuals start smoking and why they then find it impossible to quit are neither simple nor well understood. Psychological studies of smokers have, however, confirmed the truth of several common assumptions.
It is indeed true that people who are depressed or stressed are more likely to smoke (and, consequently, more likely to die from lung cancer). Smokers really do experience a stronger desire to smoke at times of heightened anxiety. To add to their problems, psychological stress is associated with a higher failure rate among smokers trying to kick the habit. One long-term study of smokers found that individuals who had been depressed as much as nine years earlier were 40 per cent less likely to be successful in their attempts to give up smoking.
It gets worse. The psychological and emotional factors that make people inclined to smoke induce them to do other unhealthy things as well. Research has shown that moderate-to-heavy smokers are, on average, significantly less conscious of health-related issues, hold less favourable attitudes towards healthy behaviour and have a generally less healthy lifestyle in comparison with non-smokers or light smokers. (Conversely, wholesome behaviour patterns also come in clusters; researchers at Harvard University Medical School found that individuals who drank only decaffeinated coffee also tended to eat lots of vegetables, take regular exercise and wear their seatbelts.)
As well as prompting people to smoke, stress is also linked to increased alcohol consumption – at least, in certain types of individual. The health implications of excessive drinking can be profound. Approximately 20 per cent of all male in-patients in British hospitals have alcohol-related problems. Alcohol can rot people’s livers and kill them in drunken accidents (though alcohol is not the only recreational drug capable of damaging health: there is reasonably good evidence, for example, that marijuana impairs the immune system, with potentially adverse consequences for the health of long-term users.)
The perils of the grape are amusingly described in Othello. The scheming Iago lures the unwitting Cassio into getting steamingly drunk, as a result of which Cassio lands himself in serious trouble and loses his job. On sobering up, Cassio bemoans the loss of his reputation and curses the demon drink:
‘Drunk! And speak parrot! And squabble! Swagger! Swear! And discourse fustian with one’s own shadow! O thou invisible spirit of wine, if thou hast no name to be known by, let us call thee devil! … O God, that men should put an enemy in their mouths to steal away their brains! That we should with joy, pleasance, revel and applause, transform ourselves into beasts!’
Literature is amply stocked with characters who drink themselves into an early grave in reaction to emotional crisis or unhappiness. There are roistering drunks who drink to escape boredom or poverty, like J. P. Donleavy’s Ginger Man, Sebastian Dangerfield. There are determined drunks who drink to escape from grief. In Wuthering Heights, the unfortunate Hindley Earnshaw becomes a hopeless alcoholic after the death of his wife (from consumption, naturally) and drinks himself into the grave by the age of twenty-seven. And there are aimless drunks who drink to forget their own pointlessness. In F. Scott Fitzgerald’s The Beautiful and Damned, for example, we have Anthony Patch, an independently wealthy and well-educated young man blighted by indolence, boredom and melancholy. A turbulent marriage and self-imposed idleness push him into self-destructive alcoholism and he degenerates into ‘Anthony the poor in spirit, the weak and broken man with bloodshot eyes’.
Incidentally, when it comes to self-destruction by alcohol the track record of doctors is almost unrivalled. As a profession, they rank second only to pub-owners and bar staff in the league table of deaths from alcohol-related liver disease. Doctors are 3.4 times more likely than the average worker to die from cirrhosis of the liver. According to one 1995 estimate, as many as one in twelve British doctors is addicted to alcohol, drugs or both, thanks mainly to the enormous stress the majority of them are constantly under. (But I should not be too smug about this statistic because ‘literary and artistic workers’ also fare badly, with twice the average death rate from cirrhosis.)
On the other hand, moderate alcohol consumption can be an effective buffer against stress – and here again science has only of late managed to verify thousands of years’ worth of everyday experience. Psychological studies have confirmed what countless millions of people have discovered for themselves, namely that when we are under stress we often feel less anxious if we drink alcohol. (A moderate intake of alcohol also appears to reduce the risk of coronary heart disease, but that is another story.) Sir Winston Churchill’s opinion was clear: ‘I have taken more out of alcohol than alcohol has taken out of me.’
There is nothing surprising about the fact that alcohol has its good side. It has, after all, been an intimate part of human life since the dawn of civilization. Alcohol was in use for medicinal purposes (in the literal rather than euphemistic sense) over four thousand years ago and was probably quaffed for recreational purposes long before that.
Opinions differ as to when exactly humans first discovered the joys of booze, but there is evidence that wine was being drunk in Transcaucasia eight thousand years ago – long before the wheel was invented. Some authorities have argued that Stone Age man was cultivating vines as early as ten thousand years ago. Wine growing was well established in the Middle East by 4000 BC and was an integral part of daily life in ancient Egypt and Mesopotamia. It says something that wine is mentioned 150 times in the Old Testament.
Then there are the social benefits of communal drinking to add to the purely pharmacological pleasures of alcohol. Samuel Johnson spoke for many when he declared that: ‘There is nothing which has yet been contrived by man, by which so much happiness is produced as by a good tavern or inn.’
Yet the things that give us pleasure carry risks, and we are very poor at assessing those risks. While we consistently overestimate the dangers posed by rare or exotic threats like plane crashes, murders, nuclear accidents or shark attacks, we tend to disregard the risks of common killers like heart disease and vehicle accidents. We are especially prone to underestimating the risks arising from our own behaviour, such as smoking, travelling in cars, abusing alcohol or having unprotected sex.
Smokers now acknowledge the unappetizing fact that their behaviour significantly increases their risk of dying prematurely from heart disease or cancer. Nevertheless, psychological research has established that they seriously underestimate the magnitude of that risk. There is a consistent ‘optimistic distortion’ of perceived health risks among smokers; they know smoking is bad for them but they do not recognize just how bad. No matter how often the statistics are quoted they do not seem to sink in. One reason why the health consequences of smoking have such a muted impact on people’s perceptions is the large delay, often measured in decades, between starting to smoke and falling ill.
If you should happen to be an overweight, tobacco-addicted, boozing, couch potato who loves fried food, you can take a few crumbs of comfort from the fact that others’ attempts at healthy living can backfire. Dieting, for example, almost invariably fails to bring about the desired result of sustained weight loss. The sense of personal failure that comes as the scales lurch upwards again can produce a damaging drop in self-esteem and a sense of losing control; the frustrated dieter’s response may be to abandon the diet and thus swing back to even greater porkiness. Mother Nature also conspires against the earnest dieter. People whose body weight oscillates because of dieting have a greater risk of premature death from coronary heart disease or other causes. Unsuccessful dieting can be bad for your health – and most dieting is ultimately unsuccessful.
What of behavioural self-destruction in literature? Fiction is littered with protagonists who recklessly expose themselves to danger, neglect their health or run themselves into an early grave because of great unhappiness or emotional turmoil.
An early case history of self-destruction appears in Le Morted’Arthur, Sir Thomas Malory’s fifteenth-century version of the legends of King Arthur and the knights of the Round Table. It is the sad tale of the Fair Maiden of Astolat and her doomed love for Sir Launcelot.
The brave, noble, irresistibly attractive Sir Launcelot rides to Astolat en route to a joust, and stays the night there at the home of the elderly baron, Sir Bernard of Astolat. Sir Bernard has a beautiful and virginal young daughter, the Fair Maiden of Astolat, who is at once smitten by Sir Launcelot. She is, as Malory so engagingly puts it, ‘hot’ in her love for the noble knight: ‘for he is the man in the world that I first loved, and truly he shall be last that ever I shall love.’ (Astolat, by the way, is Guildford and the maiden’s name is Elaine. Fortunately, ‘The Fair Maiden of Astolat’ has more Arthurian resonance than ‘Elaine of Guildford’.)
Sir Launcelot is grievously wounded and the Fair Maiden goes to look after him. Night and day she tends him, until his wounds are healed and Sir Launcelot is ready to take his leave. The Fair Maiden of Astolat beseeches Sir Launcelot to marry her or, failing that, at least go to bed with her. But the upstanding knight will not countenance marriage and refuses to dishonour the Fair Maiden by indulging in extramarital frolicking. She begs him again to be her husband or her lover, but to no avail. ‘“Alas,” said she, “then must I die for your love.”’ The noble knight leaves Astolat to get back to some real man’s work (fighting), leaving the emotionally wrecked Fair Maiden of Astolat behind him. Her mental state and self-destructive behaviour soon wreak havoc upon her physical health:
Now speak we of the Fair Maiden of Astolat that made such sorrow day and night that she never slept, ate, nor drank … So when she had thus endured a ten days, that she feebled so that she must needs pass out of this world, then she shrived her clean, and received her Creator … ‘it is the sufferance of God that I shall die for the love of so noble a knight … I loved this noble knight, Sir Launcelot, out of measure, and of myself, good Lord, I might not withstand the fervent love wherefore I have my death.’
True words from the Fair Maiden of Astolat, because very soon she dies. Clutched in her hand is a letter proclaiming her love for Sir Launcelot. That love has sent the Fair Maiden to her death, a death achieved through her behaviour.
Reckless behaviour allied with emotional distress can destroy an individual’s physical health, as illustrated in Jude the Obscure, Thomas Hardy’s novel about ‘a deadly war waged between flesh and spirit’.
Jude Fawley, a self-educated young man of lowly origins, aspires to leave his unlovely country village and enter the hallowed portals of Christminster (Oxford) University. But the restrictions imposed upon Jude by class and poverty mean that he must instead make his way as a humble stonemason. Jude’s romantic life is as frustrating and unsuccessful as his academic life. After being trapped into an ill-fated marriage to a pig-breeder’s daughter he falls in love with his cousin Sue. The two are drawn together by an almost mystical affinity, but Sue leaves him to marry an older man. The two lovers are eventually united and live together, unmarried and condemned by society, in poverty and unhappiness. In the end Jude loses Sue, who returns to her husband.
Having failed to fulfil both his intellectual and romantic desires, Jude goes into physical and mental decline. Like many a nineteenth-century tragic hero, he succumbs to a consumptive illness which proves to be terminal. Jude’s behaviour exacerbates his medical condition. With careless disregard for his health he makes a long journey on foot in the pouring rain to see Sue for the last time. She rejects his pleas and he returns to Christminster, physically and emotionally broken. But, as Jude explains to his former wife, he was fully aware of the risk to his health when he undertook the journey:
I made up my mind that a man confined to his room by inflammation of the lungs, a fellow who had only two wishes left in the world, to see a particular woman, and then to die, could neatly accomplish those two wishes at one stroke by taking this journey in the rain. That I’ve done. I have seen her for the last time, and I’ve finished myself – put an end to a feverish life which ought never to have begun!
Eventually he dies, alone and neglected, not yet thirty years old. Hardy implicitly takes a multi-causal view of Jude’s final illness, since environmental and constitutional factors play a role in it, together with psychological stress.
(#litres_trial_promo) His emotional distress at losing Sue and at the death of their children acted as a trigger, but the illness also has antecedents in Jude’s weak constitution and the harsh conditions he endured during his time as a stonemason:
I was never really stout enough for the stone trade, particularly the fixing. Moving the blocks always used to strain me, and standing the trying draughts in buildings before the windows are in, always gave me colds, and I think that began the mischief inside.
Most of us die sooner than we have to because of the way we behave and the choices we make. Personally, though, I have some sympathy with Publilius Syrus, who two thousand years ago expressed the opinion that: ‘They live ill who expect to live always.’
Mind over immune matter (#ulink_ad758723-b2cd-54cf-bd62-6e7905c819b6)
In this struggle Tarrou’s robust shoulders and chest were not his greatest assets; rather, the blood which had oozed under Rieux’s needle and, in this blood, that something more vital than the soul, which no human skill can bring to light.
Albert Camus, The Plague (1947)
We turn now to a less visible, but no less important, mechanism by which the mind and body interact to affect health: the immune system. Among the most important developments in recent years has been the discovery of numerous biological pathways connecting the brain with the body’s defence and regulatory mechanisms. Through these pathways the biological system that underlies our thoughts, emotions and behaviour – the brain – can exert a pervasive influence on the biological system that defends the body against most forms of disease – the immune system.
Our physical health depends critically on how well our immune system is functioning. One reason why a person suffering from psychological stress is more susceptible to colds and infections is because their immune system is less able to resist when they are exposed to disease-causing viruses or bacteria. In the following chapters we shall be exploring the manifold ways in which the mind and immune system affect each other. But before we do this we need to clarify a few basic issues.
So far I have referred rather sweepingly to the mind’s effect on the immune system, as though the immune system were a homogeneous entity whose activities could be measured in a simple way, like temperature or blood pressure. In reality, the immune system is a breathtakingly complex and subtle entity whose intricate workings are still far from being fully understood. Immunology is one of the branches of science that has made the most spectacular leaps in understanding over the past thirty years, but it still has a very long way to go. To unravel how the mind influences physical health we must first establish what the immune system does and how it works.
UNDERSTANDING IMMUNITY (#ulink_6bdbb82d-593a-53f7-a479-5797f6f2517a)
The immune system is one of the great wonders of nature, rivalled only by the brain in its intricacy and elegance of design. It is a multi-layered system of biological defences whose primary purpose is to defend the body from bacteria, viruses, fungi, parasites, toxins, cancerous cells and other disease-causing agents. The immune system is indeed a system, in the strict sense of the word: a highly complex and co-ordinated array of interrelated, interacting elements.
Like the economy of a nation, the immune system is not located exclusively in one place. In fact, the cells of the immune system are spread out all over the body. The majority are located in those organs whose purpose often seems slightly mysterious to the layperson: the thymus (located at the base of the neck); the spleen (below and behind the stomach); the lymph nodes (clumps of tissue in the armpit, groin, behind the ears and elsewhere); the bone marrow; the tonsils; and obscure backwaters of the gut (Peyer’s patches and the appendix).
Immune cells are also to be found in the blood. These are the white blood cells (or leucocytes). Immune cells are carried in the bloodstream to locations in the body where they are needed, particularly sites of injury or infection. When an area of tissue is injured or infected an inflammatory response is triggered: the blood vessels swell up and become more permeable, thus increasing the supply of blood and immune cells to the damaged area.
There are numerous types of white blood cell, but here we are primarily concerned with the lymphocytes, which make up about a quarter of all white blood cells in humans. Lymphocytes can be subdivided into three main categories: B-lymphocytes, T-lymphocytes and natural killer cells.
(#litres_trial_promo) The latter are capable of spontaneously killing certain virus-infected or cancerous cells.
The body is protected by layer upon layer of immune defences, rather like the proverbial onion. Simple accounts of the immune system (and this is a very simple account) usually divide its actions into two categories: the very clever and the mind-bogglingly clever; or, more conventionally, non-specific immune responses and specific immune responses.
Non-specific immune responses are the body’s first line of defence against bacteria, parasites and other foreign material. Their basic purpose is to prevent potentially harmful foreign materials from entering the body in the first place, or to destroy them when they do enter. They achieve this without recognizing precisely which foreign material they are dealing with.
At the simplest level, non-specific defences include the physical barrier of the skin; the minute hairs called cilia in the respiratory tract and elsewhere which expel foreign particles from the body; and chemical defences such as stomach acid and bacteria-destroying enzymes in saliva and tears. A more sophisticated layer of non-specific immune defence is provided by various classes of white blood cells, notably the monocytes and neutrophils. These can ingest and destroy bacteria and foreign particles, a process known as phagocytosis (literally ‘cell-eating’). They also help other white blood cells to kill microorganisms, and produce vital chemical messenger molecules called cytokines which co-ordinate different aspects of the immune response.
Now we come to the mind-bogglingly clever part of the immune system: the part that can recognize and respond specifically to each and every type of foreign material it encounters. This is the specific (or acquired) immune response. It has the ability to make ultra-fine distinctions between material that forms part of your body and material of foreign origin – in other words, between ‘self’ and ‘non-self’. This can be achieved because the immune system contains within it a detailed image of your body. Anything that deviates from this image, including some cancer cells, is recognized as foreign and attacked. A foreign substance that generates a specific immune reaction when it encounters the immune system is referred to as an antigen (short for antibody generator).
The ability to distinguish reliably between ‘self’ and ‘non-self’ allows the immune system to attack foreign material without harming your body’s own healthy cells. Your immune system could detect the difference between a cell from your body and an apparently identical cell from my body. This is why transplanting tissue from one person to another can be such a tricky business, requiring the use of immune-suppressive drugs. In order to circumvent the immune response certain parasites have evolved the ploy of disguising themselves as the host’s own tissue, tricking the host’s immune system into regarding them as ‘self’ rather than ‘non-self’.
It is helpful to subdivide the specific immune response into two main categories: humoral (or antibody-mediated) immunity; and cell-mediated immunity. Humoral immunity is concerned with attacking antigens that are floating around in the body fluids surrounding your cells as opposed to antigens inside the cells – hence ‘humoral’ from the old word ‘humour’, meaning bodily fluid. Humoral immunity essentially involves the production of antibodies by B-lymphocytes.
Antibodies are a type of protein molecule called the immunoglobulins.
(#litres_trial_promo) They are the body’s mainstay against bacterial infection. Each antibody is unique to one particular antigen, so there are as many types of antibody as there are antigens. When a B-lymphocyte meets the particular antigen to which it responds, it undergoes biochemical changes and starts producing multiple copies of itself, a process known as proliferation. The newly formed cells that result from this proliferation, called plasma cells, then secrete antibodies into the blood. These antibodies latch on to the antigen and, all being well, the antibody-antigen complex is then chomped up by a passing phagocyte.
Cell-mediated immunity, the other main variety of specific immune response, is primarily concerned with attacking antigens inside the cells – for example, viruses. It is also responsible for the body’s immune reactions to transplanted tissues and tumours. Its main agents are the T-lymphocytes, which can recognize and kill target cells, such as those infected with viruses and foreign cells. Unlike antibodies, however, T-lymphocytes are unable to attack antigens that are floating around by themselves; instead they are dependent on other immune cells which ‘present’ the antigen to them, while at the same time stimulating the T-lymphocytes to attack by releasing chemical messenger substances known as cytokines. When stimulated in this way, T-lymphocytes proliferate and transform themselves into various subclasses with specific functions. Cytotoxic T-cells attack the antigen, while suppressor T-cells and helper T-cells regulate the whole delicate process. They do this by producing cytokines which alter the activity of other immune cells. Helper T-cells also stimulate B-lymphocytes to produce antibodies. The biological mechanisms regulating all of this are immensely complex.
The immune system learns and adapts each time it encounters a new antigen, setting a pattern for the way it will respond should it meet that antigen again. This is why you can be immunized against certain diseases, such as polio, typhoid, tetanus, rabies, diphtheria and chickenpox, and why there are diseases you catch only once in a lifetime. In this respect the immune system is like the brain: it detects and responds to specific stimuli in the outside world and then forms a long-lasting memory of those stimuli.
Vaccination exploits these immunological memory processes. A harmless fragment or heat-killed version of the bacteria or viruses is injected into the body. The antigens in the vaccine trigger the production of antibodies, but not the disease. The immune system is thus better prepared when it encounters the genuine item. Some micro-organisms are able to keep changing their biochemical appearance, which prevents the immune system from learning about them. The viruses responsible for the common cold and influenza are particularly good at this trick, which is why we do not develop permanent immunity to colds and ’flu.
Many things can impair the effectiveness of the immune system, including genetic defects, drugs and disease. There is also a general decline in immune function with old age. Sleep deprivation and poor nutrition both have marked effects on the immune system, too. Experiments on volunteers have ascertained that two or three days of sleep deprivation will produce significant reductions in various aspects of immune function. Even modest disturbances in sleep patterns can bring about measurable changes in the immune system. A study of healthy male volunteers found that depriving men of sleep for a few hours between 3 a.m. and 7 a.m. was enough to lower the immunological activity of their natural killer cells by more than a quarter. A good night’s sleep returned it to normal.
What happens when the immune system goes wrong? Although it is vital to our existence, most people have only a vague understanding of what the immune system does and seldom give it a thought until it malfunctions. If it fails to recognize and destroy potentially harmful agents such as bacteria, viruses or cancer cells the result may be a serious disease. Those born with defects in their humoral immune responses suffer from recurrent, severe infections.
AIDS is a vivid example of what happens when the immune system is damaged. The human immunodeficiency virus (HIV) wreaks its havoc mainly by destroying the victim’s helper/inducer T-lymphocytes. The eventual outcome is the almost invariably fatal condition known as Acquired Immune Deficiency Syndrome, or AIDS. One of the hallmarks of AIDS is a dramatic fall in the number and activity of helper/inducer (CD4) T-lymphocytes, though HIV does affect the immune system in other ways as well. An individual whose immune system is crippled by HIV becomes easy prey for a range of opportunistic infections and tumours, such as pneumonia, tuberculosis, Kaposi’s sarcoma and non-Hodgkin’s lymphoma, and it is usually one of these that kills the victim in the end.
AUTOIMMUNITY (#ulink_188ccfb4-f94d-59b7-9f97-eb562e6eed72)
In addition to destroying potentially harmful antigens, the immune system must be able to identify and avoid attacking its own body. Discriminating accurately between ‘self’ and ‘non-self’ is a fundamental requirement. There are times, however, when this discrimination fails for some reason and the immune system starts attacking ‘self’. B-lymphocytes manufacture antibodies against other cells in the body and these autoantibodies start to attack healthy tissue. The result is an autoimmune disorder. Those who liken the immune system to an army repelling foreign invaders have used the illuminating metaphor of ‘friendly fire’ to describe the phenomenon of autoimmunity.
Autoimmunity is thought to play a role in at least twenty (and perhaps in excess of forty) diseases, and the list is growing. Among those included are rheumatoid arthritis; various thyroid disorders such as Graves’s disease and Hashimoto’s disease; primary biliary cirrhosis of the liver; systemic lupus erythematosus; Guillain-Barré syndrome; multiple sclerosis; diabetes mellitus; uveitis; pernicious anaemia; myasthenia gravis; and inflammatory bowel disorders such as celiac disease, ulcerative colitis and Crohn’s disease.
The mechanisms of autoimmunity are not fully understood. Certain autoimmune diseases appear to arise because cells become altered in various ways – perhaps by viral infection or mutation – so that the immune system no longer recognizes them as ‘self’. In other cases, autoimmunity results from a failure in the complex and delicately balanced mechanisms that regulate the immune system.
Genetic factors are known to play an important role in some autoimmune disorders. For example, insulin-dependent diabetes mellitus (otherwise known as childhood-onset diabetes) results from the autoimmune destruction of cells in the pancreas, the organ responsible for producing the blood sugar-regulating hormone insulin. Diabetics have a genetic predisposition to develop the disease. But environmental factors, including stress, also play their part in determining whether a genetically predisposed individual actually develops the disease. Even if one of a pair of genetically identical twins has diabetes there is still a 50–70 per cent chance that the other twin will not get the disease. Chronic psychological stress significantly increases the risk that those who are genetically predisposed will advance to full-blown diabetes.
Females are much more susceptible than males to a number of autoimmune diseases, and this is true both in humans and other species. Women are three times more likely than men to suffer rheumatoid arthritis, six times more likely to develop autoimmune thyroiditis, and at least ten times more likely to suffer from systemic lupus erythematosus. This sex difference in disease susceptibility is at least partly a consequence of hormonal differences; male and female sex hormones, such as testosterone, progesterone and oestradiol, influence the immune system in various ways.
Autoimmune diseases result from excessive or inappropriate immune activity. Accordingly, they may be ameliorated by drugs that suppress the immune system – the opposite of what happens in normal infectious diseases. This is why doctors use immune-suppressive drugs to treat autoimmune diseases.
MEASURING IMMUNITY (#ulink_30c6c5a0-efbb-5e71-9c97-7afa7fb79ad8)
