4 World Health • 47th Yeor, No. 2, Morch-Aprill994 Stress and the immune system Tracy B. Herbert

any people have the effects of factors as diverse as experienced the examinations, bereavement, divorce, Mconnection between stress unemployment, mental arithmetic, and getting sick. Colds, influenza, and looking after a relative with herpes and allergies seem worse Alzheimer's di sease. In general, when we are severely stressed at these studies find that stress is work or in the home. Others are related to changes in both the never sick until they go on vacation numbers of white blood cells in (that is, after the stress is over), and circulation and the quantity of then they spend the whole time antibody in the blood. Moreover, fighting the virus. Because of stress is associated with changes in intrinsic connections like these, the functioning of immune cells. many researchers are today That is, there is a relatively large exploring whether (and how) stress decrease in both lymphocyte and illness are actually linked. One proliferation and natural killer cell specific focus of this research is to activity in individuals who have study the effects of stress on the experienced stress. There seems to immune systems; after all, if stress A lymphocyte: stress may weaken the capacity be some connection between the affects immunity, that would be one of lymphocytes to combat infection. duration of the stress and the amount way in which stress could contribute of immune change. For example, the to illness. longer the stress, the greater the The function of the immune proliferation"- by incubating these decrease in the number of specific system is to protect us from cells for several days with types of white blood cells. It also organisms that cause disease, and substances that cause them to appears that interpersonal stress from other materials that would be multiply (proliferate). More (such as bereavement or divorce) harmful to the body. Cells of the proliferation is thought to reflect produce different immune outcomes immune system (i.e., white blood better white blood cell functioning; compared with the stress due to cells) circulate throughout the body proliferation is important because, exams or unemployment. in the blood and are also located in when a harmful substance invades Connections between negative various organs, including the bone the body, immune cells must psychological states (such as anxiety marrow, thymus, lymph nodes and multiply to increase their numbers and depression) and immune system spleen. There are a number of before they can successfully variables have also been explored. different kinds of white blood cells, eliminate it. Another test assesses The results suggest that depressed but the most important in this "natural killer cell cytotoxic and anxious mood states are context are lymphocytes. Of the activity". In this test, white blood associated with decreases in various tests that reflect the integrity cells are incubated for several hours lymphocyte proliferation and natural of the immune system, some simply with tumour cells to determine their killer cell activity, as well as assess the number of white blood effectiveness in killing the tumour changes in the numbers of white cells circulating in the blood; others cells. More killing is thought to blood cells and the quantity of quantify the amount of antibody in reflect better natural killer antibody circulating in the blood. It the circulation. Antibodies are functioning; the killing potential of also appears that the body's ability proteins produced by certain natural killer cells is important to produce antibody to a specific lymphocytes when harmful because they are one of the fastest substance is related to the level of substances invade the body. Once responders of the immune system in anxiety that the individual is antibodies are produced, they attach the fight against viruses and experiencing: with more anxiety the to the harmful substance, mark it for tumours. less antibody is produced after destruction by other white blood exposure to the potentially harmful cells, and prevent it from causing susbtance. infections. Stressful factors How could stress or negative Other tests of the immune system emotional states alter the immune determine how well specific Studies aimed at determining the system? Both physiological and lymphocytes are functioning. One relationship between stress and the behavioural mechanisms provide test assesses "lymphocyte immune system have investigated possible explanations. In the case of World Health • 47th Year, No.2, March-Aprill994 s physiological mechanisms, stress is decreased when there are acute specific behaviours that modulate associated with the activation of increases in cortisol and the immune response. Stressed several systems, including the epinephrine. persons tend to sleep less, exercise hypothalamic-pituitary-adrenal axis Other hormones released under less, have poorer diets, smoke more, and the sympathetic nervous system. stress - such as growth hormone, and use alcohol and other drugs The activation of these two prolactin, and the natural opiates more often than non-stressed people. pathways results in elevated blood (beta endorphin and enkephalin)­ These behaviours have all been levels of specific hormones, namely have been implicated in influencing shown to affect the immune system. cortisol and the catecholamines the immune system. At a cellular The interpretation of these (epinephrine and norepinephrine). level, these hormones become changes in the immune system due Blood levels of these hormones are attached to receptors on white blood to stress is difficult. Even though related to immune functioning. For cells and so affect them. decreased natural killer cell activity example, acute increases in cortisol is evident in certain human diseases and epinephrine are related to (such as cancer, chronic viral decreases in the number of white The way we behave infection or autoimmune diseases), blood cells in circulation. the direct health consequences of Lymphocyte proliferation and An alternative explanation involves such a decrease have not been natural killer cell activity are also the association of stress with established. A decreased lymphocyte proliferation response is associated with increased levels of mortality and an increased number of hospitalizations among the elderly, but there is no clear link with specific diseases that are mediated by the immune system. Nevertheless, it is clear that stress has an adverse effect on health, probably mediated- at least in part -by the body's immune system. It is hoped that future research will show how, by reducing stress, we can improve health. •

Or Tracy B. Herbert is in the Deportment of Psychology of Carnegie Mellon University, Pittsburgh, PA 152 13, USA

Looking for a job. Uncertainty about employment is on important contributor to stress .

Stress and cancer For as long as 2000 years, doctors have recogn ized As one goes down the w ide range of animal forms , sig ni fica nt associati o ns between str ess a nd the ca ncer becomes progress ively rarer, and it is not seen development of malig nancy. In th e 19th century , Bri tish in prim itive forms of life . On th e other hand , the a bili ty physicians beli eved that emotiona l distre ss was th e most to regenerate parts of th e organi sm that have been powerfu l cause of cancer, and increased rates of th e inj ured or lost increases in a proportion al fas hi on . In disease were subsequently correlated with the humans, it has been observed that tissue injury and loss psychosocial stresses that have progressively developed of important emotional relationshi ps are associated alongside "modern " lifestyles . w ith a greater li kelihood of developin g cancer. According to Stress, the newsletter of the American Some phys icians propose that these trau ma invoke Institute of Stress , stud ies over the past five decades atavistic responses - reverti ng back to ou r remote have convi ncing ly demonstrated the profound effects ancestry - tha t once had a pu rposefu l repa ir function, that stress can exert in accelerati ng the development but now resul t in new growth , or neopla sia, th at is and g rowth of different ma lignancies, w ithout actua lly uncontrollable and therefore ma lig nant. O n the other causing them. Sim ilarly, stress reduction strategies have ha nd , such positive emoti ons as a strong faith, soc ial been shown to retard tumou rs in laboratory a nima ls support a nd other stress red uction strategies seem able and to prolong life in cancer patients . The disease has to retard or even reverse ma li gna nt growth, as occurs been ca ll ed a "d isease of adaptation ." in cases of spontaneous remiss ion of ca ncer .