The relationship between stress and the immune system
“There are two main categories of stress: acute and chronic. Acute stressors include unpleasant films, understimulation/work underload, overstimulation/work overload, unexpected or uncontrollable noise, prestige or status loss, electric shock, uncontrollable situations, physical illness, surgery, threats to self-esteem, and traumatic experiences. Chronic stressors include sleep deprivation, daily “hassles”, work overload or underload, role strains, or social isolation.
There are, of course, many more things that can cause stress, but these are the stressors most commonly used in experimental research and most commonly seen in the general population” Elliott and Eisdorfer, (1982). The immune system protects the body from germ and virus organisms as well as other foreign bodies, known as antigens. The first line of defence is local barriers such as the skin, peritoneum, etc, and inflammation due to immunoglobulins (antibodies). If these fail to block or destroy the antigens, the cell-mediated response and the humoral immune response go to work.
The cell-mediated response uses leucocytes (white blood cells) to recognise and render antigens inactive. One of the most important types of white blood cell is the lymphocyte. These cells develop as either B-cells or T-cells. One specific B-cell is tuned to a specific germ and when that germ is present in the body the B-cell produces millions of anti-bodies designed to destroy the germ. T-cells detect cells in the body that are harbouring viruses and when found they bump into them and destroy them.
The GAS model proposes that the reason why stress leads to an increased risk in illness is that because the body’s resources (glucose reserves) dwindle under extreme stress, proteins for the immune system cannot be created and the body is far less able to fight off foreign organisms. However, it was found that many bodily resources do not in fact become depleted hence this is an unlikely explanation for the effect of stress on the immune system. The most likely cause for the weakening of the immune system is cortisol. Cortisol is released from the adrenal gland in situations of long-term stress (chronic stress).
This is because the presence of cortisol decreases the production of lymphocytes, in particular T-cells, and anti-bodies. This is theory is supported by a significant amount of psychological research. Kiecolt-Glaser et al (1995) conducted an experiment to show evidence of the direct effects of stress on the immune system by looking at how quickly wounds heal.
To do this they took a group of women who were caring for relatives suffering from senile dementia, a task that has been shown to be associated with chronic stress. 3 women, aged 47-81 years who were carers, were placed in the experimental group whilst an additional 13 were matched with the carers on the basis of age and income but not marital status as the control group. This method is known as a matched participants design. The participants were given a ‘punch biopsy’ (a 3. 5mm cut) just below the elbow. In addition, their levels of cytokines, biochemical substances involved in regulating the body’s immune system, were assessed. Patients were also given a 10-item perceived stress scale to how stressed they felt.
The findings of this experiment were that the wound took on average 9 days (24%) longer to heal amongst the carers than the control group. It was also found that the levels of cytokines were lower in the carers than in the control group whilst on the perceived stress scale the carers indicated that they felt more stressed. This supports the view that chronic stress depresses the immune system due to the slower wound healing experienced among the individuals suffering from it. The lower level of cytokines supports the view that stress directly lowers immune system response.
This is an important study as it has valuable implications for medical treatment as the recovery of patients who had experienced surgery could be dramatically increased if they experienced the least possible stress. However the experiment did not take into account the effects that smoking and marital status could have on the levels of stress. There are an abundance of other studies that show the negative effects of stress on the immune system. Brady (1958) conducted an experiment involving two monkeys. One monkey was given the job of controlling electric shocks that were administered to itself as well as another monkey (“yoked control”).
So long as the “executive” monkey pressed a lever every 20 seconds then neither monkey received an electric shock. The executive monkey died within a few weeks due to a perforated ulcer. This suggests that stress, not electricity, causes ulcers as although both monkeys received shocks only the one who experienced high levels of chronic stress suffered ill consequences. Cohen et al (1993) used the “viral challenge technique where 400 participants were exposed to the common cold virus and given a questionnaire to assess their levels of perceived stress.
A positive correlation between levels of stress and the likelihood of catching a cold was found. Riley (1981) placed mice on a rotating turntable and found that within 5 hours this lead to a decrease in the number of lymphocytes. Some mice were implanted with cancer cells and after 3 days of 10 minutes of rotation per hour they were more likely to develop tumours the control mice who had experienced no stress. This shows that stress reduced immune activity was related to illness. However, there can sometimes be positive effects of stress.
Cortisol is in fact thought to help lower a temperature and also reduce inflammation. Evans et al (1994) looked at the activity of a single antibody, sIgA, which coats the mucous surfaces of the mouth, lungs and stomach to prevent infection. Students were arranged to give talks to other students (mild but acute stress). These students showed an increase in the levels in sIgA but a decrease during the examination periods that went on for several weeks. Evans et al (1997) proposed that stress has two effects on the immune system: up-regulation for very short-term acute stress, and a down-regulation for chronic stress.