AS Psychology Unit 2: The immune system notes on Stress

by thenainoji (student)

AS Psychology Unit 2: Stress-illness and The Immune System Notes

The immune system refers to the mechanism in the body that provides a defence against infections, e.g. bacteria, viruses, parasites and toxins.

The immune system fights off invaders that cause disease (antigens).
The cells in the system are leukocytes (white blood cells) called phagocytes and lymphocytes.
Phagocytes are the first line of defence, providing a general barrier against antigens.
Leukocytes are more focused and are a second line of defence against specific antigens.
T-lymphocytes (T-cells) attack anything carrying disease in the body.
B-lymphocytes (B-cells) are tuned to a particular antigen, and produce antibodies to destroy them.
Immunosuppression is a reduction in the effectiveness of the immune system and can be caused by stress.

Arnetz et al (1991) - Reduced lymphocyte activity in farm labourers was associated with periods of stressful unemployment.

Irwin et al (1987) - Immune system of recently widowed women functioned at a lower level than age-matched women who had not experienced a stressful event.

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Fawzey et al (1993) - Cancer patients who reduced their stress through stress-management during illness showed higher immune system functioning six months after treatment and less likelihood of a recurrence of cancer six years later.

Brady et al (1958) Stress and physical illness

Aim: To investigate whether the stress of receiving electric shocks would lead to stress-related illness in monkeys, and whether this would interact with the degree of control over the shocks.

Procedures:

Monkeys received electric shocks to their feet at 20 second intervals for periods of six hours at a time, with six hours` rest in between
The electric ...

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Brady et al (1958) Stress and physical illness

Aim: To investigate whether the stress of receiving electric shocks would lead to stress-related illness in monkeys, and whether this would interact with the degree of control over the shocks.

Procedures:

Monkeys received electric shocks to their feet at 20 second intervals for periods of six hours at a time, with six hours` rest in between
The electric foot shocks were not signalled
Monkeys were run in pairs, with one in each pair - the so called "executive monkey" - able to press a lever to postpone shocks for 20 seconds
The other monkey in the pair could not press the lever, but received all the foot shocks that were delivered (this second monkey in the pair was the `yoked` animal)

Findings:

Not all shocks could be avoided on this schedule
After 23 days the `executive` monkeys began to die of gastric ulceration
The yoked control monkeys, who received shocks but could not try to avoid them, remained healthy.

Conclusions:

Brady concluded that the shocks themselves were not severely stressful as the yoked monkeys showed little gastric ulceration; the critical factor was the stress associated with trying to avoid the shocks.
Having control was the stressful element in this study, causing gastric ulceration in the `executive` monkeys.

Criticisms:

Brady used monkeys, so there is a problem of generalising his results to humans. Monkeys have a different physiology to humans and may respond to stress in different ways. However, Brady did show that trying to cope with stressors is highly stressful for monkeys.
Brady also chose monkeys who were the most active bar-pressers as the executives; as a group, they were more active generally than the yoked control group, and this may have made them more sensitive to the stress of the footshocks. This means that the experiment was poorly controlled, as both groups should have been made up of monkeys that were equally active.
Stressing monkeys (or any animals) until they die or become severely ill is highly unethical and would not be permitted today. All researchers are now obliged to follow clear ethical guidelines which ensure that such a study could not be carried out again.

Kiecolt-Glaser et al - Stress and the immune system

Aim: To investigate whether stress of important examinations has an effect on the functioning of the immune system.

Procedures:

This was a natural experiment using 75 medical students
Blood samples were taken: (a) one month before their final examinations (relatively low stress), and (b) during the examinations (high stress)
Immune functioning was assessed by measuring NK cell activity in the blood samples
The students were also given questionnaires to assess psychological variables such as life events and loneliness

Findings:

NK cell activity was significantly reduced in the second blood sample, taken during their final examinations, compared with the first sample (taken one month before their final examinations)
NK cell activity was most reduced in participants who also reported high levels of life events and loneliness.

Criticisms:

This was essentially a correlational study, so a strong conclusion about cause and effect relationship cannot be drawn.
It was a natural experiment using a natural source of stress and therefore had reasonable ecological validity, but students may be a special group and generalisations should be made with caution.
There may be a sampling bias - different people respond to stress in different ways.