aqa  The role of stress in illness, including reference to immunosuppression and cardiovascular disorders.


immune-system101-2-1

During times of stress the adrenal cortex produces steroids (called corticosteroids since they’re produced by the adrenal cortex).  These stop the body producing lymphocytes (white blood cells) that attack foreign bodies such as viruses, in the bloodstream. Viruses have antigens on their surface.  In order to neutralise the effects of a virus the body must produce antibodies.  Antibodies need to be specific to the antigens present and are produced by white blood cells.  There are different types of white blood cell, e.g. T-cells, B-cells and natural killer cells.  B-cells have antibodies on their surface.  These lock onto antigens.  When a B-cell is mature it can produce thousands of antibodies an hour.  Importantly, the cells appear to ‘remember’ previous attackers so that a future infection can be fought off quickly.  Unfortunately, B-cells only ‘live’ for two days so need to be continually replaced.  Increased levels of steroids, caused by stress, slows down the production of B-cells, leaving us more susceptible to infection. Leucocytes are the main group of white blood cells that deal with alien invasion.  Leucocytes are made in the bone marrow.  Some stay here and others move to other parts of the body:

B cells (B for bone) stay in the bone marrow

T cells (T for thymus) move to the thymus gland in the upper chest area. T cells are more aggressive, for example the NK (natural killer cells).  When faced with a potential thret from antigens they destroy the antigens and the cells hosting them.[space=10]

Kiecolt-Glaser et al. (1984)

Medical Student

Aim: To investigate whether the stress of important exams affects immune system functioning.

Procedure: Natural experiment using 75 medical students. Blood samples were taken one month before the 1st exam (low stress) and during the exam period (high stress). Immune system was assessed measuring T cell activity in the blood samples. Students also given questionnaires to assess their psychological vulnerability.

Findings: T cell activity was significantly reduced in the second blood sample, taken during their final examinations compared with the first sample. T cell activity was most reduced in those participants who had reported themselves as having high life events and loneliness.

Conclusions: Examination stress reduces immune functioning, potentially leaving the individual vulnerable to illness and infection. Immune functioning is also affected by psychological factors, these long term stressors may make individuals more vulnerable to the added effects of short term stress.

Cohen et al. (1991)

Common Cold

Cohen et al. (1991) carried out an impressive study on 394 participants.  They each had their stress index measured using a questionnaire that also took into account their ability to cope and their feelings about their stress.  They were then given nasal drops that infected them with cold viruses.  When tested by doctors there was a direct correlation between their stress index and the probability that they developed a clinical cold after 7 days.

 

Evaluation of Research

Correlational research: As both pieces of research were natural experiments there was no direct manipulation of the independent variable (amount of stress in each case). Therefore it is not possible to establish cause and effect (i.e. whether stress causes reduced immune system functioning, or is just linked to it).

How do we measure immune system functioning? The immune system is extremely complex and made up of both natural and specific immunity. Each of these interact in complex ways to fight illness, thus how can scientists actually measure its effectiveness? Kiecolt-Glaser’s study looked at a direct measure of natural immunity (T cell activity), whilst Cohen’s looked at an indirect measure (a health outcome). It is therefore difficult to compare studies and draw any ultimate conclusion as to the effects of stress on immune system functioning.

Cannot be tested empirically with humans: It is unethical to manipulate the amount of stress a person is under (unless very briefly using the Stroop test, for example), therefore research in this area is only correlational (see issues with this above). Research has been carried out on animals, by placing them under great stress (for example rats, by restricting their movement), however it is difficult to generalise the findings to humans, who experience different and complicated sources of stress not applicable to animals.