Mood

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STRESS AND ILLNESS
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1981) and showed that changes in the immune system brought about by an immunosuppressive drug could be paired with a sweet taste. This meant that after several
pairings, the sweet taste itself began to bring about immunosuppression. These results
were important for two reasons. First, they confirmed that the immune system could
be manipulated. Second, the results opened up the area for PNI and the possibility that
psychological factors could change an individual’s immune response.
Measuring immune changes
Although it is accepted that the immune system can be changed, measuring such
changes has proved to be problematic. The four main markers of immune function used
to date have been as follows: (1) tumour growth, which is mainly used in animal
research; (2) wound healing, which can be used in human research by way of a
removal of a small section of the skin and can be monitored to follow the healing
process; (3) secretory immunoglobulin A (sIgA), which is found in saliva and can be
accessed easily and without pain or discomfort to the subject; and (4) natural killer cell
cytoxicity (NKCC), T lymphocytes and T helper lymphocytes, which are found in the
blood.
All these markers have been shown to be useful in the study of immune functioning
(see Chapter 14 for a discussion of immunity and longevity). However, each approach to
measurement has its problems. For example, both wound healing and tumour growth
present problems of researcher accuracy. But, both these measures are actual rather
than only proxy measures of outcome (i.e. a healed wound is healthier than an open
one). In contrast, whereas measures of sIgA, NKCC, T lymphocytes and T helper cells are
more accurate their link to actual health status is more problematic. In addition, the
measurement of immune function raises questions such as ‘How long after an event
should the immune system marker be assessed?’ (i.e. is the effect immediate or delayed?),
‘How can baseline measures of the immune system be taken?’ (i.e. does actually taking
blood/saliva, etc., cause changes in immune functioning?) and ‘Are changes in immune
functioning predictive of changes in health?’ (i.e. if we measure changes in a marker do
we really know that this will impact on health in the long term?).
Psychological state and immunity
Research has focused on the capacity of psychological factors to change immune
functioning. In particular, it has examined the role of mood, beliefs, emotional
expression and stress.
Mood
Studies indicate that positive mood is associated with better immune functioning (as
measured by sIgA), that negative mood is associated with poorer functioning (Stone et al.
1987) and that humour appears to be specifically beneficial (Dillon et al. 1985–1986;
Newman and Stone 1996). Johnston et al. (1999c) explored the impact of mood on the
progression of the disease, disability and survival in patients with amyotrophic lateral
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