respiratory infectious illness. This is noteworthy given that historically these two realms
were considered quite distinct (i.e. the mind versus body debate).
The term psychoneuroimmunology or PNI was coined by Robert Ader and
Nicholas Cohen of the University of Rochester in the USA, to describe this new area
of science that explored the interaction between psychological processes and the
nervous and immune systems. Ader and Cohen were at the forefront of this area and
demonstrated the link between the brain and the immune system early on (Ader and
Cohen, 1975). Using a paradigm called conditioned immunosuppression, based upon
Pavlov’s classical conditioning, they discovered that the immune system of rats could
be conditioned to respond to external stimuli unrelated to immune function. They
found that after an artificially flavoured drink was paired with an immune suppressive
drug in rats, the presentation of the drink alone was sufficient to suppress immune
functioning. Studies such as this one have provided the starting point for researchers
to examine the effects of various psychological factors on human immunity. Over the
last 25 years or so, a large amount of research effort has concentrated on exploring the
extent to which psychological stress may influence different aspects of the immune
system. Two areas that have received particular attention are respiratory infectious
illness and wound healing (cf., Kiecolt-Glaser et al., 1998; Cohen, 2005). However,
in order to understand the link between stress, the common cold and wound healing,
we need to appreciate how the immune system works. Therefore, the next section
provides a basic introduction to the immune system.
The immune system
The function of the immune system is to defend the body against invaders. Microbes
(germs or microorganisms), cancer cells and transplanted tissues or organs are all
interpreted by the immune system as ‘non-self’ against which the body must be
defended. Although the immune system is incredibly complex, its basic strategy is
straightforward: to recognize the enemy, mobilize forces and attack. Amazingly, the
immune system can distinguish between ‘self’ and ‘non-self’ and learns to remember
the distinctive cellular features of invaders. Moreover, it is able to form an
immunological memory of infectious agents and so mount a more effective response
the next time the invader attacks. It is this process that is exploited when a person is
vaccinated with a mild dose of an infectious agent – the body becomes primed for a
real invasion.
What are the basic features of the immune system? Broadly speaking, the human
body has the capacity to mount two types of immune defence:
1 cell-mediatedimmunity; and
2 antibody-mediatedimmunity.
In both cases, the basic immune response is brought about by the actions of two
types of white blood cells known as lymphocytes and monocytes. Importantly, there
are two types of lymphocytes with different functions: T (for thymus) cells and B (for
bone) cells. Both types are formed in the bone marrow, but the T cells migrate to the
thymus to mature while the B cells remain in the marrow. B cells produce antibodies
(i.e. large proteins that will recognize and bind to invading infectious agents), whereas
32 BIOLOGICAL BASES OF HEALTH AND ILLNESS