Download PDF - Microbiology Society

Stockxpert
In the year of the
Olympics, SGM
explores the impact of
exercise on our ability
to fight infections.
INFECTIONS of the nose, throat, windpipe
(trachea) or the two airways that branch from
the trachea as it reaches the lungs (bronchi) are
common. These upper respiratory tract infections
(URTIs) include the common cold, sinusitis and
tonsillitis, and most are due to a viral infection.
The average adult has two to three URTIs each
year. We are constantly exposed to the viruses
Couch potato
or elite athlete?
Finding the
happy medium
that cause these infections, but some people
Digital Vision
seem more susceptible to catching URTIs than
to a long-term improvement in
others. Every day our immune system protects
immune response. His research
for this research is not usually
us from an army of pathogenic microbes
showed that those who walk at
based on detection of the
that bombard the body. Immune function is
70–75% of their VO
virus in isolates but taken
influenced by an individual’s genetic make-up as
of oxygen that can be utilized
from medical records or via
well other external factors such as stress, poor
while exercising at maximum
an individual’s response to
nutrition, lack of sleep, the normal aging process,
capacity for 1 minute) for
questionnaires, so some of the
lack of exercise or overtraining. These factors can
40 minutes a day have half as
reported sore throats may not
suppress the immune system making a person
many sick days due to colds
be due to infectious agents
more vulnerable to infection.
or sore throats as those who
but to non-infectious airway
2 max
(volume
Evidence of URTIs collected
don’t exercise. Conversely,
inflammation caused by allergies
EXERCISE AND ITS EFFECT
ON THE IMMUNE SYSTEM
other studies have reported
or inhalation of pollutants.
a 100–500% increase in risk
Exercise can have both a positive and negative
in developing an URTI in the
diagram below) has been used
effect on immune function and can influence
weeks following marathons
to describe the relationship
an individual’s vulnerability to infection.
and ultra marathons. Following
between the amount of physical
The underlying reasons for this variability
strenuous exercise, athletes
activity that is undertaken and
are multifactorial and include infectious,
enter a brief period of ‘open
risk of URTI. There is some
neuroendocrine and metabolic factors, with the
window’ time in which they
evidence that this increased
diet and training regime of the individual also
experience weakened immune
susceptibility to infection
playing a role. For athletes, environmental factors
resistance and are more
is due to a depression in
such as travel and accommodation also contribute
susceptible to viral and bacterial
immune system function of
to the risk of infection.
infections, in particular of the
the individual. Studies have
respiratory tract.
shown that exercise causes
Researchers have found a link between
A ‘J’-shaped model (see
moderate regular exercise and reduced frequency
of URTIs compared with a sedentary state and
High
excessive amounts of exercise and an increased
out by Matthews et al. in 2002 on moderate
to vigorous activity and risk of URTI showed
that regular moderate exercise per day was
associated with a 29% reduction in the risk of
getting a URTI compared to individuals that
Risk of infection
risk of URTIs. An epidemiological study carried
Average
had a sedentary lifestyle. Professor Nieman of
Appalachian State University, USA showed that
when moderate exercise is repeated on a near
daily basis there is a cumulative effect that leads
Low
Sedentary
Moderate
Training intensity
High
physiological changes in the
immune system.
is enhanced. Studies show that NK cells are
been shown to inhibit NK cell
recruited to peripheral blood during exercise
activity in vitro and also in vivo
and that the cells recruited respond to
when measured more than
interleukin. Intense activity experienced by elite
24 hours after administration
athletes involved in training and competing in
of the synthetic corticoid drug
IMMUNE RESPONSE –
NATURAL KILLER (NK)
CELLS
During moderate activity, NK cell activity
system. Corticosteroids have
NK cells are a type of white blood endurance events such as marathons and ultra-
methylprednisolone. However,
cell that plays an important role
marathons has been shown to downregulate NK
other studies have shown
in the host’s defence against
cell activity. This immunodepression is thought
that NK cell activity increases
virally infected cells. NK cells
to be caused in part by prostaglandins.
4 hours after cortisol is given.
are cytotoxic and recognize and
kill host cells that have become
Whilst it is known that during
HORMONES
intense physical exertion stress
are known as natural killers
Adrenaline
immunity, further research is
because they don’t need to react
Adrenaline, often known as the ‘flight or fight’
needed to determine how such
to specific antigens, they just
hormone, is produced by the adrenal gland in
exercise might influence NK cell
need to recognize that a cell is
response to physical activity. It is constantly
activity.
foreign. They form part of the
produced in small amounts to maintain
innate immune system. When
normal blood pressure. During exercise, larger
GET A MOVE ON …
NK cells come into close contact
amounts of the hormone are released into the
The message from current
with an infected cell they release
bloodstream where it prepares the body for
research seems to be that
infected with virus. NK cells
hormones temporarily lower
granules of protein called perforin increased physical activity by speeding up the
and proteolytic enzymes called
heart rate, diverting blood flow to the muscles,
moderate exercise does have a
granzymes from their cytoplasm.
widening the airways, dilating the pupils and
system. So to keep colds at bay
Perforin forms pores in the cell
raising the blood sugar level. Increased NK cell
we should all go out for a brisk,
membrane of the infected cell,
activity during exercise may relate to adrenaline
daily walk.
allowing the granzymes to enter
levels, since it has been shown that the increase
and cause apoptosis. The infected
in activity occurs within 15–30 minutes after
cell breaks up into membrane-
subcutaneous administration of adrenaline to
bound fragments that are then
healthy individuals.
removed by phagocytes. An
positive effect on the immune
Dariel Burdass, Head of
Communications, SGM
Thanks are due to Professor Mike
Gleeson, University of Loughborough,
advantage of killing infected
Corticosteroids
cells by apoptosis is that the
Corticosteroids are a class of hormones with a
cell’s contents, including virus
wide range of physiological functions that are
particles are not released as
produced in the adrenal cortex. They include
Gleeson, M. (2007). Immune function
they are during cell lysis, thus
glucocorticoids – the most important of which
in sport and exercise. J Appl Physiol 103,
preventing their spread into
in humans is cortisol. Cortisol is known as a
uninfected cells. NK cell activity
stress hormone as it is secreted at higher levels
can be modulated by many
in response to stressful situations. Elite athletes
different agents. The cytolytic
are exposed to the psychological stress of
activity of NK cells is enhanced by competition (worry/anxiety). During endurance
cytokines such as interferon and
events and over-training, the body is exposed to
interleukin, signalling molecules
the physiological stress of prolonged exercise,
that are released by the host
and taking part in extreme environments – heat,
cell in response to infection by
cold and altitude can also put stress on the body.
the virus particle. Conversely,
Repeated bouts of intensive exercise can cause
prostaglandins and immune
the elevation of stress hormones, particularly
complexes downregulate NK
glucocorticoids, which may suppress the immune
for reviewing this article.
FURTHER READING
693–699.
Gleeson, M. (2000). Maximizing
your immune system and preventing
infections. www.abcc.co.uk/Articles/
immune1.html
Matthews, M. & others (2002).
Moderate to vigorous physical activity
and risk of upper-respiratory tract
infection. Med Sci Sports Exerc 34,
1242–1248.
Walsh, N.P. & others (2011). Position
Statement Parts 1 & 2. Exercise
Immunology Review 17, 6–63, 64–103.
cells.
NK cells are highly influenced
by physical exercise. The possible
important mechanisms behind
exercise-induced changes in NK
cell function are cytokines and
stress hormones.
This article from Microbiology Today was
reproduced for Biology in the Real World
(www.societyofbiology.org/bitrw) at
the Association for Science Educators
Conference 2012. For more microbiology
articles which can be used in the classroom
see www.microbiologyonline.org.uk