veNTIlATIoN - Green Cross Publishing

probiotics
36
Part 4
deIrdre JordAN bsc ANutr (SCIENCE OFFICER, yAKULT IRELAND)
lINdA v ThomAs bsc Phd FIFsT (SCIENCE DIRECTOR, yAKULT UK LTD)
There is now a reasonable body of evidence to
indicate that certain probiotic strains may help
support the immune system and, in general, the
body’s natural defences. In this four part series
on probiotics we have looked at the evidence for
probiotics (i) as a risk reduction measure against antibioticassociated
diarrhoea and Clostridium difficile infection; (ii)
in reducing the effects of irritable bowel syndrome and
associated symptoms, and more recently (iii) in the general
health benefits of probiotics for the elderly. A fundamental
aspect of regular probiotic consumption is their modification
of the intestinal microflora such that numbers of beneficial
bacteria are maintained or increased, and the effects or
numbers of harmful or pathogenic bacteria are decreased. This
is associated with a range of positive effects on the health and
functioning of the digestive system, as well as modulation of
immune function. 1 Probiotics can also have many related and
more specific modes of action. By supporting the beneficial
bacteria in the commensal flora, they may help inhibit the
growth and reduce any harmful effects of other bacteria,
antigens, toxins and carcinogens in the gut. In addition,
and very importantly, probiotics can influence the immune
system via the gut-associated lymphoid tissue, with positive
modulation reported for the innate and even the acquired
immune system (Box 1).
The gut is the most vulnerable site in the body, which is
why the majority of the immune system is based there in the
form of the gut-associated lymphoid tissue (Figure: GALT).
The small intestine contains hundreds of Peyer’s patches
(concentrations of lymphoid tissues), but lymph nodes are
found through the whole length of the gut (in fact, 85% of
the body’s lymph nodes are estimated to be in the gut). This
immune network must recognise and tolerate the commensal
microflora (otherwise inflammation results), and it must also
tolerate food antigens. But importantly, it must recognise and
deal with pathogenic microbes. Studies with germ-free animals
have clearly shown that the commensal microflora is important
in educating and supporting the immune system; animals
without any gut bacteria have a poorly developed immune
The immune
system and
your gut:
a closer look at an
intricate relationship
(Part 4 of a 4 part series)
system with significantly fewer antibody-producing cells.
Probiotics can support the work of the commensal flora
in interacting and supporting the immune system, which
explains why certain probiotics have been shown to benefit
the health of the whole body, not just that of the gut.
box 1: Innate and acquired immune system
• The innate or non-specific immune response
defends the host from infection in a non-specific
manner. Cell surface receptors (Toll-like receptors)
on tissue recognise and bind different microbial
components. This can trigger phagocytosis and
production of pro-inflammatory cytokines, which
attract a local increase in white blood cells. The innate
immunity is an immediate response but it does not
confer long-lasting or protective immunity. Example
constituents of this system are natural killer (NK)
cells and phagocytic cells such as neutrophils and
macrophages. Examples of Toll-like receptors are TLR-4
(recognises lipopolysaccharide, the cell wall of Gramnegative
bacteria) and TLR-9 (recognises bacterial
DNA).
• The acquired/adaptive or specific immune
response recognises and remembers specific
pathogens and is thus able to mount a rapid and
stronger defence when the pathogen is next
encountered. Lymphocytes (T and B cells) recognise
specific and different parts of a pathogen, and then
can activate different pathways against it. Humoral
immunity is an antibody-mediated specific response
by B cell production of immunoglobulins (antibodies)
such as IgA, IgG and IgE. (Humoral refers to the bodily
fluids and comes from the old idea of ‘humors’ of the
body). The other response is cell-mediated, mainly
involving antigen-specific T cells.