Immuno-Nutrition
Nutrition
is important for organ function and immunity. Malnutrition
results in atophy (shrinking) of the organs, impaired immunity
and increased risk of infection. When people die from starvation,
it is not normally a lack of food, it is dying from an infection
that under normal circumstances would not be lethal. Traditional
diets protect against disease, and our Western diet initiates
disease because it is filled with 'empty calorie foods'
- high calorie foods with little nutrients - for example
white flour has only one tenth of the nutrients of wheatgerm
- all the nutritious parts of the wheat are thrown away
so we are left with pure white flour at the expense of our
health.
There
are special cases where enhances immunonutrition is certainly
required - anyone who is critically ill, including postoperative
and chemo patients; as well as HIV patients - a deficiency
of zinc and selenium is associated with increased mortality;
and athletes - supplementation is important as exercise
depletes nutrients and triggers a depressed immune system.
Innate
Immunity
- Non-adaptive/non-specific
immunity
- This
is the first line of defence in the body
- No
prior exposure to the allergen is required
Immunity
is mediated by leucocytes - the innate immunity uses neutrophils,
monocytes and macrophages. The cells in this system have
receptors on their surface that recognise common molecules
produced by pathogens. Once recognised, macrophages etc
engulf the pathogen (eg bacteria or virus) and degrade it
in a process called phagocytosis. It releases cytokines
to recruit other cells to the site of infection which triggers
an inflammatory response, so inflammation and innate immunity
are really the same.
Fragments
of the degraded pathogen are recycled to the cell surface
with MHCII, and then these cells act as Antigen Presenting
Cells and migrate to the lymph nodes where it will be recognised
by Tcells and trigger the adaptive immune response.
The
innate immunity triggers the adaptive immunity, which coats
pathogens in antibodies for the innate to engulf.
Supplements
or neutraceuticals for suppressing the innate immunity are
useful for cancer prevention, arthritis treatment and tissue
treatment, but may promote infection.
Supplements
for enhancing the innate immunity are useful for infection
treatment, and cancer treatment, but may promote further
inflammatory disease, so the correct dose is required.
Adaptive
Immunity
- Humoral,
acquired or specific immunity
- Highly
specific for a particular antigen
- Memory
involved
Immunity
is mediated by leucocytes - the adaptive immunity uses B
cells and Plasma cells.
Bcell
receptors recognise and engulf plasma antigens, digest them
and display them on MHCII molecules for reference. TH2 helper
cells recognise Bcell MHCII/antigen complex and secrete
lymphokines that trigger Bcell maturation into plasma cells.
Plasma cells secrete antibodies - immunoglobulins. Antiobodies
bind the pathogen with the original antigen and phagocytic
cells destroy antibody coated pathogens.
Tcells
are divided into:
- Tc
- cytotoxic T cells - these recognise the antigen presented
on MHCI molecules or infected cells and in response secrete
factors which kill the cell.
- Th1
- helper T cells - these recognise the antigen presented
on MHCII molecules of Antigen Presenting Cell and secrete
lymphokines to attract other cells to the infection.
- Th2
- helper T cells - these co-operate with Bcells in the
production of antibodies
- Ts
- suppressor T cells - these down-regulate the adaptive
immune response once infection is over.
Supplements
or neutriceuticals for suppressing the adaptive immunity
are useful for treating allergies, arthritis and autoimmune
disorders, but may also promote infection.
Supplements
for enhancing the adaptive immunity are useful for treating
infection, but may promote allergies, arthritis and autoimmune
problems.
Mucosal
Immunity
The
lining of the digestive and respiratory systems encounter
lots of foreign molecules. Only some trigger an immune response.
In the gastrointestinal tract, immune cells are localised
in organised structures of Gut Associated Lymphoid Tissue
(GALT). The most important of these are the Peyer's Patches
in the small intestine. Orally introduced antigens are presented
to the mucosal immune system through lymphoid Peyer's Patches.
These are found between the gut lumen and gut wall. Mcells
at the lumen-epithelium edge act as antigen samplers. Bcells
in the Peyer's Patch follicle secrete IgA antibodies into
the mucus lining the gut lumen. These antibodies bind pathogens,
which impedes their progress across the mucus and prevent
exit from the gut. Tcells and Antigen Presenting Cells in
the Peyer's follicle protect against pathogens that do cross
the epithelium. Peyer's Patches induce mucosal production
of IgA and IgM which initiates oral tolerance (no longer
allergic to that food chemical). This means the antigens
will not trigger a hypersensitivity response and inhibits
the production of IgE and IgG.
Other
factors preventing infection are rapid peristalsis movements,
and ensuring the mucosal layer acts as a diffusion barrier.
Gut
Microflora
Oral
tolerance is important as some bacteria require eradication,
and others are beneficial for example probiotics. Probiotics
break down food that the small intestine couldn't and they
help maintain mucosal immunity. They prevent colonisation
of pathogenic microorganisms and stimulate the generation
of the mucosal barrier. Malnutrition affects the microorganism
balance and causes infection to occur. The ability to adhere
to mucosal surfaces appears to be important for optimal
function of probiotic bacteria - yoghurt bacteria does not
adhere.
Lactobacillus
plantarum is a common helpful bacteria. It is able to stick
to the mucosa, colonise the intestines and inhibit pathogens.
It can tolerate lower pH than other microorganisms. It is
found in fermented foods, vegetables, fish and meat, sourdough,
sauerkraut, green olives, wines and beer. It is often used
by the food industry as a preservative against pathogens,
and it can even produce omega-3. Lactobacillus is dependent
on glucose and arginine for growth - arginine degrades to
nitric oxide which is essential for GI immune functions,
for example bacteriostasis, stimulation of immune defence
and mucus secretion - all these control ecoli, salmonella,
hpylori and parasites. Lactobacillus binds to the mucosal
surface through a mannose-specific adhesion, which competes
with other gram-negative bacteria or pathogens for receptor
sites. This is how it is able to repopulate the gut with
healthy bacteria. Read more>
Sulphur
Amino Acids - Cysteine, Methionine and Taurine
These
act as substrates for acute phase protein and immunoglobulin
synthesis. During infection, demand for these can exceed
production so dietary intake is extra-important. These amino
acids are also useful for glutathione production, which
protects tissue against prooxidant inflammation, and augments
the activation of Tc cells. Insufficient sulphur amino acids
results in a proinflammatory influence and reduces overall
immune efficiency.
Taurine
is sourced from the diet or made from cysteine and
methionine. It is rare to have a deficiency, unless in times
of very poor immunity. Taurine constitutes ¾ of the amino
acid pool in the neutrophils. It preserves neutrophil phagocytic
activity that has been decreased by hyperlipidemia. Taurine
helps kill bacteria by reacting with hydrochlorus acid produced
by the neutrophils. A deficiency is seen in cats and results
in defective phagocytic function and lymph node regression.
Arginine
may be depleted during an immune response. It is the
precursor for polyamine synthesis which is necessary for
DNA and RNA to be correct. It is also required for Nitric
Oxide Synthase which is secreted by macrophages to kill
pathogens.
Glutamine
is the specific fuel for proliferation of lymphocytes.
It enhances phagocytosis and increases the cytotoxicity
of neutrophils. It is required for the energy source of
the gastric mucosal barrier. Glutamine supplementation is
useful for treating and preventing infection.
Omega
3 and 6 provide essential fatty acids which are incorporated
into cell membranes for membrane stability, fluidity, cell
mobility and receptor signal function. Omega 3 provides
EPA and DHA which have immunosuppressive properties, reduce
infection and selectively suppress inflammatory cytokines.
Omega 6 provides AA which is proinflammatory. The balance
between both is important, and an ideal ration is 4:1 or
less.
Zinc
deficiency is associated with depressed immunity. Poor
zinc status causes lymphopenia which is reduced Tcells and
Bcells. The thymus reduces in size and Tcells are depleted
from the spleen and lymph nodes, and Bcells are depleted
from bone marrow. Zinc is a critical component of the enzymes
involved with DNA, and immune cells are sensitive to DNA
errors due to the increase in cell proliferation in infection.
A deficiency results in impaired Tcell cytotoxic activity,
and impairs chemotactic responses of neutrophils, monocytes,
macrophages and affects cytokine concentration and enhances
inflammatory cytokines. Zinc is beneficial in the prevention
and treatment of infection, but an excess is associated
with copper deficiency, anaemia, growth retardation and
immunodepression.
Copper
is essential for proper immune function. A defiency
results in decreased Tcell and neutrophil killing action.
Selenium
deficiency results in decreased antibody production
by Bcells. Supplementation enhances Tcell response and increases
antibody synthesis. It offers antioxidant protection of
tissue against ROS damage from inflammatory responses. Selenium
is a key component of glutathione peroxidase which detoxifies
ROS.
Iron
deficiency results in reduced neutrophil function,
Tcell numbers and impaired IL2 production from lymphocytes.
Iron is required by many pathogens however.
Green
Tea - EGCG protects against carcinogenesis and inhibits
inflammatory response (suppresses innate immunity). Inflammation
promotes cancer, so preventing it reduces risks. Read more>
Echinacea
is an antioxidant which is suitable for the innate
immune system. However it increased cytokines, NK cells
and macrophages which may promote inflammation. Read more>
Summarised
from Martin Philpot lecture, University of Auckland Medical
School October 2003
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