and more people are allergic, children and adults. Our genes, as well as the
environment and living conditions, will affect the occurrence of allergies.
Could it be the disease of the XXIe century?
of the most prevalent ailments of modern time is, once again, involved with our
immune cells. The WHO (World Health Organization) itself ranks allergies,
manifesting by a hypersensitivity, in fourth place of worldwide diseases. Allergy
etymology comes from Greek allos: other and ergon:
reaction. It implies a different reaction, often stronger, when a second
encounter happens with the same compound. Hypersensitivities are linked to a
tolerance lost regarding environment compounds, usually harmless, which induce
a danger signal to the immune system in allergic people.
panel of allergens
are compounds that induce allergic reactions. It varies in nature such as aeroallergens
that we breathe in, trophallergens that we eat, transcutaneous allergens that
touch our skin, drug related allergens, professional allergens but also bugs’
and reptiles’ venoms.
also called airborne allergens include ever-present dust mites, pets’ hair,
pollens, molds, gluten, cockroaches, and latex. It can be a bit surprising to
find those last two in the list of airborne allergens, but cockroaches and
latex produce airborne proteins in the environment that can become allergens.
trophallergens we can find child food allergies related to milk, eggs, peanuts,
and gluten. Milk and eggs allergies are often temporary and are not found in
adults. Concerning food allergies in adult are fruits allergies, vegetables
allergies, seafood allergies and gluten.
is important to notice that allergies and intolerances to food are different
and have not the same mechanisms of action. Gluten intolerance is an
auto-immune chronical gut disease which evolves during several years whereas
gluten allergy is acute and happens almost immediately. Allergies are tricky since
cross-over allergies can occur when someone is, for example, pollen allergic
but also fruit allergic because both specific pollen and fruit happen to have a
common allergen compound.
Figure 1 : Allergens ultimate trial. (Source: Adapted
from Page 15 / Numéro 117 / Allergologie Pratique / Juin 2016)
Different types of allergies
allergy is an immune system dysregulation that induces loss of tolerance for
normally harmless compound, allergens. There are different forms of allergies
which may be generalized, cutaneous (skin related) or respiratory (lungs
allergy is the anaphylactic shock which can be lethal if not treated fast. It
can be triggered by food intake or bug bite that possess the allergen. It will
induce a decrease in arterial pressure, swellings, respiratory inconveniences,
diarrheas, awareness troubles and hemorrhagic syndrome.
allergies are allergic hives, eczemas, or dermatitis. They mainly appear as big
red blotches that can become infected if the wound is open.
allergies, rhinitis and asthma, will provoke respiratory troubles. For asthma,
the patient won’t be able to let out the air within his lungs and will have choking
sensation. Hay fever is an allergic rhinitis. The symptoms are conjunctivitis (irritated
eyes) as well as a nasal airway obstruction and sneezes. It is important to
bear in mind that an allergy form is not naturally linked to the allergen form.
If the triggered allergy is asthma, it doesn’t have to be provoked by an
airborne allergen. A food allergen could have induced asthma just as well.
2: Incidence of allergies during life. (Source: Adapted from Czarnowicki et al,
Factors influencing allergies
factors take part in development of allergies. One of the first is the genetic
predisposition. Indeed, atopy, which means the ability to produce IgE antibodies
against allergens, is a hereditary phenomenon. Yet, most of allergies are
induced by IgE antibodies. A study led on penicillin allergy, a drug related
allergy, brought to light genetic differences within some genes ruling the
immunomodulation. Thus, genetic variations have been discovered for people
having an atopic tendency. Some of these variations impact MHC genes (see
system‘s G.I. in action) which is a
protein involved in immune response.
balance doesn’t exist in immune disorders since women are more affected than
men. In fact, in vitro experiments have shown that testosterone was able
to inhibit the maturation of some immune cells involved in inflammation and
allergy. Furthermore, rodent studies demonstrated similar results since androgenous
hormone receptors, male hormones, seems to play a protecting role against
hypothesis to explain the rise of allergies in past years is hygiene abuse. Increase
of sanitation has diminished the risk of infections but has introduced a
weakness in regard of allergies. A child too protected while young has less
tolerance against allergens due to unconditioned immune system. Moreover,
children born from caesarean section tend to develop allergies since they lack
encounters with maternal bacteria. The same also applies to breast feeding versus
baby milk formula in the early life of a child.
is of utmost importance to bring a varied diet to children as a mean to teach
immune cells tolerance. There is a strong link between microbiota and
allergies. Food industry has been formatted to create processed and pasteurized
products in the last decade which diminishes the bacteria existing within food who
educate our immune cells. Tolerance to symbiotic bacteria, which exist
naturally in the body can occur. Thanks to those bacteria, intestinal
microbiota is taking shape. This last one is essential because the presence of
commensal bacteria provides protection against other harmful pathogens (see article Immune system‘s G.I. in
action).That tolerance induces a lymphocyte Treg enrichment in our body that will modulate
and reduce the immune response. Probiotics
and prebiotics have been introduced for that purpose in the last several years.We could see them as adjuvants helping to
provoke an immune response (see article Vaccination:
They promote microbiota proliferation to control allergies by bringing a
tolerance to modulate the immune response.
3: Factors involved in allergies. (Source: Adapted from Burbank et al 2017)
warming causes some tree species to grow in area that were previously
inhospitable and pollen season are longer. Air pollution takes part greatly in
allergy development. Stress, more and more present in our life, is also
involved in allergy onset. Many external factors are able to modify gene
expression without changing the DNA by mechanisms called epigenetic. Hence,
someone’s environment and lifestyle greatly affect the occurrence of allergies.
Allergies are part of our everyday lives and will be for a long time.
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