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Allergies – podcast

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Discover our podcast on History of Science and on health made by Florian and Yannick.

Today, almost one in three people suffer from allergies. Scientists estimate that in 2050, one in two people will be concerned. How do allergies work? Why is this disease expanding? What are the reasons?



Hypersensitivity: between allergies and intolerances

Hypersensitivity is an abnormal and excessive response to a foreign substance or molecule, called an antigen, even at very low doses. However, we must differentiate the allergy, which is a hypersensitivity related to the immune system, to non-allergic hypersensitivity. This type of hypersensitivity is benign, but these signs are strongly similar to an allergic reaction. These reactions can occur following the ingestion of certain foods or drugs and often result from a deficiency in an enzyme. For example, lactose intolerance comes from a deficiency of an enzyme, the lactase, which degrades this sugar into galactose and glucose. However, this intolerance should not be confused with milk protein allergy, which is much more serious. Here, the symptoms are flatulence, abdominal pain, diarrhea, nausea, migraine, fatigue, etc.



Allergy, an abnormal and excessive immune reaction

Allergy is a specific immune, abnormal and exaggerated response to a foreign agent (allergen). This molecule induced an allergic response in genetically predisposed individuals and in a favorable environment.

However, nobody reacts strongly after the first contact. Indeed, a sensitization phase is initially observed. Our body is protected from the outside by various barriers (skin, respiratory or digestive mucous membranes). And, every day, multiple molecules arrive in our bodies through nutrition, breathing or skin. These border tissues, and especially the digestive tract, are used to it and are consequently tolerant. However, some foreign elements are recognized by immune cells which induce a normal immune response (when you cut yourself for instance). Sometimes, under certain conditions, the immune cells did not produce the traditional antibodies, but those of the type E (IgE). These antibodies recognize the allergen very well but bound first to mast cells and basophilic polygranular and can consequently persist for months waiting a second contact. Indeed, the return of the allergen will lead directly to the type E antibodies. This has the immediate effect of causing the release of the contents of the granules these cells contained. Among the plethora of molecules released, we find the main effector of allergy, the histamine. This molecule is diffused through the tissues and cause vasodilatation and an increase in the permeability of the blood vessels. This results in edema, urticaria, circulatory insufficiency, bronchospasm (sudden muscle contraction can block breathing) that can lead to asthma. Moreover, the more the allergen is able to spread in the body, the more the allergic response will be generalized.

Other molecules are released at the same time or even later. These signal molecules initiate and maintain a quite strong immune response, including inflammation. And this helps to maintain, for example, chronic conditions such as rhinitis. Finally, there are also allergies that are not related to these mechanisms. Other immune cells may come into play and generate much less immediate allergic responses.



Asthma, a major symptom of allergies

About 10% of children suffer from asthma and 80% of which are allergic in nature. Unfortunately, this figure is constantly rising and already causes 60,000 hospitalizations and nearly 900 deaths per year.

Asthma is a chronic inflammation of the bronchi resulting in contractions of bronchial smooth muscle (bronchoconstriction) and swelling of the walls. This leads to a reduction in the diameter of the bronchi and will therefore prevent breathing.



What are the causes?

Of course, allergy is the main factor. Indeed, many allergens present in our homes or outside (mites, molds, dander, cat) can trigger asthma. However, other non-allergic factors may also come into play, such as tobacco smoke, irritating chemicals, air pollution, and especially fine particles. Scientists have conducted extensive studies on a large number of patients and have shown a clear relationship between outdoor air pollution and the risk of becoming asthmatic. Other studies have also shown that exposure to air pollution is particularly harmful during the first 3 years of life (in utero life included). Air pollutants create daily stress in the bronchi, leading to inflammation that causes asthma. But the causes do not stop there. Indeed, we are highly exposed to indoor pollution, places where we spend most of our time (house, schools, offices, shops, etc.). Many chemical products are used for the construction and maintenance of our houses and buildings as well as for the manufacture of materials, furniture, utensils, etc. It is estimated that, in industrialized countries, pollutant concentrations are sometimes higher indoor than outdoor. Indoor air pollution may increase the risk of irritation, allergic sensitization, and therefore asthma. However, causal relationships are often complex and therefore difficult to determine. But a recent study has shown a clear link between this pathology and exposure to pollutants such as formaldehyde, benzene, paints, etc. So, it is not a surprise that the population of asthmatic patients is much larger in the city than in the countryside. Moreover, in the countryside, the environment is not as sanitized as in the city and is even rich in antigens (bacteria, animals, plants, etc.). Some scientists have shown that early exposure to germs, preferentially promotes a normal immune response rather than an allergic response.



Which treatments?

In general, when allergies are diagnosed, one of the first things is to identify the involved allergen(s) to avoid crises. For example, dust mites are often a cause of asthma and therefore cleaning with specialized products will be advised to eliminate them.

Afterwards, a treatment will surely be prescribed in order to limit the risk of a crisis. These are blockers of the immune system, such as histamine or leukotrienes, or cortisol that treats inflammation.

As for asthma more specifically, since the problem is in the bronchi, the drugs is often delivered by inhalation. This helps to act faster and limit the potential side effects. In case of crisis, patients usually take salbutamol which acts very quickly (1 to 3 minutes) to reopen the bronchi.

Finally, the desensitization is also used in cases of some severe allergy involving insect venom or allergic rhinitis caused by cats, pollens and mites. This involves the repeated administrations of increasing doses of the allergen over a period of three to five years. This treatment accustoms the body to the allergen and reduces the intensity of the allergic reaction. According to Mayo Clinic experts in the United States, this therapy has been shown to be effective in cats, mites and pollen allergies.


Food allergies

Food allergies are a major public health issue. In just 15 years their frequency has doubled. Nearly one in ten young people is affected!

Once ingested, the allergen obviously causes a reaction in the digestive tract (vomiting, diarrhea, abdominal pain can be violent). Also, the symptoms can be more global. In fact, the following signs can be observed: urticaria, laryngeal edema (choking), swelling of the tongue, rhinitis, conjunctivitis, cough, asthma attack or bronchial muscle contraction (often the cause of death) and also cardio-vascular signs (tachycardia, low blood pressure and anaphylactic shock).


Anaphylactic chock

Anaphylaxis is a severe and generalized hypersensitivity reaction, with an acute lethal risk. The state of anaphylactic shock involves an acute decrease in the blood circulation, putting even more in danger the patient who already suffers from several symptoms related to the allergy. Doctors distinguish 4 grades in anaphylaxis. Grade I corresponds to a generalized involvement of the skin and mucous membranes and grade IV corresponds to the observation of a cardiac and / or respiratory arrest.

If you see someone who is in an anaphylactic shock, calling 911 is essential. Generally, allergic people have adrenaline syringes on them. The injection is done directly in a muscle of the thigh. Without this adequate and rapid treatment, the state of the anaphylactic shock becomes inevitably lethal. Adrenaline counteracts the most serious effects of anaphylaxis by reversing the generalized vasodilatation and capillary permeability (both responsible for edema) and stopping the contraction of the bronchial muscles to resume breathing.


Avoiding allergens

Avoidance of the allergen remains the best way to prevent allergic attacks or anaphylactic shocks. France has defined a list of 14 allergens and legally obliges manufacturers and restaurant managers to mention their presence. This list is of course updated and contains cereals containing gluten, crustaceans, eggs, fish, peanut, soy, milk, nuts, celery, mustard, sesame, sulfur dioxide and sulphites, lupine and mollusks.


The first promising trials to better live with some food allergies

Fortunately, some of these allergies evolve over time. Indeed, cow’s milk can trigger a reaction in babies but also disappears in 80% of cases around the age of one or two. For egg allergies, it heals itself in 60% of children around the age of three. On the other hand, the allergies to groundnuts, oilseeds, fish and / or crustaceans disappear much less frequently.

Until recent years, desensitization did not exist for food allergies. However, promising research and clinical trials have recently been completed to allow patients to better tolerate eggs, milk, peanuts or shrimps.

For instance, a trial was conducted in 99 patients suffering from peanut allergies. Half of them regularly ingested over 6 month increasing doses of peanut (from 2 to 800 mg). The other half was a placebo group. At the end of this period, 84% of them tolerated a dose of 800 mg (5 peanuts per day) and 62% a dose of 1400 mg (almost 10 peanuts).


Gluten: between allergies, hypersentivities and coeliac disease?

Gluten are proteins contained in certain cereals (wheat, rye, barley, oats) which are able to form an elastic structure enabling the production of bread or brioches, for example.

3 case have to be differentiated:

  • Allergy to gluten (very rare). In these patients, type E antibodies are produced and quickly trigger classic symptoms of allergy: red patches, edema, itching, anaphylactic shock that can lead to death.
  • Celiac disease. Contrary to intolerances, the immune system is involved and triggers a reaction against gluten. This reaction causes destruction of the intestine villi, which are essential for digestion. The symptoms are unfortunately important: diarrhea, vomiting, bloating, abdominal pain, neurological disorders or problems of fertility. This disease occurs in genetically predisposed individuals (mostly women), but recent data also indicate that some bacteria in our intestinal flora may contribute to the disease.
  • Gluten In this case, people have difficulties to digest gluten and this may lead to symptoms similar to celiac disease. This disease is more and more recognized, but still poorly characterized. Approximatively, 0.5% to 6% of the population would be concerned.





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