Peanut allergy is a common variant of food allergy, which is caused by 18 specific groundnut proteins. The probability of food intolerance increases with genetic predisposition, the use of cosmetics with peanut oils, late introduction of the product into the diet. Allergic reactions are manifested by skin rashes, gastrointestinal and respiratory symptoms, in severe cases anaphylactic shock develops. To diagnose the disease, an analysis is performed for total IgE to peanuts and antibodies to individual proteins, skin tests, provocative tests. Allergy treatment involves the lifelong appointment of an elimination diet.
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More than 150 million of the world’s population suffer from various forms of food allergies, 20% of them are intolerant of peanut proteins. Most of these patients are in the USA (3 million), which is due to the national traditions of eating peanut butter. A great danger is the increase in peanut intolerance among children – by 3 times over the past 20 years, which is associated with a change in the nature of nutrition.
Peanuts are a representative of the “big eight” allergens, along with cow’s milk, eggs, fish and other products. It is these eight components that cause up to 90% of food-related allergies. Peanuts have a high allergenic potential: they contain 32 specific proteins, 18 of which can provoke disease. The most practical importance in allergology are 6 types of proteins, such as:
- Arah1 (konarakhin, vitsilin). Sensitization to this protein occurs in 35-95% of patients with food allergy to peanuts. Arah1 intolerance is associated with a high risk of anaphylaxis and is considered the most severe variant of the disease.
- Arah2 (conglutin). Conglutin intolerance is observed in more than 75% of patients, which is due to the increased resistance of the protein to heat treatment, the action of pepsin.
- Arah3 (glucinin). Allergic reactions to glucinin are most common in Italy, but they also occur in other European countries. Protein mainly causes skin symptoms.
- Arah6 (2S albumin). According to the molecular structure and properties, the protein resembles conglutin, therefore it belongs to the main group of allergens. Sensitivity to 2S albumin is observed in 20% of cases.
- Arah8 (PR 10). Sensitivity to this protein develops among patients with preliminary sensitization to birch allergens, since antigens are homologues. Intolerance to PR 10 causes milder allergic reactions.
- Arah9 (lipid transfer protein). Another common variant of the allergen, to which up to 90% of patients with peanut intolerance react. In addition to skin symptoms, the Arah9 protein can provoke bronchoobstructive syndrome.
The likelihood of developing a peanut allergy depends on the way it is cooked. Roasted nuts bind IgE antibodies 90 times faster than raw or boiled, so it is considered the main provoking factor of anaphylactic reactions. The decrease in the allergenicity of the cooked product is caused by the transfer of part of the antigens into boiling water. Soaking groundnuts in vinegar according to the Asian tradition reduces the risk of allergies due to the destruction of proteins.
It has been proven that when the introduction of peanuts into the child’s diet is delayed, the risk of developing food intolerance increases significantly. Among the genetic factors, mutations of the filaggrin gene R501X and 2282del4 are distinguished, which are most often found in the European population. Gene pathologies are registered in every fifth patient, increase the risk of allergies by 3 times. Regular use of lotions with peanut butter increases the likelihood of disease by 2 times.
The basis of a true allergic reaction is sensitization and an immune response upon repeated penetration of the antigen. Food allergy to peanuts mainly develops according to the IgE-mediated type. In the human body, during primary contact with nut proteins, IgE antibodies to specific protein epitopes are synthesized. Antibodies bind to receptors on mast cells of various organs: skin, gastrointestinal tract, respiratory tract.
At the next contact with allergens, complexes consisting of IgE and mast cells become activated, begin to secrete pro-inflammatory mediators and cytokines. As a result, immune inflammation develops, characteristic symptoms appear on the part of one or more organ systems. IgE-dependent processes are characterized by rapid development and progression, they occur in a matter of minutes after interaction with the antigen.
Symptoms of peanut allergy
In most patients, pathological reactions are formed after eating one nut grain, in severe cases, trace amounts of the product act as a trigger factor. In addition to eating nuts, the trigger of allergies is the inhalation of its smell, skin contact. Due to the high concentration of Arah1 in saliva, symptoms may be triggered by a kiss. Clinical symptoms occur within 60 minutes after the trigger action.
In 89% of cases, peanut allergy manifests itself with skin symptoms: redness, urticaria, itching. In severe cases, there is swelling of the face and lips. Respiratory symptoms are in second place by prevalence (52%), which are represented by itching and tickling in the nose, sneezing, tickling in the throat and a feeling of difficulty breathing. Gastrointestinal manifestations occur in 34% of patients in the form of nausea, vomiting, abdominal cramps and stool disorders.
Peanut allergy is characterized by a combination of symptoms: in 15-25% of cases, the skin, gastrointestinal tract and respiratory system are simultaneously affected. 1% of patients have signs of disorders in 4 organ systems. In 38% of patients, cross-sensitivity to allergens of legumes and other types of nuts was noted. With cross-sensitization to pollen antigens, oral allergy syndrome occurs, represented by IgE-dependent reactions on the mucous membrane of the mouth and pharynx.
The most dangerous consequence of peanut allergy is considered to be anaphylactic shock, which occurs with hypersensitivity to the Arah1 antigen or polysensitization. The emergency condition is manifested by a sharp decrease in blood pressure, loss of consciousness, respiratory and cardiac arrhythmias. In 20-30% of cases, anaphylaxis occurs biphasically: 1-8 hours after the seizure is stopped, the symptoms repeat.
To examine patients with signs of food intolerance, an allergist-immunologist is involved. If necessary, a dermatologist, gastroenterologist, therapist participates in the diagnostic search. First, a detailed questioning of the patient about the time of the appearance of symptoms, possible predisposing factors, the frequency and nature of exacerbations of allergies is carried out. To confirm the diagnosis , the following research methods are prescribed:
- Skin tests. With a scarification test with peanut allergens, predisposed individuals experience local redness, a blister with transparent contents, itching and burning of the skin. In case of questionable results (papule size less than 5 mm), the diagnosis is supplemented by oral provocative testing.
- IgE testing for peanuts. If the value of IgE antibodies is more than 15 kEd/l, the diagnosis of peanut allergy is established unmistakably even without scarification and provocative tests. The indicator over 2.08 15 kEd / l has a specificity of 85%, more than 7.7 15 kEd / l – 97%.
- Component allergodiagnostics. To determine the risk of severe anaphylactic reactions, sensitization to the most dangerous groundnut antigens is determined. Hypersensitivity to Arah2 has the greatest clinical significance, which in 87% is accompanied by allergic symptoms when eating minimal amounts of peanuts.
Peanut allergy treatment
The basis of the treatment of the disease is the complete elimination of the product from the diet. It is important not only to limit the consumption of peanuts and products based on it, but also products that may contain trace amounts of allergen. Nuts are a source of fats used in the production of confectionery products, so when buying them, you need to look at the appropriate labels. Peanuts can also be in dry mixes and muesli, the use of which is prohibited.
Patients with peanut allergies need to be especially attentive in catering establishments, where the product is often part of multicomponent dishes. Contamination of food with protein antigens is possible if the cooking technology is not followed, therefore, even when the composition is indicated in the menu, there is a risk of an acute allergic reaction. For emergency help in an unforeseen situation, patients are prescribed syringe pens with adrenaline.
In allergology and immunology, the search for effective methods of peanut allergy therapy does not stop. The role of sublingual oral immunotherapy, which increases the safe dose of allergen by 20 times, is discussed. The results of the studies show a decrease in the level of specific IgE within 1 year from the start of treatment, but the content of interleukins and gamma interferon does not change during therapy.
TNX-901 monoclonal antibodies are being developed that block IgE epitopes and prevent their binding to peanut antigens. Anti-IgE therapy increases the threshold of sensitivity to allergen, reduces the intensity of clinical manifestations of allergy. The use of DNA vaccines with the participation of plasmids, which inhibit an immediate type of allergy, induce the development of a Th1 response, is also being investigated.
Prognosis and prevention
With strict adherence to the elimination diet, patients do not face allergic reactions and live a full life. Over time, 22-25% of people develop a natural tolerance to antigens, but in another 44% of cases, peanut allergy becomes severe with manifestations of anaphylaxis. The main method of prevention: complete restriction of contact with peanut proteins, since drug treatment is under development.