Causes of food allergies

Risk factors for food allergy. Hereditary burden of allergic diseases predisposes to the development of food allergy. In patients with a burdened heredity, the frequency of occurrence of HLA antigens such as B27, Bw35, Bw41 is increased. In a number of groups of patients, these antigens had a significant increase: HLA-B27 was more common in children with an unburdened atopic heredity, HLA-Bw35 - in patients with monovalent sensitization, and HLA-Bw41 - in patients with a wide range of sensitization and with an unburdened heredity.

In addition to a burdened heredity, sick children with food allergies have a number of other risk factors. This is the consumption by a pregnant woman of obligate allergens or products that caused allergic reactions in the mother. Of particular importance is the excessive consumption of dairy products against the background of toxicosis of pregnancy, leading to changes in the mother-placenta-fetus system with an increase in the permeability of the placental barrier for both allergens and maternal globulins, possibly with an altered structure and affinity for the epithelial covers of the fetus, as well as sensitized lymphocytes. Risk factors for food allergies in children include late breastfeeding (deficiency of secretory IgA, bifidogenic factors); early artificial feeding and failure of a breastfeeding woman to follow a hypoallergenic diet; irrational introduction of complementary foods to the child, deficiencies of trace elements (zinc, selenium, copper). Acute and chronic inflammation of the gastrointestinal tract; intestinal dysbiosis, congenital or acquired deficiency of secretory immunity contribute to the development of food allergies.

Other risk factors for developing food allergies:

• acute and chronic inflammation of the gastrointestinal tract, intestinal dysbacteriosis, acquired hypovitaminosis (especially often hypovitaminosis A and E and/or deficiencies of zinc, selenium, copper, carnitine, taurine);
• aggressive environmental influences: increased “aggressiveness” (pollution) of drinking water, long-term exposure to small doses of radionuclides, xenobiotics, industrially preserved food products lead to a decrease in the barrier function of the gastrointestinal tract and a disorder of immunological regulation in general, which aggravates the violation of food tolerance;
• congenital or acquired deficiency of secretory immunity.

Causes of food allergy. In children, the most common cause of food allergy is increased sensitivity to cow's milk - 72-76.9%. The data indicate that children with milk allergy received cow's milk proteins significantly more often in the first three, especially in the first month of life, and the average age of clinical symptoms of milk allergy in patients was 2 months. I. M. Vorontsov and O. A. Matalygina noted the absence of a significant difference between the frequency of mixed feeding and the conditions for switching to artificial feeding in groups of children with milk and non-milk allergy. No clear difference was also observed in the duration of mixed feeding periods. A sharp change from breastfeeding to artificial (1-2 days) was observed in 32% of children with food allergy.

A clear connection has been established between the development of allergic reactions in children in the first months of life with the presence of food antigens in the milk of nursing mothers. When examined using immunoelectrophoresis, cow's milk antigens were detected in the milk of 52% of nursing women. During an 8-month observation period, cow's milk allergy developed in 65% of the children of these women, and only in 14% of children whose mothers did not secrete cow's milk antigens in their breast milk.

According to the results of the study by Balabolkin I. I. (1997), using the enzyme immunoassay method, specific IgE to cow's milk in children with gastrointestinal food allergy is found in 85% of cases, antibodies to alpha-lactoglobulin (61%), beta-lactalbumin (43%), bovine serum albumin (37%), casein (57%).

According to research data, sensitivity to chicken eggs was detected in 59% of children with food allergies, to fish - in 54%, to wheat - in 39%. And in children with gastrointestinal food allergies, according to enzyme immunoassay data, specific IgE to chicken eggs was determined in 97%, to fish - in 52.9%, to beef - in 50%, to rice - in 47%, to chicken meat - in 28.6%.

In children from 6 months to 3 years old, according to research data, food allergies were noted in 36% to buckwheat, 11.5% to corn, 50% to apples, 32% to soy, 45% to bananas; 3% to pork, 2% to beef, and 0% to turkey.

Chicken eggs contain several antigen components: ovalbumin, ovomucoid, ovomucin in the protein and vitellin in the yolk. When boiling an egg, their activity decreases, so hard-boiled yolk and protein have less allergenic activity. It should be taken into account that children with increased sensitivity to chicken eggs may have an allergic reaction to vaccinations containing an admixture of chicken embryo tissue.

The most powerful allergenic effect is exerted by cow's milk lactoglobulin. It has been noted that whole cow's milk causes an allergic reaction more often than sour milk or milk that has undergone other processing (boiling, drying, etc.). Increased sensitivity to cow's milk may appear in children on artificial feeding in the first months of life. Allergic reactions to vegetables (carrots, tomatoes), fruits (oranges, red apples, bananas), berries (strawberries, black currants, wild strawberries) can be associated with both protein and non-protein components. Allergy symptoms may appear as a result of exogenous histamine intake with vegetables and berries. When taking certain foods, processes may develop that lead to direct liberation of biologically active substances of mast cells and basophils.

The younger the child, the higher the permeability of his intestines to food antigens. With age, especially after 2-3 years, with a decrease in intestinal permeability, a decrease in the level of antibodies to food proteins is determined.

Pathogenesis of food allergy. Reduction of systemic impact of foreign antibodies is provided by immune and non-immune barrier systems of the gastrointestinal tract.

Non-immune factors include gastric secretion of hydrochloric acid and proteolytic enzymes that break down proteins into less antigenic molecules by reducing their size or changing their structure. Physical barriers (production and secretion of mucus, peristalsis) reduce the duration and intensity of contact of potential allergens with the gastrointestinal mucosa. The intact intestinal epithelium prevents the absorption of macromolecules.

The gastrointestinal tract has a unique immune system - intestinal-associated lymphoid tissue, consisting of discrete clusters of lymphoid follicles; intraepithelial lymphocytes, plasma and mast cells of the proper layer of the mucous membrane; mesenteric lymph nodes.

The formation of tolerance (from the Latin tolerantia - patience, endurance) to food is ensured by factors of local and systemic immunity.

In the intestine, the antigen is converted into a non-allergenic (tolerogenic) form. This form of the allergen has minor structural differences from the original, which causes suppression of the cellular immune response by stimulating CD8+ T cells.

Food allergies develop in children predisposed to allergies due to a lack of tolerance to food allergens or its loss, which can be caused by many reasons:

• functional immaturity of the immune system and digestive organs;
• lower production of Ss IgA and CD8+ T cells compared to adults;
• lower production of hydrochloric acid and lower activity of digestive enzymes;
• less mucus production.

All of the above factors contribute to increased contact between food antigens and the cells of the intestinal immune system, which leads to hyperproduction of specific antibodies with the subsequent development of hypersensitivity.

The development of an atopic reaction on the mucous membrane of the gastrointestinal tract increases its permeability and increases the passage of food allergens into the bloodstream. Food allergens can reach individual organs (lungs, skin, etc.) and activate mast cells there. In addition, biologically active substances formed during the pathophysiological stage enter the blood and can also determine remote reactions outside the gastrointestinal tract.

Isolated immune mechanisms of allergic reactions (reaginic, cytotoxic, immune complex, delayed-type hypersensitivity) are quite rare. Most patients with food allergies develop various combinations of them over time. Delayed hypersensitivity plays a significant role in the mechanism of food allergy, in which the elimination (lysis) of antigens is carried out directly by lymphoid cells.

Various mechanisms of pseudoallergymay be carried out in parallel with the current atopic reaction or exist independently of it. In this case, the release of biologically active substances from mast cells occurs without the participation of the immunological stage, although the clinical manifestations are not much different from the usual reaginic reaction. This is probably why 30-45% of children with food allergies have normal IgE levels in the blood.

Paraallergic phenomena are characteristic of the "cell membrane instability" syndrome, the genesis of which is extremely broad: excess xenobiotics and anutrients in the diet (various additives in industrial canning of food products), use of fertilizers (sulfites, alkaloids), hypovitaminosis and deficiency of microelements. The "cell membrane instability" syndrome is formed and aggravated by chronic diseases of the gastrointestinal tract, dysbacteriosis, and is characteristic of children with exudative-catarrhal and lymphatic-hypoplastic constitutional anomalies.

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