Main groups of food allergens
In the early stages of the disease development, food sensitization plays a key role. All triggers can be divided into several groups according to their clinical significance and aggressiveness:
- Cow's milk proteins. Traditionally, these exhibit the highest allergenic activity among all foods. The main culprits of immune reactions are most often the protein fractions of $eta$-lactoglobulin and casein.
- Chicken egg whites. The sensitizing potential of various egg components is heterogeneous. Egg white, containing ovomucoid and ovalbumin, causes allergic reactions much more frequently and with greater severity than the yolk (which contains livetin and phosphovitin).
- Seafood. Various species of fish, as well as crustaceans (including shrimp and crabs), regularly act as potent triggers for exacerbations.
- Plant proteins. High allergenic activity is observed in legumes (peanuts, soy, green peas). The role of cereal crops is also important—allergies to them arise due to reactions against albumin, globulin, gluten, and gliadin fractions.
- Rare allergens. This group includes various types of meat (pork, beef, poultry), certain grains (buckwheat and oatmeal), as well as a number of vegetables, berries, and fruits (tomatoes, strawberries, citrus fruits).
Pathogenetic rationale in infants during the first year of life
The high incidence of food allergies specifically among infants has a clear anatomical and physiological rationale. The gastrointestinal tract of a child in the first year of life is functionally immature.
During this period, there is insufficient production of endogenous digestive enzymes, which prevents the proper breakdown of dietary proteins into amino acids. The situation is aggravated by an initially reduced barrier function of the intestinal mucosa. As a result, large protein molecules, which possess pronounced allergen properties, pass unhindered through the intestinal wall directly into the bloodstream, where they encounter the immune system and trigger a cascade of sensitization reactions.
Age-related evolution of triggers and non-food allergens
As the child grows older, their sensitization profile changes drastically. The clinical significance of exclusively food-related factors gradually decreases, giving way to reactivity to environmental factors (inhalant agents) and infections.
- Aeroallergens. In older age, microscopic house dust mites come to the forefront (primarily Dermatophagoides pteronyssinus and Dermatophagoides farinae species). Pollen from various plants and pet dander also begin to play an important role.
- Bacterial sensitization. Staphylococcus aureus acquires critical importance in maintaining chronic inflammation. In children with moderate-to-severe atopic dermatitis, this microorganism massively colonizes affected skin areas. Sensitization develops specifically against staphylococcal enterotoxins A and B. These toxins act as superantigens that nonspecifically activate the immune system and continuously sustain the focus of inflammation.
- Fungal sensitization. Manifests as the development of hypersensitivity to spores of various mold fungi, as well as to the patient's own cutaneous yeast flora.
Basics of pathogenesis and immunological profile
From the perspective of immune system involvement, atopic dermatitis and its associated allergic manifestations represent a disease with a mixed mechanism of development. Pathogenesis is not limited to a single pathway; it is based on two powerful parallel processes:
- IgE-mediated reactions. This is the classic mechanism of immediate-type hypersensitivity, in which specific immunoglobulin E antibodies are produced in response to contact with an allergen, provoking a rapid response.
- Cell-mediated reactions. These are reactions occurring with the direct participation of specific T-lymphocytes. This mechanism is largely responsible for maintaining chronic allergic inflammation in tissues.
"Milk and Eggs, Fish and Beans" — the main groups of severe food allergens in infants, listed in descending order of significance.
Class and exam questions
Why do food allergies most often start in the first year of life?
This is due to GI immaturity: reduced mucosal barrier function and a lack of digestive enzymes lead to large proteins (allergens) being absorbed into the bloodstream intact.
Which fractions of the chicken egg are most allergenic?
Egg white possesses the highest sensitizing potential due to its ovomucoid and ovalbumin fractions; the allergenicity of the yolk (livetin, phosphovitin) is significantly lower.
What role does Staphylococcus aureus play in atopic dermatitis?
It colonizes the affected skin in moderate-to-severe cases. The enterotoxins A and B produced by it act as superantigens, sustaining allergic inflammation.
What is the mixed mechanism of development of allergic inflammation?
Because the pathogenesis simultaneously includes immediate-type hypersensitivity (IgE-mediated) and cell-mediated reactions involving T-lymphocytes.
What else to study on this topic
- Structure and properties of cow's milk protein fractions (beta-lactoglobulin, casein)
- Mechanism of action of superantigens (staphylococcal enterotoxins) on the immune system
- Differential diagnosis of house dust mite species
- The role of T-lymphocytes in cell-mediated allergic reactions
- Anatomical and physiological features of the GI tract in newborns and infants
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Other topics in "Chapter 5. Allergic Diseases"
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