1. Methods of inducing allergy
There are five ways to induce food allergy in children: gastrointestinal intake, respiratory inhalation, skin contact or injection, and entry through human milk and placenta.
2. Food allergens cause
Food allergen refers to food antigen molecules that can cause immune response. Almost all food allergens are protein, and most of them are water-soluble glycoproteins with molecular weight of 65438+100000 ~ 600000. The protein of each food may contain several different allergens. Food allergens have the following characteristics:
(1) Any food can induce allergic reaction: However, the common food allergens for children are milk, eggs and soybeans, among which milk and eggs are the most common allergic foods for children, and they also vary according to different eating habits in different regions. Peanut is a common allergen in children and adults, seafood is not the main allergen in children, and allergy caused by nuts is rare in children. Although any food can be allergic, about 90% of allergic reactions are caused by a few foods, such as milk, eggs, peanuts and wheat.
(2) Only some ingredients in food are allergenic: Take milk and eggs as an example, there are at least five allergens in milk, among which casein and β -lactoglobulin (β-LC) are the most allergenic. There are relatively few allergens in egg yolk, and ovalbumin and ovomucin in egg white are the most common allergens in eggs.
(3) Variability of food allergenicity: Heating can reduce the allergenicity of most foods. The increase of gastric acid and the existence of digestive enzymes can reduce the allergenicity of food.
(4) There is cross-reaction between foods: Different protein may have the same antigenic determinant, which makes allergens cross-react. For example, at least 50% people who are allergic to milk are also allergic to goat milk. People who are allergic to eggs may also be allergic to eggs of other birds. There is no cross reaction between milk and beef, and there is no cross reaction between eggs and chicken. The cross-reactivity of plants is more obvious than that of animals. For example, people who are allergic to soybeans may also be allergic to other members of leguminous plants, such as lentils and alfalfa. Patients who are allergic to pollen will also react to fruits and vegetables, such as birch pollen, apples, hazelnuts, apricots, cherries and carrots. People who are allergic to mugwort are also allergic to Umbelliferae vegetables such as celery, fennel and carrots.
(5) Allergy to intermediate metabolites of food: Very rare, patients often have symptoms 2-3 hours after eating.
3. Caused by genetic factors
Food allergies are related to heredity. The prevalence rate of children with a history of food allergy is 30%, and the prevalence rate of children with both parents suffering from this disease is as high as 60%.
4. Causes of antibody decrease
Anatomical factors of non-specific and specific mucosal pathogens in human gastrointestinal tract can limit the invasion of intact protein antigens, while food antigens entering the intestine combine with secretory IgA(SIgA) to form antigen-antibody complexes, which limits the absorption of food antigens in the intestine, thus directly or indirectly reducing the immune response to food proteins. Children's digestive tract mucosa is tender, with high vascular permeability and poor digestive tract barrier function. Various food allergens easily enter the blood through intestinal mucosa, causing allergic reactions. The IgA level of infants under 3 months old is low, and the number of plasma cells producing SIgA in lamina propria of mucosa is small. When the digestion and absorption process and mucosal immunity are abnormal, allergens of various foods easily enter the blood through the intestinal mucosa, resulting in allergic gastroenteritis.
5. Other factors lead to
Inflammation of digestive tract is one of the reasons for the increase of the incidence of intestinal allergy. This is because inflammation of the digestive tract causes damage to the gastrointestinal mucosa, increases the permeability of the gastrointestinal mucosa, and causes excessive food antigens to be absorbed, resulting in allergic reactions.
pathogenesis
The sensitized antigen activates IgE plasma cells in the lamina propria of the intestine to produce a large number of IgE antibodies, which combine with mast cells and are fixed on the surfaces of these cells. When allergens in food re-enter the body and combine with IgE on the surface of mast cells in gastrointestinal mucosa, mast cells are activated to thresh and release a series of inflammatory mediators involved in allergic reactions, which increases vascular permeability. Some antigen substances that cause type I allergic reaction can also selectively combine with plasma cells IgG, IgM, IgA or T cells to form immune complexes, thus causing local or (and) systemic type III or IV allergic reactions, which are related to age, food digestion process, gastrointestinal permeability and so on. Food allergies are most common in the first few years after birth. Most children develop tolerance to this food when they are 2~3 years old, and their symptoms disappear. IgE medium may last for a long time. The initial severity has nothing to do with the disappearance of clinical symptoms in the future, but the sensitivity of food allergens persists because it is not completely avoided, especially among teenagers.