Allergic diseases in children

Dr. Michaël Hofer

Immunology & Allergology, Pediatrics, CHUV, Lausanne

May 26, 2021

For several decades, the incidence of allergy diseases in children has been increasing and particularly asthma, with its significant impact on the world Health constantly increasing. According to recent comparative studies on the frequency of Allergies in former East Germany and in West Germany depend on this increase with our western lifestyle.

How do we become allergic?

Asthma, atopic dermatitis, allergic hay fever, and food allergy are clinical manifestations of atopy, a genetic disposition that leads to excessive production of allergy antibodies (IgE), affecting at least 20 to 30% of the population. The development of allergic manifestations in an atopic person largely depends on the environmental factors they are exposed to. For example, early exposure to high concentrations of allergens can promote sensitization to these allergens and the occurrence of allergic hay fever and asthma. So you become allergic if you are genetically predisposed and exposed to an environment that promotes allergies.

When does the allergy sensitization take place?

A study carried out in Germany with a large group of patients shows that allergic sensitization can develop very early in life. The frequency of sensitization to mites increases from 2% in one-year-olds to 22% in six-year-olds and that of pollen from 1% in one-year-olds to 13% in six-year-olds. Early sensitization is to be associated with a type of immune response (Th2 polarization) that predominates in allergic diseases in children in early childhood. This polarization favors the synthesis of allergy antibodies (IgE), in contrast to the Th1 polarization common in older children and adults. During intrauterine life, the Th2 polarization prevails at the interface between the fetal and maternal blood circulation, which avoids the perception of the fetus as a foreign body and its rejection. The blood of the umbilical cord also shows this Th2 polarization, but it is excessive in children who are prone to allergies, the atopics. Between birth and the age of five, the Th2 polarization gradually develops into Th1 polarization. In atopic patients, however, the Th2 polarization persists. The balance between Th1 and TH2 polarization changes with age and usually evolves from Th2 in the infant to Th1 in the adult. The environmental factors that influence this balance can promote or inhibit early sensitization to allergens. It follows that the influence of the environment during the first years of life is crucial for the development of allergic sensitization and clinical manifestations of allergy, although sensitization can occur throughout life.

When do we develop various allergy diseases?

The various allergy diseases do not occur randomly: the first manifestation of atopy is generally atopic dermatitis, as in the infant. Asthma often begins in infancy and rhinitis (hay fever), especially pollen-related, in adolescence. There is also a sequence for sensitization to different allergen groups: the infant tends to be more sensitive to food allergens and the child from the age of three to inhalation allergens with a simultaneous decrease in food sensitization. The atopic child, who is prone to allergies, develops a series of allergic phenomena, which is known as an allergic career.

Can you avoid this allergic career?

Since allergic sensitization mainly develops in the first few years of life and is highly dependent on the environment to which the child is exposed, effective preventive measures should make it possible to reduce the frequency of allergies in the population. The effect of early prevention on the delayed introduction of food allergens has been studied for several years. It has been shown that a diet containing hydrolyzed beef protein reduces the incidence of milk allergy and atopic dermatitis during the first few months of life. However, this measure does not seem to affect the frequency of allergies in the long term. Further studies, especially on the early exposure to infectious pathogens, which influence the type of reaction generated by cells of the immune system and in this way can promote or inhibit allergic sensitization, are still ongoing. A better understanding of the mechanisms by which the environment influences the development of allergic reactions during the first few years of life should enable us to identify the exact cause (s) of the increasing frequency of allergies and to improve the effectiveness of preventive measures.

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