Exposure to birch pollen and development of atopic disease in childhood

Abstract

Background: In 1993 extremely high levels of birch pollen were recorded in Stockholm, Sweden. This provided an opportunity to evaluate the effects of aeroallergen exposure on the early immune response. Objective To assess the influence of exposure to birch pollen during pregnancy and early infancy, on the allergen-specific IgE- and IgG4-antibody (ab) response and development of atopic disease in children.

Methods: A total of 970 children with atopic heredity and born in Stockholm in 1992, 1993 or 1994 were investigated at age 4.5-5 years. They were divided into five groups: high-dose exposure (exp.) at 1 year of age, high-dose exp. at 0-3 months, low-dose exp. at 0-3 months, high-dose exp. during pregnancy and low-dose exp. during pregnancy. The children were examined and skin prick-tested with inhalant and food allergens. IgE-abs (against birch pollen and recombinant Bet v 1) and IgG4-abs (against rBet v 1) were analysed in serum. The same tests were performed on the mothers of the children exposed during pregnancy.

Results: Exposure to high levels of birch pollen in the first three months of life increased the risk of sensitization to the same allergen in children, and also the risk of pollen and/or animal dander-induced asthma attacks. Combined high-dose exposure to birch pollen and cat allergen increased the risk of sensitization to cat. Exposure of the mother during pregnancy to high levels of birch pollen resulted in a tendency towards increased risk of sensitization to the same allergen and symptoms of atopic disease in the children. Exposure of the mother during pregnancy to birch pollen was less likely to result in sensitization in the child than exposure of the child in early infancy. Maternal pollen allergy seemed to have a stronger influence on the development of rhinoconjunctivitis in children with a family history of atopy than the degree of allergen exposure during pregnancy. Exposure to high doses of inhalant allergens during the early postnatal period was associated with detectable levels of allergen-specific IgG4-ab even at five years of age. IgE-sensitization towards inhalant allergens appeared to have more influence on development of atopic disease than the IgG4-ab levels. An immune modulating effect of IgG4 on symptoms of allergic rhinoconjunctivitis was suggested in children sensitized to birch.

Conclusion: Our studies showed that birch pollen exposure early in life increased IgE-sensitization and IgG4-response to the same allergen, and these findings confirmed that early life is a sensitive period for environmental influence, although genetic factors also are important. Furthermore, a certain immune modulation can occur during the prenatal period, but the effect of allergen exposure during this time period is less likely to result in sensitization and atopic symptoms than exposure early in life. Specific IgE-sensitization had more influence on development of disease than the IgG4-antibody-response.