Humoral immune responses to allergens in early childhood

• Sensitivity to eight standardized allergen extracts (Solu-Prick SQ, ALK, Hørsholm, Denmark) was assessed in 1580 schoolchildren. The prevalence of atopic sensitization among these 10-12-year-old children was 3--4 times lower in Estonia (8.1-14.3%) than in Sweden (24.2-35.3%). Sensitization among schoolchildren was associated with atopic heredity, gender of the child (boys were more often sensitized) and passive smoking during infancy and inversely related with crowded living.In a prospective study 298 infants were followed from birth to 2 years of age. Clinical examination and skin-prick tests (SPT) were carried out, and venous blood samples were collected at 6, 12 and 24 months. SPT were done with natural food allergens (cow's milk (CM), egg white (EW)), and standardized inhalant allergens (cat, dog, house-dust mite (D. pteronyssinus), birch, timothy, mugwort). Serum IgE and circulating IgE antibodies against allergens were determined by a chemiluminescence method. IgG and IgG4 antibodies to ovalbumin, ~-lactoglobulin, cat allergen and birch (rBet v l) were analyzed with ELISA. Atopic sensitization according to SPT results (7%) among the Estonian children during the first two years of life was not significantly less common than among the Swedish children of the same age. The prevalence of SPT positivity to CM at 6 months of age (2%) was also similar in the Estonian and the Swedish children during the first two years of life, while positive SPT to EW (5%) was three times less common among the Estonian children.The prevalence of circulating IgE antibodies to food allergens increased over the first two years of life in the Estonian children. Sensitization to indoor allergens (18%) seemed to be more prevalent among the Estonian, as compared to the Swedish children, however sensitization to cat allergen ( 12%) was equally common during the first two years of life but not so in schoolchildren. IgG subclass antibodies to food and inhalant allergens generally developed with similar kinetics as in the Swedish children. In contrast to the Swedish children, however, the levels of IgG4 antibodies to the inhalant allergens were higher during the first two years of life. The antibody levels to ß-lactoglobulin in the Estonian children did not peak in infancy and they did not have higher levels of antibodies to ß-lactoglobulin than non-atopic children.When the infants were about 6 weeks old, visits were performed to  197 homes. Questionnaires about living conditions were completed and three dust samples were collected from each home. The levels of Der p I, Der f I, Fe/ d I and Can f I in the dust samples were determined by ELISA, using monoclonal antibodies (ALK, Hørsholm, Denmark) .The levels of dog, cat and house-dust mite allergens were comparable in the homes of Estonia and Sweden and thus the differences in allergy prevalence in Estonia and Sweden cannot be explained by different levels of exposure to indoor allergens.Microbiological investigations of faeces samples of 27 Estonian and 29 Swedish one-year-old infants indicated major differences in the composition of the colonic microflora with high counts of lactobacilli and eubacteria in the Estonian and increased number of clostridia in the Swedish infants. Differences in the indigenous intestinal flora might affect the development and priming of the immune system in early childhood.Whether the increase of IgE antibodies was related to new environmental factors or temporary production of IgE will be revealed by a follow-up of the children. The different kinetics of IgG subclass responses to food and inhalant allergens could support the hypothesis that Th2-like responses during infancy are more transient in the Estonian as compared to the Swedish children. Future follow-up of the children will reveal if this is the case.

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