Environmental and immunological factors associated with allergic disease in children

Abstract: Background: Allergic diseases are characterised by dysregulated immune responses. The first manifestation of the atopic phenotype is often food allergy, with symptoms like eczema. Food allergy in children is generally outgrown before 3 years of age, but a temporary food elimination diet is often advocated. The prevalence of allergic diseases has increased in affluent countries during the last decades, possibly as a consequence of a changed lifestyle leading to decreased microbial load.Aim: To investigate humoral, mucosal and cell-mediated immunity in association to allergy and allergy development in young children and relate this to environmental factors.Subjects: Two cohorts of children were investigated; 1) Children from countries with high (Sweden) and low (Estonia) prevalence of allergy that were followed prospectively from birth to 5 years of age. 2) Infants with eczema and suspected food allergy that were followed prospectively to 4 ½ years of age.Methods: Endotoxin levels were analysed in house dust samples. Antibodies were measured in serum and saliva samples with ELISA. Food allergen induced cytokine responses were analysed in mononuclear cells.Results: The microbial load, delineated as endotoxin levels, was higher in house dust from Estonia than Sweden and was, in Swedish children, inversely associated with sensitisation and clinical symptoms of allergy. The decreased microbial load in Sweden may have an impact on mucosal immune responses as different IgA antibody patterns were observed in Sweden and Estonian children with much lower secretory (S)IgA antibody levels and high proportion of non-SIgA, i.e. IgA antibodies lacking the secretory component, in the Swedish children. Moreover, low levels of SIgA were associated with clinical symptoms in sensitised children.High IgG4 antibody levels to food allergens during infancy were associated with faster tolerance development in food allergic children. Cytokine responses by mononuclear cells after allergen stimulation was upregulated with age in children with prolonged food allergy, but not in children who develop tolerance before 4 ½ years of age, possibly because of the prolonged elimination diet in the former group.Summary: Reduced microbial exposure in affluent countries may affect the mucosal immune responses during infancy, possibly resulting in an increased risk of developing allergic disease. High levels of IgG4 antibodies during infancy are associated with faster achievement of tolerance in food allergic children. Allergen elimination during infancy may result in a dysfunctional cytokine response.