Atopy: A mirror of environmental changes?

Abstract

Allergen-specific IgE can be detected in cord blood, and prenatal exposures have been identified to determine atopic sensitization at school age. These findings fit well into a concept of early-life inception of atopic sensitization and disease. In a mouse model this hypothesis has been verified by protective prenatal effects on allergic asthma. In this issue of the Journal, Soza nska et al present a report, ‘‘Atopy and allergic respiratory disease in rural Poland before and after accession to the European Union,’’ in which they demonstrate that the prevalence of atopic sensitization increased dramatically within 9 years in a rural area of Poland. The most striking finding is that the increase in the prevalence of atopic sensitization affected all age groups. This challenges the notion of the early origin of atopic sensitization. The authors had the unique opportunity to collect questionnaire data on atopic diseases and assess skin prick test (SPT) response positivity in the same population 9 years apart. One might argue that the time lag might be associated with changes in measurement instruments, resulting in a spurious increase in SPT response positivity. However, this increase was much more pronounced in the rural than in the urban population. The specificity of this effect renders a systematic bias extremely unlikely. Moreover, the discrepancy between rural and urban populations is informative in itself. The authors suggest a farm-related exposure or better its loss as the driving force in the increase of atopy in the rural population. Rural and urban environments differ in a multitude of interrelated exposures; hence associations with distinct farmrelated exposures on an individual level are impossible in this data set. Moreover, observational studies do not achieve the same level of evidence as experiments, although one might consider the described phenomenon an ‘‘experiment by nature.’’ The stratification for the town versus village populations reveals 2 distinct phenomena. To focus on these, we have created Fig 1 from the original figures on the study population