Toll-like receptors link atopic march to the hygiene hypothesis.

In recent decades, the prevalence of atopic diseases has increased substantially worldwide, but their molecular pathologies are now being elucidated. The report by Haapakoski et al. in this issue suggests that the manner in which the immune system encounters an allergen is key to the subsequent polarization of its responses, and the presence of microbial ligands appears to be important in this process. Data in this report provide further proof of the hygiene hypothesis that combine it with known features of the atopic march.