Pandemic of Atopic Diseases - A Lack of Microbial Exposure in Early Infancy?

An increase in the frequency of allergic diseases during last several decades has been linked to improved hygienic conditions. This review focuses on a few recent findings in this extensive field. Accumulative data suggest that a spectrum of CD4+T cells, including type 3 T helper cells, T regulatory 1 cells, CD25+T cells, and natural killer T cells, has a crucial role in the regulation of allergic inflammation. Farming environments, found protective against atopic diseases, contain great amounts of microbial compounds, pathogen-associated molecular patterns, which have been shown to induce activation of immunomodulatory genes. These microbe-derived signals are mediated by pattern-recognition receptors which activate different signal transduction pathways in immune and non-myeloid cells. Both pathogens and commensals express these immunomodulatory components. Better understanding of the mechanisms operative in situ may result in new probiotic and other microbe-derived therapies against allergic diseases.