Pathogenesis of allergic diseases: interactions between pollutants and pollens really important?

Abstract

Nowadays, the prevalence of atopic diseases in so-called developed countries is estimated to exceed 30%. Furthermore, it may reach over 50% in two generations. Based on such facts, the so-called "atopic predisposition" can not be defined as an abnormal genotype consisting of certain "atopic gene(s)" possessed by a minority of unfortunate people. Rather, the gene(s) that cause atopic diseases reside in the common human gene repertoire, and several environmental factors would cause the overexpression of some constitutive gene(s), leading to the development of atopic diseases. The author considers that overexpression and production of Th2 cytokines, especially IL-5, may be a key event. The recent prevalence of atopic diseases in developed countries may be mediated by a change of Th2 polarization due to modern retrogression of environmental factors such as bacterial and viral infections that favor Th1 polarization. The "atopic trait" might be actually an "atopic phenotype" rather than an "atopic genotype". In other words, the atopic trait seems not to be a genotype that decides the development of an atopic disease on an all or nothing basis, but a phenotype that determines the susceptibility to the disease. Of course, the familial nature of atopic diseases is undeniable, but this does not necessarily indicate the genetic nature of atopic diseases. For example, if a parent suffers from tuberculosis, the possibility that the children will develop tuberculosis markedly increased. However, tuberculosis is a truly infectious disease. In this article, several environmental factors those may affect the recent sharp increase of atopic diseases are discussed.