[Pathophysiological mechanisms of asthma and atopy: old and new concepts].

After the discovery of IgE, fundamental immunology studies done during the 1980s and 1990s established that allergic reactions were a particular form of inflammatory reaction governed by Th2 lymphocytes. However, this model, while relevant to atopy, is insufficient to explain allergies, and notably asthma, in which Th1 inflammation is associated. The recent concept that natural tolerance is deficient in atopic subjects, increased in allergic subjects, and maximal in symptomatic allergic subjects, reconciles these conflicting findings by proposing a model in which three axes of T cell activation are involved, namely Th2, Th1 and regulatory T cells.