IL-4 as a key factor influencing the development of allergen-specific Th2-like cells in atopic individuals.

In the last years Th2-like cells, able to produce IL-4, IL-5, IL-6 and IL-10, have been shown to play an important role in the pathogenesis of allergic diseases. They are absolutely required for IgE production by B-cells and are expanded at the level of target tissues of atopic patients. Very recently, much attention has been focused on the genetic and environmental factors responsible for the differentiation and ongoing expansion of allergen-specific Th2-like cells in atopic subjects. In this review possible cellular sources of IL-4 in the primary, secondary and ongoing responses to allergens are discussed. In atopics, Th cell precursors themselves could be proposed as a main source of IL-4 in the primary responses to allergens. However, there is extensive evidence for the role of other cells such as mast cells, basophils and eosinophils as important sources of IL-4 the secondary and ongoing responses to allergens.