[The Th1/Th2 concept--its importance for regulation of IgE]

T helper type 2 (TH2) cells are a major source of interleukin- (IL-)4 which plays a critical role in the induction of the IgE synthesis. Their counterplayers, the T helper type 1 (TH1) cells produce interferon- (IFN-)gamma which inhibits the IL-4-induced IgE synthesis. Thus, the TH2/TH1 ratio plays an important role in the regulation of the IgE synthesis. Moreover, IL-4 seems to be the crucial factor controlling the switch of T helper precursor (THp) cells to the TH2 phenotype. However, the primary cellular source of IL-4 that skews an immune response towards the TH2 phenotype is not yet known. For future prophylactic and therapeutic interventions, e.g. in allergy, it will be crucial to know the type of cell involved and the factors that are activating this cell, i.e. the exact mechanism that is controlling the switch to the TH2 phenotype.