Figure 2: A mechanism to explain defective innate immunity in asthma. The differentiation of Th1 and Th2 T-helper cell lineages is mutually antagonistic. Th2 cells produce IL-4 which blocks Th1 differentiation and Th1 cells produce IFN-γ which blocks Th2 differentiation. Thus, individuals with an immune system skewed towards Th2 tend not to produce eosinophils and IgE-producing B cells, but not Th1 cells. The relative lack of IFN-γ limits the antiviral response.