Th1 and Th2 cytokines are made by separate, Th1 and Th2 like cells, not by double producing, Th0 cells. Representative cytokine production (IL-4 and IFN-γ or IL-5 and IL-2) of total gated lymphocytes from high (A-C) or low IgE-producers (D-F). Isotype controls show the lack of non-specific staining (A and D). The absence of double producing, IL-4+/IFN-γ+, lymphocytes is evident in the high IgE group (B), with essentially all IL-4 producing cells being negative for IFN-γ production. In all cases, there is a clear segregation of IL-4 and IFN-γ producing cells (B and E), or of IL-5 and IL-2 producing cells (C and F).