Further characterization revealed that, depending upon the microenvironment, TH1 populations might engender a TH17 subpopulation, whose cytokine profile (e.g., IL17-A, IL-17 F, TNF-α, IL22, IL23, and IL9 in low concentrations) lends to a state of sustained T cell-driven inflammation seen in in autoimmune diseases and allergic reaction, or TH2 cells may generate TH9 subpopulations characterized by elevated levels of IL9 and IL10. This evidence concerns the gene IL9 and allergic disease.