Transcriptional studies have revealed that the production of IL-9 by TH9 cells is regulated by PU.1 (an ETS family transcription factor) (62), and there is ample evidence to suggest that the TH9 cytokine IL-9 could be a strong proinflammatory factor in the induction of experimental colitis (38, 63–65). The gene discussed is SPI1; the disease is colitis.