While some studies reported that PGE2 regulates T cells in a facilitative manner in the immune system, our recent studies showed that mPGES-1 deficiency promotes the development of experimental colitis, mouse models of inflammatory bowel disease, by affecting IL-17 A-producing CD4+ T cells, suggesting a protective role for mPGES-1 and its derived PGE2 by negatively regulating immune responses involving Th17 cells [34, 35]. The gene discussed is CD4; the disease is colitis.