CD4 and inflammatory bowel disease: Effector CD4+ T cells (Th1, Th2, Th17) are critical in the defense against pathogens, whereas regulatory T cells (Treg) play a significant role in limiting the expansion and overactivity of CD4+ effector T cells.2–4 Inflammatory bowel disease seems to be due to either an excessive activation of effector T cells and/or an alteration of T cell-mediated tolerance mechanisms, the latter through defects in the development of Treg or impairment of their immunosuppressive properties.2