MiR-21 (increased in the colon of IBD patients [242]) is known to increase the intestinal epithelial permeability (through an action on the tight junctions) [242,243,244] and plays a crucial role in T-cell differentiation, apoptosis and activation [242,245,246,247] and promotes the production of inflammatory cytokines (including TNF-α, IFN-γ and IL-1β) by immune cells, contributing to tissue inflammation and IBD pathogenesis [248,249,250]. The gene discussed is TNF; the disease is inflammatory bowel disease.