AbstractIL‐15, a T‐cell growth factor, has been shown to be increased in inflammatory bowel disease (IBD). It has been suggested that neutralization of IL‐15 could protect from T cell‐dependent autoimmune inflammation. On the other hand, an anti‐apoptotic effect of IL‐15 has been demonstrated in kidney epithelial cells during nephritis. We therefore tested the role of IL‐15 in two different experimental models of colitisin vivo, and in models of intestinal epithelial cell (IEC) apoptosisin vitro. IL‐15 blockade in chronic dextran sulphate sodium‐induced colitis resulted in aggravation of the disease with a significantly 2.1‐fold increased epithelial damage score compared to controls. TUNEL staining clearly revealed increased apoptosis. IL‐6, TNF and IFN‐γ secretion by mesenteric lymph node cells were increased. In the T cell‐dependent SCID transfer model of colitis IL‐15 neutralization reduced the inflammatory infiltration and proinflammatory cytokine production. Despite that, the intestinal epithelial damage was not reduced.In vitro,IL‐15 pre‐incubation prevented up to 75% of CH11 antibody‐induced apoptosis in SW‐480 cells and reduced caspase‐3 activity. According to this, endogenously produced IL‐15 in chronic colitis does not only act as a proinflammatory cytokine but has at the same time the potential to reduce mucosal damage by preventing IEC apoptosis.