LEP and colitis: Indeed, modulatory effects of leptin on immune cells of the gastrointestinal tract have been widely investigated in mice, showing that leptin stimulates the release of IL-18 by mononuclear cells of the lamina propria in experimental colitis of leptin-deficient ob/ob mice (Siegmund et al. 2002) and exerts, through the modulation of Ob-R expression on ileum epithelial cells, as well as in cells of the lamina propria, an inflammatory effect in Clostridium Difficile toxin A-induced enteritis (Mykoniatis et al. 2003).