Interleukin-25 Inhibits Interleukin-12 Production and Th1 Cell-Driven Inflammation in the Gut

Background & Aims: During the pathogenesis of Crohn's disease (CD), interleukin (IL)-12, a cytokine produced by mucosal CD14(+) monocyte-like cells, promotes tissue-damaging T helper cell (Th) 1-mediated inflammation through mechanisms that are not fully understood. IL-25 promotes Th2 cell responses by activating major histocompatibility complex class II-positive non-T and non-B cells. Because Th1 and Th2 cells, and the cytokines they release, are often mutually antagonistic, we examined whether IL-25 affects IL-12 production or Th1 cell-mediated inflammation in the gut. Methods: Studies were performed using colonic samples from patients and mice with peptidoglycan (PGN)-, 2,4,6-trinitrobenzenesulphonic acid (TNBS)-, or oxazolone-induced colitis. IL-25 receptor (IL-25R) levels were evaluated in intestinal lamina propria mononuclear cells by flow cytometry, and IL-25 levels were measured by real-time polymerase chain reaction, immunoblotting, and immunohistochemistry. Mucosal CD14(+) cells from patients with CD were incubated with IL-25 and/or lipopolysaccharide or PGN. Mice were injected with IL-25, and some mice first received injections of an IL-13 blocking antibody. Cytokines were quantified by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Results: CD14(+) cells from the mucosa of CD patients expressed IL-25R and responded to IL-25 by decreasing the synthesis of IL-12 and IL-23. IL-25 prevented PGN-induced colitis in mice. IL-25 induced IL-13 production in the colon, but IL-13 was not required for suppression of PGN colitis. IL-25 ameliorated TNBS- and oxazolone-colitis. Patients with CD or ulcerative colitis produced significantly less IL-25 compared with controls. Conclusions: IL-25 inhibits CD14(+) cell-derived cytokines and experimental colitis. IL-25 could be a useful treatment of CD and ulcerative colitis.