Background & aims: Crohn's disease (CD) is associated with an increased number of infiltrating macrophages, which release a variety of proinflammatory cytokines. Interleukin (IL)-18 has been implicated in the modulation of mucosal CD4(+) T cells towards Th1 responses, which are implicated in the pathogenesis of CD. Here we assess the role of macrophages and of IL-18 in the murine model of intestinal inflammation that mimics the immunologic characteristics of human CD.
Methods: Colitis was induced in C57BL/6 mice immunized with 2,4,6-trinitrobenzene sulfonic acid (TNBS) followed by rectal administration of TNBS in ethanol. Mice were treated with either an antibody directed against macrophages conjugated to the ribosome-inactivating protein saporin (anti-Mac-1-saporin) or with a neutralizing antibody against IL-18. In addition, we assessed whether an identical TNBS immunization/challenge protocol could induce colitis in IL-18(-/-) mice.
Results: The colonic mucosa of TNBS-treated mice was marked by infiltration of Mac-1-positive macrophages and up-regulation of IL-18. The administration of the anti-Mac-1-saporin antibody or the neutralizing anti-IL-18 antibody resulted in a dramatic attenuation of mucosal inflammation in this model. In addition, TNBS was unable to induce significant colitis in the IL-18(-/-) mice.
Conclusions: Our data underscore the pivotal role of macrophages, and the macrophage-derived IL-18, in the establishment of TNBS-induced colitis in mice. Our results highlight the potential use of therapy directed against IL-18 in the treatment of patients with CD.